Max Coltheart

Macquarie University, Sydney NSW 2109, Australia

Selected references: recent papers on modeling of reading; earlier position papers and books


Coltheart, M., Tree, J. J., & Saunders, S. J. (2010). Computational modeling of reading in semantic dementia: comment on Woollams, Lambon Ralph, Plaut, and Patterson (2007). Psychological Review, 117, 256-271.
Notes: Woollams, Lambon Ralph, Plaut, and Patterson reported detailed data on reading in 51 cases of semantic dementia. They simulated some aspects of these data using a connectionist parallel distributed processing (PDP) triangle model of reading. We argue here that a different model of reading, the dual route cascaded (DRC) model of Coltheart, Rastle, Perry, Langdon, and Ziegler (2001), not only provides a more accurate simulation of these aspects of reading in semantic dementia than does the PDP model but also provides highly accurate simulations of other aspects of reading in this disorder that the PDP approach has not simulated. We conclude that our findings add to evidence both from simulations of normal skilled reading and from simulations of other kinds of acquired dyslexia that the nonconnectionist DRC model of reading offers a better account of normal and disordered reading than the connectionist PDP models of reading

Coltheart, M., Saunders, S. J., & Tree, J. J. (2010). Computational modelling of the effects of semantic dementia on visual word recognition. Cognitive Neuropsychology, 27, 101-114.
Notes: Rogers, Lambon Ralph, Hodges, and Patterson (2004) studied two-alternative forced-choice visual lexical decision performance in patients with semantic dementia. With item pairs where the target word was more "typical" (i.e., higher in bigram and trigram frequency) than the foil (all foils were pseudohomophones), lexical decision performance was good and was unaffected by word frequency. With item pairs where the target word was less "typical" (i.e., lower in bigram and trigram frequency) than the foil, lexical decision performance was worse and was affected by word frequency, being particularly inaccurate when the word targets were low in frequency. We show (using as materials all the monosyllabic items used by Rogers and colleagues) that the same pattern of results occurs in the lexical decision performance of the DRC (dual-route cascaded) computational model of reading when the model is lesioned by probabilistic deletion of low-frequency words from its orthographic lexicon. We consider that the PDP (parallel distributed processing) computational model of reading used by Woollams, Plaut, Lambon Ralph, and Patterson (2007) to simulate reading in semantic dementia is not capable of simulating this lexical decision result. We take this, in conjunction with previous work on computational modelling of reading aloud in surface dyslexia, phonological dyslexia, and semantic dementia using the DRC and PDP reading models, to indicate that the DRC model does a better job than the PDP model in accounting for what is known about the various forms of acquired dyslexia
Macquarie Centre for Cognitive Science, Macquarie University, Sydney, New South Wales, Australia.

Coltheart, M. (2006). John Marshall and the cognitive neuropsychology of reading. Cortex, 42, 855-860.
Notes: Macquarie Centre for Cognitive Science, Macquarie University, Sydney, Australia.
Contemporary cognitive neuropsychology owes a great debt to John Marshall. His pioneering work on acquired and developmental disorders of reading established the principles by which cognitive-neuropsychological theorizing operates as well as leading to a profound understanding of the nature of reading disorders which has subsequently influenced their assessment and treatment

Coltheart, M. (2006). Acquired dyslexias and the computational modelling of reading. Cognitive Neuropsychology, 23, 96-109.
Notes: M. Coltheart, Macquarie Centre for Cognitive Science, Macquarie University, Sydney, NSW 2109
Two current approaches to the computational modelling of reading are the connectionist triangle model approach (parallel processing; distributed representations; models developed via a connectionist training algorithm such as backpropagation) and the DRC ("dual route cascaded") model (serial processing components permitted; local representations; model architecture specified by the modeller rather than acquired by a learning algorithm). One way of testing such computational models is to lesion the computer programs that instantiate the models and study how well the impaired reading of such damaged models corresponds to the patterns of impaired reading seen in people with acquired dyslexia. This is computational cognitive neuropsychology. It has been used with both types of model in attempts to simulate acquired surface dyslexia and acquired phonological dyslexia. The results of this body of work currently favour the DRC model over connectionist models developed within the triangle model framework.

Blazely, A. M., Coltheart, M., & Casey, B. J. (2005). Semantic impairment with and without surface dyslexia: Implications for models of reading. Cognitive Neuropsychology, 22, 695-717.
The two best-developed computational models of reading aloud, the DRC model of Coltheart and colleagues and the connectionist attractor model of Plaut and colleagues, offer very different views about the degree to which semantic knowledge is involved in lexical processing, and hence make differing predictions about how semantic impairment (as seen, for example, in semantic dementia) will impact on lexical processing in clinical cases. Two cases meeting the criteria for semantic dementia, PC and EM, were given a battery of tests comprising comprehension tasks, a reading task, and a visual word recognition (lexical decision) task. AD tasks used the same target words allowing cross-test and cross-patient comparisons. Both cases showed significant impairment of semantic memory, and word comprehension was found to be related to the word frequency of the target words. PC demonstrated poor reading of irregular words, with a surface dyslexic pattern of reading aloud, and he performed poorly on the visual lexical decision task. His ability to read irregular words was related to their frequency and to his ability to comprehend them. In contrast, his visual lexical decision performance was not reliably influenced by his comprehension of the same words or by their frequency. EM demonstrated essentially perfect reading aloud of irregular words and essentially perfect visual lexical decision, despite her severe semantic impairment. The pattern of performance shown by EM is consistent with the DRC model of reading, but inconsistent with the connectionist attractor model and with the view, associated with that model, that orthographic and phonological processes cannot remain intact when semantic representations are degraded.

Coltheart, M. (2004). Are there lexicons? Quarterly Journal of Experimental Psychology A,Human Experimental Psychology, 57, 1153-1171.
Notes: Macquarie University, Sydney, Australia.
Many models of the processing of printed or spoken words or objects or faces propose that systems of local representations of the forms of such stimuli--lexicons--exist. This is denied by partisans of the distributed-representation connectionist approach to cognitive modelling. An experimental paradigm of key theoretical importance here is lexical decision and its analogue in the domain of objects, object decision. How does each theoretical camp account for our ability to perform these two tasks? The localists say that the tasks are done by matching or failing to match a stimulus to a local representation in a lexicon. Advocates of distributed representations often do not seek to explain these two tasks; however, when they do, they propose that patterns of activation evoked in a semantic system can be used to discriminate between words and nonwords, or between real objects and false objects. Therefore the distributed-representation account of lexical and object decision tasks predicts that performance on these tasks can never be normal in patients with an impaired semantic system, nor in patients who cannot access semantics normally from the stimulus domain being tested. However, numerous such patients have been reported in the literature, indicating that semantic access is not needed for normal performance on these tasks. Such results support the localist form of modelling rather than the distributed-representation approach

Coltheart, M., Rastle, K., Perry, C., Langdon, R., & Ziegler, J. (2001). DRC: a dual route cascaded model of visual word recognition and reading aloud. Psychological Review, 108, 204-256.
Notes: Macquarie Centre for Cognitive Science, Macquarie University, Sydney, NSW 2109, Australia.
This article describes the Dual Route Cascaded (DRC) model, a computational model of visual word recognition and reading aloud. The DRC is a computational realization of the dual-route theory of reading, and is the only computational model of reading that can perform the 2 tasks most commonly used to study reading: lexical decision and reading aloud. For both tasks, the authors show that a wide variety of variables that influence human latencies influence the DRC model's latencies in exactly the same way. The DRC model simulates a number of such effects that other computational models of reading do not, but there appear to be no effects that any other current computational model of reading can simulate but that the DRC model cannot. The authors conclude that the DRC model is the most successful of the existing computational models of reading

Jackson, N. E. & Coltheart, M. (2001). Routes to reading success and failure: Toward an integrated cognitive psychology of atypical reading.  New York: Psychology Press.
Notes: 225pp; 8 chapters. 1. Introduction. 2. Proximal and distal causes of individual differences in reading. 3. Dual-route theories of reading. 4. Acquired dyslexia. 5. Reading acquisition. 6. Reading acquisition difficulties. 7. Prococious reading. 8. Conclusions

Coltheart, M. (2000). Deep dyslexia is right-hemisphere reading. Brain and Language, 71, 299-309.
Notes: Department of Psychology, Macquarie University, Sydney, New South Wales, 2109, Australia. ; ABSTRACT: Two views exist concerning the proper interpretation of the form of acquired dyslexia known as deep dyslexia: (a) that it represents reading by a multiply damaged left hemisphere reading system; (b) that it represents reading which relies extensively on right-hemisphere orthographic and semantic processing. Price, Howard, Patterson, Warburton, Friston, and Frackowiak (1998) have recently reported a brain-imaging study whose results, they claim, "preclude an explanation of deep dyslexia in terms of purely right-hemisphere word processing." Their claim conflicts with the conclusions of previous published work, which strongly supports the RH hypothesis, work which they do not mention. Furthermore, I argue that their own results also favor the RH hypothesis (even though they claim otherwise); indeed, their results permit the formulation of a much more detailed version of the RH hypothesis than has hitherto been possible. Hence I conclude that the right-hemisphere interpretation of deep dyslexic reading remains the preferred explanation of deep dyslexia.

Coltheart, M. (1998). Seven questions about pure alexia (letter-by-letter reading). Cognitive Neuropsychology, 15, 1-6.
Notes: I discuss ways in which the subsequent papers offer answers to some basic questions about pure alexia (letter- by-letter reading).Is the disorder a homogeneous one? Is the relevant impairment specific to the reading system or is it a more general visual impairment? What is the nature and the locus of the letter-by-letter reader's impairment, within some functional model of reading? What causes the patients to read letter-by-letter? What contribution does the right hemisphere make? Why is letter-by-letter reading accuracy affected by imageability (concreteness)? Why do some letter-by- letter readers show covert processing and others not?

Stuart, M. & Coltheart, M. (1988). Does reading develop in a sequence of stages? Cognition, 30, 139-181.

Coltheart, M. (1987). Deep dyslexia: a right-hemisphere hypothesis. In M.Coltheart, K. Patterson, & J. C. Marshall (Eds.), Deep dyslexia (2 ed., pp. 326-380). London: Routledge & Kegan Paul.

Coltheart, M. (1987). Deep dyslexia: a review of the syndrome. In M.Coltheart, K. Patterson, & J. C. Marshall (Eds.), Deep dyslexia (2 ed., pp. 22-47). London: Routledge & Kegan Paul.

Coltheart, M. (1987). Reading, phonological reading, and deep dyslexia. In M.Coltheart, K. Patterson, & J. C. Marshall (Eds.), Deep dyslexia (2 ed., pp. 197-226). London: Routledge & Kegan Paul.

M.Coltheart (Ed.), Attention and performance XII. The psychology of reading. Hove: Erlbaum.

 K.E.Patterson, J. C. Marshall, & M. Coltheart (Eds.), Surface dyslexia: Neuropsychological and cognitive studies of phonological reading. London: Erlbaum.

Coltheart, M. (1985). Right-hemisphere reading revisited. Behavioral and Brain Sciences, 8, 363-365.

Besner, D. & Coltheart, M. (1979). Ideographic and alphabetic processing in skilled reading of English. Neuropsychologia, 17, 467-472.



Anders Gade