Touch and Tactile Perception

Touch and Tactile Perception
Li Liu
☺ Skin Stimuli and Receptors
☺ Neural Responses
☺ Neural Pathway
☺ Tactile Perception
Tactile sensory receptors
Thermoreceptors
change in skin temperature
Mechanoreceptor
pressure, vibration, slip
Nocioreceptor
pain
Cross section of the skin
Neutral Responses
Receptor responds to stimulation
Mechanical energy deforms
the receptor cell
Tiny holes at the membrane open,
positive ions flow through the cell
(Na+ in and K+ out).
An action potential is
generated.
Electrical activity.
Sensory adaption
Receptors have different rates of adaption to stimuli:
Slow adaption (SA):
The fibers fire when stimulated, continue responding as
long as the stimulus exits.
Rapid adaption (RA):
The fibers fire when stimulated, then drop rapidly to
zero, even if the stimulus continues, i.e., wearing clothes
Which receptors are rapidly adapting
and which are slowly adapting?
Receptors for touch
Which receptor has the largest receptive field
In the brain, the same response often signals very
different sensations.
How do we know what the stimulus is?
How do we know what the stimulus is?
A similar problem occurs on the internet
On the internet, your message and those of many
others, travel down a shared common line.
To separate your message from that of others,
each packet is giving a tag or label.
At the end of the line a decoder separates your
packet from that of others.
How do we know what the stimulus is?
Each type of skin receptor has its own private
line, where the touch information is sent
through spinal cord to the somatosensory
cortex.
There are lots of lines in our spinal cord,
In this way, each message is separated and
sent to its own location in the brain.
Neural Pathways
Neural pathways
Maps of the body on the cortex
Tactile Perception
Measuring tactile activity: the two-point threshold
Two-point threshold
the smallest separation between two points on the skin
that is perceived as two rather than one.
Method
Two pencils side by side, and they are 12 mm apart;
Then touch both points to any part of the body;
If you feel only one, increase the distance until you feel two;
The distance is the threshold.
Two - Point Threshold
- measure of pressure acuity
- varies greatly over
different areas of the body
Sensory humunculus
What a person would look like
if their sensory humunculus
represented size rather than
sensitivity
Braille code
Natural letters
ABCDEFGHIJKLMN
OPQRSTVUWXYZ
Neural response to letters
Braille alphabet
Braille board
Play cards
Electronic book
Picture perception by touch
Picture perception by touch
Touch pictures
2D or 3D graphics as output
Receptive fields responds to movement across
fingertip
Active touch
Exploratory procedures
Tactile perception (1965)