Connectionist neuropsychology: uncovering ultimate causes of acquired dyslexia

Abstract

Acquired dyslexia offers a unique window on to the nature of the cognitive and neural architecture supporting skilled reading. This paper provides an integrative overview of recent empirical and computational work on acquired dyslexia within the context of the primary systems framework as implemented in connectionist neuropsychological models. This view proposes that damage to general visual, phonological or semantic processing abilities are the root causes of different forms of acquired dyslexia. Recent case-series behavioural evidence concerning pure alexia, phonological dyslexia and surface dyslexia that supports this perspective is presented. Lesion simulations of these findings within connectionist models of reading demonstrate the viability of this approach. The commitment of such models to learnt representations allows them to capture key aspects of performance in each type of acquired dyslexia, particularly the associated non-reading deficits, the role of relearning and the influence of individual differences in the premorbid state of the reading system. Identification of these factors not only advances our understanding of acquired dyslexia and the mechanisms of normal reading but they are also relevant to the complex interactions underpinning developmental reading disorders.

Are children with developmental dyslexia all the same? A cluster analysis with more than 300 cases

“…Interestingly, individuals with DD have also been reported to show a hypo‐activation of the VWFA and an impairment in processing non‐verbal visual stimuli (e.g., Sigurdardottir et al, ) as, for instance, faces (e.g., Gabay et al, ). The measure of processing speed in WISC‐IV uses non‐verbal visual stimuli and the difficulties shown by children with DD on this task confirm a domain general impairment, supporting the predications of the triangle model (Woollams, ). Notably, children in the second cluster present with a dual‐system deficit in visual and phonological processing.…”

When words fail us: insights into language processing from developmental and acquired disorders

“…Woollams [35] discusses the Primary Systems Hypothesis-an account of the language system, allied with PDP computational modelling, that is informed by developmental issues. It sets our ability to read words within a broader context, arguing that as a recent skill in human evolution, reading is likely to depend on more general systems that have evolved to support primary functions such as vision and language.…”

“…First, we now have several implemented models for processing of written and spoken language that have been applied to acquired disorders [22,35,[42][43][44]. Some of these model the learning process as well as the stable state, yet applications to developmental disorders are rare (but see Ziegler et al [33]).…”

Lexical learning and lexical processing in children with developmental language impairments

“…executive function) have also been considered in some detail. It is interesting to see a more developmental approach characterizing discussion of acquired disorders, as embodied in the primary systems hypothesis for example [92], and in reflections on the nature of the relationship between domain-general factors such as executive function and lexical-semantic processing in patients with acquired disorders [84].…”