Journal of Research in Reading, ISSN 0141-0423 DOI: 10.1111/j.1467-9817.2006.00315.x

Transcription

Journal of Research in Reading, ISSN 0141-0423 DOI: 10.1111/j.1467-9817.2006.00315.x
Journal of Research in Reading, ISSN 0141-0423
Volume 29, Issue 4, 2006, pp 400–417
DOI: 10.1111/j.1467-9817.2006.00315.x
What is orthographic processing skill
and how does it relate to word
identification in reading?
Jennifer S. Burt
University of Queensland, Brisbane
The role of orthographic processing skill (OPS) in reading has aroused the interest of
many developmental researchers. Despite observations by Vellutino that current
measures of OPS primarily are indicators of reading (and spelling) achievement,
OPS commonly is distinguished from both reading achievement and phonological
skills. An analysis of the reading literature indicates that there is no theory in which
OPS meaningfully plays a role as an independent skill or causal factor in reading
acquisition. Rather, OPS indexes fluent word identification and spelling knowledge,
and there is no evidence to refute the hypothesis that its development relies heavily
on phonological processes. Results of correlational studies and reader group
comparisons (a) cannot inform about on-line processes and (b) may be
parsimoniously explained in terms of phonological skills, reading experience,
unmeasured language abilities and methodological factors, without implying that
OPS is an aetiologically separable skill. Future research would profit from the
investigation in experimental studies of the nature and development of orthographic
representations.
The individual differences approach to the investigation of reading acquisition has
produced a substantial body of evidence that points to a causal role in reading and
spelling acquisition for the phonological skills deployed in speaking and listening
(Bradley & Bryant, 1985; Lundberg, Frost & Peterson, 1988; Perfetti, Beck, Bell &
Hughes, 1987). Specifically, phonological sensitivity, the ability to discriminate and
manipulate sound units of spoken words (cf. Stanovich, 1992), strongly predicts reading
and spelling acquisition. These speech-based skills are thought to promote phonological
coding of orthography (but see Castles & Coltheart, 2004), thus allowing readers to
unlock the partially systematic way that English spelling patterns represent words that
readers use in speech.
Equipped with knowledge of the relevant abilities, researchers now are well placed
to devise, test and apply theories about reading acquisition in training and other
experimental studies. However, apart from a few exceptions (Cunningham, Perry,
Stanovich & Share, 2002; Dixon, Stuart & Masterson, 2002; Ehri & Saltmarsh, 1995;
Share, 1999), the majority of developmental researchers continue to search for individual
differences that might ‘explain’ differences in reading skills. One skill, termed
orthographic processing, is the focus of the present paper.
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Interest here centres on the use of the term orthographic processing to describe a skill or
facility that varies over individuals, rather than the act of processing orthography during
reading. In this individual-difference sense it has been defined most broadly by Stanovich
and West (1989) as ‘the ability to form, store, and access orthographic representations’
(p. 404). Wagner and Barker (1994) note that definitions vary according to whether they are
expressed within the context of the dual route theory (Coltheart, 1978; Coltheart, Curtis,
Atkins & Haller, 1993) or within alternative approaches (Perfetti, 1992; Vellutino, 1994).
The purpose of the present paper is to examine the theoretical and empirical approaches
relating OPS with reading, and to ask whether the current pursuit of individual differences
in OPS is justifiable on scientific or practical grounds. The emphasis is on visual word
recognition rather than syntactic analysis or comprehension of connected text. Several of
the points made here are already in the literature. Notably, some researchers have argued
that measures of OPS tap reading achievement (Vellutino, 1994; Vellutino, Scanlon &
Tanzman, 1994), and that OPS exceeding expectations (based on individuals’ phonological
skills) may reflect reading experience (Harm & Seidenberg, 1999; Snowling, Bryant &
Hulme, 1996; Stanovich, Siegel & Gottardo, 1997b).
Of particular concern are inferences drawn by researchers apparently motivated by
views (a) that OPS indexes a possibly heritable ability that is an independent causal factor
in reading acquisition, or (b) that OPS is a component reading skill that is aetiologically
distinct from phonological coding and print exposure. The position argued here is that
there is no theoretical, practical or evidential justification for either of these claims.
Theoretical issues
Orthographic representations
Identification of a visually presented word is thought to involve matching an input letter
sequence with a representation of the word’s orthography that has been learned through
experience with print. Recent evidence supports the common assumption that the
orthographic representations acquired primarily during reading are used for both reading
and spelling (Burt & Tate, 2002; Holmes & Carruthers, 1998). Phonological coding may
contribute to word identification via a role in establishing orthographic representations, as
suggested by Share’s self-teaching hypothesis (1995). For example, phonological coding
may promote full decoding of a letter string, link it with experience with a word from
speech and provide a structure to letter sequences that facilitates their learning.
OPS as defined earlier, that is, the ability to form, store and access orthographic
representations, can most directly be measured by assessing a child’s success in learning
unfamiliar word-like letter strings. To date inferences about the status of OPS largely
have been based on measures of OPS that tap a child’s current word-specific orthographic
knowledge. This reliance on pre-existing knowledge as a measure is problematic because
some individuals may have required many more learning trials than others to achieve
similar scores on OPS. More critically, because OPS measures that rely on existing
orthographic knowledge are heavily contaminated by reading achievement, it is unsurprising that they are good predictors of visual word identification.
OPS as an independent causal factor or component skill
Strong claims about an independent causal role of OPS in reading have been made in the
recent developmental literature on reading. The basis of such claims is that OPS is an
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additional predictor of word reading over and above phonological skills (e.g. Juel,
Griffith & Gough, 1986; Tunmer & Nesdale, 1985).
For example, Wagner and Barker (1994) suggested that, across individuals with
comparable print exposure and phonological coding, there are differences in the facility
for forming, storing and manipulating orthographic images, and that these differences
contribute to word identification. Bowers, Golden, Kennedy and Young (1994) noted that
some problems in oral reading fluency may result from individual differences in a child’s
ability to induce orthographic knowledge from the kind of exposure to print that usually
is sufficient for it.
An alternative justification for the predictive analyses involving OPS is that the
analyses ascertain the relative importance of components of word identification. The dual
route model’s distinction between sub-lexical (phonologically mediated) and lexical
(orthographic) procedures for lexical access leads to the idea that individuals might differ
in these component skills. OPS has been viewed as a distinct component process of word
identification, perhaps indexing the effectiveness of the lexical procedure for lexical
access (e.g. Manis, Szeszulski, Holt & Graves, 1990; Olson, Forsberg & Wise, 1994).
The utility of this inference for understanding word identification is questionable because
tests of orthographic knowledge do not provide a window into on-line processes in word
identification. Visual word identification is thought to involve a cascading sequence of
processes that cannot readily be separated empirically (e.g. Harm & Seidenberg, 2004),
and the rapidity and efficiency of these processes cannot be tapped by ‘off-line’ tests of
orthographic knowledge or learning.
The limitations of current approaches to OPS are evident in the following illustration.
Suppose that in a test analogous to the commonly used orthographic choice test,
participants are asked to make speeded classifications about existing vs. fictitious athletic
events. For example, given video clips of an athlete throwing a discus and a runner
passing a discus to another runner, the correct choice is the first clip. An individual would
be expected to respond correctly as a result of learning about the event, just as a child
responds on the basis of prior learning in typical measures of OPS. In a test phase a
number of additional athletic events might be depicted on video, with the participant
being required to name as quickly as possible the athletic event. If scores in the event
classification task explained a modest amount of unique variance in the event-naming
task when relevant verbal abilities and sport-related experience were controlled, it is
unlikely that a researcher would judge it useful to draw a conclusion that the ability to
select actual from fictitious athletic events indexes a component process in athletic-event
identification, or that event classification indexes a causal factor in event naming that is
independent of factors already known to affect event-naming speed and accuracy.
There is, of course, good reason to believe that there are abilities that contribute to
orthographic learning, and that these abilities show a measurable variation over
individuals (Reitsma, 1983). However, there are many already-identified skills and
knowledge bases that predict reading and arguably, given enough learning opportunities,
are sufficient for the acquisition of well-specified orthographic representations for word
identification and spelling. These include an understanding of the alphabetic principle
and familiarity with the letters of the alphabet, oral language skills (e.g. oral vocabulary,
precise phonological representations) and phonological coding skill.
The central argument of the present paper is that it is not necessary to reify
unexplained variance by positing the existence of a separate ability to store orthography
as an explanation for individual variation in word reading skill. A second argument of the
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present review is that some analyses based on the component skills approach confuse
processes occurring in word identification with the knowledge that supports word
identification. Furthermore, the utility of OPS as a component skill is limited if it cannot
be shown to be aetiologically distinct from other reading-related skills. As discussed
below, the evidence does not indicate that there is a new, non-phonological skill that
underlies OPS.
Are there viable hypotheses about the distinct origins of
orthographic processing skill?
If OPS is a skill that is an independent causal factor in word identification, or an
aetiologically separate component of word identification, then it must be empirically
and conceptually distinguished from other predictors and from achievement in
word identification. Measures of OPS that involve processing of words or orthographically legal letter strings cannot distinguish pre-reading skills from the consequences of
reading. Because it is implausible to suppose that script-specific abilities have evolved
(Diamond, 1998), any pre-reading orthographic processing ability must be constituted in
some more generic skill or cognitive associated with language, visual processing or visual
memory.
There has been recent interest in rapid auditory processing (Tallal, Miller, Jenkins &
Merzenich, 1997) and more general temporal processing (Farmer & Klein, 1995),
cerebellar function (Nicolson, Fawcett & Dean, 1995) and rapid naming (Bowers &
Wolf, 1993) as predictors of word identification skill. These plausibly are related to
phonological skills but there is no plausible hypothesis linking them to OPS. Although
Bowers & Wolf (1993) have suggested that rapid naming indexes the ‘automatic
induction of good quality orthographic codes’ (p. 77), it is likely that the predictive utility
of this measure reflects differences in children’s reading experience and their early
familiarity with digits and letters. The only study reporting a substantial contribution of
rapid naming when reading experience was controlled (Badian, 1993) used an insensitive
index of reading experience (number of years of schooling). Some candidate abilities
more relevant to the visual domain are considered briefly below.
Skill in visual processing and visual memory
Higher-order skills having to do with encoding and storing visually presented symbol
sequences (e.g. Seymour & MacGregor, 1984) are likely candidates for abilities
underlying OPS. However, available evidence overall supports the claim made by
Vellutino (1979) that visual processing and visual memory do not play an important role
in reading acquisition. There are a number of reports of a lack of association between
visual search and memory tasks and OPS (Olson et al., 1994; Olson, Wise, Conners &
Rack, 1990). In addition, poor readers do not show severe deficits on tasks requiring itemmatching or order judgements about visual symbols presented in sequences, and the
deficits that have been found (e.g. Willows, Corcos & Kershner, 1993) have not been
shown to be independent of the effects of reading experience and phonological skills.
Generally, differences between good and poor readers on matching strings of visual
symbols may be found when the symbols are letters or digits but not when they are rather
unnameable symbols (e.g. Assink, Lam & Knuijt, 1998).
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Eye movements in reading
In the substantial research literature on eye movements in the reading of connected text it
is commonly reported that poor readers have less efficient eye-movement co-ordination
than good readers (Biscaldi, Gezeck & Stuhr, 1998; see the review by Rayner, 1998).
However, it is not clear whether these deficits affect single word reading, which has been
the focus in the literature on OPS and reading. In addition, the current evidence is
consistent with the common interpretation that in the vast majority of dyslexics these
differences are consequences rather than causes of reading deficits. That is, inefficient
eye-movement control, such as regressive eye movements and re-fixations, reflect
decoding and comprehension difficulties (Olson, Kliegl, Davidson & Foltz, 1984;
Rayner, 1998, 1999).
Magnocellular system deficit
A fundamental visual processing deficit that has received recent attention is the
magnocellular system that predominates in peripheral vision and is thought to specialise
in processing transient stimuli, thus detecting flicker or motion (Lovegrove, 1996). At
present the evidence is inconsistent over studies and difficult to interpret (Hogben, 1996).
If this processing deficit in perceptual tasks is to be tied to deficits in OPS, it is necessary
to provide an empirically supported causal story that links a clearly identified
magnocellular deficit with sequential processing of letters, and in turn, with OPS. One
difficulty in making these links is that deficits in magnocellular function are more readily
applied to reading connected text rather than individual word decoding, and thus may not
apply to the single-word reading tests that are the focus of the literature on OPS
(Lovegrove, 1993).
The genetic basis of OPS
Consistent with the above overview, there is no compelling evidence that OPS relies on a
heritable skill that originates separately from phonological skills. Recent twin studies
have reported significant heritability estimates for OPS (Gayán & Olson, 2001, 2003;
Olson et al., 1994); but in these studies there also was a substantial bivariate heritability
estimate for OPS and phonological skills. Also, selective deficits in OPS (surface
dyslexia) have been found to have a smaller heritability component than deficits in
phonological skills (Castles, Datta, Gayan & Olson, 1999). In any case, an independent
genetic basis of OPS might reflect constitutional or temperamental factors that make a
child more like to engage in reading rather than a specific ability in the visual learning
domain.
In summary, there currently is no clear theoretical rationale for claiming that OPS
plays a causal role in reading acquisition independently of task-specific strategies and
other method variance, phonological processing, more general language skills and
vocabulary, motivational factors, reading experience and reading achievement. A number
of authors have suggested that deficiencies in OPS result from a lack of detailed
processing of word orthography during reading (e.g. Burt & Fury, 2000; Frith, 1985;
Manis et al., 1990; Stanovich, 1992). Importantly, however, this reading style most
parsimoniously may be linked with phonological coding (which promotes full processing
of orthography) rather than with a constitutional cognitive factor (e.g. a global cognitive
style) that is more general than reading.
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Measurement issues
The observation already has been made that typical tests of OPS are alternative measures
of reading and spelling achievement. This observation is substantiated here through a
closer examination of the individual OPS tests most commonly used in the reading
literature (Table 1).
The most typical OPS measure is an orthographic choice test in which a visually
presented word must be selected over a pseudohomophone distractor, as in boat vs. bote.
Like other moderately common OPS tasks, such as homophone choice/verification,
spelling recognition, lexical decision, masked orthographic priming in word recognition
and word finding, this version of the orthographic choice task receptively assesses wordspecific orthographic knowledge. Occasionally productive assessments are made, for
example, spelling to dictation. An alternative version of the orthographic choice test
assesses abstract orthographic knowledge, that is, the ability to select orthographic
patterns that are permissible in English (e.g. tilk) over letter sequences that are not found
in English (e.g. tilv). It is likely that the tasks requiring correct memory for word-specific
orthography are the most demanding in terms of their reliance on an individual’s reading
skill and learning history (cf. Pennington, Lefly, Van Orden, Bookman & Smith, 1987).
The remaining, less commonly used tests deal with recognition of letters and letter-like
forms (Awaida & Beech, 1995; Badian, 1997), and recognition memory for letter clusters
(Berninger, Yates & Lester, 1991).
None of the above tests is independent of reading experience, print exposure and the
concomitant familiarity with letters and permissible letter sequences of English. Among
the visual processing tests, all those used by at least two laboratories involve letters, so all
must require familiarity with letters that most obviously comes from reading experience
or exposure to print.
Examining the evidence
Relationship between OPS, phonological coding and exposure to print
Phonological coding appears to play a role in orthographic learning (see the review by
Share, 1995), even for words with exceptional spelling–sound correspondences (Gough
& Walsh, 1991; Manis, 1985). The magnitude of the association between phonological
coding and OPS measures often is not reported, but available evidence suggests that the
shared variance typically ranges from 10% to 25% in grade 1–4 children (Barker et al.,
1992; Berninger et al., 1991; Braten et al., 1999; Cunningham et al., 2001, 2002).
Similarly, OPS has been found to have a positive association with reading experience
as assessed by print exposure measures (Stanovich & West, 1989; Stanovich et al., 1991).
Nagy and Anderson (1984) have estimated that skilled readers in the middle grades of
elementary school may read from 1,000,000 to as many as 50,000,000 words per year,
whereas poor readers may read only 100,000. Phonological coding (measured by nonword pronunciation) also typically correlates with print exposure (Vellutino, 1994).
In children, measures of print exposure have been found to account for significant
variance in OPS measures after phonological skill and coding or phonological coding
alone has been partialled out. The unique variance estimates range from 7% to 28% in a
range of studies (Braten et al., 1999; Cunningham & Stanovich, 1990; Cunningham et al.,
2001; McBride Chang et al., 1993; Stanovich et al., 1991). In skilled adult readers,
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Braten et al. (1999); Hultquist (1997).
walktreemother npmqsickqr
yacht, eye
Orthographic priming in lexical decision
Embedded words
Oral reading of irregular words
Castles et al. (1999); Sprenger-Charolles, Siegel, Bechennec and Serniclaes (2003).
Holmes and Standish (1996); Manis et al. (1990).
Andrews and Scarratt (1996); Castles, Davis and Letcher (1999).
Lexical decision
Cunningham and Stanovich (1993); Foorman et al. (1996).
Spelling production
Manis et al. (1990, 1993); Stanovich and Siegel (1994).
Gayán and Olson (2001).
Streat? street?
Manis et al. (1990, 1993).
Barker et al. (1992); Cunningham et al. (2001); Cunningham and Stanovich (1990); Gayán
and Olson (2001); Hultquist (1997); Patterson, Marshall and Coltheart (1985);
Stanovich et al. (1991); Wagner and Barker (1994).
Bailey, Manis, Pedersen and Seidenberg (2004); Barker, Torgesen and Wagner (1992);
Braten, Lie, Andreassen and Olaussen (1999); Cunningham et al. (2001); Cunningham
and Stanovich (1990); Foorman, Francis, Fletcher and Lynn (1996); Gayán and Olson
(2001); Holmes (1996); Holmes and Standish (1996); Hultquist (1997); Jackson,
Donaldson and Mills (1993); Manis, Seidenberg, Doi, McBride Chang and Petersen
(1996); Manis et al. (1996, 2000); McBride Chang, Manis, Seidenberg, Custodio and
Doi (1993); Newby, Recht and Caldwell (1993); Olson et al. (1984, 1990, 1994); Olson,
Wise, Conners, Rack and Fulker (1989); Pennington, Gilger, Olson and DeFries (1992);
Samuelsson, Gustafson and Ronnberg (1998); Sloboda (1980); Stanovich and Siegel
(1994); Stanovich and West (1989); Stanovich, West and Cunningham (1991); Wagner
and Barker (1994).
Cunningham and Stanovich (1993); Cunningham, Perry and Stanovich (2001); Manis,
Seidenberg and Doi (1999); Manis, Doi and Bhadha (2000); Massaro and Hestand
(1983); Siegel, Share and Geva (1995); Stanovich and Siegel (1994); Stanovich et al.
(1997a).
Papers
PIAT spelling test multi-choice
spelling recognition
Spelling recognition/orthographic verification
Pair vs. pear
Homophone choice
A fruit: pear? pair?
Bote vs. boat
Orthographic choice word-specific;
also termed spelling recognition.
Homophone verification
Tilk vs. tilv
Example items
where available
Orthographic choice abstract
Task
Table 1. Commonly used tests of OPS.
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Chateau and Jared (2000) found that print exposure differences were associated with the
significant differences in the efficiency of orthographic processing in homophone choice,
the LDT and form priming in the LDT.
Consideration of the relationship between print exposure and OPS may shed light on
the inconsistent findings reported when dyslexics and reading-level controls are
compared on OPS. There are common reports of no difference between reading disabled
and reading-level controls on OPS (Badian, 1997; Olson et al., 1984; Stanovich et al.,
1997b), or lower OPS scores in disabled readers (Hultquist, 1997; Manis, Custodio &
Szeszulski, 1993; Manis et al., 1990). Of more interest to researchers are occasional
findings that disabled readers perform better on OPS than reading-level controls (Olson et
al., 1990; Siegel et al., 1995), or better than predicted from their phonological skills
(Foorman et al., 1996; Stanovich & Siegel, 1994). Reading-level controls typically are
younger than their matched reading-disabled partners by at least several years.
Consequently the disabled readers may have an advantage over the controls in OPS
tests by virtue of their reading experience and skills that depend heavily on reading
experience, as has been suggested previously (Foorman et al., 1996; Stanovich & Siegel,
1994). There is no compelling evidence for an alternative view (Holmes, 1996; Siegel et
al., 1995) that those with deficits in phonological skills may be able to use OPS to
compensate partially for deficits in phonological skills. This view about compensation
implies that OPS is a facility that does not rely heavily on phonological skills.
In summary, the finding that OPS is associated with phonological coding and print
exposure is entirely predictable given the substantial literature documenting the
association between these variables and visual word identification, and in turn, the
dependence of word identification on orthographic knowledge. More fundamentally,
phonological coding and reading experience can be expected to play a crucial role in the
acquisition of new orthographic representations.
Predictive studies: unique contributions of OPS to word identification
Contemporary research in OPS generally has taken the form of assessing the unique
contribution of OPS measures as predictors of visual word identification when other
relevant predictors are controlled. Commonly controlled variables are phonological
sensitivity and phonological coding, and less commonly, reading experience. It has been
shown in hierarchical multiple regression analyses of data collected in a number of
independent studies of children and adults that OPS accounts for unique variance in
measures of word identification when phonological sensitivity (e.g. phoneme deletion) or
phonological coding (e.g. non-word pronunciation) have been entered at a previous step
in the analysis (Barker et al., 1992; Berninger et al., 1991; Conners & Olson, 1990;
Cunningham & Stanovich, 1993; Cunningham et al., 2001; Holmes, 1996; Olson et al.,
1994; Stanovich et al., 1991; Wagner & Barker, 1994).
Although substantial variance in word identification might be explained when only
phonological sensitivity is controlled (e.g. 30% in grade 1 children, Cunningham &
Stanovich, 1993), the contribution of OPS to word identification is modest when the
controlled variable includes phonological coding, which has a stronger and presumably
more direct relationship with word identification. Estimates for children range from 7% to
10% (Barker et al., 1992; Cunningham & Stanovich, 1990; Olson et al., 1994; Stanovich
et al., 1991). In the Stanovich et al. study the contribution for adults was 7%. It might be
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argued that the contribution of OPS is under-estimated because phonological coding tests
measure orthographic processing and knowledge that is shared with OPS. However, in
the absence of evidence for a specific orthographic processing skill this argument is
circular. The overlap between phonological coding and OPS would merit investigation if
there were an independent basis for proposing that OPS is a distinct skill.
Adding print exposure to the set of predictors to be controlled in studies of the
relationship between OPS and word identification has produced a decrement in the
unique contribution of OPS. For example, Stanovich et al. (1991) found that the unique
variance explained by OPS dropped 2% or 3% points to 4% (adults) and 6% (children)
when a print exposure measure was controlled together with a composite of phonological
coding measures. These decrements were not assessed for statistical significance but the
information provided by the authors’ tables suggests that they were reliable. Olson et al.
(1994) reported in their twin study that controlling the Title Recognition test in addition
to phonological coding caused the unique contribution of OPS to word identification to
fall by 2% points to 8%. In this study the age of twins ranged from 8 to over 18 years, and
the authors commented on the rather low sensitivity of the Title Recognition test.
In interpreting the unique contribution made by OPS in predictive studies, it is
important to acknowledge the effect of method variance and task-specific factors, in
addition to measurement issues. For example, appropriately difficult tests of wordspecific knowledge can be expected to better predict word identification than tests of
abstract knowledge. Print exposure tests like the ART and the Title Recognition test lack
sensitivity, because typically they tap primarily popular fiction.
When the above procedural factors are considered together with the potential effects of
unmeasured variables (e.g. oral vocabulary, motivation, instruction), it is a simple matter,
without postulating that OPS is a distinct skill, to explain the modest prediction by OPS
of visual word identification that has been reported in studies controlling phonological
coding and print exposure.
As noted, the present view is that OPS reflects orthographic learning that largely is
shaped by phonological skills and reading experience. It must be acknowledged that
commonality analyses would provide a more informative assessment of the viability of
this hypothesis and the possible influences of underlying constructs. Such analyses would
determine the overlapping variance between phonological skills and OPS, and between
print exposure and OPS, in the prediction of word identification.
Component skills analyses
As indicated earlier, research largely motivated by dual route theories (Coltheart, 1978;
Patterson & Morton, 1985) has treated phonological coding and OPS as distinct
components of visual word identification. Although phonological coding may be
interpreted as an on-line word identification process within the dual route model, OPS
cannot be identified with on-line processes in visual word identification. Conventional
tests of OPS and phonological coding do not provide information about the accrual of
activation in lexical representations, or the interplay and time courses of processes
occurring on-line in word identification. As noted, there are limits on the empirical
separation of component on-line processes in word identification (e.g. Besner & Stolz,
1998). Thus component skills analyses are most accurately characterised as analyses of
the skills that underlie or predict processes occurring on-line in word identification.
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Although it is consistent with available evidence to describe OPS as one of several
component skills and knowledge bases that support word identification there is no
compelling evidence that OPS is aetiologically separable from other component skills.
Despite the lack of evidence, OPS frequently is assumed to be aetiologically separable
from phonological coding (as illustrated below). Once this assumption is made, a
component skills analysis effectively rests on the previously described strong claim that
OPS is an independent causal factor in word identification skill.
Typically researchers conducting component skills analyses have assessed the relative
utility of OPS and phonological coding skills as predictors of word identification, or they
have compared the skill pattern of normally achieving readers and dyslexics. A third
approach, an attempt to identify reader subtypes based on relative strengths in component
skills, is discussed in the next section.
Manis et al. (1990) have delineated within the dual route framework the development
of the lexical route, involving the acquisition and updating of orthographic entries, and
development of the sub-lexical route, based on an ‘inductive process of rule creation’ (p.
213). In their analysis of a sample of dyslexic children, they note deficiencies in both
phonological coding and OPS, coupled with reliance on a phonological decoding strategy
for identifying words. They suggested that the children’s reliance on a weak phonological
coding mechanism may have been a response to their deficiencies in OPS. This
suggestion implies that the skills are aetiologically distinct, when a more parsimonious
interpretation of the weakness of the two skills is that OPS relies on phonological coding.
In an analysis of dyslexia Badian (1997) reported that the majority of the poorest
readers in a sample of children aged 6–10 years had a double or triple deficit when
assessed on phonological, naming-speed and orthographic skills. It was suggested that
children with multiple deficits among these skills have fewer compensatory mechanisms
to fall back on. The implication is that skills like OPS are separable factors in word
identification, but no justification was given for this view.
In light of reports of individual differences in OPS that are independent of reading
experience, intellectual ability and phonological coding and awareness, Stanovich (1992)
examined the small number of studies in which children had been trained on a set of
unfamiliar words. He suggested that a lack of ability to form precise orthographic
representations may be a significant factor in reading acquisition difficulties, but that
isolating a specific problem in OPS requires a demonstration (not yet reported in training
studies at that time) that a child has no deficit in phonological sensitivity or the required
spelling-sound knowledge.
A recent study does indicate that phonological skills predict the efficacy of learning
orthographic representations (Cunningham et al., 2002). The authors reported, consistent
with the self-teaching hypothesis of Share, that the ability of second-grade children to
learn the orthography of pseudo-words (as assessed by a composite score over several
measures) was predicted by their ability to pronounce the items in context (r 5 .52). In
addition, they reported that orthographic choice accounted for significant variance in the
orthographic learning composite when pronunciation accuracy for the pseudo-words was
controlled. However, the conclusion that OPS was a unique predictor of orthographic
learning was undercut by the results for their test of non-word pronunciation, which had a
correlation with the orthographic learning composite (r 5 0.58) similar to that between
orthographic choice and the orthographic learning composite (r 5 0.57). Pronunciation
accuracy for the target items may have been unreliable because each child learned only
10 items and apparently only one pronunciation per item was taken as correct, although
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several of the 20 items in total had inconsistent word neighbours (e.g. trow–brow, crow;
yait–plait, bait; kear–wear, near).
Component skill analyses: subtypes and case study approaches
Interest in OPS and phonological coding as component skills has led to attempts to
subtype dyslexics and normally achieving readers on the discrepancy between
orthographic and phonological skills. A review of the literature is beyond the scope of
the present paper. It is worth noting, however, that there has been some debate about the
validity of the posited typologies (Gough & Walsh, 1991; Sprenger-Charolles &
Serniclaes, 2003; Stanovich et al., 1997b). Of particular relevance here are the postulated
surface type in developmental dyslexia, and the sub-lexically reliant normal reader. In
both categories individuals are characterised as having a specific or relative weakness in
knowledge or use of whole-word orthography in reading (Olson et al., 1989). Equally,
they may be described as having deficits in OPS. The diagnosis has been made in terms of
a discrepancy between sub-lexical and lexical skill levels within an individual, or in terms
of the relationship between lexical and sub-lexical skills in the target group compared
with a reference group. Typically lexical skills are assessed via the naming of irregular
words (which cannot be pronounced sub-lexically) and sub-lexical skills are assessed via
the naming of non-words (which cannot be pronounced lexically).
At issue is whether there is convincing evidence of a sub-lexically reliant reading
typology that is based on either a deficit in OPS or a deficit in previously unidentified
skills or knowledge. Sub-lexically reliant patterns of performance may be attributable to
measurement error, impoverished reading experience, problems in reading instruction,
motivation or other background variables. As indicated previously, lack of comparability
of reader groups on reading experience has been flagged as an interpretational problem by
a number of authors.
The literature on reading typologies relating to the lexical and sub-lexical routes of the
dual route model reveals some concerns about the status of the sub-lexically reliant type.
For example, when reading age is taken into account, the surface dyslexic pattern that
was moderately common in the Castles and Coltheart (1993) analysis based on
chronological age is rare (Manis et al., 1996; Stanovich, Siegel & Gottardo, 1997a). In
addition Manis, Seidenberg, Stallings, Joanisse, Bailey et al. (1999) reported that
classification of the surface dyslexic profile was not stable over a year. There is some
agreement that the surface developmental dyslexic profile is best characterised as a delay,
in that it resembles normal reading at a younger age (Manis et al., 1996; Stanovich
et al., 1997b).
Stanovich et al. (1997b) noted that surface dyslexia may arise from a milder form
of phonological deficit conjoined with ‘exceptionally inadequate reading experience’
(p. 124). Inadequate reading experience is likely to be reflected in more marked deficits
for irregular than regular words because the orthography of irregular words is more
difficult to learn than the orthography of regular words. Some support was provided by
Gustafson (2001), who reported that in addition to having more general cognitive
weaknesses, his surface dyslexic group had fewer books at home. The hypothesis about
the dependence of surface dyslexia on impoverished reading experience was challenged
in a recent study (Bailey et al., 2004) on the grounds that surface dyslexic children did not
score lower on print exposure than phonological dyslexics. Although it is not clear what
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group comparison was implied by Stanovich et al., it seems more appropriate to compare
surface dyslexics with their age-matched peers. The Bailey et al. study found that 13
surface dyslexics tended to have lower print exposure percentage scores (29.5) than 13
chronological age controls (39.9) although the difference fell short of reliability. In the
Manis et al. (1999) longitudinal study a delayed reading group showed a small and
unreliable deficit in print exposure relative to the chronological age controls. However, a
subgroup of nine delayed readers, classified as surface dyslexics based on their exception
word reading, showed a marginally reliable (po.10) deficit in print exposure compared
with the chronological-age controls.
Admittedly, the above evidence for an effect of print exposure in surface dyslexia is
not clear-cut, but it suggests that studies of larger samples may provide support for the
hypothesis that surface dyslexia reflects deficient reading experience. At present there is
no strong evidence that this group has a specific deficit in orthographic learning. A study
by Castles and Holmes (1996) that found an impairment in the learning of irregular nonwords in surface dyslexia is problematical because the irregular non-words were devised
on the basis of irregular words that may have been unfamiliar to some of the group (e.g.
yacht, corps, cf. Bailey et al., 2004).
A critical case: superior OPS with weak phonological skills
If OPS depends substantially on phonological skills and reading instruction and
experience then it will be difficult to find a developmental pattern of excellence in OPS
with a deficiency in phonological coding or sensitivity. Furthermore, any individual with
such an ability pattern would be expected to have a history of intensive reading
instruction or reading experience, together with high motivation.
Although studies of reader subtypes have found groups of children who have better
than expected irregular word reading given their phonological skills, these lexically
reliant groups rarely show OPS superior to mixed strategy readers. For example, the
subgroup with stronger OPS and weaker phonological coding in the study of Samuelsson
et al. (1998) showed weaker OPS than controls. In other studies the irregular word
performance of the lexically reliant or sub-lexically impaired groups has been reported to
be within the normal range, for example, within 1 standard deviation (SD) of the
performance of normally achieving controls (Castles & Coltheart, 1993; Castles &
Holmes, 1996; Manis et al., 1996).
Against a background of a strong relationship between reading experience and OPS,
Braten et al. (1999) found a group of five children who had phonological coding scores in
the lowest quartile but OPS scores above the median, together with reading experience
scores below the mean for their sample of 117 children. They inferred that these children
may have a unique talent to ‘establish, store and/or access orthographic representations in
memory’ (pp. 83–84). These results are intriguing but not compelling, given that
available measures of print exposure are not sufficiently direct and sensitive to serve as
robust indicators for individual children, and all five children scored close to or within 1
SD of the mean on the reading experience measure.
Indeed, there appears to be no unambiguous case of a developmental weakness in
phonological skills accompanied by clearly superior OPS. Holmes and Standish (1996)
described a young woman (K.Q.) who excelled at orthographic processing despite
deficient phonological processing and oral word reading. However, although K.Q. was
highly proficient at a word-specific orthographic choice task and lexical decision, she was
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a poor speller relative to her undergraduate student peers, a problematic finding given that
poor spelling is likely to be diagnostic of imprecise orthographic representations.
Importantly, K.Q. had above average reading experience, liked reading, and indicated
that she had spent a great deal of time rote learning the spellings of words. A similar
observation about intensive reading practice was made in relation to a case study of an
individual with poor phonological skills by Olson et al. (1994).
In summary, OPS and phonological coding have been found to have at least a moderate
positive association but also to contribute independently to the prediction of visual word
identification. This finding is equally compatible with dual route and alternative, integrative
approaches to understanding reading processes. An imperfect association does not provide
evidence for an aetiological distinction between the two skills. Similarly, with respect to
individuals or subtypes with an imbalance in sub-lexical and lexical skills, imbalances
provide little information about the origin of the skills and their role in on-line reading.
Certain clear-cut cases, for example, superior OPS with deficits in phonological skills, have
the potential to provide compelling evidence of the independence of the two skills.
However, such clear-cut cases have not been reported, and the evidence is more consistent
with the proposal that OPS development depends substantially on already identified skills,
especially the effective use of phonological coding in the learning of word orthography.
It may be possible to make a case for the aetiological separation of OPS by showing
that it is more heavily dependent on reading experience and individual background
factors (e.g. motivation) than is phonological coding. However, a substantial contribution
of reading experience to orthographic learning is already accepted, and few researchers
would disagree that background variables may play a significant role in orthographic
learning directly, as well as indirectly (through print exposure).
Finally, the dual route framework that drives the component skills approach does not
address developmental issues. For example, the approach does not address how the two
procedures are acquired and it does not explain why there is a moderate or strong
association between them.
Summary
A selective review of the reading literature indicates that measures of OPS tap reading and
spelling achievement. There is no theoretical account of variation in reading skill that
provides a viable causal hypothesis about a visual or memory skill (distinct from reading
achievement and phonological skills) that might underlie OPS. Reading experience is known
to be associated with OPS, and method variance plus differences in reading experience,
reading achievement, oral vocabulary, motivation and instruction may explain why OPS
scores do not always closely track the level of phonological coding skill in dyslexic and
normal readers. The formation and fluent access of well-specified orthographic representations are viewed here as fundamental processes of word identification in reading, rather than
independent predictors of word identification skill. Component skills analyses and
classification into subtypes have not found clear-cut cases (e.g. strong OPS accompanied
by inadequate phonological sensitivity) that would justify inferences that OPS is a distinct
skill that is aetiologically independent of phonological coding. Predictive and subtyping
approaches employing measures of existing knowledge are limited in that they cannot
provide information about on-line processes in reading. In addition, component-skills
approaches to reading skills that are not informed by theories about the development of
word identification skills have limited application to reading remediation and instruction.
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Future research on OPS
The current interest in OPS is well founded in the sense that word recognition and literacy
research has been limited in its value for reading instruction and perhaps its progress in
theory development by a neglect of the nature and acquisition of lexical representations
(but see Ehri, 1986; Perfetti, 1992). Training studies that assess the skills and processes
involved in the effective learning of unfamiliar letter strings assess directly the
development of orthographic (and lexical) representations and as such they are ideal for
devising and assessing remedial programmes (see the studies by Cunningham et al., 2002;
Ehri & Saltmarsh, 1995; Share, 1999).
Additionally, the implications of OPS for spelling should not be overlooked. Acquiring
the orthographic knowledge tapped by measures of OPS essentially is the same problem
that writers face when they set about learning to spell. Also, recognition that OPS as
assessed by reading researchers is a reading achievement measure highlights the
theoretical and remedial utility of using OPS measures for tracking the development of
orthographic representations (cf. Castles et al., 1999). Finally, it was suggested by
Stanovich et al. (1991) and others that OPS deficits may result from a habitual shallow
and non-analytic processing style in readers when encountering words (see also Frith,
1985; Barker et al., 1992). Consistent with this proposal, good adult spellers perform
better than poor spellers in tests of orthographic processing accuracy in silent reading
(Baron & Strawson, 1976; Burt & Fury, 2000). This non-analytic style may result from
less effective use of phonological information during reading by poor spellers, a
possibility that awaits empirical investigation.
Conclusion
The purpose of the present paper was to make a case that progress in reading theory and
practice depends upon the experimental evaluation of causal models of reading
development. Statistical partialling of variance in word identification scores is a tool
for testing hypotheses about relevant individual differences rather than a justification for
positing causal variables or distinct component skills to account for unexplained variance.
Task analyses indicate that visual word identification, spelling and OPS as currently
measured rely on knowledge of the orthography of words, and that this fact is sufficient to
explain their prediction of word identification that is independent of phonological coding.
Investigation of the conditions and skills governing the acquisition of new orthographic
representations promises to increase researchers’ understanding of OPS and more
generally, the development of visual word identification and spelling.
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Received 17 October 2005; revised version received 3 May 2006.
Address for correspondence: Jennifer S. Burt, School of Psychology, University of
Queensland, QLD 4072, Australia. E-mail: [email protected]
r United Kingdom Literacy Association 2006