Cognitive profiles of adult developmental dyslexics: theoretical implications

Abstract

The aim of this study was to establish cognitive profiles of dyslexic adults on tests developed within the three main theories of developmental dyslexia: phonological, visual magnocellular and cerebellar and to investigate which theory can account for these profiles. The sample consisted of 15 Polish university students or alumni with a formal diagnosis of dyslexia, without ADHD and 15 controls matched on education, age, gender, IQ and handedness. The results revealed a striking heterogeneity of profiles. Nine dyslexics exhibited only a phonological deficit; one a phonological and a visual magnocellular deficit; a further three a phonological and a cerebellar deficit; two either a cerebellar or a visual magnocellular deficit. None of the three main theories of dyslexia can account for all the cases studied here. It is suggested that the best account of these data is in terms of different sub-types of dyslexia with different underlying causes, such as phonological, visual magnocellular and cerebellar, or a combination of these. However, an account in terms of Ramus' (Trends, Neurosci. 2004; 27(12): 720-726) model, according to which the phonological deficit is a core deficit in dyslexia and other deficits (magnocellular and cerebellar), are just co-morbid markers without a causal relationship to dyslexics' literacy difficulties, cannot currently be ruled out.

Auditory Temporal Processing and Working Memory: Two Independent Deficits for Dyslexia

“…These findings imply that the deficiency in working memory and the deficiency in auditory temporal resolution are two independent sources of difficulty for the dyslexic readers in processing written material. Two independent deficits, each of which predicts reading ability in a population of dyslexic readers, may help explain the large inter-individual differences found in this population (Ramus et al, 2003;Reid, Szczerbinski, Iskierka-Kasperek, & Hansen, 2007;Wright et al, 2000). Similarly, while addressing the issue of the relatively large inter-individual differences found among dyslexic readers, Wright et al (2000) suggested that reading problems are in fact multidimensional in nature.…”

Speech Perception Abilities of Adults With Dyslexia: Is There Any Evidence for a True Deficit?

“…The method used to identify participants in each task who were performing below norm was as first described in Ramus et al (2003) and also used by Reid et al (2007). Average readers performing below 1.65 standard deviation of the mean for the AR group (i.e., 5 th percentile) were removed, and the mean and standard deviation for the AR group was then recalculated.…”

“…In both adults and children, evidence of poor performance on phonological awareness tasks is rather pervasive (e.g., Elbro, Nielsen & Petersen, 1994, Snowling, Nation, Moxham, Gallagher & Frith, 1997Ramus et al, 2003;Ziegler and Goswami, 2005;Snowling, 2000, although see also Reid, Szczerbinski, Iskierka-Kasperek & Hansen, 2007 for cases of individuals with dyslexia who have unimpaired phonological awareness). However, there is increasing debate as to whether poor performance on phonological awareness tasks reflects impoverished phonological representations or rather difficulties with the access or manipulation of these representations.…”

“…Generally, in the dyslexia literature, it is increasingly recognized that it is not sufficient to show that significant group differences occur at some level of processing, but that it must also be shown that a substantial number of individuals show a performance that differs significantly from the norm (Ramus et al, 2003;Reid et al, 2007;Heath, Bishop, Hogben & Roach, 2006;Ziegler, Castel, Pech-Georgel, George, Alario & Perry, 2008;McArthur and Hogben, 2001;McArthur, Ellis, Atkinson & Coltheart, 2008). In studies with dyslexic children and adults that have reported individual data, there is ample evidence of significant individual differences in performance on speech perception tasks.…”

Dyslexia in the University. Guidelines for inclusion and teaching of the University of Florence

“…Therefore, we know quite well the difficulties that a 6-10 years student meets compared to the demands at school, but we are still far from a thorough understanding of the nature and characteristics of such disorders in adolescence and adulthood (Hatcher et al, 2002;Reid et al, 2006, Genovese E. et al, 2011.…”