The Illusion of Ambiguity: from Bistable Perception to

Transcription

fiammetta ghedini
T H E I L L U S I O N O F A M B I G U I T Y: F R O M
B I S TA B L E P E R C E P T I O N T O
ANTHROPOMORPHISM
T H E I L L U S I O N O F A M B I G U I T Y: F R O M B I S TA B L E
PERCEPTION TO ANTHROPOMORPHISM
fiammetta ghedini
A dissertation submitted in partial fulfilment of the requirements for
the degree of Doctor in Philosophy in Innovative Technologies of
Information and Communication Engineering and Robotics
30 May 2011
Fiammetta Ghedini: The Illusion of Ambiguity: from Bistable Perception to Anthropomorphism, A dissertation submitted in partial fulfilment of the requirements for the degree of Doctor
in Philosophy in Innovative Technologies of Information and
Communication Engineering and Robotics, © 30 May 2011
No lesson of psychology is perhaps more important for the
historian to absorb than this multiplicity of layers, the peaceful
coexistence in man of incompatible attitudes.
— Sir Ernest Gombrich
There is an universal tendency among mankind to conceive all
beings like themselves, and to transfer to every object, those
qualities, with which they are familiarly acquainted, and of
which they are intimately conscious.
— David Hume
ABSTRACT
This thesis is a multidisciplinary work at the merging of neuroscience, art and human interaction with technologies. Its objectives are:
1. Review the literature and further investigate, by means of
a brain imaging study, which are the mechanisms allowing the illusion of ambiguity in the brain, by proposing a
framework of analysis based on different levels of ambiguity;
2. Discuss the concept of the illusion of life, defined as a perceptual phenomenon included into the wider category of
ambiguity and caused by intentionality and animacy being
hard-wired in the brain (part of that previous knowledge
necessary to successfully process sensory inputs);
3. Explore features in behaviour and form which are most
likely to trigger anthropomorphism, drawing insights from
art, technological applications and cognitive sciences, and
focusing on human interaction with artificial creatures.
vii
P U B L I C AT I O N S
Some ideas and figures have appeared previously in the following publications:
Perception of Ambiguous Figures: an fMRI study, F. Ghedini
& M.Bergamasco, VRR-IJCAI 2011, 18-24 July, Barcelona, Spain
[Ghedini and Bergamasco, 2011b]
Life evocation in art: from representation to behaviour. F. Ghedini & M.Bergamasco, ISEA 2011, 12-16 September, Instanbul,
Turkey [Ghedini and Bergamasco, 2011a]
Robotic Art: Perceiving and inventing reality. F. Ghedini &
M.Bergamasco, Art and Science: exploring the limits of human
perception, Conference Proceedings, Benasque, Spain, on July
12-16, 2009 [Ghedini and Bergamasco, 2009]
"Passages: An Artistic 3D Interface for Children’s Rehabilitation and Special Needs" F. Ghedini, H. Faste, M. Carrozzino, M.
Bergamasco ICDVRAT International Conference Series on Disability, Virtual Reality, and Associated Technologies, Portugal,
09-08-2008 [Ghedini et al., 2008]
Robotic expression. Developing an applied framework for the
integration of artistic approaches and technological competences,
2008, PhD Application for the Scuola Superiore Sant’Anna [Ghedini, 2008]
A conversation with Bill Vorn (on robotic art creatures and
other believable living machines) Scuola Superiore Sant’Anna,
Pisa, Italy, 09-17-2007[Vorn, 2007]
"Enactive Network of Excellence, Digest 2006: Multimodal
Interfaces," Massimo Bergamasco, Fiammetta Ghedini, Haakon
Faste, Editors Enactive Consortium Press, project IST-2004-002114ENACTIVE, 02-15-2007
Haptic interaction with virtual sculptures, 2007 Massimo
Bergamasco, Marcello Carrozzino, Fiammetta Ghedini
"Enaction and Inactive Interfaces: A Handbook of Terms,"
Enactive Systems Books, 2007
"Le interfacce aptiche per i Beni Culturali" M. Bergamasco,
C.A. Avizzano, F. Ghedini, M. Carrozzino Proceedings of LUBEC
2007, "Valorizzazione dei Beni Culturali e Innovazione", Lucca,
Italy, 2008 ISBN 978-88-89766-10-1 [Bergamasco et al., 2007]
ix
ACKNOWLEDGMENTS
This dissertation would not have been possible without the support and encouragement of Professor Massimo Bergamasco, my
Ph.D. supervisor at Perceptual Robotics Laboratory of Scuola
Superiore Sant’Anna. Throughout my thesis he provided guidance, advices and inspiration. I would like to thanks all the
colleagues with whom I had the pleasure of collaborating: Carlo
Alberto Avizzano, Franco Tecchia, Antonio Frisoli, Chiara Evangelista, Elisabetta Sani, Federico Vanni, Walter Aprile, Andrea
Bizdideanu, Vittorio Spina, Davide Vercelli, Rosario Leonardi,
Paolo Tripicchio, Paolo Gasparello, Emanuele Giorgi; Vittorio
Lippi and Emanuele Ruffaldi for their precious help with LateX
and those other colleagues whom I have neglected to mention.
A special thanks to Haakon Faste for his inspiring enthusiasm
and eclectic skills, Marcello Carrozzino for providing useful
feedback and to Francesca Farinelli and Alessandra Scucces for
being not only helpful colleagues but also very dear friends,
and for supporting me during my thesis-writing period. My
gratefulness goes also to all the people working in the administration of the Scuola Sant’Anna and especially Laura Bevacqua.
For enlightening conversations, encouragement, feedback and
inspiration I would like to thank Israel Rosenfield. I owe a lot to
him and to his perspectives on neuroscience. I also would like
to thank Simon Penny and Bill Vorn for visiting our Laboratory
and inspiring me with their artworks on artificial life. My deepest gratefulness goes to Professor Semir Zeki who made possible
the fMRI experiment described in this thesis. Thank you for your
guidance and for working with me for over one year at the Wellcome Lab of Neurobiology at UCL, London. I am indebted to all
the people working in Professor Zeki’s lab: Barbara Nordhjem
for her continuous support, John Romaya for his experience, Jon
Stutters for his skills, Shelley Tootell for her helpfulness and
Tomohiro Ishizu and Sam Cheadle for being always supportive,
through difficult times too. Thanks for you friendship and kindness. Thanks to all the people from the academic world who in
conferences, seminars and workshops provided new inspiring
ideas, feedback on my research and good company: Mel Slater,
Mavi Sanchez, Doron Friedman, Peggy Weil, Nonny de la Pena,
Marcelo Wanderlay, Elena Pasquinelli, Benoit Bardy and many
xi
others. A very special thanks goes to Tommaso Andreussi: you
will print your next book on Luoyang paper! Finally, "merci"
to François Pachet for his encouragement, for being a model
of what a researcher should be, and most importantly for coming into my life. And "grazie" to my parents, Anna Casanova
and Fabio Ghedini, because they taught me the importance of
knowledge: to them I dedicate my thesis.
xii
CONTENTS
i introduction
1 introduction
1.1 Perception: Making Sense of the Senses . . .
1.1.1 Watching without seeing . . . . . . . .
1.1.2 The Brain: an Abstraction Machine . .
1.1.3 The Case of Colour Vision . . . . . . .
1.2 Concepts and Categories in the Brain . . . .
1.3 Seeing through Illusions . . . . . . . . . . . .
1.3.1 Two Different Categories of Illusions .
1.3.2 Ambiguity and Ambiguities . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
ii first and second level ambiguity
2 perception of bistable ambiguity
2.1 What is multistable ambiguity . . . . . . . . . . . .
2.1.1 Neural processes underlying multistable
phenomena . . . . . . . . . . . . . . . . . .
2.1.2 Attention and perception of bistable figures
2.1.3 Levels of ambiguity . . . . . . . . . . . . . .
2.2 An Experiment on Two-Levels Bistable Ambiguity
2.2.1 General fMRI Analysis . . . . . . . . . . . .
2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.1 Behavioural results . . . . . . . . . . . . . .
2.4 Discussion . . . . . . . . . . . . . . . . . . . . . . .
2.4.1 Conclusion . . . . . . . . . . . . . . . . . . .
iii third level ambiguity
3 third level ambiguity: the illusion of life
3.1 Perceptual knowledge of life . . . . . . . . . . . .
3.2 The illusion of intentionality . . . . . . . . . . . .
3.3 The illusion of life in the brain . . . . . . . . . .
3.3.1 Emotional clues in the illusion of life . .
11
13
14
15
17
19
22
24
24
27
31
33
33
36
41
42
42
46
48
48
50
53
61
63
. 63
. 66
. 69
. 72
iv forth level ambiguity
4 aesthetics of anthropomorphism
4.0.2 Anthropomorphism as a forth level ambiguity . . . . . . . . . . . . . . . . . . . . . .
4.0.3 Variability in anthropomorphisation . . . .
4.1 Life evocation in the arts . . . . . . . . . . . . . . .
4.1.1 Defining life away . . . . . . . . . . . . . . .
75
77
77
77
78
78
xiii
xiv
contents
4.2
4.3
4.1.2 Art and the illusion of life . . . . . . . . . .
4.1.3 From art to technology . . . . . . . . . . . .
4.1.4 Uncanniness as a result of life evocation . .
The illusion of life in artificial creatures: features
of believability . . . . . . . . . . . . . . . . . . . . .
4.2.1 Form: is realism a necessity? . . . . . . . .
Conclusions . . . . . . . . . . . . . . . . . . . . . .
bibliography
79
83
84
85
86
90
95
LIST OF FIGURES
Figure 1.1
Figure 1.2
Figure 1.3
Figure 1.4
Figure 1.5
Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4
Figure 2.5
Figure 2.6
Figure 2.7
Figure 2.8
Figure 2.9
Figure 2.10
The response of an orientation selective cell
The response of an orientation selective
cell in V5 . . . . . . . . . . . . . . . . . . . .
A rotation of a mask: the forth image shows
the inside of the mask, appearing convex
even if it is hollow . . . . . . . . . . . . . .
Model of perception, based on (Gregory
2009) . . . . . . . . . . . . . . . . . . . . . .
Different kinds of ambiguities . . . . . . . .
a) Necker Cube - b) Rubin Vase . . . . . . .
Binocular rivalry . . . . . . . . . . . . . . .
Auditory streaming is a case of multistable
perception in the auditory modality . . . .
Experiment stimuli: bistable intra-categorical
images + stabilized versions . . . . . . . . .
Experiment stimuli: bistable inter-categorical
images + stabilized versions . . . . . . . . .
Bistable Figures > Stable Figures . . . . . .
Global 3D view of activations for the contrast internal change > external change for
a random effects analysis with 16 subjects:
selected activations superimposed on to
averaged anatomical sections . . . . . . . .
T statistic for Bistable > Stable in conjunction with Intra-categorical: Bistable > Stable switches (left) and Inter-categorical:
Bistable > Stable switches (right) . . . . . .
Bistable activations conjoined with Intercategorical and intra-categorical bistable
activations . . . . . . . . . . . . . . . . . . .
Bistable faces > All. FFA activation projected onto averaged structural scans (left)
and main HRF and TD plotted for FFA [38
-58 -14] (right) . . . . . . . . . . . . . . . .
18
19
25
27
29
34
35
36
54
55
56
57
57
58
59
xv
xvi
List of Figures
Figure 4.1
The Uncanny Valley graph following Mori
85
Part I
INTRODUCTION
1
INTRODUCTION
This thesis is a multidisciplinary work, whose goal is to merge
insights and research from fields as different as art, neuroscience
and technology. My original question was: how do we attribute
features of animacy (such as emotions and intentions) to objects,
in spite of the certain knowledge of their non-animacy? This
question brought me to consider, in the first place, some basic
phenomena of perception, and in particular, illusions. Illusions
make evident that perception is not a passive mapping of inputs coming from the environment, but an active interpretation,
involving a mechanism of inference. As illustrated in Chapter I,
studies on optical illusions may be very useful in order to reveal
the active role of the brain in the organisation of perceptual
processes. Among all different kinds of illusion, ambiguity is
one of the most interesting, since it clarifies how our brain disambiguates the information received. Ambiguity is traditionally
defined as an alternation in time of two mutually exclusive interpretations of the same stimulus [Zeki, 2004]. As I propose in the
framework of this thesis, this definition fits to a specific kind of
ambiguity, namely the "intra-categorical" one, taking place when
the two possible interpretations of the same stimulus belong
to the same semantic category, for example the two recessional
planes of the Necker cube. This kind of ambiguity is the basic
model of a mechanism that probably happens endlessly in our
brain, since our everyday environment contains ambiguities
and conflicts which we do not usually notice because our brain
successfully - and continuously - disambiguates them. It can be
hypothesised that such an evaluation process is occurring all
the time, but becomes evident when ambiguities are maximised,
as in the case of ambiguous stimuli. Indeed, also multistable
ambiguity involves a continuous and frequent evaluation of
sensory inputs, but it results in puzzling flips (or reversals) in
perception, since ambiguous percepts do not provide enough
clues for "deciding" which is the "good" interpretation. But, in
partial contrast with the above quoted traditional definition, I
do not consider all possible interpretations of an ambiguous
image as mutually excluding. In Chapter II, on the basis of
brain imaging data, I will propose the notion of different levels
13
From bistable
perception to
anthropomorphism
14
introduction
of ambiguity, including in such a framework the concepts of the
illusion of life and of life evocation as "higher level" ambiguities.
The illusion of life is a phenomenon that can be considered
as the perceptual basis of anthropomorphising, or attributing
animacy, emotions, intentionality, personality and other traits
common to living agents to non-animated stimuli. The illusion
of life takes place when geometrical stimuli showing certain
features of motion and behavior automatically elicit attribution
of animacy and intention, as investigated in the seminal studies
of [Michotte, 1946] and [Heider and Simmel, 1944]. While the
illusion of life is automatically and universally perceived, with
the only exception of persons with very specific brain damages,
anthropomorphising is a psychological tendency implying an
individual variability and depending on factors such as social
isolation and need of mastering the environment. In Chapter III
I will focus on the features and neural events underlying the
illusion of life, outlining why it can be considered as an illusion
of ambiguity. As illustrated in Chapter IV, perception of animacy
of non-animated objects has always been exploited and explored
by artists, who have been featuring in their works the aesthetics
of life evocation. Finally, life evocation triggering anthropomorphising has a great potential of application in today’s society,
where humans interact more and more with technological objects such as robots and avatars, designed to embody believable
creatures. In Chapter IV I will discuss some features of animacy
perception drawing inspiration from arts and insights from the
cognitive sciences, with the objective of outlining believability
issues for the design of technological applications.
1.1
Perception as an
active process
perception: making sense of the senses
Philosophy and science have traditionally separated intelligence
from perception, vision being interpreted as a passive windows
on the world. It was German fellow Hemann von Helmholtz
(1821-1894) who first proposed the principle that visual perceptions are unconscious inferences [von Helmholtz, 1962]. Von
Helmholtz thought that human perception is only indirectly
related to objects, being inferred from fragmentary data. There
have been researchers who maintained a "direct" theory of perception, notable American psychologist J. Gibson [Gibson, 1950]
who outlined the theory of affordances, proposing a model in
which our senses "pick up" information form the environment
giving significance to pattern of stimulation without recurring
1.1 perception: making sense of the senses
15
to further processing. But the majority of studies today agree on
the hypothesis that perception is not a passive reception of the
information coming from the surrounding environment, rather
affirming that the brain is a story-teller who actively builds
the reality surrounding us, as illustrated by [Rosenfield, 1988].
Researchers point out that our senses are faced by a chaotic, persistently changing world without labels. What our brain actively
does is organising external reality, allowing us to generalise
and thus use the information we need from the environment,
imbuing it with meaning. Since meaning is not in things but
is in the brain, information, if not interpreted by the brain, is
empty of meaning.
1.1.1
Watching without seeing
Researchers supporting the thesis of "active perception" often refer to the argument of born-blind people regaining sight during
adulthood. Indeed, born-blid individuals who recuperated their
sight after many years, even if visually perceiving objects, do
not "see" them (they do not understand what the objects are), or
learn to do it after a long and difficult training. In this brain condition, generally labelled as agnosia, sensations of light, colour,
movement and shape can reach the brain but are meaningless;
therefore for individuals suffering from this condition, objects
are seen as "meaningless" items. The first debate about this topic
can be traced back to a correspondence between English philosopher John Locke and William Molyneaux [Gregory, 1987]. In
1688 the Irish scientist and politician William Molyneux (1656
–1698) sent a letter to John Locke in which he asked whether
a man who has been born blind and, during the course of his
life, has learnt to distinguish and name a cube and a sphere
by touch, would be able to distinguish and name these objects
simply by sight, once he had been enabled to see. The so-called
"Molyneaux problem" has been solved forty years later, when
the English surgeon William Chelsden operated a 13 years old
from a cataract, allowing the boy to see for the first time in his
life. The first impression of the boy was objects were "disproportioned". Moreover he did not have any sense of distance, and of
the relation between size and distance: a little object very close
to his eyes was equivalent to a big house seen from far away. He
was not able to distinguish a cat from a dog, unless he could
touch them.
The born-blind issue
16
introduction
a case of sight recovery When he first saw, Cheselden
writes, he was so far from making any judgement of distances, that he thought all object whatever touched his
eyes (as he expressed it) as what he felt did his skin, and
thought no object so agreeable as those which were smooth
and regular, though he could form no judgement of their
shape, or guess what it was in any object that was pleasing
to him: he knew not the shape of anything, nor any one
thing from another, however different in shape or magnitude; but upon being told what things were, whose form
he knew before from feeling, he would carefully observe,
that he might know them again; and (as he said) at first
learned to know, and again forgot a thousand things in a
day. One particular only, though it might appear trifling,
I will relate: Having often forgot which was the cat, and
which the dog, he was ashamed to ask; but catching the
cat, which he knew by feeling, he was observed to look
at her steadfastly, and then, setting her down, said, So,
puss, I shall know you another time. He was very much
surprised, that those things which he had liked best, did
not appear most agreeable to his eyes, expecting those
persons would appear most beautiful that he loved most,
and such things to be most agreeable to his sight, that were
so to his taste. We thought he soon knew what pictures
represented, which were shewed to him, but we found
afterwards we were mistaken; for about two months after
he was couched, he discovered at once they represented
solid bodies, when to that time he considered them only as
party-coloured planes, or surfaces diversified with variety
of paint; but even then he was no less surprised, expecting
the pictures would feel like the things they represented,
and was amazed when he found those parts, which by
their light and shadow appeared now round and uneven,
felt only flat like the rest, and asked which was the lying
sense, feeling or seeing? [Cheselden, 1683-1775]
The boy thus had a troublesome learning path, in which nothing came natural or spontaneous; he was conscious of the effort
and he was trying to learn and record things everyday. For instance, he knew that he had a cat and a dog, and that he had
to distinguish them by seeing them; this task was probably as
difficult as for a normal-sighted person learn to distinguish at a
glance two very similar specimen of the same breed. But, tridimensionality appeared to Cheselden’s patient as some kind of
17
illusion. Even after he acquired the capacity to correctly interpret
bidimensional images, he was still "amazed" to perceive the
body represented by paintings as flat. The phenomenon thanks
to which he could see a bidimensional object as tridimensional
was so obscure to him that he was convinced that one of his
sensory channels must have being lying. Several similar operations have been conducted afterwards, and always with the
same results. In particular, bidimensional representations are always troubling for born-blind individuals recovering their sight,
because they see such representations in three dimensions, and
they cannot understand how this can be, when they touch the
image finding it flat. "Normal" perception of size, distance and
tridimensionality is a phenomenon that we take for granted but is actually the result of an operation of abstraction produced
by the brain.
1.1.2
The Brain: an Abstraction Machine
Distance, size and tridimensionality are abstractions produced
by the brain among all the mechanisms allowing us to recognise objects. Acquiring the capacity to create the abstraction of
"representation on two dimensions" is probably something that
we learn to do very early in time, and blind born individuals
do not have the possibility to develop at "due time". Studies
affirm that the common capacity of the cerebral cortex - whether
visual, auditory, somato-sensory ot otherwise- is namely the
one of abstraction: "the capacity to abstract seems to accompany,
and to be a corollary of, every specificity" [Zeki, 2009]. What it
is meant for abstraction, in this specific context, is the capacity
to grasp a general property instead of the particular one. An
example of this process at a single cell level is orientation selectivity [Hubel and Wiesel, 1977]. Orientation selectivity is the
property of some cells in the visual brain, which respond to
objects (lines) of a specific orientation and do not respond to
lines oriented orthogonally at their "preferred" orientation: there
are cells which will respond only to vertical lines, and other
to horizontal ones. For instance, a vertical-selective cell will
respond when the stimulus is vertical, without being concerned
with what is vertical, whether a tree or a vertical line or a tower:
this means that the cell has abstracted the property of verticality
from different stimuli discarding individual specificities.
In Figure 1.1, we can see the reponse of an orientation selective
cell. Such a response can be studied by inserting an electrode
Abstraction at cell
level
18
introduction
Figure 1.1: The response of an orientation selective cell
into the visual cortex (a) and showing bars of light of different
orientation into the Receptive Field (the small rectangle on the
left, RF), that is to say that part of the global visual field (the
bigger rectangle) which will trigger an electrical discharge in the
studied cell. (b) shows the representation of the cell’s selectivity
to orientation: the cell responds positively to the oblique line
moved in two opposite directions (first three records) while it
is unresponsive to the orthogonal orientation. In the same way,
cells of the brain area specialised for processing motion, V5, are
directionally selective. This means that they respond to motion
in a specific direction and not in the opposite one, as illustrated
in Figure 1.2. This kind of abstraction does not concern exclusively the visual brain, but also other sensory modalities. Cells
"designed" for perceiving pressure in the somatosensory cortex
will respond to pressure independently from what causes it; the
same thing is true for a cell responding to temperature, pain,
and for the auditory system.
19
Figure 1.2: The response of an orientation selective cell in V5
1.1.3
The Case of Colour Vision
Abstraction is the strategy used by the brain in order to create a
coherent environment out of a chaotic and ever-changing world.
As in the largely discussed example of colour vision, we cannot
help but perceive and organise constant features; we cannot
avoid seeing a leaf as green at dawn and dusk, or a rose as red
both in a sunny and cloudy day, taking for granted that "colours"
are features intrinsic to objects. Since the world we see is always
changing and the retina receives a constant flow of different
kinds of visual information, the brain must be able to select
visual properties of objects and surfaces in order to give them
meaning. In acquiring this ability, the brain has developed specialized functions for the analysis of different properties, such
as colour, shape, and movement. For example, contrary to our
visual experience, there are no colours in the world, only electromagnetic waves of many frequencies. Our retinal receptors
for colour are divided in three categories, responding optimally
to long (red), middle (green), and short (blue) wavelengths. The
brain compares the amount of light reflected in the wavelengths,
and from these comparisons creates the colours we see. The
amount of light reflected by a particular surface - a table, for
example - depends on the frequency and the intensity of the
What are colours?
20
The Land hypothesis
introduction
light hitting the surface; some surfaces reflect more short-wave
frequencies, others more long-wave frequencies; but the particular sensation produced by a specific colour is created by
our brain. Indeed, if our perception of an object as red were to
change with every change in the wavelength of light reflected
from it, the object would constantly change in appearance. If we
were aware of our ’real’ visual worlds we would see constantly
changing images of dirty grey - constantly changing images that
would be very confusing, often making it impossible for us to
see forms. While, thanks to this mechanism, the brain is able
to attribute a constant colour making itself largely independent
of the amount of light of the waveband reflected from objects’
surfaces. This mechanism is a way of our brain of "inventing" an
attribute allowing us to identify objects by means of a constant
and meaningful feature. How can this happen in the brain? Von
Helmholtz [von Helmholtz, 1962] based this phenomenon on
learning: he thought that since we know that a leaf is green,
we operate a mechanism, which he names "unconscious inference", allowing to "attribute" a colour to the leaf even if the
illuminant (the wavelength composition of the light reflected in
different lighting conditions) always changes. Another German
psychophysicist, Ewald Hering, thought that memory played
a central role [Hering, 1964 (originally pub. 1877]. Higher cognitive functions have therefore always been addressed when
trying to explain mechanisms underlying colour vision, until
Edwin Land (the inventor of the Polaroid) finally proposed
another point of view [Land, 1974]. He hypothesised that the
assignment of constant colours to objects is the result of a simple computational process of the brain, due to some kind of
innate capacity of organisation of visual signals. Following Land,
colours are the result of the comparison between the amount of
light of different wavebands reflected from a surface and from
its surrounds. This comparison has as a result a ratio, which is
constant (differently from the amount of reflected light).
the inherited concept of ratio-taking: In the Land
experiment, a green surface is surrounded by yellow, red
and blue surfaces. If the surface is lighten by a projector
projecting blue light, the surface will reflect let’s say 60
units (milliwatts) of green light. The surrounds will be
reflecting less green light. The same surface is seen under
a red light: the green surface will now reflect 30 units of
green light. But we will still see it as green! This is because the surrounding surfaces will reflect even less units
of green light than before. Indeed, the ratio (relationship
between the amount of green light reflected by the green
surface and the one reflected by non-green surfaces) is
always identical.
Colour perception is the most powerful example of how our
experience of the world is based on the brain’s capacity to
perform operations related to inherited concepts rather then
mere physical reality. The crucial feature of the colour system in
the brain is the ability to ascribe a constant colour to an object
despite of wide-ranging changes in the wavelengths-energy composition of the light reflected by such an object. If the colour of
the surface would change along with every change in its lighting
environment, objects would have ever-changing surfaces (e.g.,
leafs would be green in the morning and red in the evening).
This mean that colours would not mean much and, rather than
provide us with information about things, would actually confuse us, being a non-constant overflow of useless information.
The importance of understanding colour as a construction of
the brain is that colour is an example of mechanism that the
brain has developed through evolution, and that concurs to
instil meaning and thus gain additional knowledge from the
environment: our visual worlds are stabilized because the brain,
through colour perception, simplifies the environment by comparing the amounts of lightness and darkness in the different
frequencies from one moment to the other. In the same way,
an object maintains its identity independently from the point
of view and distance we look at it. The capability to organize
constantly changing stimuli in a stable and meaningful way is
an impressive feature of perception and is the way our brain
allows us to cope with reality. And just as colours are different
in kind from the images projected on our retinas, space and
depth are different in kind from the individual images projected
the retinas of our eyes. In creating three-dimensionality and
depth the brain in actually invents subjective experience. The
three-dimensionality we normally see is not part of the "real"
world; all of our perceptions are from a particular point of view
and that individual point of view is our subjectivity; it is created by the brain as it makes sense of the physical world that
surrounds us.
21
22
introduction
1.2
Categorising
behaviour
concepts and categories in the brain
We saw how the brain can be independent from the continual
change of the surrounding information, allowing us to recognize
essential and non-changing characteristics of objects and situations, optimising knowledge acquisition by abstraction. Colour
perception is an example of categorisation intrinsic to the brain’s
design. The capacity to see colours can be lost, as happened
to the most famous case of cerebral achromatopsia, the one of
the colour-blind painter Johnathan I. [Sacks, 1995]. But, even
if the capacity to see colours stays intact, the brain can lose
the capacity to abstract; and in this case, even if colours are
"viewed", they are not "understood", becoming useless. Gelb
and Goldstein [Gelb and Goldstein, 1925] have reported the case
of a patient who was incapable to define the colours of objects,
even if, apparently, he could perceive them. The patient could
not indicate the name of the colour of an object mentioned to
him, neither he was able to point out a colour corresponding
to a colour-name. Presented with colour samples, he uttered
some names, giving the impression that words had no meaning.
When he was asked to choose a red object among a sample of
different objects, he would choose by chance. But, if he was requested to chose a colour sample fitting to a coloured object, he
always succeed: he never chose a wrong colour. On the contrary,
he was never satisfied: if the colour specimen did not match
perfectly with the colour of the object, he continued looking for
a more fitting specimen. This proved that he could "perceive"
colours. But, when the patient had to assort different specimen
of colours, the patient was incapable to find a unifying category
in order to group them: the factor of hue, brightness, or other
factors may prevail. Gelb and Goldstein explained the patient’s
behaviour (as well as other patients symptoms) as effects of the
reduction from the level of "categorical" behaviour to the level of
"concrete" behaviour. Confronted with the same task (grouping
colour specimina according to hue) the normal person immediately assorts the same specimina, e.g. a very light and a very
dark red, by categorizing them as "red". In doing so, she is not
unaware of the difference between them; she is performing an
operation of abstraction (abstracting the "redness") and categorisation (by discarding "individual" differences among specimina
and unifying under the category "red"). Gelb and Goldstein’s
patient, even seeing colours, was unable to establish abstract
relations between the category (red, blue, green, etc.) and the
1.2 concepts and categories in the brain
concrete colour. When he was asked to define the colours, he
always had to make a comparison (e. g. "like an orange, like a
cherry") and he was meticulously grouping colours but without
backing up on a categorical sense. The patient was confined to
the content of perception as it is actually experienced (he was
seeing the "real" world, in a way); in other words he could not
go through his perceptual experience under the perspective of
a principle external to the perceptual experience itself, being
unable to refer his actual experience to any conceptual order.
In the framework of this regression to a "concrete" behaviour,
there is no hierarchy or differentiation between the experiential
features and their significance. All features are equally important; each features is of paramount importance because all of
them are encountered "at the same level" in actual perception.
The patient was overwhelmed by the actual experience, and he
could not emancipate from it by imposing a structure able to
create meaning in the world.
What Goldstein refers to as "categorising" behaviour is parallel to Zeki’s theory of inherited and acquired concepts: "The
inherited concepts organize the signals coming into the brain so
as to instil meaning into them and thus make sense of them",
[Zeki, 2009] while acquired concepts are generated throughout our existence, with the goal of simplifying perceiving and
recognizing things and situations. Inherited brain concepts are
identifiable by three features, in Zeki’s view: absence of free
will, immutability and autonomy. Therefore, in this perspective
colour perception may be classified as an inherited concept, since
we can not choose what colours we perceive, nor we can choose
of seeing the "real" colours of things instead that the colours
"invented" by our brain; secondly, our system of perception for
colours is immutable, does not change over years - in normal
conditions - and thirdly, the generation of colours is dependent
on a specialised cortical system that differs from other systems
designed for processing other kinds of visual features. While
acquired concepts are a way to organise knowledge throughout
our life (for instance, we can learn to define a specific set of
paintings as "still life" and we will be able to insert in such a category all still life that we will see afterwards, even if they will be
composed of different objects, lighting conditions, colours, etc.).
Still, what acquired and inherited concepts have in common is
the capacity of the brain to abstract and to generalize.
23
Inherited and
acquired concepts
24
introduction
1.3
seeing through illusions
The way in which our brain organises knowledge can be more efficiently investigated in exceptional conditions: those situations
in which things do not work as usual. This means analysing
those circumstances in which the brain’s capacity of stabilisation
and abstraction is invalidated, temporary or permanently discarded, as in the cases of brain damages and illusions [Gregory,
2009]. It is hard to give a satisfactory definition of the term "illusion". The OED (Oxford English Dictionary) defines it as "an
instance of a wrong or misinterpreted perception of a sensory
experience"; here I will refer more precisely, to those phenomena implying a discrepancy measurements and inner perception.
Such a discrepancy can happen when the knowledge (inherited
or acquired) that we "superimpose" to perception is inappropriate or misapplied; in other words, where the "assumptions"
we are doing are wrong. Indeed, perception is - following this
perspective - based on inferences that we deduce from sensory
signals; being an inference, it requires a previous knowledge.
This is why illusions can clarify many mechanisms behind perception, indicating where and how this "previous knowledge"
(abstraction, categories and things we learn throughout our life)
play a role. As Chelsden’s blind born boy asked himself whether
was the sight or the touch which was lying: he thought that
perceived tridimensionality was an illusion. And in a way it
is, because behind our capacity to view tridimensional images
in pictures there is a level of abstraction: illusions can provide
evidence of working rules of perception.
1.3.1
Physical illusions
Two Different Categories of Illusions
Gregory identifies two different kinds of illusion, the cognitive
and the physical ones. While the latter ones have a physical
cause, cognitive illusions are due following Gregory to "misapplication of knowledge" employed by the brain in interpreting
sensory signals [Gregory, 2009]. Illusions due to the disturbance
of light, between objects and the eyes, are different from illusions due to the disturbance of sensory signals of eye, though
both might be classified as physical. Among these, we can list
with Gregory mist (loss of information increasing uncertainty),
mirage (refraction of light between the object and the eyes displacing objects or parts of objects, rainbow. Discussing this
1.3 seeing through illusions
taxonomy is nevertheless outside the scope of this thesis, and
for further reading on this subject we remand to [Gregory, 2009].
Cognitive illusions are further devided by Gregory into "specific knowledge" of objects from "general knowledge". An example of specific knowledge cognitive illusion is the "hollow face"
illusion.
Figure 1.3: A rotation of a mask: the forth image shows the inside of
the mask, appearing convex even if it is hollow
As illustrated in Figure 1.3, when seeing a hollow mask we
are strongly biased in seeing it as convex. This bias of seeing
masks as convex is so strong it competes with monocular depth
cues, such as shading and shadows, and also very considerable
unambiguous information from the two eyes signalling stereoscopically that the perceived object is hollow. Also, a texture
imitating wood could look like wood even if it is plastic, or if it is
painted; this is because we apply our specific knowledge to the
texture and make an inference about the material on the basis
of a specific and repeated experience (wood is grainy, brownish,
etc.). An example of general knowledge leading to cognitive
illusions is misleading rules of Gestalt (Wertheimer, 1923/1938)
applied to tricky objects (designed to trigger the illusion) e. g.
Kanitsa triangle, due to postulating a nearer occluding surface to
25
Cognitive illusions
26
A model of
perception
Automaticity of
illusions
introduction
explain "surprising" gaps [Gregory, 1972]. General knowledge,
in this case, is the rules of Gestalt (closure, proximity, continuity,
common fate) singled out by Wertheimer and influencing our
vision of objects (independently from the objects themselves).
In order to trigger illusion related to misapplication of general
knowledge it is necessary to investigate the perception of exceptional and atypical objects. For Gregory [Gregory, 1972] this is
the evidence of top-down knowledge applied to perception: this
means that since we know, due to our experience, that faces and therefore masks - are generally convex, we perceive it as
such. The top-down knowledge applied to this experience is
very strong, and even if we know that the mask is hollow, we see
it as convex. Interestingly, patients affected by schizophrenia do
not perceive this illusion [Schneider et al., 1996]. This may mean
that they are more inclined to top-down influences since they
are affected by a lack of connectivity: Dima [Dima et al., 2009]
demonstrated that schizophrenic patients show an increased
activity of bottom-up processes if compared to healthy controls,
who do perceive the hollow face illusion; schizophrenic subjects
in this sense see the world "as it really is" relying on stimulusdriven processes. On the basis of this perspective on illusions as
a model of perception is illustrated in Figure 1.4: perception is
an hypothesis, or an inference in Von Helmotz’s defition [von
Helmholtz, 1962] coming from a continuous dialogue of signal
processing, perceptual and conceptual knowledge. Signals from
the senses (bottom-up) are not only influenced (top-down) by
pre-existing knowledge (e.g.: faces are convex) but also by perceptual "rules", which constitute the "language of the brain" (e.
g. Gestalt rules, colour view); this continuous loop gives rise to
qualia, sensations about what we perceive.
What is typical of several illusions is that they are experienced
perceptually though the observer knows conceptually that they are
illusions. This phenomenon can tell us something interesting
about the nature of knowledge that we superimpose to perception. It is not "conceptual" knowledge, but it is a separated kind
of knowledge, that could be defined as "perceptual knowledge".
This perceptual knowledge is probably linked to evolution allowing perceptual mechanisms to work very fast and efficiently,
this being useful in case of danger. Perceptual knowledge is the
assumptions that our brain takes, and can coexist with conceptual knowledge even when in contradiction, as in the case of
several illusions. Also, if perceptual knowledge would not be
different from conceptual knowledge, our beliefs would deter-
Figure 1.4: Model of perception, based on (Gregory 2009)
mine perception making us blind to the new or strange, which
would be dangerous in unusual situations, and would limit
perceptual learning. What is this previous knowledge? For von
Helmoltz, signal processing interpretation is resolved thanks
to previous knowledge by unconscious inductive inference. As
we saw above, Zeki [Zeki, 2009] declines this definition in inherited and acquired concepts, granting the brain a grasp on
the world (but also demanding a "prize to pay" when misapplied). Gregory [Gregory, 2009] organises "previous knowledge"
in general knowledge and specific knowledge, proposing that
perceptions are hypothesis predicting "unsensed characteristics"
of the objects. I will use the term "conceptual knowledge" for indicating top down higher cognitive knowledge and "perceptual
knowledge" for indicating bottom up impressions that can, as
investigated in the next chapters, overcome and/or coexist with
conceptual knowledge.
1.3.2
Ambiguity and Ambiguities
Among different illusions, it is especially the phenomenon of
ambiguity that make us think of perception as actively creative:
indeed, it makes clear that some kind of interpretation and
27
28
A general definition
Four levels of
ambiguity
introduction
previous knowledge is necessary. Ambiguity, understood as it
is defined in the OED ("ambiguous: uncertain, open to more
than one interpretation, of doubtful position") is a feature of
the environment that our brain faces every day, since it is confronted with situations or views that are open to more than
one interpretations. Retinal images are inherently ambiguous
(for example for size, shape and distance of objects), but also
language, situations, sounds. If, on the basis of the above model
of perception, interpretations are hypothesis, thus, ambiguity
means openness to two or more alternative hypothesis. Such
hypothesis can be mutually excluding in the instant but coexisting over time, or just coexisting. This thesis will explore
the hypothesis of different levels of ambiguity, on the basis of
the possibilities of different interpretation to be mutually exclusive, partially or totally coexist. In certain cases, as the above
discussed case of colour vision, the "choice" among interpretation is relatively simple, since it is limited by the design of
the brain. It becomes more complex in other cases, when no
single solution is more likely than other possible solutions. Each
interpretation becomes as valid as the other interpretations, and
there is no correct interpretation. As illustrated in Figure 1.5,
I will propose a framework of analysis identifying four levels
of ambiguity, whose first two levels are illustrated in Chapter
II as results of a brain imaging study on neural bistability. In
Chapter III I will introduce the concept of "illusion of life", as a
third level ambiguity, in which two possible interpretations are
coexisting in the conscious stage of the qualia but not mutually
excluding; the illusion of life always coexist with the awareness
of the non-animacy of the stimuli; nevertheless, such an illusion
is automatically and universally perceived (except for patients
with specific brain damages). Going further, we could identify
a phenomenon of ambiguity in anthropomorphism, in which
the concept of individual variability has to be introduced (cfr.
Chapter IV).
Figure 1.5: Different kinds of ambiguities
29
Part II
FIRST AND SECOND LEVEL
AMBIGUITY
2
P E R C E P T I O N O F B I S TA B L E A M B I G U I T Y
This chapter will discuss literature about how and where ambiguous perception takes place in the brain, and why ambiguity
is a crucial issue for understanding how the mind works and
how do we gather information from the surrounding environment. It will also discuss the results of an fMRI experiment
carried out in the general framework of ambiguity with a focus
on visual bistability, proposing a framework of analysis based
on multiple levels of ambiguity, which takes into account that
different interpretations of the stimulus content may not only exclude each other, but also coexist, depending on different levels
of ambiguity.
2.1
what is multistable ambiguity
Bistable ambiguous images are puzzling because they can be
spontaneously experienced as two equally valid percepts. Following the model of perception illustrated in Chapter I, when
the brain is confronted with an ambiguous stimulus perceptual
knowledge is oscillating between two different interpretation,
while conceptual knowledge is aware that the percept is not
actually changing. Following the literature, during the so-called
bistability illusion, the brain is confronted with one ambiguous
stimulus that can be stably interpreted in only one way at any
given moment, but will present two possible interpretations
over time; in other words, a stimulus is ambiguous when it is
consistent with two or more mutually exclusive interpretations
[Zeki, 2004].
Repeated viewing of ambiguous stimuli lead to spontaneous
perceptual switches, or "flips", where the brain alternates between two or more stable perceptual interpretations every few
seconds. Multistable ambiguity is an especially interesting illusion because it can help us understand the mechanisms generating a meaningful and coherent experience of the world,
even though the the information we have is fragmentary and
ambiguous. Visual illusions of ambiguity are actually a sort
or quintessential and simplified model of the choices that our
brain is confronted with everyday, and in every modality. Some
33
34
perception of bistable ambiguity
Figure 2.1: a) Necker Cube - b) Rubin Vase
Binocular rivalry
Auditory
multistability
Verbal
transformation effect
of the most well-know ambiguous figures are the Necker cube
and the Rubin vase (Figure 2.1). The perceptual interpretation
of the Necker cube oscillates between two different recessional
planes, while the interpretation of the Rubin vase alternates
between one vase and two profiles. Ambiguity is present also
in other perceptual phenomena, namely bistable apparent motion and binocular rivalry (Figure 2.2). Binocular rivalry results
from presentation of different images to each eye, thanks to a
dispositive separating the view of one eye to the other one. The
result is bistable alternation between the two images: the subject
is conscious of one stimulus at the time, and the perception is
incessantly fluctuating between the two stimuli. For instance,
the subject represented in Figure 2.2, looking at the vertical lines
with his left eye and looking at the horizontal lines with his
right eye will cyclically perceive only vertical lines alternating
with only horizontal lines.
Multistable perception (when the possible interpretations are
more than two) can characterise the auditory modality as well,
in the form of auditory stream segregation [Bregman, 1990] and
verbal transformation effect [Warren and Gregory, 1958]. Auditory stream segregation happens when two tones of a different
frequency are presented alternately in a repeating temporal pattern, as illustrated in Figure 2.3. Subjects’ perception alternates
between interpreting the sequence either as one stream with
fluctuating tones or as two segregated streams (in the picture,
indicated by the grey thick line).
Verbal transformation effect occurs when a word is cycled
in continuous repetition [Warren and Gregory, 1958] like for
2.1 what is multistable ambiguity
35
Figure 2.2: Binocular rivalry
instance the word "life". Initially, a percept corresponding to the
original form prevails, but after a certain period another percept
takes over and it stably alternates with the original one: in the
case of the repeated word "life", at a certain point the subject
will perceive the word "fly" alternating with "life".
Ambiguity is also a feature of many sentences, which can
mean two very different things, being in a way "bistable" and interpretable only by means of the context in which they are used.
There is a distinction between vagueness and real ambiguity:
truly "bistable" sentences are the ones whose "meaning" can flip
and can be stabilized only by context, for instance. "People like
us" [Gregory, 2000] or "She can’t bear children".
Bistability exist also in the modality of touch, even if it has
to be triggered artificially. A tactile illusion has been developed by Carter et al [Carter et al., 2008]. By means of a device
designed to provide the subject with vibrotactile stimuli, the
researchers could lead participants to report switches between
the perception of motion directed either up and down or left
and right across their fingertip, while the sensory input due to
the vibrotactile device stayed unvaried.
Nevertheless, visual ambiguity is undoubtedly the most studied phenomenon among all these. Indeed, ambiguous figures
have become an experimental tool to study interpretive cognitive
processes related to conscious awareness because the perceptual
experience alternates over time without any external changes of
the stimuli [Leopold and Logothetis, 1999]; [Sterzer et al., 2009].
Ambiguity in
language
Tactile ambiguity
36
Figure 2.3: Auditory streaming is a case of multistable perception in
the auditory modality
In particular, interest in this field has been growing thanks to the
advent of non-invasive brain imaging techniques such as fMRI
(functional magnetic resonance imaging), which is the technique
used for the experiment described further on.
2.1.1
Top-down vs
bottom-up
Neural processes underlying multistable phenomena
Even tough perception of ambiguous figures has been extensively studied, there are many contradicting findings and controversies. Traditionally, two main theories explain why ambiguous
figures reverse; the main distinction is between supporters of the
central role of bottom-up versus top-down processes [Leopold
and Logothetis, 1999]. The bottom-up theory proposes that neurons maintaining one percept fatigue over time and give rise to
neurons supporting the other percept; the switch should thus
be independent from high-level (cognitive) control. According
to the top-down theory, ambiguous figures do not switch spontaneously: the preconditions for seeing reversals are that the
viewer knows the figure is bistable, knows the possible interpretations of the figure, and switches are initiated by intention.
There are experimental findings supporting both theories, thus
more recent studies have adopted an hybrid model explicating bistability as the result of a continuous dialogue between
bottom-up and top-down processes [Toppino and Long, 2005]
[Mitroff et al., 2006]
Concerning the localisation in the brain where bistable ambiguity takes place, several studies show that changes in early
visual activity precedes conscious changes of perception. Thanks
to fMRI studies, it has been consistently demonstrated that binocular rivarly strongly effects V1, the earliest visual processing
area [Polonsky et al., 2000], [Tong and Engel, 2001] [Lee, 2005]. A
MEG study [Parkkonen et al., 2008] shows that early visual brain
areas (V1 and V2) reflect how an ambiguous figure is perceived,
both for binocular rivalry and for Rubin’s vase. Also activity in
primary visual cortex recorded with EEG could predict what
perspective is perceived even before a geometrical ambiguous
figure was presented [Kornmeier and Bach, 2005]. This study
demonstrated that perceived reversal of perspective was preceded by 160 ms with negativity in primary visual cortex. A
similar negative component was found 50 ms earlier doing the
experiment with a stabilized version of the figure. fMRI studies
have also shown that activity not only in V1 but also in another
post-retinal processing area, the LGN (lateral geniculate nucleus)
reflects the perceptual outcome of binocular rivalry [Tong et al.,
2006]. These experiments alone could support the bottom-up
thesis, that is to say the hypothesis that perception of ambiguous figures is resolved in a feed-forward manner by primary
sensory areas without the involvement of higher cognitive areas;
but, since there is evidence also for top-down processes, this
data can be interpreted as a proof that early visual processing
stages including V1 and LGN are the prerequisite for conscious
interpretation of percepts. In any case, the role of this early
visual areas is that of processing information but also influence
interpretation ("am I going to see a vase or a face?") either via
local interactions or through modulation by feedback signals
from higher cognitive areas [Tong, 2003]. Evidence for the latter
hypothesis comes from fMRI experiments on bistable apparent
motion. Indeed, whenever the perception of apparent motion is
inconsistent with added clues, early visual activity is suppressed
[Sterzer and Kleinschmidt, 2005].
Most studies agree on the role of the extrastriate cortex in
perceiving multistable ambiguities (extrastriate visual cortex
includes those areas lying beyond V1). Many fMRI studies revealed correlations between subjective perception and activity
37
Subcortical and
early cortical visual
processing
Extrastriate visual
cortex
38
Neural correlates of
flips
in the functionally specialised extrastriate cortex, that is to say,
areas specialised to process a certain type of information, reflecting the "content" of the stimulus itself. fMRI studies (see
[Sterzer et al., 2009] for a review) demonstrated that during
binocular rivalry, fluctuations in signals in extrastriate cortex
are similar to those during actual alternation of two different
stimuli, suggesting that the interpretation of ambiguous stimuli
are fully resolved at the stage of processing, without maintaining a representation of the temporally suppressed stimulus.
Actually, perception of binocular rivalry is influenced by information linked to the suppressed stimulus as well [Andrews
and Blakemore, 1999] indicating that the suppressed stimulus
is somehow "present" and processed in the brain. For instance,
the emotional content of a suppressed stimulus (e. g. a fearful
face) is still processed in the amygdala [Jiang and He, 2006],
[Williams, 2004], where activity is expected when the stimulus
is consciously perceived. A more recent and high resolution
fMRI study has also found activities corresponding to responses
to different object category in "houses versus faces" binocular
rivalry, namely activations in the fusiform face area (FFA) and
in the parahippocampal place area (PPA) even during binocular
suppression of one of the two categories of stimuli [Sterzer et al.,
2008]; in the same way, face-specific responses are reduced but
still present in EEG during a face-suppression period [Sterzer
et al., 2009]. In parallel with these findings on binocular rivalry,
studies on ambiguous motion and bistable images confirm that
activity in the extrastriate visual areas correlates with conscious
perception, and also that those areas are involved in the cyclical resolution of ambiguities. Following [Andrews et al., 2002]
and [Hasson et al., 2001], signals from FFA are greater during
the perception of two faces in the Rubin vase-face illusion; and
following the same principle, a bistable illusion whose elements
can be perceived either as a coherent shape or as a random
structure, will correlate with lateral occipital complex (LOC,
which preferably activates processing objects) activations when
the stimulus is perceived as coherent. In the case of ambiguous
apparent motion versus flicker, the conscious perception of motion will correlates with activations in V5 (area which processes
motion) while the conscious perception of flicker will not.
Another line of research has been focusing not on the perceptual states between one conscious perception and the other
one, but on the flips themselves, in other words neural events
correlating with perceptual reversals. Flips-related activity is
generally observed in extrastriate visual areas and it is associated with activations tuned to the features of the percept that is
perceived. For instance, perceptual reversals from faces to object
correlates with activations in the ventral stream [Leopold and
Logothetis, 1999] while apparent changes in motion direction
correlates with activation in V5, motion sensitive area. [Sterzer
and Kleinschmidt, 2007] suggested that prefrontal areas set off
changes in perception of ambiguous motion. In an fMRI study
they used both ambiguous and unambiguous moving dots; activation in right inferior frontal cortex appeared earlier than V5
activation in both conditions. Moreover, the frontal activation
happened earlier for spontaneous flips when looking at ambiguous stimuli, compared to when a flip was stimulus driven.
By using EEG, [Britz et al., 2009] were able to predict stimulus
perception in a similar manner to Kornmeier and Bach (2004),
they found significant increase of activity in right inferior parietal cortex 50 ms before a flip in perception occurred. It has
also been demonstrated that activity in the FFA can be used to
predict whether faces or a vase is perceived during presentation
of the Rubin figure [Hesselmann et al., 2008]. Indeed, activity
in the FFA is higher when subjects subsequently report perceiving two faces instead of a vase, suggesting that pre-stimulus
neural activity precede subsequent perceptual inference. Such
activations suggest that ongoing brain activity influences the
resolution of ambiguity before stimulus driven processes, and
a key role of functionally specialised areas in processing and
interpreting conscious visual perception.
fMRI activations correlated with perceptual reverals or flips
are also assessed in the parietal and frontal areas [Lumer et al.,
1998]. While extrastriate areas are equally activated both by
non-ambiguous and by ambiguous stimuli, parietal and prefrontal regions show higher levels of activity during ambiguity
illusions [Lumer et al., 1998]. Such special activations in frontal
and prefrontal cortex could suggest top-down mechanisms triggering a re-organisation of activity in the primary sensory areas
during flips as in [Leopold and Logothetis, 1999]. Or, from the
bottom-up perspective, they could reflect the feed-forward communication of events from the earlier visual cortex to higher
cognitive areas, a sort of initiating gateway for further processing. For example, changes in apparent motion perception
show that activations of the prefrontal cortex precede that of
V5 for bistable motion perception [Sterzer and Kleinschmidt,
2007]. This "initiating" role is corroborated by other findings,
39
Parietal, frontal and
prefrontal cortex
40
Bottom up versus
top down:
conclusions
drawn from a study suggesting that flips during observation of
a Necker cube are preceded by activations in the right parietal
cortex [Britz et al., 2009]. In such a framework, it is noteworth
that many people are able to control flips of bistable figures,
which suggest that perception is also influenced by top-down
factors. For instance, participants were able to voluntarily increase or suppress the frequency of switches for the Necker
cube [Tracy et al., 2005]. It is demonstrated that higher cognitive
areas have an effect on voluntary switches. Indeed, the ability
to voluntarily increase switches is diminished in frontal cortexdamaged patients; but, the same patients did not experience a
significantly different rate of reversals when flips where happening spontaneously [Windmann et al., 2006], while research of
effects of meditation consistently demonstrate that meditators
can alter the normal fluctuations in conscious state induced by
binocular rivalry [Carter et al., 2005]. The role of frontal cortex
in active switches suggests that top down influence may not be
necessary, but higher cognitive areas can play a role voluntarily
initiation changes, while alternation during passive viewing is
less dependent on prefrontal cortex. Activities in frontal and
parietal cortex is not only associated with flips, but also in
percept stabilisation. Indeed, the tendency of an individual to
stabilize a percept during, for instance, periods in which the
stimulus has been removed, is correlated with activations in the
frontal and parietals areas [Raemaekers, 2009].
In conclusion, experimental findings neither support a pure
top-down or bottom-up account. There is both support for reversals driven by primary visual areas, processing specific areas
such as the FFA and parietal and frontal regions. Even though
activations in typical higher cognitive areas appear to be related
to perceptual switches [Kleinschmidt et al., 1998]; [Lumer et al.,
1998]; [Sterzer et al., 2002] their involvement is still debatable.
[Zeki, 2004] argues that the frontoparietal network is involved
when there is a change in perception, without being involved
in the actual visual percept. One solution to the contrasting
experimental findings is that there might be interaction between
higher cognitive and primary sensory regions. Indeed, recent
studies do not point to either a purely top-down or bottom-up
model. For instance, [Britz et al., 2009] found that activation
in right inferior parietal cortex precedes the flips, while [Kornmeier and Bach, 2005] were able to predict perception from
activation in primary visual cortex. Also behavioural findings
seem to contrast a purely cognitive top-down account. It is true
41
that subjects who are not informed that a picture is ambiguous
do not always experience reversals, but evidence supports that
perceptual bistability be spontaneously experienced by children
as young as 5 years [Mitroff et al., 2006].
2.1.2
Attention and perception of bistable figures
The overlap between areas involved in spatial attention and
perception of bistable figures have lead to speculation about the
role of attention processes, suggesting that frontoparietal regions
could activate when re-directing attention to sensory input and
re-initiate an evaluation of the current interpretation, leading
either to maintain stable the current interpretation or change it.
[Slotnick et al., 2003] found common neural activation for both
voluntary shifts of attention and voluntary perceptual reversals.
Since perceptual reversals usually occur spontaneously there has
been some debate about the exact role of the frontoparietal network [Sterzer et al., 2009]. Areas involved in voluntary attention
may serve several functions, such as being engaged in feedback
to the sensory areas and perform an ongoing re-evaluation or
the visual experience [Leopold and Logothetis, 1999]. Another
suggestion is that ambiguous information is detected in early
sensory areas activates the frontoparietal network, which shifts
attention between the possible versions over time. According
to the so-called focal-feature hypothesis, local areas within an
ambiguous figure favour different global interpretations. Necker
himself (quoted in [Toppino, 2003] proposed that reversals are
driven by eye movements. Perception of the Necker cube can be
biased by moving the point of fixation during viewing [Peterson
and Gibson, 1991]; [Toppino, 2003], and similar effect has been
found other bistable figures as well [Tsal and Kolbet, 1985]. Also
free viewing conditions support that eye gaze and perception of
the Necker cube is closely linked [Einhauser et al., 2004]. After a
switch, the eye position also shifts. The authors suggest that the
changes of eye position serves as a negative feedback signal to
suppress the previous percept. [Leopold and Logothetis, 1999]
propose that the same motor processes underlie both selective
attention and bistable perception, and that there in most cases is
a close coupling between saccades and percept switches. Changing eye gaze and perceptual reversals could both reflect the way
we actively explore and constantly reinterpret the stimuli. It may
however be possible to alternate bistable figures without eye
movements.
The attention issue
42
To sum up, while previous studies opposed top-down [Leopold
and Logothetis, 1999] to bottom-up [Attneave, 1971], [Blake,
1989] models, now multistable illusion is considered as a continuous and frequent dialogue between low-level (sensorial)
and high-level (parietal and frontal) areas, aiming to verify in
time interpretation of stimuli (and initiating changes in perception). There may be a relation between selective attention and
perception of bistable figures, but this still needs to be clarified.
2.1.3
Levels of ambiguity
In his essay "The Neurology of Ambiguity" [Zeki, 2004] distinguishes between different levels of ambiguity, introducing
a new component in a discussion traditionally limited to the
bottom-up/top-down approach. Zeki proposes that ambiguity
has different layers, or levels, which correlate with the neural
activity in one or more processing regions with a conscious
correlate. Following Zeki, figures like the Necker cube belong
to the most simple form of ambiguity because brain activity
remains within the same area over time, with the same neural
correlates for both states it can be experienced. At a higher
level of ambiguity such as the Rubin figure, several processing
areas are involved and the current perceptual state becomes
conscious by fluctuation of neural activity between these areas.
The Necker cube is always seen as a cube, while some images
fluctuate between image categories such as the Rubin figure.
On a much more sophisticated level, artwork such as Vermeer’s
paintings are ambiguous in terms of narrative interpretation.
Zeki’s differentiation between levels of ambiguities is rooted
in his theory of ’microconsciousness’, where consciousness is
seen as distributed over functionally specialized processing sites
in the brain, which give rise to consciousness without further
higher interpretation. The level of ambiguity can be defined
at fluctuations within one or between several microconscious
states.
2.2
an experiment on two-levels bistable ambiguity
In the work reported here, to investigate if there are general
patterns of neural activations when looking at bistable figures,
we compared perception of bistable images, where the physical
stimulus remains the same but perception alternates between
two interpretations, with perception of two externally alternat-
2.2 an experiment on two-levels bistable ambiguity
ing stable images. Subjects were instructed to repetitively report
their conscious experience of the visual stimuli by key-presses,
reporting the occurrence of perceptual endogenous reversals
and the occurrence of actual reversals of stable percepts during a
"replay condition". Based on previous research we hypothesized
increased activation in the ventral occipital cortex, in parietal areas, as well as in frontal areas during bistable stimuli compared
with stable stimuli [Ilg et al., 2008]; [Kleinschmidt et al., 1998];
[Lumer et al., 1998]; [Sterzer et al., 2002].
Further we wanted to test the theory of levels of ambiguity, verifying if perception of figures with different levels of
ambiguity engage different brain areas. To compare levels of
ambiguity we used two types of bistable images. We define
those images where perceptual flip takes place within the same
category as "intra-categorical". This is the case for the Necker
cube (Figure 2.1 a). Here, what appears to be in the front can
occupy a different recessional plane with prolonged viewing,
but nevertheless it conceptually remains the same figure. This
contrasts with what we refer to as "inter-categorical", namely
the two images created by a single picture belong to different
categories, as in the face- vase bistable image (Figure 2.1 b). We
define as "intra–categorical" those images in which the perceptual flip takes place within the same category. In the present
study, inter-categorical stimuli alternates between bodies and
faces, since studies have demonstrated the selectivity of different
brain regions to the visual representation of faces [Kanwisher
and Yovel, 2006] and bodies [Peelen and Downing, 2007]. We
compared how neural activity during perception of bistable
intra-categorical images and bistable inter-categorical images
contributed to the overall activations during perception of all
bistable figures. To our knowledge, this is the first imaging
study comparing two levels of ambiguity. In line with [Zeki,
2004] above quoted theory we expected more involvement of
higher cognitive areas for the ambiguous inter-categorical images. As a third approach, we also addressed how brain activity
fluctuates over time, and if transient patterns of activation are
related to the type of images perceived. We investigated if separate neural mechanisms are involved in the transition from one
percept to another. The goal was to investigate if two percepts
belonging to the same attribute or category, for example the two
recessional planes of the Necker cube, evoke different areas of
activation compared to when the transition is from one category
to another, as in the Rubin face-vase bistable image. We looked
43
Levels of ambiguity
Content of the
percept
44
Experimental design
at neural activation during alternating percepts for both intraand inter-categorical figures. We hypothesized that same brain
area would be active when the translation would take place
within images belonging to the same category, while areas of
activation would change when the two percepts belong to two
different categories. Based on previous findings, we further hypothesized that during reported face perception the FFA would
respond stronger [Andrews et al., 2002]; [Hasson et al., 2001];
[Tong et al., 1998], while the same areas would be active when
the translation would take place within images belonging to the
same category.
Design: We used bistable images to separate, and therefore
compare, perceptual from stimulus-driven changes. In our study,
subjects were requested to repetitively report by key-presses
their conscious experience of flips during the observation of
bistable figures. Their responses were recorded and the subjective occurrence of perceptual reversals was replayed by alternating the two stabilized versions of the same percepts. We
used two sets of bistable images: intra-categorical and intercategorical. Subjects were instructed, when looking at "geometrical figures" (intra–categorical stimuli) to alternate key presses
when spontaneously perceiving a flip. For the inter–categorical
ambiguous figures, subjects were requested to press a specific
key indicating body perception and another key indicating face
perception. During the replay condition, subjects were presented
with stabilised versions of the ambiguous figures. The onsets of
the alternating stabilised pictures were the same as when subjects indicated seeing a flip in the ambiguous condition. Subjects
were also requested to perform key presses during the replay
condition, in order to control for motor responses.
Subjects: 16 healthy subjects (with normal or corrected to
normal vision; 8 females) were recruited through advertisements
requesting volunteers for a study about optical illusions. Their
age varied from 21 to 40 years (mean 29,8 years). Two subjects
were left handed. Informed written consent was obtained from
all participants and the study was covered by the Minimum
Risk Ethics (Minimum risk magnetic resonance imaging studies
of healthy human cognition, UCL Ethics Project ID number:
1825/003 / Data protection ref: Z6364106/2010/03/04). During
a first visit to the laboratory, prior to scanning, each subject
was requested to do a pre-test in order to qualify for the fMRI
experiment, by performing the same task to be carried out in
the scanner. X participants were excluded because they were not
able to perform the task correctly. During each scanning session
subject’s heart-rate and respiration were continuously recorded,
providing physiological measurements to be subsequently used
as regressors-of-no-interest in the first-level SPM analysis for
each subject.
Stimuli: Stimuli were generated using Cogent 2000 and Cogent Graphics (http://www.vislab.ucl.ac.uk/cogent.php). Four
intra-categorical images were chosen from the images in The
Psychophysics of Form: Reversible-Perspective Drawings of Spatial Objects, Hochberg and Brooks, The American Journal of
Psychology, Vol. 73, No. 3 (Sep., 1960), pp. 337-354, University of
Illinois Press) and 1 was created manually. Images were selected
following a pre-test in which four subjects viewed 8 images and
chose the ones that most easily flipped between two states for
all subjects. All five intra-categorical ambiguous images were
generated using Adobe InDesign CS3. Five inter–categorical images were chosen from existing ambiguous figures. The chosen
inter–categorical images were those displaying two mutually
exclusive interpretation, a body OR a face. Subsequently, each
ambiguous image was modified to create two stable versions,
which could be shown successively to the subjects using Photoshop CS3, and two stable versions of each image were created
(see Figures 2.4 and 2.5 ).
Each subject was exposed to two runs displaying the same
images in the same order. Each run began with a neutral background, lasting 26 s, during which the first six brain volumes
were discarded to allow T1 equilibration effects to subside. The
stimulus sequence then began. During each session the 10 ambiguous images (5 intra–categorical + 5 inter–categorical) were
displayed; subjects were instructed to alternate key presses
when perceiving a flip from one percept to the other. With
inter–categorical ambiguous images, subjects were instructed
to press a button to indicate whether it was a body or a face
that they perceived. During each session, ambiguous images
were mixed with a following replay condition of the subjects’
perception, displaying the two alternating stabilised versions of
each ambiguous image. The replay condition was implemented
using the recorded button presses relative to each ambiguous
image so that the time sequences remained the same. Consequently, the onsets of the alternating stabilised pictures were
the same as the alternating perceptual flips indicated by the
subjects. In order to control for motion correction, subjects were
also required to press buttons during the replay condition, each
45
46
time that the image changed. Each epoch lasted 16 s with an
inter—stimulus interval varying in duration between 3 and 5
s between stimuli where a blank grey screen was presented.
Stimuli were presented in a pseudo-random sequence, ensuring
that each ambiguous image was presented before its stabilized
versions.
Scanning details: Scans were acquired using a 1.5–T Siemens
Magneton Sonata MRI scanner fitted with a head volume coil
(Siemens, Erlangen, Germany) to which an angled mirror was
attached, allowing subjects to view a screen onto which stimuli
were projected using an LCD projector. An echo-planar imaging (EPI) sequence was applied for functional scans, measuring
BOLD signals (echo time TE =50 ms, repeat time TR= 90 ms,
volume time 4.32 s). Each brain image was acquired in a descending sequence comprising 48 axial slices covering the whole
brain. The experiment consisted of 2 runs; 100 volumes were acquired per run. After functional scanning had been completed,
a T1* weighted anatomical scan was acquired in the sagittal
plane to obtain a high resolution structural image (176 slices per
volume).
2.2.1
General fMRI Analysis
Analysis: Data were analysed using SPM8 (http://www.fil.ion.ucl.ac.uk/SPM).
The time series of functional brain volume images for each subject was realigned and normalized into MNI space (voxel size
3 x 3 x 3 mm) and then smoothed using a Gaussian smoothing kernel of 9 mm. The stimulus for each subject was modelled as a set of regressors in the SPM8 general linear model
(GLM) (first–level) analysis. The stimulus was a block design
merged with an event-related design; boxcar functions were
used to define regressors which modelled the onsets and durations of each stimulus, as indicated by each subject by means
of key–presses. Consequently, the regressors were: faces, bodies, geometrical state 1 and geometrical state 2. Regressors were
further subdivided in stables versus unstable; stable onsets corresponded to actual changes, while unstable onsets corresponded
to perceptual changes, as indicated by key-presses. Key-presses
were modelled as delta functions in an additional regressor.
Head-movement parameters calculated from the realignment
pre-processing step and physiological data acquired during the
scan (heart-rate and respiration) were included as regressors of
no interest. Regressors were convolved with the default SPM8
canonical hemodynamic response function (HRF), its temporal
derivative (TD) and dispersion derivatives (DD). The resultant
parameter estimates for each regressor (at each voxel) were compared using t–tests to establish the significance of differences in
activation between conditions. We have investigated five main
effects: Unstable Figures vs Stable Figures; in respect to inter–
categorical stimuli, Unstable Faces vs baseline and Unstable
Bodies vs. Baseline; in respect to inter-categorical stimuli, Geometrical State 1 vs. Baseline and Geometrical State 2 vs Baseline.
Contrast images for these effects for each subject were entered
into random–effect analyses at the second level.
A conjunction analysis [Friston et al., 1999] was performed
to asses how the two types of bistable images, intra-categorical
and inter-categorical, each contributed to the areas of activation
found when contrasting all bistable with all stabilised figures.
Separate contrasts were made for each for both types of figures: Bistable intra-categorical vs. Stable intra-categorical, and
Bistable inter-categorical vs. Stable inter-categorical. To make the
conjunctions, the contrast Bistable Figures vs. Stable Figures was
paired separately with the contrasts Bistable intra-categorical vs.
Stable intra-categorical, and Bistable inter-categorical vs. Stable
inter-categorical.
For the even-related part of the analysis we made contrasts for
inter-categorical stimuli: Bistable Faces vs. All and Bistable Bodies vs. All, and in respect to inter-categorical stimuli: Bistable
state 1 vs. All and Bistable state 2 vs. All. Regressors were
convolved with the default SPM8 canonical hemodynamic response function (HRF) and a first-order Taylor approximation
in terms of the temporal derivative (TD) was added [Friston
et al., 1998]. Whole brain t-maps for main effects of interest and
for temporal and dispersion derivatives were created for each
subject. Contrast images for the main HRF and its TD were computed separately for each effect investigated. Then, second level
random-effects models were created for each contrast, using the
t-maps from the first-level fixed effects analysis. The onsets of
internally and externally driven changes were modelled based
on the recorded key presses and set to a fixed duration of one
second. Perception of faces and bodies as well as the two states
of the intra-categorical figures were also modelled separately
based on the recorded key presses. A more complex model for
analysing the event-related results has been chosen; adding the
TD to the canonical HRF gave us the possibility to model BOLD
signals with deviations in onsets. The Henson et al. (2002) have
47
Conjunction
analysis
Event-related
analysis
48
demonstrated that it can be useful to model differential latencies
of the HRF as a to investigate if BOLD signal may occur earlier
or later then what the canonical parameter estimates.
2.3
2.3.1
Blocked fMRI
analysis: Neural
specificity of bistable
images
Conjunction
analysis: comparing
levels of ambiguity
results
Behavioural results
All subjects reported that they were able to see the stimuli
during scanning and alternate their key-presses according to the
instructions. Overall, subjects perceived each type of state for a
similar period of time during presentation of bistable images;
bistable faces mean 2.5, ± 2.35 s., bistable bodies mean 2.1,±
1.47 s., bistable geometrical 1 mean 2.3, ± 1.64 s., and bistable
geometrical 2 mean 2.51, ± 2.29 s. Subjects indicated percept
durations ranging from .02 to 15.12 s. The periods between
flips found here are shorter than what subjects indicated in
Kleinschmidt et al. (1998) who had inter-reversal times of 9.0
±2.6 s and 8.1 ± 1.9 s, but in line with studies of ambiguous
motion where similar durations of alternating percepts were
observed ([Ilg et al., 2008]).
We compared spontaneous and stimulus-driven perceptual
switches. We first contrasted perception of Bistable Figures with
perception of Stable Figures with blocked design analysis. Spontaneous perceptual changes were correlated with increased activations in right inferior and superior parietal lobules, and in
bilateral inferior frontal, middle frontal, and insular cortex. Increased activity was also observed in regions of the anterior
cingulate cortex, supplementary motor area, and left primary
motor and somatosensory cortex. Selective activation during
perceptual transitions were also found in the right extrastriate
visual cortex and the cerebellum, putamen and thalamus (see
Figures 2.6 and 2.7).
A conjunction analysis was performed to provide more insight into how each type of figures contributed to the overall
activation found during perception of bistable stimuli. Several
similar areas of activation were identified for overall bistable
perception in conjunction with both inter- and intra-categorical
bistable perceptions respectively (Figures 2.8 and 2.9 ). There
were clearly also differences between the two conjunctions: the
intra-categorical figures evoked bilateral activation of superior
parietal lobule while inter-categorical figures only showed significant right activation of this region. The significant regions
2.3 results
were also noticeably larger for the intra-categorical conjunction,
both in frontal and parietal areas.
We assessed if face perception was correlated with increased
BOLD activation in the FFA, known as a region specifically
involved in face processing. We predicted that we would find
percept specific activation during face perception, which has
also been demonstrated, in previous studies [Andrews et al.,
2002]; [Hasson et al., 2001]. As hypothesized, our results showed
clear activation in the fusiform gyrus when subjects indicated
perceived faces during inter-categorical stimulus presentation,
an activation pattern we did not find in any of the other contrasts
with bistable stimuli. To ensure we did not miss any activation
for the contrast Bistable bodies > All, we did a small volume
correction for the contrast Bistable bodies > All with a 16 mm
sphere at [38 -58 -14] which was identified as the extrstriate body
area (EBA) [Downing et al., 2001]; no significant voxels were
revealed. For the intra-categorical stimuli we did expect to have
activations in the same areas for both Bistable state1 > All and
Bistable state2 > All. Our results showed significant activation
only for Bistable state2 in right middle occipital gyrus. We did a
small volume correction to test if there was possible activation
in the same area for State1 with a 16 mm sphere at [36 -85 7].
The small volume search revealed a highly significant cluster
(x, y, z = 36, -82, 7, Z = 4.79). The central interest of the eventrelated part of this study was to investigate if activation would
change between the two perceptual states for both inter- and
intra-categorical bistable images. For the inter-categorical images
there was a correlation between face perception and activation in
the fusiform face area, which was not found during perception
of bodies. For both states of the intra-categorical figures we
identified significant activation in the same area, the middle
occipital gyrus. The middle occipital gyrus has previously been
associated with spatial attention [Noesselt et al., 2002]. All eventrelated contrasts showed deactivations in primary visual regions
in line with previous findings by [Kleinschmidt et al., 1998],
where deactivations in occipital areas also were found during
bistable perception.
The contrast estimates showed that the main canonical HRF
accounted for very little of the activation (see figure 2.10 for
a representative example), while the TD is much larger and
positive which shows that activation actually takes place earlier
than the events [Friston et al., 1998]. For the deactivations in the
occipital regions the TD was negative, indicating that suppres-
49
Event-related
results: contrasting
interpretations
Latency
50
sion might take place just before upcoming perceptual switches.
Also for the deactivations, the main signal modelled with the
canonical HRF was much lower compared to the estimate of the
TD. This could indicate that the deactivations are more transient,
and may occur in the transition between perceptual states rather
than in the period when the percept is temporarily stable.
2.4
Neural specificity of
bistable images
discussion
The aim of the first part of our study was to compare spontaneous perceptual reversals with externally driven changes
in terms of neural activity. In accordance with previous imaging studies using bistable percepts [Kleinschmidt et al., 1998];
[Lumer et al., 1998], we observed activations in several frontal
and parietal areas. As expected we did not find any notable
activations in the primary visual system because the image was
held constant. It is unlikely that our results reflect the motor task,
because subjects were doing the same key presses during both
bistable and stabilised stimuli presentation. The frontoparietal
activations could reflect a continuous loop of communication
from the visual cortex to higher-order areas. One interpretation
is that these areas are involved in a feedback to early visual areas,
re-evaluating the multistable percept over: this would support
a top-down explanation. Alternatively, changes are driven by
signals from lower perceptual areas due to destabilization of
the current percept, in line with the satiation / bottom-up hypothesis. The role of the frontoparietal attention network would
then be to detect changes or to momentarily stabilise the current interpretation. The frontal and parietal regions identified
in our study are similar to the areas found during both voluntary reversals of bistable images and changes in visual spatial
attention [Slotnick et al., 2003]. In the current study, it is not
likely that frontoparietal regions reflect voluntary changes in
attention because we specifically instructed the subjects not to
try to voluntary elicit the flips, but to signal report reversals.
The involvement of these regions in this context suggests a coupling between spatial visual attention and dynamic changes of
visual perception. It is still debatable if these activations reflect
initiation or detection of changes in interpretation. We speculate that the brain is constantly engaged in interpretation and
revaluation of perceptual input, and during this process attention is shifted to different features of the figure. These changes
of attended local features could initiate switches. Our expla-
2.4 discussion
nation corresponds to the theoretical framework suggested by
[Leopold and Logothetis, 1999], and is supported by behavioral
results showing that attending to different local features of an
ambiguous figure bias perception [Peterson and Gibson, 1991];
[Tsal and Kolbet, 1985]. The pre-central gyrus has found to be
involved in selective processing of relevant visual targets rather
than directing attention towards a cued target [Hopfinger et al.,
2000]. The area also contains the frontal eye fields, an area also
found in the study by [Kleinschmidt et al., 1998]. In our study
a fixation cross was not used, so activation could be due to
reversal-related changes of gaze or covert shifts of attention. Several areas in the cerebellum were identified when contrasting
whole periods of bistable perception with stabilised replays. The
cerebellum is traditionally associated with movement at speech
function, but recent studies also show involvement in mental
activities such as attention, error detection (see [Ito, 2008] for a
review). It has also been demonstrated that the posterior part
of cerebellum (lobule VII, crus I) supplies temporal information
to frontoparietal spatial attention network involved in visual
attention [O’Reilly et al., 2008]. Involvement of the posterior
cerebellum was more active when subjects had to predict the
trajectory of an occluded moving object. In our study, it may be
possible that the cerebellum predicts the upcoming dominant
visual percept.
In the conjunction analysis, larger parts of the overall activations during bistable perception were accounted for by activation
during viewing of intra-categorical figures. There may be several
ways to interpret this finding. Our initial hypothesis, in line with
[Zeki, 2004], was that reversing figures represent a very simple
form of ambiguity and are not affected by top-down factors,
while face/body figures should trigger an activation in frontal
areas (top-down). Zeki’s hypothesis seems to contrast the fact
that we found larger areas of frontal and parietal activation
during perception of intra-categorical figures. However, there
may also be other explanations.
If, indeed, we are less able to control alternations of intracategorical figures, and the frontoparietal network reflects detection of changes in perception, then increased activity could
be due to less anticipation of changes. In our study, several
subjects spontaneously reported that they were able to see both
figures at the same time for the inter-categorical figures, while
this was not the case for the intra-categorical ones. This implies
that inter-categorical are not "purely" bistable, then they are
51
Levels of ambiguity
52
Contrasting
interpretations
less effective as stimuli and that could also account for why
we found less ambiguity-specific activation. In order to check
this hypothesis, after the experiment we asked subjects whether
they had the impression they could see both images at the same
time in geometrical stimuli and in face/body stimuli. while only
12% of the subjects said they could perceive geometrical (intracategorical) two interpretations at the same time, 56 % said they
had the impression they could see both face and body in the
intra-categorical images. Therefore in terms of ambiguities level,
we affirm that intra-categorical images belong to second level
ambiguity. For the event-related analysis we hypothesized that
activation would take place within the same brain area for both
states of the intra-categorical stimuli, while activation would
change back and forth between two areas during perception
of inter-categorical stimuli. As expected, we did find increased
activation in the same area for both states of the intra-categorical
stimuli. For the inter-categorical stimuli, we did find activation
in FFA during face perception in line with previous studies
[Andrews et al., 2002]; [Hasson et al., 2001]; [Tong et al., 1998].
This supports the general idea that the conscious experience of a
figure is correlated with activation in its processing specific area.
A cube will remain a cube even if it is seen from a different perspective, and therefore processing takes place within the same
area. Activation for one state was only found using a small volume correction. A weakness of this study is that it was difficult
for subjects to report which was the dominant interpretation of
intra-categorical stimuli, while it was much easier to assign one
button to perception of faces and one to perception of bodies
for the inter-categorical figures. In further studies, our findings
could be supplemented with a similar experiment using ambiguous motion in the future because direction of movement is
easier to report than perspective. The TD of the HRF modelling
perception of faces indicates that activation in FFA actually occur
before the reversal is consciously perceived. This finding is in
line with the study by [Andrews et al., 2002] showing that FFA
activation can be detected before subjects report seeing a face
when looking at the Rubin figure. Also transient deactivations
were found in occipital areas, most consistently in the lingual
gyrus. This area has been shown to be sensitive to direction of
spatial attention [Giesbrecht et al., 2003], and similar patterns of
deactivation have been found during inhibition of unattended
visual stimuli [Hopfinger et al., 2000]; [Slotnick et al., 2003].
2.4 discussion
2.4.1
Conclusion
We addressed the general question of ambiguous perception
in three different ways. We compared endogenous with exogenous changes by contrasting perception of bistable figures with
a replay condition using stable figures. With our results, we
support the hypothesis that frontoparietal processes constantly
re-evaluate the current interpretation of the sensory stimulus
input causing changes in subjective perception. The neural processes underlying spatial attention and perception of ambiguous
stimuli appear to be similar, but the exact role of attention needs
to be further investigated. In general, endogenously driven perceptual changes seem to involve widely distributed brain areas.
Further, we investigated neural correlates of different levels
of ambiguity. Surprisingly, intra-categorical stimuli evoked a
larger magnitude frontal and parietal activation than the intercategorical figures. The implication of this finding is that it
may be useful to distinguish between different types and levels
of ambiguity. We propose that in first level ambiguity frontoparietal activations are more significant and this fact correlates
with a subjective experience of a more "pure" perception of
bistability, implying the mutual exclusiveness of the stimulus
interpretation. Second level ambiguity, when activations take
place in two or more different brain areas, may correlate with
the coexistence of interpretations and with a diminished activity in the fronto-parietal network, which appears to be an
ambiguity-specific neural activity. Our findings could further
be expanded to involve cognitive multistability, such as more
open-ended ambiguities, referring to gender or racial ambiguities [Chiu et al., 2011], situation-related ambiguity [Zeki, 2004]
or, as we are going to discuss in the next chapter, the illusion
of life. We also found support for the hypothesis that for first
level ambiguity, activation takes places within one brain area.
During perception of ambiguous figures changing between different categories, neural activity fluctuates between two or more
processing areas. Our study confirms that activation changes in
processing areas are correlated with the each stable experienced
percept over time.
53
54
Figure 2.4: Experiment stimuli: bistable intra-categorical images + stabilized versions
2.4 discussion
Figure 2.5: Experiment stimuli: bistable inter-categorical images + stabilized versions
55
56
Figure 2.6: Bistable Figures > Stable Figures
2.4 discussion
Figure 2.7: Global 3D view of activations for the contrast internal
change > external change for a random effects analysis
with 16 subjects: selected activations superimposed on to
averaged anatomical sections
Figure 2.8: T statistic for Bistable > Stable in conjunction with Intracategorical: Bistable > Stable switches (left) and Intercategorical: Bistable > Stable switches (right)
57
58
Figure 2.9: Bistable activations conjoined with Inter-categorical and
intra-categorical bistable activations
2.4 discussion
Figure 2.10: Bistable faces > All. FFA activation projected onto averaged structural scans (left) and main HRF and TD plotted
for FFA [38 -58 -14] (right)
59
Part III
THIRD LEVEL AMBIGUITY
T H I R D L E V E L A M B I G U I T Y: T H E I L L U S I O N O F
LIFE
Chapter II has illustrated how and where in the brain the illusion of ambiguity takes place. Introducing the concept of levels
of ambiguity correlating with fronto-parietal activations and
coexistence, at the conscious level, of different possible interpretations. In this chapter I propose the concept of life perception
as an illusion, the illusion of life. This specific illusion results
in the qualia of attributing aliveness, and animacy attributes
such as intentions and emotions to objects, in spite of the certain
knowledge that such objects are not alive. This illusion could
descend by the specific knowledge of behaviour and appearance
of alive entities; but it is so strong an so compelling that suggests
that animacy perception is due to a perceptual knowledge, or an
inherited concept, that is present in our mind and organises our
perceptions even when we face blatantly non-animated stimuli,
like geometrical figures. This illusion may represent a higher
(third) level of ambiguity, in line with our results of Chapter
II. Such results demonstrate that ambiguity-related activations
are more likely to correlate with intra-categorical images, that
are also the most decidedly "mutually exclusive" interpretations.
Inter-categorical images are more likely to be less exclusive. As
the illusion of life represents a higher level ambiguity, the observer will attribute aliveness-related features to objects while
continuously maintaining the awareness of their non-aliveness.
The illusion of life is so strong and compelling that many studies
reported the impossibility of preventing the subjects of anthropomorphizing stimuli [Schultz et al., 2004]. [Castelli et al., 2000]
pointed out that several subjects were anthropomorphising also
random-moving stimuli.
3.1
perceptual knowledge of life
Attributes and features of animacy can elicit in us strong automatic reactions that may be classed under that label of "perceptual knowledge" which persists in qualia and can contradict
conceptual knowledge in illusions. The ability of perceiving
animacy, being obviously useful and especially robust, allows
63
3
Automaticity of
illusions
64
The importance of
life perception
third level ambiguity: the illusion of life
us not only to immediately spot all "living beings" surrounding
us, but also to attribute intentions, emotions, thoughts, and a
theory of mind to them. The mechanism of "life perception"
is so powerful that it invariably leads us to assess some "false
positives", hence the illusion of life: to perceive inanimate objects
as animate, to ascribe them life-related attributes (e.g. intentions,
awareness, perceptions), and to experience towards them feelings such as empathy and affection. The false positives caused
by the efficiency of "life perceptions mechanisms" are always experienced as ambiguous, since they conflate cognitive awareness
of "non-aliveness" with partial perception (qualia) of "aliveness"
(e.g. attribution of personality, feeling of sympathy). The nature
of the life perception as a crucial specific knowledge causes its
manifestation as illusion of life in ambiguity-generating situations.
The evolutionary necessity of spotting alive creatures is mirrored in our perceptual ability to identify biological movements,
which is amazingly effective. This was first demonstrated in
classical experiments by [Johansson, 1973], who showed that a
few dots of light placed strategically on a moving human or
animal body are instantaneously organized into the coherent
percept of a living creature.
[Baron-Cohen, 1995] defines a partial aspect of life perception
as the ID: the Intentionality Detector. ID is a "perceptual device
that interprets motion stimuli in terms of the primitive volitional
mental states of goal and desire", thus attributing intentionality to anything with (apparently) self-propelled motion. ID is
supposed to be a very basic function, working through sensory
modalities. It is based on [Premack, 1990] argument that infants
distinguish between two kinds of objects, those that are and
those that are not self-propelled. Premack follows research lines
by [Leslie and Keeble, 1987] that describe the "appropriate stimulation" (the percept needed to elicit the concept of causality)
as temporal and spatial contiguity between appropriate events.
Applying and extending this argument, Premack affirms that
the brain deduces basic assumptions from motion features, inferring the principles of causality, intention and reciprocation.
Premack follows the hypothesis that the perception of intention
and causality are "hard-wired perception based not on repeated
experience but on appropriate stimulation". It is not motion
itself that is critical but change: a switch from rest to motion
(or vice versa), and from one speed/direction to another; "just
as causality is the infant’s principal hard-wired perception for
3.1 perceptual knowledge of life
non self-propelled objects, so intention is its principal hardwired perception for self-propelled objects". [Mandler, 1992]
also attempts to investigate what distinguishes the "animate"
from the "inanimate", arguing that this is one of earliest concepts formed in early development stage, and attributing its
perceptual "gateway" to the analysis of different kinds of motion.
Causal perception through motion is a perceptual mechanism
first studied by [Michotte, 1946]. Causal perception is what allows us to "attribute" cause-and-effect relations to facts; this
concept is so strong that we attribute causality and intentions
even to bi-dimensional moving shapes moving schematically, by
describing their motions with intentionality verbs. All these results demonstrate that hard-wired brain functions related to "life
perception" would lead to "false positives" provoking attribution
of intentions and goals to inanimate objects or even shapes. The
classical demonstration of this mechanism is a study by [Heider
and Simmel, 1944], where subjects were asked to describe a film
in which geometric shapes moved. The subjects tended to ascribe intentionality and causality to the shapes themselves or to
construct narratives where squares and triangles act as human
characters. From the neurobiological point of view, Warrington
and Shallice [Warrington and Shallice, 1984] led a seminal study
on four patients struck by herpes simplex encephalitis. In all patients, researchers identified a specific difficulty in identifying visually and verbally - living things more than inanimate objects.
This kind impairment has been defined as "category-specific
semantic deficit". Since then, many studies have been carried
out on patients investigating the animate / inanimate categories
as issues concerning the organisation of conceptual knowledge
in the brain. For a complete review of the approaches to this
debate, see [Caramazza and Mahon, 2006] where it is suggested
that the domains in which conceptual knowledge regarding
this issue are organised are living animate, living inanimate,
conspecifics and tools. Inside each of these domains, the authors
suggest that there would be different mechanisms for the analysis of visual form, visual motion, and conceptual knowledge, as
well the attribution of intentional content. From the biological
perspective, a "perceptual life detector" has been proposed in
relation with biological motion perception in animals [Johnson,
2006]. Experiments with scrambled point light displays gave
results that the researchers interpreted as evidence of a visual
filter "tuned" to motion of the limbs of an animal in locomotion,
65
Animacy perception
as a category
66
thus functioning as a general detection system for articulated
terrestrial animals.
3.2
Intentionality in the
social brain
Seminal studies on
the illusion of life
the illusion of intentionality
As discovered by Johansson, biological motion perception is
exceptionally robust in humans (and animals); but, a feature
allowing of the illusion of life is that some movements are perceived as animate even if what is moving is a blob, dots or
geometrical objects. Motion perception is central to life perception; indeed, motion-related information can not only provide
the observers with the feeling of animacy but also cause attribution of roles, goals, intention, personality and emotions. As
a common characteristic of illusion, (see Chapter I, about the
hollow face perception), also the illusion of life triggered by motion information is perfectly compatible with the awareness of
its deceptive nature. When viewers make "inferences" ascribing
animacy to moving geometric shape, they do it being fully aware
that what they are seeing are geometric shapes. Nevertheless,
the illusion is so compelling that it is impossible not to ascribe
animacy to these shapes. Such an automaticity, once again, typical of illusions, is a finding that may be interpreted against a
pure top-down framework of analysis. Activations correlating
with animacy attribution of non-alive stimuli are surprisingly
coincident with neural activations relative to perception of other
individuals: the temporal parietal junction (TPJ), the FFA and
both ventral and dorsal medial prefrontal cortex (VMPC and
DMPC). This areas constitutes what is known as the "social
brain" [Brothers, 1990], [Skuse et al., 2003]; [Adolphs, 2003] because it is generally activated during social tasks. [Michotte,
1946] and [Heider and Simmel, 1944] where the first to investigate how do motion features could lead to animacy attribution,
working in the same years but separately. Michotte with his experiment demonstrated that different features of motion can be
interpreted as physically caused while other as psychologically
caused. For instance, if the surface of moving objects A comes
to contact with the surface of object B, and B immediately starts
moving, the event is interpreted by all the viewers as a transfer
of physical motion. But if B moves not immediately but after a
pause, the attribution of animacy becomes compelling and the
motion is interpreted as psychologically-caused: object B moves
because object A told it to move or it tries to escape from A etc.
Heider and Simmel (1946) have been working on a 2.5 minutes
3.2 the illusion of intentionality
movie. The video casts three geometrical shapes, two triangles
(a small one and a big one) and a circle. The three shapes were
moving around, in and out a rectangular perimeter, displaying
different motion features. During the experiment, subjects were
requested to describe what happened in the video; with very
few exceptions, the subjects were reporting a narrative including attribution of intentions, goals, social relations, gender. For
example, the circle is almost always interpreted as an aggressive
man and the two triangles as a couple trying to avoid him or
escape him, while the perimeter is interpreted as a building.
Other studies [for a review see (Scholl and Tremoulet, 2000)]
have been following this first experiments, trying to identify
motion features of the Michotte tradition and theory of mind
issues for Heider and Simmel. In the Michotte tradition, studies
on a single moving object have singled out some features linking
motion to animacy attribution demonstrated that self-propelled
motion is crucial [Stewart, 1982]; [Tremoulet and Feldman, 2000];
also, environmental features are important, since animacy can
be seen as emerging from an interaction with the context, as well
as changes in velocity and directions. Studies containing two or
more moving object seems to be more compelling in eliciting the
illusion of life, probably because objects constitute environment
and create interaction for each others. [Bassili, 1976] demonstrated that timing is crucial for perception of animacy, since
temporal events suggest whether the objects are interacting (and
therefore animated) or not; and time contingencies would influence the psychological interpretation. When motion paths
and timing coincided with each other an object was interpreted
as "leader" and another one as the "follower", and especially
the following object was eliciting intentionality attribution, but
when motion paths were random, the impression of agency was
lessened [Dittrich and Lea, 1994] Nevertheless, intentionality
does not correspond to animacy, which is a propriety on its own,
but contributes to create the illusion of animacy. This is demonstrated by an experiment by [Opfer, 2002] which designed two
sets of blobs, identical in shape - but one was autonomously
moving whilst the other one was "chasing" objects; the rates
of animacy were higher for the intentionality provided blob.
[Blythe et al., 1999] studied the interaction possibilities implied
by two objects moving in pair with each other; objects were simple computer cursors "moved" by participants to the experiment
whose had roles to interpret (chase, court, follow). An algorithm
based on a very few motion parameters could successfully cate-
67
68
The role of motion
The obligatory
nature of illusions
gorise the trials, suggesting that not only intentionality but also
psychological content can be delivered with very few motion
clues. Affective content can be delivered also by motion clues,
as demonstrated by [Rime et al., 1985] who found a very high
consensus between US and European subjects while defining the
emotions conveyed by geometrical shapes such as the ones used
by Michotte. What is interesting here is that the consensus was
remarkably lower when the shapes were substituted by human
silhouettes. Minimal information seems to be more adequate
to elicit the illusion of life, and especially robust in the case of
stimuli like point light displays, and even just limbs [Troscianko
et al., 1996].
Summing up, literature demonstrates that autonomous motion, is quite a good way to elicit animacy illusion, but less then
goal directed motion showing an interaction with the environment or between two objects. The illusion of life is so compelling
since based on strong perceptual clues that this mechanisms
are valid not only for human adults but also for children and
babies. Infant under 1 year can categorise goal-directed shapes.
Furthermore, motion as a clue of intentionality and animacy is
stronger when "pure" and not associated with other information
like form (even if the form openly leads to anthropomorphism).
This suggest that intention attribution or agency may be hardwired in the brain [Scholl and Tremoulet, 2000]; [Tremoulet and
Feldman, 2000]. Slightly more complex movement can go furher
and convey not only intention but emotions and mental content,
as in te study of [Blythe et al., 1999]. Another clue indicating that
form is not useful if not counter-productive is that attribution
of intentions and psychological content to Heider-like objects is
due to movements features and changes of location over time,
but not to the shapes themselves. Other version of the Heider
movie has been produced, in which movement has been disrupted, causing the absence of illusion in the description of the
scenes; whilst in a version in which the forms where changed
the description remained the same as with the original movie
(Berry et al, 1992).
The most striking feature of the illusion of life is its compulsory nature, as we said above, typical of illusions. Despite
knowing that we are watching geometrical shapes, the urge to
attribute them animacy features is compelling. This "qualia" of
"obligatory" perception has been studied by [Hashimoto, 1966]
who has been working with a group of observers looking to a
Heider-like movie. He told the subjects that they had to describe
3.3 the illusion of life in the brain
the shape moving by keeping in mind that they were just looking at geometrical objects and thus avoiding any reference to
animacy. The subjects were nevertheless describing the movie
with anthropomorphic terms "leaking" out of the descriptions,
and this has been the first demonstration of the obligatory nature of the illusion of life. Following Hashimoto’s study, other
researchers have been investigating such a compelling impression. Other methods used have been counting in the descriptions
the words depicting social roles, affective content, and a specific
analysis tool - the Linguistic Inquiry and Word Count [Heberlein, 2008], organising in 74 categories the references to animacy
in the description of the stimuli. Using this software, Heberlein
and colleagues found that, even explicitly forbidding subjects
to describe in anthropomorphic terms a Heider-like movie, the
percept of intentionality is powerful enough to leak through
the verbal descriptions: all the subjects failed in describing the
shapes without using animacy-related terms. They also found
that the rate of speech in subjects forbidden to describe the
movie in anthropomorphic terms was significantly slower then
the control group who describing the scene without any instruction; these data demonstrate the effort in overriding the percepts
of intentionality, supporting the hypothesis that intentionality
and animacy are hard-wired being inherited concepts in the
brain.
3.3
the illusion of life in the brain
fMRI studies have been investigating the neural events correlating with the attribution of intentions and perception of animacy.
As anticipated at the beginning of the Chapter, many structures
that appear active when perceiving stimuli eliciting the illusion
of life seems to be also involved in perceiving social facts, and
indeed the active circuit has been labelled "social brain". These
brain areas involve the posterior sperior temporal sulcus (pSTS),
the amygdala, the fusiform gyrus, the ventral and medial prefrontal cortices, the tempo-parietal junction. The social brain
also include this areas, as proposed by [Brothers, 1990] who
defined as a circuit specialised in making inferences about behaviour (mental states and predictions of actions based on them).
fMRI studies have been obtaining such a brain map by scanning
subjects while they were looking or describing Heidder-like
or Michotte-like movies. Generally, this movies were depicting
shapes animated by intentions, but animacy, as specified in the
69
70
Superior temporal
sulcus
Other activations
previous section, does not overlap with animacy (but it is a
very good cue for it). Animacy correlates have been isolated
with a contrast analysis from perception of intentions attribution
by showing movies of goal directed motions versus physically
random [Schultz et al., 2004], physically but not psychologically
caused [Blakemore et al., 2003] or geometrical motions [Castelli
et al., 2000].
[Schultz et al., 2005] have been designing an experiment isolating perception of movement from animacy perception. The
stimuli used were animations of two autonomously propelled
discs, in which, periodically, one "chases" or "follows" the other
one. By continuously varying the disc movements, alternating
between interactive and non-interactive, the analysis could grasp
the perception of interaction isolating it from the perception of
movement. In the moments in which the movement was interactive (when one disc was chasing the other one) the stimuli were
perceived as more animated. When subjects were indeed observing interactive motions, bilateral regions of posterior STS/STG
were found to be activated in contrast with the non-interactive
(non correlated) motions. This area was active even when the
task given to subjects was meant to distract their attention from
the perceived animacy of the objects, for instance, when the
subjects were told to judge velocity or other features irrelevant
to animacy. This means that this brain area processes animacy
even in absence of conscious attention devoted to it; nevertheless, when attention is elicited towards animacy (when subjects
are instructed to observe the interaction between the shapes, or
to try to "interpret" the casing strategy of one object) activity
in the posterior STS/STG is even increased [Blakemore et al.,
2003]; [Schultz et al., 2004]. This suggests that the pSTS/STG
is the area specialised for perceiving animacy, as the same area
is active is animated in correlation with the event of spotting
biological motion while viewing a point light display stimulus
[Zacks et al., 2006].
Researchers have been trying to identify neural correlates of
animacy perception. [Castelli et al., 2000] compared activations
of subjects viewing three kinds of Heider-like stimuli: random
movements, goal-directed movements and movements triggering psychological content (e. g. seducing, bullying, etc). Four
regions, pSTS regions, medial prefrontal cortex, fusiform gyrus
and extrastriate regions of the lateral occipital cortex were more
active looking at goal-oriented movements (chasing, following)
and in the high-psychological content movements if compared
to random moving stimuli. [Martin and Weisberg, 2003] have
found a consistent map of activations viewing animated actions
compared to objects. In a study showing thre geometrical objects
interacting, subjects were asked to judge whether the objects
were friends (thus imposing a priori an attribution of animacy)
[Schultz et al., 2004] and they showed activations, if compared
to non animated stimuli of which subjects had to evaluate the
weight, in the fusiform gyrus, amygdala temporal pole, medial
PFC and STS. Particular activations as been found in the FFA, after a localization. This activation of FFA in stimuli without faces
might mean that either the FFA is included in social judgements
even whether stimuli have no faces, or that the FFA might by
potentiated by inputs from the amygdala which as we saw may
be implicated in processing social stimuli. This latter interpretation is reinforced by a damage study [Heberlein and Adolphs,
2004] on a subject with a bilateral amygdalal damage, who was
describing in totally non-anthropomorphic terms the original
movie by Heider and Simmel.
The amygdala is known for processing emotional content,
in particular processing fear and rating trustworthiness. The
amygdala may be relevant for directing attention towards socially relevant stimuli, since it projects to frontal and temporal
regions; thus the amygdala may project signals to pSTS, prefrontal regions and FFA. pSTS has been considered as related
to animacy perception and among that area TPJ has been isolated among other regions for inference about other’s people
mind and intentions in contrast with other’s representations
[Saxe and Kanwischer, 2003]. Also mPFC has been found to
be active during representations of mind [Amodio and Frith,
2006], but bilateral damage does not affect intention attribution
[Bird et al., 2004]. Studies did not give any definitive answer,
but mPFC seems to be important for processing people-related
information.
[Wheatley and Martin, 2009] have been addressing the question whether the illusion of life (which they refer to as anthropomorphising) is due to a top-down or bottom-up mechanism.
The same set of moving geometrical objects was duplicated and
associated with two different context, one encouraging and the
other one discouraging animacy attribution. Brain regions active
in the animacy-stabilised versions of the stimuli were once again
overlapping with the social brain: fusifom gyrus, STS, amygdala,
insula, mPFC, thus overlapping with the regions active during
attribution of animacy to simple geometrical figures without
71
The role of
amygdala and pSTS
Top-Down versus
Bottom-up
72
biasing for anthropomorphising, and also when subjects were
asked to imagine anthropomorphic attributions. So apparently
top down information influences the activations of these regions,
and not just perceptual information, in a hybrid mechanism as
for first and second level ambiguity.
3.3.1
Brain damage
preventing the
illusion of life
Negative bias
Emotional clues in the illusion of life
Following neuroscience, then, what are the features allowing
the illusion of life, and thus the activation of the social brain’s
circuit? Goal-directedness alone is not enough, as suggested by
[Blakemore et al., 2003] and [Schultz et al., 2004] and [Schultz
et al., 2005]. Contextual clues also are not crucial, since a very
simple and contextual-free stimulus as the Heider and Simmel
movie is undoubtedly apt to trigger the illusion. On the contrary, the original movie features several interactions between
the shapes (fighting with, escaping and hiding from, protecting
and chasing each other). The fact that a bilateral brain damage
at the amygdala prevents from anthropomorphizing the Heider
and Simmel movie [Heberlein and Adolphs, 2004] is an important clue of what can triggers anthropomorphism. The Heider
and Simmel movie contains emotionally-charged interactions,
since it is interpreted as a story of bullying or threatening. It is
very interesting to observe that the emotions observed in the
movie are negatives ones. In the movie, the two triangles are
bullied, or persecuted, or chased, by the bigger shape; there
is an "happy end", since they gently touch each other in a behaviour described as "kissing", "celebrating", "high-fiving" by
the subjects. But, this last "event" is seldom included in the
description of the movie, while the most negative events are
always explicitly described, as the "destruction of the house" (the
rectangle). Negative events, and thus negative emotions, seems
to be more important and drive more attention, and they are
the one which trigger the social interpretation of the stimulus,
thus the illusion of life. In this sense, the amygdala damage
preventing anthropomorphism is very meaningful since as specified above the amygdala processes emotional information and
especially fear and threat-related clues. The negative bias in the
illusion of life has been suggested also by [Morewedge, 2009]
who showed that a negative intention or outcome is more easily
interpreted as human. During an ultimatum game, subjects were
asked to judge wheter on the "other side" there was a human
or a computer. If confronted with negative behaviours, such a
selfish ultimatum, the subjects would generally rate the agent
as human, while if confronted with a generous offer, the agent
would have been rated as a computer. Negativity bias seems to
be linked with the evolutionary necessity of dealing with unpredictable and potentially harmful living entities, other humans or
animals; thus, we appear to be more inclined to attribute social
attribution to negative events. It is a necessity which gives rise
to false-positives, that from an evolutionist point of view are
less harmful than negatives.
73
Part IV
F O RT H L E V E L A M B I G U I T Y
4
AESTHETICS OF ANTHROPOMORPHISM
4.0.2
Anthropomorphism as a forth level ambiguity
The illusion of life is probably the perceptual basis of those
common and inescapable phenomena of anthropomorphism,
that all of us experienced. Our capacity to invent living agents
and superimpose this belief on objects that are clearly non animated is impressive: we name our cars, curse computers and
love gadgets. I consider the illusion of life as the perceptual
knowledge leading to inference of aliveness. In this Chapter
this psychological phenomenon is declined in life evocation in
the arts and anthropomorphism in human-machine interaction.
Anthropomorphism includes the illusion of life, since it represents a process of inference allowing people imbue the real or
imagined behaviour of other agents with human-like characteristics, motivations, intentions, or underlying mental states
[Epley et al., 2007]. While the illusion of life is universally perceived, with the only exception of brain damaged patients, life
evocation and anthropomorphism are variable depending on
bias. Indeed, some agents are more easily anthropomorphised
than others, some cultures are more likely to anthropomorphise
than others [Asquith, 1986], children anthropomorphise more
than adults [Carey, 1985] and some situations and needs lead to
anthropomorphisation [Epley et al., 2008]. On the basis of such
an individual variability, anthropomorphism can be defined as
a forth level ambiguity, being a conflation of the awareness of
non-animacy and qualia of animacy, but which is not always
and automatically perceived, as in the case of the illusions we
explored in the previous chapters.
4.0.3
Variability in anthropomorphisation
Research has outlined that different people react in a different
way to anthropomorphisation; research has just begun to explain
and predict the variability of this phenomenon [Waytz et al.,
2010a]. [Epley et al., 2007] identified three primary determinants
explaining anthropomorphism. The first is motivation for social
connection (in a situation of loneliness); experimentally induced
77
78
The need for
anthropomorphism
Ambiguity and art
aesthetics of anthropomorphism
isolation increased tendency to anthropomoprhisation [Epley
et al., 2008]. The second is the need to master our environment.
Anthropomorphising a stimulus makes it seem more predictable
and understandable, demonstrating that anthropomorphism is
increased by effectance motivation. Effectance is the possibility
to attribute predictability to "behaving" things allow us to have
the impression to understand them easily, and to familiarise,
having thus the perception of increased mastery, with the final
goal of making sense of an otherwise uncertain environment.
Research on experimental psychology has demonstrated that
the experience of unpredictability stimulates attempts to gain
mastery [Berlyne, 1962]; [Whitson, 2008]. A study by [Waytz
et al., 2010b] demonstrated that unpredictable and unexpected
behaviour triggers the motivation to understand and explain it.
Life evocation has long been exploited by artists, and anthropomorphism has a great potential of application in today’s society, where we interact more and more with technological objects
such as robots and avatars, implicitly designed for embodying
believable creatures. Identifying features of believability, and
drawing examples and inspiration from arts and technology
could lead to insights useful both in terms of design and in cognitive studies. Yantis identified an analogy between ambiguity
and artistic phenomena [Yevin, 2000] proposing a modelisation
of perceptual ambiguity (proposing the model of saturation of
attention). Ambiguities have been exploited in artworks such
as paintings by Dali. The most famous example of artistic ambiguity is the Mona Lisa, in the words of Gombrich: "Even in
photographs of the picture we experience this strange effect, but
in front of the original in the Paris Louvre it is almost uncanny.
Sometimes she seems to mock at us, and then again we seem to
catch something like sadness in her smile" [Gombrich, 1995]. In
the same perspective, Zeki makes reference to Vermeer’s painting as featuring a higher level ambiguity [Zeki, 2004], where
ambiguity displayed here refers to ambiguity of different situations, that can can be interpreted in many different ways.
4.1
4.1.1
life evocation in the arts
Defining life away
The attribution of intention to shapes, motion features and emotional clues are all involved in the illusion of life. But, what is
"life"? Even if the answer seems to be intuitive and straightfor-
4.1 life evocation in the arts
ward, researchers propose that we lack of an adequate theoretical
framework [Cleland and Chyba, 2002]. As Cleland and Chyba
argument, the possibility of define life is now facing the same
difficulties hindering the definition of "water" before the invention of molecular theory, since we still lack a "theory of biology
that allows us to attain a deep understanding of the nature of life
and formulate a precise theoretical identity for life comparable
to the statement water is H20. The distinction between life and
non-life has also been a central issue discussed by Artificial Life
researcher. The so-called "strong thesis of Artificial Life" has also
argued that it would be possible to create "life" in some other
medium, abstracting the essence of life from the details of its
implementation in any particular model, trying to build models
that are so life-like that they cease to become models of life and
become examples of life themselves. Yet, despite the difficulties
in agreeing upon a scientific definition of life, everybody knows
what "being alive" means in the "ordinary sense"; the difficulties
lie in "defining it away", to say reducing it to its "independently
intelligible properties". Even if there is no consensus about how
to "define life away", our perception of something as alive can be
elicited by pressing some Darwinian button able to evoke in us
a visceral reaction. Life evocation arises when we are confronted
with perceptions that we know are deceptive, but we feel as true
and real.
4.1.2
79
What is life?
Art and the illusion of life
One of the main objectives of art has always been to represent
and evoke life. Many myths illustrate this idea, beginning from
the one about the origin of the first painting, as narrated by
Pliny: the first painting was actually a silhouette draw at candlelight by a "Corinthian Maid". She traced the features of her
sleeping lover onto a wall. He was about to leave for a far away
country, and she traced this image in order to keep his presence
with her. Another meaningful story is the one of Giotto. Vasari
recounts that when Giotto was only a boy in the studio of his
master Cimabue, "he once painted a fly on the nose of a face
that Cimabue had drawn, so naturally that the master, returning
to his work, tried more than once to drive it away with his hand,
thinking it was real"[De Vere, 1912-1915]. Realism and accuracy
were intended as the tool for not only representing life, but to
attribute to the work of art the ideal feature of communicating
the feeling of life-like presence, or life evocation. Several other
Art imitating life
80
stories establish a relation between the realism of life representation creating the "illusion" of life with aesthetic appreciation
and artistic value. In literature, many histories portraying artists
and focusing on creativity and inspiration stage the ambiguity
between the inanimate and the animate. Typically, the topoi of
art-related literature include works of art awakening to life, the
will of creating life by means of art, the uncertain nature of a
character (animate or inanimate, statue or human being). The
most celebrated example of the first category is the Portrait of
Dorian Gray, in which the inanimate object (the portrait) absorbs
some specific characteristic of its animate counterpart (Dorian),
to say moral traits, embodying them through formal features.
The second category probably stages a common metaphor for
artistic inspiration and creation, ranging from the carpenter who
carved Pinocchio to Pygmalion giving life to his loved statue.
The third case, more specifically focused on ambiguity, is the
narrative expedient often used for arousing the feeling of uncanniness, thus used in fantastic and horror fiction, leaving the
reader or the main character in uncertainty as to whether a
work of art is animate or not. Examples of this mechanism are
Colomba by Merimée (1840), or A Mystery of the Campagna,
(1887) by Crawford, or the most famous Sandman (1816) by ETA
Hoffman.
Another art exposing the ambiguity of life evocation is puppetry, a literal enactment of the "animate versus inanimate"
contradiction. The main characteristic of puppetry is the "inescapable tension" that Steve Tillis identifies as being between
the material object itself and the object as "signifier of life" [Tillis,
1996], setting up a conflict between the puppet as object and
the puppet as life. Indeed, a marionette elicits a double point
of view on the spectator: it is an object but one onto which
the viewer projects her own emotions and a theory of mind.
When attending a puppet show, the spectator is drawn, little
by little, towards increasing her suspension of disbelief, finally
granting the puppet the status of an actor. Puppetry imagery in
contemporary art takes, as historic point of departure, Alfred
Jarry’s 1896 puppet play Ubu Roi. Later, other puppets were featured in works from international well-established artists (such
as Kiki Smith, Pierre Huyghe, Christian Jankowski, Kara Walker,
Laurie Simmons). [Cohen, 2006] identifies a first wave of puppet imagery appearing in avant-garde art coinciding with the
Western appropriation of masks and other artefacts from exotic
culture and folk art. He specifically refers to the Bauhaus and
Futurist artists Jan Toorop and Paul Klee who created abstract
puppet spectacles using geometric figures. In this period Picasso,
Cocteau, and Calder created mobile sculptures and puppets; and
Joan Miro designed an experimental puppet show, Death to the
Bogeyman (Mori el Merma, 1978), with monstrous painted body
puppets drawn from Ubu Roi. From where does this artistic
interest in puppetry stem? Puppets challenge the audience’s understanding of object and life, and question a complex relation
with acting, non-living beings. After the advent of photography,
representation has not being anymore the central objective of
art practices. Assuming an auto-reflexive attitude, art has been
exploring other domains, inventing a newer aesthetics including
the spectator, aware of him-or-herself existing in the same space
as the work, and being aware of the perceptual relationships that
are established. Cultural trends began to steer art theory and
practice towards concepts of interaction and perception at the
end of the 50’s. In 1957 Marcel Duchamp delivered a key lecture,
The Creative Act, in which he argued that "the work of art is not
performed by the artist alone", since "ce sont les regardeurs qui
font les tableaux" [Sanouillet, 1973]. It was the dismissal of the
Modernist conception of the art object’s internal self-sufficiency
in favour of a sense of its dependence on contingent, external
factors such as context and audience participation. How could
artists translate the traditional objective of live evocation in this
new challenging and changing phase of art development? Many
critics rejected the idea that art should mimic life, and many
artistic trends dismissed this ambition, exploring other visual
languages, such as abstraction. Especially in modernist aesthetics, the repudiation of anthropomorphism was radical. It was in
favour of medium specificity, autonomy of the artwork from its
environment, and rejected narrative. Nevertheless, life evocation
is such a powerful tool - both in terms of human perception
and artistic expression - that, even if abandoned in theory, it
reemerged very soon in practice.
Art evocation re-emerged in contemporary art practices after Modernism, beginning with Minimalism and continuing
with technological and in particular robotic art. These artistic
explorations continued the trajectory of anthropomorphism in
Western art, but switching their focus from representation of
formal features to simulation of behaviour as a form of life evocation in parallel with a greater attention to elicited perceptual
processes. Minimalists have delivered anthropomorphic and
mimetic content in their works, not by means of representing
81
The return of
anthropomorphism
in modern art
82
life in a human form, but rather by simulating the feeling of
presence and interaction. This peculiarity of minimalism has
been paradoxically pointed out by a modernist critic, M. Fried,
who analysed minimalist works specifically attacking their tendency of being "a kind of statue; a surrogate person". The basic
switch of sensibility identified by Fried lays on the fact that
minimalist art produces "objects in situation" which "[occupy] a
position in the world" [Fried, 1967]. These works interlace relations with the spectators, losing the frame and separation from
the surrounding world (as modernist aesthetics would), embracing objecthood and acknowledging audience, being concerned
with "the actual circumstances in which the beholder encounters
the work" and, eventually, concealing at the core of its theory
and practice "hidden naturalism, indeed anthropomorphism".
Robert Morris, a minimalist artist, confirms these features (of
course from a positive perspective) in "Notes on Sculpture" [Morris, 1969-1969], in which he argues that the art objects should
be designed for triggering physical participation by the visitor. In this way, the spectator is directly led towards her own
perceptual activity which is, by the same token, revealed and
disclosed. The "economy of tools" (to which is due the label
"minimalism") is precisely intended to reveal the artwork as
a relational system by means of a reductionist approach: the
work is conceived starting from elementary parameters (light,
shape, colour, size) susceptible to entertain continuous changing
relations with the spectator, whose "task" is the physical exploration of the artwork. In Fried’s words, the work "depends on
the beholder, is incomplete without him, it has been waiting for
him. And once he is in the room the work refuses, obstinately, to
let him alone - which is to say, it refuses to stop confronting him,
distancing him, isolating him". This use of intentional verbs is
very interesting: indeed, being confronted with a minimalist object "is not entirely unlike [being] distanced, or crowded, by the
silent presence of another person". But, how it is possible that
minimalist works - utterly simple, geometric 3D objects, such as
cubes or parallelepipeds - would elicit in the spectator such an
inescapable life evocation perception? Writings by minimalist
artist Tony Smiths may explain this perceptual phenomenon. In
minimalism, an important feature for eliciting the impression of
being confronted by "something alive" probably lies in the size
of the work: "(not too big, or it would become a monument) nor
too small (it would become an object)" as Smiths claims about his
six-foot cube, "Die". Minimalists have also been designing works
83
that are "unitary and wholistic shapes", having the perceptual
property of suggesting an inside: two openly anthropomorphic
features. These formal characteristics (an appropriate size, a
unitary shape) have always being part of Western traditional
sculpture; but only with Minimalism, which reduced life evocation to minimal terms expressive tools, could they be singled
out as tactics for eliciting the specific ambiguous perception of
live evocation in the brain of the spectator.
4.1.3
From art to technology
Art addresses questions on how we view, perceive and interact
with our surroundings, changing and evolving in a continuous
dialogue with the development of culture and technology. After the advent of photography and thanks to the advances of
technology in fields such as robotics and computer graphics,
one of the objectives of art practices has become not only to
represent life, but also to simulate it by creating artificial creatures crossing category boundaries, and questioning from the
cognitive point of view which features can evoke in us life perception. These artworks suggest that there is no such a thing as
a clear and discrete gap in our perception between animate creatures and inanimate objects, but rather a continuous category.
In their paradoxical status of quasi-living entities, these artificial
creatures are agents of cognitive dissonance, addressing the
ambiguities of our perceptions and confronting us with stimuli
that we know as deceptive or fictional yet accept as "true" or
"real", operating a "suspension of disbelief", feeling empathy or
attributing them intentions and self-awareness. These works are
paving the way to a time where we will have to interact more
and more with artificial creatures, in a technological world in
which emotion and its affect will have an increasing prominent
role in technological artefacts. In the future we will probably interact more and more with objects crossing category boundaries,
as the borders between artificial and organic will be less and
less clear. Both in terms of theory and practices, interaction between art, science and technology can help stimulate a new way
of feeling and thinking not achievable through purely rational
inquiry. The issue of life evocation in artificial artefacts is crucial
to our technology-oriented society. Indeed, studies demonstrate
that our relationships with machines are both natural and social,
since our brain mechanisms evoke empathy, trust, uncanniness,
etc. towards an assembly of circuits or mechanical pieces. A
Life evocation in
behaviour
84
technological object can suspend our disbelief, just as would a
literary character or a puppet; moreover, we project our feelings
and attachment more and more on virtual worlds, and we become operators or "interactors" with many on-line puppets (the
avatars) that represent ourselves or others in the digital realm.
Robots, like puppets, are an example of the ontological paradox
that can take place in our technology-saturated environment, as
entities simultaneously occluding and exposing their artificiality.
4.1.4
The Uncanny Valley
Uncanniness as a result of life evocation
The concept of the "uncanny" can be explored as a first example
of concept concerning life evocation leaked from aesthetics to
technology. Ambiguity related to life evocation has been singled out and discussed in theory of literature and psychology,
where it elicits, following Jentsch (Jentsch 1909) and then Freud
(Freud 1919), specific feeling of "uncanniness", which the two
authors define as the result of the process of familiarity (heimlich) turned unfamiliar (unheimilich, translated in English as
"uncanny"). Among the example proposed by Jentsch and then
taken up by Freud, there are wax figures, which have the "ability
to retain their unpleasantness after the individual has taken a
decision as to whether it is animate or not". Jentsch suggests that
this feeling is caused by "secondary doubts which are repeatedly and automatically aroused anew when one looks again and
perceives finer details; or perhaps it is also a mere matter of the
lively recollection of the first awkward impression lingering in
one’s mind". Jentsch intuition has been translated into robotics
in the 70’ies with the so-called "Uncanny Valley" [Mori, 1970],
promoted by robotic pioneer Mori and illustrated in Figure 4.1.
The Uncanny Valley (a translation from the Japanese "Bukimi
No Tani") theory states that as the level of human-likeness increases up to a certain point the sense of familiarity with the
robot increases as well, but only up to a certain point; beyond
this it drops off suddenly as robots become too human-like and
thus appearing uncanny. In his diagram showing this negative
peak, Mori introduces movement as a factor reinforcing the perception of uncanniness or familiarity. The first part of Mori’s
model describes the increasing of the sense of familiarity up to
the maximum peak, after which the uncanny valley opens up.
From the other side of the valley another positive peak grows in
correspondence with creatures reproducing human attributes
exactly and finally with healthy human subjects.
4.2 the illusion of life in artificial creatures: features of believability
Figure 4.1: The Uncanny Valley graph following Mori
4.2
the illusion of life in artificial creatures: features of believability
In the field of Human/Robot Interaction (HRI) and Computer
Graphics (CG), the notion of life evocation is translated into the
concept of believability. Definitions of believability are numerous
and diversified: the issues emerging from studies concern traditional agents’ properties (agents can be robots or avatars, or any
artificial artefact that acts) concern social functions, behaviour,
and a relationship with the environment. At a basic level, believability is a specific property of artificial agents aiming the user’s
suspension of disbelief and "illusion" of life, triggering one’s
"instinctive" reaction. Researchers attempting to create engaging
artificial creatures both in the HRI and in the CG fields may find
important insights in the work of artists who have explored life
evocation. Researchers in artificial intelligence and robotics have
built various types of social robots which can express emotions.
Research pursues such a goal mainly through speech, facial expressions and hand gestures. Indeed, it is generally a common
hypothesis in research that if robots have salient human-like
attributes, then people’s mental models of robotic assistants will
become more anthropomorphic as they interact with them. It is
Believability
85
86
a common hypothesis in the scientific community that in order
to achieve a higher degree of empathy robots should have a
human-or-pet-like shape, or a very realistic anthropomorphic
shape [Kiesler and Goetz, 2002].
4.2.1
Why looking at the
arts?
Form: is realism a necessity?
While the efforts of robotic design research on emotions is generally focused on developing robots with anthropomorphic features such as hand and facial expressions [Roccella et al., 2007].
A small but still focused part of qualitative research has directly
faced the question whether anthropomorphic appearance affects
believability, generally giving a positive answer, stating that the
more the artificial creature is realist and human-like the more
can trigger empathy and emotions. Other researchers tried to
get inspiration from the arts, especially in the field of CG, stating "that artists tell us are needed to present the convincing,
persistent, illusion of life" [Bates, 1994]. But, artistic practices
with the goal of believability and arousal of empathy follow the
opposite path: in order to create a believable creature, realism is
not a necessity, and for evidence we can look to artists’ creation
of believable characters. For instance, an analysis of robotic art
practice may suggest that non-humanoid creatures trigger empathy and believability as effectively as humanoid ones. Bill Vorn
is an artist whose work is focused on life evocation. His installations involve robotics, motion control, sound, lighting, video,
and cybernetic processes. The aim of his robotic art projects is
to induce empathy from the viewers towards characters which
are nothing more than simple articulated metal structures. The
strength and richness of Vorn’s mechanical machines relies on
human perception of basic reactive behaviours in robots (essentially based on sensors) and by an appropriate immersive
audiovisual context that sets an environment for the works. But,
when confronted with Vorn’s machines (which in terms of shape
are totally non-humanoid), an inevitable reflex of empathic projection arises. In Vorn’s case, the whole realistic appearance is
dismissed in favour of a few repetitive movements and simple
interactions. Artistic creatures are often a distillate of a few
traits, abstracted from reality, and allowing enough space for the
spectator to project feelings and interpretations. Caricaturing
is a means for capturing the essence, as in the words of two of
the most famous Disney animators, Thomas and Johnston, who
described their techniques they used in order to create believ-
able characters: "The more an animator goes toward caricaturing
the animal, the more he seems to be capturing the essence of
that animal. If we had drawn real deer in Bambi there would
have been so little acting potential that no one would have believed the deer really existed as characters. But because we drew
what people imagine a deer looks like, with a personality to
match, the audience completely real" [Thomas and Johnston,
1981, reprint 1997]. Believability does not require human form,
as suggested by the arts. Drawing another example from Disney
animations, we can quote the Fliying Carpet starred in the film
Aladdin (1992): it has no eyes, limbs nor even a head. It is only a
carpet that can move. And yet, it has a definite personality with
its own goals, motivations and emotions, thus is able to evoke
life.
"Petit Mal", an artwork by Australian artist Simon Penny, explicitly attempts to explore autonomous behaviour as a probe of
emotion, expression, and believability. "Petit Mal" (an epileptic
condition, a lapse of consciousness), displays an unpredictable
behaviour and is not only an artistic exploration of a medium’s
potential but also an act of humour on the typical conventional
idea of control in robotics: the device is "anti-optimized" to induce the maximum level of personality. Thanks to its sensors,
Penny’s "Petit Mal" senses and explores architectural space, reacting to people in its environment. Its form and behaviour
are neither anthropomorphic nor zoomorphic, but it is clearly
perceived as a living creature by observers interacting with it,
since they never gain complete control over the system (as in
traditional man/machine interaction). This "reactive" model is
a communication scheme which is closer to the relationship
between living organisms and their environment if compared
to the common interactive model where the system is waiting
for an input from the user in order to react. In a reactive context proper to autonomous systems, the objects react on their
own "will", by themselves, and without the required presence of
viewers, communicating a personality through motion [Penny,
1997], and eventually evoking life by other means that form. The
central feature of this robot is unpredictability: it never reacts
in the same way in the same way to people surrounding it,
therefore, is elicits anthropomorphising. [Waytz et al., 2010a]
demonstrated that increasing the perceived unpredictability of a
non-human agent increases the motivation for mastery and thus
anthropomorphism. Anthropomorphising a stimulus makes it
seem more predictable and understandable, demonstrating that
Unpredictability
87
88
Negative bias
anthropomorphism is increased by effectance motivation. Effectance is the possibility to attribute predictability to "behaving"
things allow us to have the impression to understand them easily, and to familiarise (giving names to hurricanes) having thus
the perception of increased mastery, with the final goal of making sense of an otherwise uncertain environment. For example
[Berlyne, 1950] identifies uncertainty of the environment the primary motivation for babies to master their environment. From
this seminal publication on, research on experimental psychology has demonstrated that the experience of unpredictability
stimulates attempts to gain mastery [Berlyne, 1962]; [Whitson,
2008]. A study by [Waytz et al., 2010b] carried out a study where
participants were confronted with malfunctioning computers
and unpredictable gadgets, following surprising patterns of behaviour. The more frequently computers malfunctioned, or the
more the gadget was rated as unpredictable, the higher was
the anthropomorphisation tendency. For instance, in order to
trigger anthropomorphism in the the AIBO (a dog robot) Sony
researchers have been working on programming this robot in
order to make it preserve its "free-will". Systems of behaviour of
the AIBO consisted of a base (the "instinct" of the robot"); the
robot can learn from the user and be trained, but its instincts
will never be completely cancelled. Also, the AIBO has been
programmed with "moods" influencing the reaction in time to
training and to enhance perception of unpredictability [Kaplan,
2001].
As we saw in Chapter II, negative bias can influence anthropomorphism. Anyone had the feeling of attributing a mind to
a computer after a crash, with a feeling of frustration; 790/00
of people scold and 73 0/00 curse their computer when they
do not "behave" following their intentions [Luczak et al., 2003].
Looking back at the arts, it is quite surprising that any robots
designed by artists exhibit a negative behaviour, such as suffering. The Suffering Machine by Ricardo Nascimiento, without
being anthropomorphic in shape, is a clear example of how
artistic intuition can come to the same results than neuroscience.
The Suffering Machine is a robot consisting of three arms or
legs all connected at the same joint. All of the robot’s limbs
are controlled by a separate motor, although one of the motors
is purposely weak in an attempt to invoke a type of artificial
handicap. This design poses difficulties for the machine to move
around its immediate environment and thus attempts to provoke an emotional connection between the audience and the
object, triggering individuals’ empathy with the difficulties of
movement of the robot. If someone attempts to reach down to
help it, the robot plays "dead", thus not accepting any outside
aid. Even an everyday object can trigger empathy, if its movements and behaviour are consistently designed: the animated
artwork survivor, designed by artist Laura Morelli, is a robotic
chair that walks and react to the surrounding environment, in
the attempt to emulate and suggest some feeling and behaviours
that are typical of survivors of land-mines blasts learning to use
crutches. This has the aim of sensitizing viewers and usually
provokes very strong empathy reactions in the public.
Another common way of evoking life in robotic artworks is
simulating specific kinds of animal behaviours such as flocking.
Indeed, robotic art has been linked with Artificial Life, the
study of artificial systems which exhibit behaviour characteristic
of natural living systems with a bottom-up approach. This is
in contrast with the classical Artificial Intelligence top-down
approach. Some robotic artworks are A-Life sculptures, such as
the works by Yves Klein [Klein, 1998]. The process of creating a
"living sculpture" involves developing technologies for gesture,
locomotion, sensory input, and behaviour to achieve a unified
creature. For instance, Octofungi is an eight-sided polyurethane
sculpture that uses a neural network to integrate current events
via multiple sensors and shape-metal alloy for silent, non-linear
motion. Motion provided to the robotic creatures is specific to
biological forms, chain reactions, propagation and aggregation
behaviour, herds and swarms. The same interest for biologically
specific motion is to be found in Flock by Ken Rinaldo. The Flock
consists of an assemblage of hanging robotic arms that interact
with one another and with viewers, to manifest a "flocking"
behaviour that develops from an awareness of each other and
the environment. The artworks’ behaviour is analogous to the
flocking found in natural groups such as birds, schooling fish, or
flying bats. Flocking behaviours demonstrate characteristics of
supra-organization, of a series of animals or artificial life forms
that act as one. They are complex interdependent interactions
which require individual members to be aware of their position
in relation to others.
Another important factor eliciting believability by means of
emotion attribution and empathy can be attributed to infantilelike form. For Konrad Lorenz [Lorenz, 1970] juvenile traits automatically trigger a reaction of empathy and tenderness. Features
identified by Lorenz are "a relatively large head, a disproportion-
Animal behaviour
Feeding and
empathy
89
90
Personality
ately large forehead, large eyes placed underneath, prominent
curved cheeks, short thick limbs a firm elasticity, and awkward
movements". These are the same principles used by Cynthia
Breazeal in order to design the robot Kismet [Breazeal, 2000].
Kismet is a robotic head which interact with his environment in
a non-verbal modality. The robot is very expressive, designed
with big eyes eliciting empathy and encouraging interaction.
Kismet can express emotions only by varying the position of
his head, neck, ears and eyes. Lorenz’s shapes triggering empathy are largely independent from realism, as it appears in
other robotic creatures designed for interaction, as the AIBO,
Furby or Paro. On the contrary, if the above quoted theory of the
Uncanny Valley is true, a resemblance which is too close with
an existing living being may be counter-productive in terms
of empathy. Paradoxically in this forth level of ambiguity it is
probably necessary that the creature is perceived as artificial to
fully elicit anthropomorphism. Movements, just as in the case of
the illusion of life, is a crucial feature for eliciting empathy. Contrary to the Kismet, the AIBO does not have juvenile features in
form, but in movement: his movement being awkward, he elicit
the idea of a puppy; when it is switch off, many users can find
him repulsive and cold [Kaplan, 2001].
[Thomas and Johnston, 1981, reprint 1997] refer to personality as the most important requirement for creating believable
characters, defining personality as "all the particular details especially details of behaviour, thought and emotions - that
together define the individual. The second requirement for believable agents is that they appear to have emotional reactions
and to show those emotions in some way. This is such a fundamental requirement in the traditional character-based arts that
often artists refer to expressing the emotions of their characters
as what brings them to life.
4.3
conclusions
An inspiring function of both art and technology is to go beyond
representational "likeness" for evoking the feeling of life itself,
triggering those qualia emerging when we are confronted with
an animated creature. In two domains as different as these, such
a function has different objectives and strategy of accomplishment, but a common perceptual feature: the possibility to convey
the impression that and object is alive despite the exact awareness that it is not. It is undoubtedly not too difficult to press our
4.3 conclusions
"Darwinian buttons" since, probably for evolutionary reason, we
are biased to perceive life: "there is a universal tendency among
mankind to conceive all beings like themselves, and to transfer
to every object, those qualities, with which they are familiarly
acquainted, and of which they are intimately conscious". It is
known from cognitive sciences that the human brain organises
external reality abstracting it, in order to make it meaningful;
life, therefore, could be an inborn perceptual category that we
spontaneously apply even at the price of cognitive dissonance.
Thus life perception could be thought of as an optical illusion,
not so different from seeing two lines diverging even knowing
they are parallel, and in general similar to those phenomena
causing a friction between what we know (conceptual knowledge) and what we feel (perceptual knowledge): a temporary
overriding of bottom-up impressions on top-down awareness.
In particular, life perception of non-animated objects could be
assimilated to the illusion of ambiguity, traditionally defined
in literature as the possibility for a stimulus to be stably interpreted in only one way at a given moment, but in two or
more different ways over time. In this thesis I investigated, by
means of an fMRI study, how the illusion of ambiguity relates
to perception of categories, by using stimuli whose interpretable
content is known form previous studies to be processed in different brain areas, namely geometrical figures, faces and bodies.
In line with the initial hypothesis, in the case of geometrical
ambiguous images, for both possible interpretations activations
where found in the same area, the middle occipital gyrus. In the
case of face-body ambiguous images, there was a correlation
between face perception as indicated by the subjects and the
FFA, known as the area processing faces. Previous studies on
the illusion of ambiguity have consistently shown a network
of frontal-parietal activations in correlation with the perception of ambiguous images when contrasted with their stable
counterparts. In line with literature, the contrast between stable
and bistable images revealed increased bilateral activations in
the superior frontal gyrus and in the superior parietal lobule.
Surprisingly, the activation of this network was significantly
larger for geometrical ambiguous images (intra-categorical) then
for face-body ones (inter-categorical), as if the latter were less
effective stimuli in terms of ambiguity, being not purely bistable.
A qualitative questionnaire outlined how 56 % of subjects had
the impression they could see both images at the same time
in the case of inter-categorical images. The implication of this
91
92
findings is that it may be useful to distinguish between different
levels of ambiguity, in which the first one correlates with a more
"pure" perception of bistability implying the mutual exclusiveness of the two possible interpretations. Second level ambiguity
may correlate with the coexistence of the two interpretations
and a diminished activity in the fronto-parietal network. In this
framework, we identified the illusion of life as a third level
ambiguity. The illusion of life is the attribution of aliveness
features (desires, goals, intentions, strategies) to simple geometrical moving figures. In this case, activations are surprisingly
coincident with neural activations relative to perception of other
individuals, corresponding to those activations constituting the
"social brain"; in particular, the posterior and superior temporal
sulcus and gyrus activates in correlation with animacy, as they
do in correlation with spotting biological motion while viewing
a point-light display stimulus, and the amygdala, known for
processing emotion-related information. While a frontal brain
damage can prevent subjects to see flips of ambiguous images,
an amygdala damage can prevent the illusion of life, and mental
attributions are often inappropriate in autistic children. Except
for this cases, the illusion of life is universally perceived, while
variability in what I identified as a forth level ambiguity, anthropomorphism, is much higher, depending on culture, age
and needs. In this last level of ambiguity I believe that merging
between art and technology could be especially fruitful. Indeed,
anthropomorphism as life evocation as long been exploited by
art, and it has a great potential of application in today’s society,
where we interact more and more with artificial creatures such
as robots and avatars. As a future work. it could be interesting
to investigate in depth which are the insights that art could suggest both to cognitive sciences and technological applications.
Artworks suggest that there is no such a thing as a clear and
discrete gap in our perception between animate creatures and
inanimate objects, but rather a continuum. In their paradoxical status of quasi-living entities, these artificial creatures are
agents of cognitive dissonance, addressing the ambiguities of
our perceptions and confronting us with stimuli that we know
as deceptive or fictional yet accept as "true" or "real", operating
a suspension of disbelief, feeling empathy or attributing them
intentions and self-awareness. These works are paving the way
to a time where we will have to interact more and more with artificial creatures, in a technological world in which emotion and
its affect will have an increasing prominent role in technologi-
4.3 conclusions
cal artefacts. In the future we will probably interact more and
more with objects crossing category boundaries, as the borders
between artificial and organic will be less and less clear. Both in
terms of theory and practices, interaction between art, science
and technology can help stimulate a new way of feeling and
thinking not achievable through purely rational inquiry.
93
BIBLIOGRAPHY
R. Adolphs. Recognizing emotions from facial expressions:
psychological and neurological mechanisms. Behavioural and
Cognitive Neuroscience Reviews, pages 21–61, 2003.
D. Amodio and C. Frith. Meeting of minds: the medial frontal
cortex and social cognition. National Review of Neuroscience, 7
(4):268–277, 2006.
T.J. Andrews and C. Blakemore. Form and motion have independent access to consiousness. Nat. Neurosci, 2:406–462,
1999.
T.J. Andrews et al. Activity in the fusiform gyrus predicts
conscious perception of rubin’s vase-face illusion. Neuroimage,
17:890–901, 2002.
P.J. Asquith. Primateontogeny, cognition, and social behavior, chapter Anthropomorphism and the Japanese and Western traditions in primatology. Cambridge University Press, 1986.
F. Attneave. Multistability in perception. Sci. Am, 225:63–71,
1971.
B. r. r, 2002.
S. Baron-Cohen. Mindblindness: an essay on autism and theory of
mind. MIT Press/Bradford Books, 1995.
J.N. Bassili. Temporal and spatial contingencies in the perception
of social events. Journal of Personality and Social Psychology, 33
(6):680–685, 1976.
J. Bates. The role of emotion in believable agents. Technical
report, Carnegie Mellon University, 1994.
M. Bergamasco, C.A. Avizzano, F. Ghedini, and M. Carrozzino.
Le interfacce aptiche per i beni culturali. Proceedings of LUBEC
2007, "Valorizzazione dei Beni Culturali e Innovazione", 2007.
D.E. Berlyne. Novelty and curiosity as determinants of exploratory behavior. British Journal of Psychology, 41:68–80,
1950.
95
96
bibliography
D.E. Berlyne. Uncertainty and epistemic curiosity. British Journal
of Psychology, 53:27– 34, 1962.
C.M. Bird, F. Castelli, et al. The impact of extensive medial
frontal lobe damage om "theory of mind" and cognition. Brain,
127:914–928, 2004.
R. Blake. A neural theory of binocular rivalry. Psychol. Rev., 96:
145–167, 1989.
S.J. Blakemore et al. The detection of contingency and animacy
from simple animations in the human brain. Cerebral Cortex,
13(8), 2003.
P.W. Blythe, P.M. Todd, and G.F. Miller. Simple heuristic that make
us smart, chapter How motion reveals intention: categorising
social interactions. Oxford University Press, 1999.
C. Breazeal. Proto-conversations with an anthropomorphic
robot. Proceedings of the Ninth IEEE International Workshop on
Robot and Human Interactive Communication (Ro-Man), pages
328–333, 2000.
A.S. Bregman. Auditory Scene Analysis. MIT Press, 1990.
J. Britz et al. Right parietal brain activity precedes perceptual
alternation of bistable stimuli. Cereb. Cortex, 19:55–65, 2009.
L. Brothers. The social brain: a project for integrating primate
behaviour and neurophysiology in a new domain. Concepts
in Neuroscience, pages 27–52, 1990.
A. Caramazza and B. Mahon. The organisation of conceptual
knowledge in the brain: the future’s past and some future
directions. Cognitive Neuropsychology, 23(1):13–38, 2006.
S. Carey. Conceptual change in childhood. Cambridge, MIT Press,
1985.
O. Carter, D. Presti, et al. Meditation alters perceptual rivalry in
tibetan buddhist monks. Current biology, 2005.
O. Carter et al. Tactile rivalry demonstrated with an ambiguous
apparent-motion quartet. Current Biology, 19:1050–1054, 2008.
F. Castelli et al. Movement and mind: a functional imaging
study of perception and interpretation of complex intentional
movement patterns. NeuroImage, 12:314–325, 2000.
bibliography
W. Cheselden. An account of some observations made by a
young gentleman, who was born blind, or lost his sight so
early, that he had no remembrance of ever having seen, and
was couch’d between 13 and 14 years of age. Philosophical
Transactions, 35:447–450, 1683-1775.
Y.C. Chiu, M. Esterman, et al. Decoding task-based attentional
modulation during face categorization. Journal of Cognitive
Neuroscience, 2011.
C.E. Cleland and C.F. Chyba. Defining "life". Origins of Life and
Evolution of the Biosphere, 32:387–393, 2002.
M. Cohen. The art of puppetry. Animations Online, 18, 2006.
G. De Vere, editor. Lives of the Most Eminent Painters, Sculptors
and Architects, volume 1. Macmillan and the Medici Society,
London, 1912-1915.
D. Dima et al. Understanding why patients with schizophrenia do not perceive the hollow-mask illusion using dynamic
causal modelling. NeuroImage, 46(4):1180–1186, 2009.
W.H. Dittrich and S. E. G. Lea. Visual perception of intentional
motion. Perception, 23:253–268, 1994.
P.E. Downing et al. A cortical area selective for visual processing
of the human body. Science, 293:2470–2473, 2001.
W. Einhauser, K.A.C. Martin, and G. Konig. Are switches in
perception of the necker cube related to eye position? European
Journal of Neuroscience, 20:2811–2818, 2004.
N. Epley, A. Waytz, and J.T. Cacioppo. On seeing human: A
three-factor theory of anthropomorphism. Psychological Review, 114:864–886, 2007.
N. Epley, A. Waytz, et al. When i need a human: Motivational
determinants of anthropomorphism. Social Cognition, 26:143–
155, 2008.
M. Fried. Art and objecthood. Art Forum, 1967.
K. Friston, P. Fletcher, et al. Event-related fmri: characterizing
differential responses. Neuroimage,, 7(1):30–40, 1999.
K.J. Friston, P. Fletcher, et al. Event-related fmri: characterizing
differential responses. Neuroimage, 7:30–40, 1998.
97
98
bibliography
A. Gelb and K. Goldstein. Uber farbennamenamenesie. Psychologische Forschung, 1925.
F. Ghedini and M. Bergamasco. Robotic art: Perceiving and
inventing reality. Art and Science: exploring the limits of human
perception, Conference Proceedings, 2009.
F. Ghedini and M. Bergamasco. Life evocation in art: from
representation to behaviour. ISEA 2011, 2011a.
F. Ghedini and M. Bergamasco. Perception of ambiguous figures:
an fmri study. VRR-IJCAI 2011, 2011b.
F. Ghedini, H. Faste, M. Carrozzino, and Bergamasco M. Passages: An artistic 3d interface for children’s rehabilitation and
special needs. ICDVRAT, 2008.
Fiammetta Ghedini. Developing an applied framework for the
integration of artistic approaches and technological competences. PhD Application for the Scuola Superiore Sant’Anna,
2008.
J.J. Gibson. Perception of the Visual World. Houghton Mifflin,
Boston, 1950.
B. Giesbrecht, M.G. Woldorff, et al. Neural mechanisms of topdown control during spatial and feature attention. Neuroimage,
19:496–512, 2003.
E. Gombrich. The Story of Art. Phaidon, New York, 1995.
R.L. Gregory. Cognitive contours. Nature, 238:51–52, 1972.
R.L. Gregory. The Oxford Companion to the Mind. Oxford University Press, 1987.
R.L. Gregory. Ambiguity of ambiguity. Perception, 29:1139–1142,
2000.
R.L. Gregory. Seeing Through Illusions. Oxford University Press,
2009.
H. Hashimoto. A phenomenal analysis of social perception.
Journal of Child Development, pages 3–26, 1966.
U. Hasson et al. Vase or face? a neural correlate of shapeselective grouping processes in the human brain. J. Cogn.
Neurosci., 13:744–753, 2001.
bibliography
A. S. Heberlein. How Humans See, Represent, and Act on Events,
chapter Animacy and intention in the brain: neuroscience of
social event perception. Oxford University Press, 2008.
A.S. Heberlein and R. Adolphs. Impaired spontaneous anthropomorphizating despite intact perception and social knowledge.
Proceedings of the National Academy of Sciences of the United
States of America, 101(19):7487–7491, 2004.
F. Heider and M. Simmel. An experimental study of apparent
behavior. American Journal of Psychology, 57:243–259, 1944.
E. Hering. Outlines of a theory of the Light Sense. Harvard University Press, transl. by L.M. Hurvich and D. Jameson, 1964
(originally pub. 1877).
G. Hesselmann et al. Spontaneous local variations in ongoing
neural activity bias perceptual decisions. Proc. Natl. Acad. Sci.
U. S. A., 105:10984–10989, 2008.
J.B. Hopfinger, M.H. Buonocore, and G.R. Mangun. The neural
mechanisms of top-down attentional control. Nature Neuroscience, pages 284–291, 2000.
D.H. Hubel and T.N. Wiesel. The ferrier lecure. funcitonal
achitecture of macaque monkey visual cortex. Proceedings
Royal Society London, 198:1–59, 1977.
R. Ilg et al. Neural correlates of spontaneous percept switches
in ambiguous stimuli: an event-related functional magnetic
resonance imaging study. European Journal of Neuroscience, 28
(11):2325–2332, 2008.
M. Ito. Control of mental activities by internal models in the
cerebellum. Nature Review Neuroscience, 9:304 – 313, 2008.
Y. Jiang and S. He. Cortical responses to invisible faces: dissociating subsystems for facial-information processing. Curr. Biol.,
16:231–258, 2006.
G. Johansson. Visual perception of biological motion and a
model for its analysis. Percept. Psychophys., 195(204), 1973.
M.H. Johnson. Biological motion: a perceptual life detector?
Curr Biol., 23(16), 2006.
99
100
bibliography
N. Kanwisher and G. Yovel. The fusiform face area: A cortical
region specialized for the perception of faces. Philosophical
Transactions of the Royal Society of London, 361:2109–2128, 2006.
F. Kaplan. L’Art, la pensee, les emotions, chapter Un robot peut-il
etre notre ami? Grame, Paris, 2001.
S. Kiesler and L. Goetz. Mental models and cooperation with
robotic assistants. Proceedings of Conference on Human Factors
in Computing Systems (CHI), 2002.
Y. Klein. Living sculpture: The art and science of creating robotic
life. Leonardo, 31(5), 1998.
A. Kleinschmidt et al. Human brain activity during spontaneously reversing perception of ambiguous figures. Proc. R.
Soc, pages 2427 – 2433, 1998.
J. Kornmeier and M. Bach. The necker cube - an ambiguous figure disambiguated in early visual processing. Vision Research,
45, 2005.
E. Land. The retinex theory of color vision. Proc R Inst Gt Br, 47:
23–58, 1974.
S. H. Lee. Traveling waves of activity in primary visual cortex
during binocular rivalry. Nat. Neurosci., 8:22–23, 2005.
L. Leopold and G. Logothetis. Multistable phenomena: changing
views in perception. Trends Cogn. Sci., pages 254–264, 1999.
A.M. Leslie and S. Keeble. Do six-month-old infants perceive
causality? Cognition, 25:265–288, 1987.
K. Lorenz. Essais sur le comportement animal et humain. Le Seuil,
Paris, 1970.
H. Luczak, M. Roetting, and L. Schmidt. Let’s talk: Anthropomorphization as a means to cope with stress of interacting
with technical devices. Ergonomics, 46:1361–1374, 2003.
E.D. Lumer et al. Neural correlates of perceptual rivalry in the
human brain. Science, 280:1930–1933, 1998.
J.M. Mandler. How to build a baby ii: Conceptual primitives.
Psychological Review, 99:587–604, 1992.
bibliography
A. Martin and J. Weisberg. Neural foundations for undestandinf
social and mechanical concepts. Cognitive Neuropsychology, 30
(3-6):575–558, 2003.
A. Michotte. The Perception of Causality. trans. T. R. and E. Miles
in 1963, 1946.
S.R. Mitroff, D.M. Sobel, and A. Gopnik. Reversing how to think
about ambiguous figure reversals: Spontaneous alternating by
uninformed observers. Perception, pages 709 –715, 2006.
C.K. Morewedge. A mind of its own: negativity bias in the
perception of intentional agency. Journal of Experimental Psychology, 138(4):535–545, 2009.
M. Mori. The uncanny valley. Energy, 7:33–35, 1970.
R. Morris. Notes on sculpture. Artforum, 1969-1969.
T. Noesselt et al. Delayed striate cortical activation during spatial
attention. Neuron, 5:575–587, 2002.
J.E. Opfer. Identifying living and sentient kinds from dynamic infomation: the case of goal-directed versus aimless autonomous
movement in conceptual change. Cognition, 86(2):97–122, 2002.
J.X. O’Reilly, M.M. Mesulam, and A.C. Nobre. The cerebellum
predicts the timing of perceptual events. Journal of Cognitive
Neuroscience, pages 2252–2260, 2008.
L. Parkkonen et al. Early visual brain areas reflect the percept
of an ambiguous scene. Proc. Natl. Acad. Sci. U. S. A., 105:
20500–20504, 2008.
M.V. Peelen and P.E. Downing. Selectivity for the human body
in the fusiform gyrus. Journal of Neurophysiology, 93:603–8,
2007.
S. Penny. Embodied cultural agents: at the intersection of art,
robotics, and cognitive science. In Socially Intelligent Agents
Symposium, MIT, 1997.
M.A. Peterson and B.S. Gibson. Directing spatial attention
within an object. Journal of Experimental Psychology, 17:170–
82, 1991.
A. Polonsky et al. Neuronal activity in human primary visual
cortex correlates with perception during binocular rivalry.
Nat. Neurosci., pages 1153–1159, 2000.
101
102
bibliography
D. Premack. Do infants have a theory of self-propelled objects?
Cognition, 1990.
M. Raemaekers. Widespread fmri activity differences between
perceptual states in visual rivalry are correlated with differences in observer biases. Brain Res, 1252:161–171, 2009.
B. Rime, B. Boulanger, et al. The perception of interpersonal
emotions originated by patterns of movement. Motivation and
Emotion, 9(3):241–260, 1985.
S. Roccella et al. Design and development of five-fingered hands
for a humanoid emotion expression robot. International Journal
of Humanoid Robotics, 4(1), 2007.
I. Rosenfield. The Invention of Memory. Basic Books, New York,
1988.
O. Sacks. The case of the colorblind painter. In An Anthropologist
on Mars, pages 3–41. Random House, 1995.
E. Peterson Sanouillet, editor. The Creative Act. Salt Seller, New
York, 1973.
R. Saxe and N. Kanwischer. People thinking about people. the
role of the temporal-parietal junction in "theory of mind".
Neuroimage, 19(4):1835–1842, 2003.
U. Schneider, F.M. Leweke, U. Sternemann, M. Weber, and
H. Emrich. Visual 3d illusion: a systems-theoretical approach
to psychosis. Eur. Arch. Psychiatry Clin. Neurosci, pages 256–
260, 1996.
B.J. Scholl and P.D. Tremoulet. Perceptual causality and animacy.
Trends in Cognitive Sciences, 4(8):299–309, 2000.
J. Schultz et al. Activation of the human superior temporal gyrus
during observation of goal attribution by intentional objects.
Journal of Cognitive Neuroscience, 16(4):1695–1705, 2004.
J. Schultz et al. Activation in posterior superior temporal sulcus
parlallels parameter inducing the percept of animacy. Neuron,
45(4):625–635, 2005.
D. Skuse, J. Morris, and K. Lawrence. The amygdala and development of the social brain. Annals of the New York Academy of
Sciences, 1008:91–101, 2003.
bibliography
S.D. Slotnick, J. Schwarzbach, and S. Yantis. Attentional inhibition of visual processing in human striate and extrastriate
cortex. Neuroimage, 19:1602–1611, 2003.
P. Sterzer and A. Kleinschmidt. A neural signature of colour
and luminance correspondence in bistable apparent motion.
Eur. J. Neurosci., 21:3097–3106, 2005.
P. Sterzer and A. Kleinschmidt. A neural basis for inference in
perceptual ambiguity. Proc Natl Acad Sci U S A, 104:323–328,
2007.
P. Sterzer et al. Neural correlates of spontaneous direction
reversals in ambiguous apparent visual motion. Neuroimage,
15:908–916, 2002.
P. Sterzer et al. Fine-scale activity patterns in high-level visual
areas encode the category of invisible objects. Curr. Opin.
Neurobiol, 13:433–439, 2008.
P. Sterzer et al. Electromagnetic responses to invisible face
stimuli during binocular suppression. Neuroimage, 46:803–808,
2009.
J.A. Stewart. Perception of animacy. PhD thesis, University of
Pennsylvania, 1982.
F. Thomas and O. Johnston. The Illusion of Life: Disney Animation.
Hyperion, 1981, reprint 1997.
S. Tillis. The actor occluded: Puppet theatre and acting. Theatre
Topics, 6(2):109–119, 1996.
F. Tong. Primary visual cortex and visual awareness. Nat. Rev.
Neurosci., pages 219–229, 2003.
F. Tong and S. A. Engel. Interocular rivalry revealed in the
human cortical blind-spot representation. Nature, pages 195–
199, 2001.
F. Tong, K. Nakayama, et al. Binocular rivalry and visual awareness in human extrastriate cortex. Neuron, 21:753–759, 1998.
F. Tong et al. Neural bases of binocular rivalry. Trends Cogn. Sci.,
pages 502–511, 2006.
T.C. Toppino. Reversible-figure perception: Mechanisms of intentional control. Perception and Psychophysics, pages 1285–1295,
2003.
103
104
bibliography
T.C. Toppino and G.M. Long. Dynamic cognitive processes, chapter Top-down and bottom-up processes in the perception of
reversible figures: Toward a hybrid model, pages 37–58. Tokyo:
Springer-Verlag, 2005.
J. Tracy et al. The brain topography associated with active
reversal and suppression of an ambiguous figure. European
Journal of Cognitive Psychology, 17:267–288, 2005.
P.D. Tremoulet and J. Feldman. Perception of animacy from the
motion of a single object. Perception, 29:943–951, 2000.
T. Troscianko, S.E. Lea, and D. Morgan. Perception of emotion from dynamic point-light displays represented in dance.
Perception, 25(6):727–738, 1996.
Y. Tsal and L. Kolbet. Disambiguating ambiguous figures by
selective attention. Quarterly Journal of Psychology, pages 25–
37, 1985.
H. von Helmholtz. Handbuch der Physiologischen Optik, English translation, J.P.C. Southall, Treatise on Physiological Optics.
Dover, New York, 1962.
B. Vorn. A conversation with bill vorn (on robotic art creatures
and other believable living machines). Interview by Fiammetta
Ghedini, Walter Aprile and Haakon Faste, 2007.
R.M. Warren and R.L. Gregory. An auditory analogue of the
visual reversible figure. Am. J. Psychol, 71:612–613, 1958.
E. Warrington and T. Shallice. Category specific impairments.
Brain, 107:829–854, 1984.
A. Waytz, J. Cacioppo, and N. Epley. Who sees human? : The
stability and importance of individual differences in anthropomorphism. Perspectives on Psychological Science, 5(219), 2010a.
A. Waytz, C.K. Morewedge, et al. Making sense by making
sentient: Effectance motivation increases anthropomorphism.
Journal of Personality and Social Psychology, 2010b.
B. Weiner. Spontaneous’ causal thinking. Psychological Bulletin,
97:74–84, 1985.
Milleville Wheatley and Martin. Understanding animate agents:
distinct roles for social networks and mirror system. Psychological Science, 18(6):469–474, 2009.
bibliography
J.A. Whitson. Lacking control increases illusory pattern perception. Science, 322:115–117, 2008.
M.A. Williams. Amygdala responses to fearful and happy facial
expressions under conditions of binocular suppression. J.
Neurosci., pages 2898–2904, 2004.
S. Windmann, M. Wehrmann, et al. Role of the prefrontal cortex
in attentional control over bistable vision. Journal of Cognitive
Neuroscience, 18:456–471, 2006.
I. Yevin. Ambiguity and art. URL Publication on VisMath, 2000.
URL www.vismath1.tripod.com/igor/.
J.M. Zacks, K.M. Vettel, and J.M. Avoy. Visual motion and the
neural correlates of event perception. Brain Research, 1076(1):
150–162, 2006.
S. Zeki. The neurology of ambiguity. Consciousness and Cognition,
13:173–196, 2004.
S. Zeki. Splendors and miseries of the brain. Blackwell, London,
2009.
105

The Illusion of Ambiguity: from Bistable Perception to

Transcription

Similar documents

3-D Paper Illusion

Brain Child Learning

Neural Basis of the Ventriloquist

David Beckham

OJOK David Stephen

How does my dog see?

leonardo da vinci airport

art 2 – trompe l`oeil pencil drawing “fool the eye”