Deficits in reading, writing and calculation tend to co-occur, such that both isolated cases (eg children with only dyslexia) and mixed cases (eg children with dyslexia and dyscalculia) are present. The aim of the study is to account for both associations and dissociations by reference to the same unitary "proximal" model of the factors accounting for performance in these skills. We plan to examine a sufficiently large number of children to have a sufficient number of both dissociated cases and associated cases (N = 50 to 70 children between 10 and 12 years of age). All children will have with a diagnosis of dyslexia, dysgraphia and dyscalculia (made according to current clinical standards) whether "isolated" or in a mixed form.
As dependent variables, we will use measures with a clear functional value in everyday life such as reading a meaningful text aloud, writing upon dictation a meaningful passage, and carrying out a variety of calculation tasks (including all four operations) with both accuracy and speed being considered.
Independent variables (i.e., cognitive dimensions) will be modeled on the basis of an integrated model of reading, writing and calculation developed by the our research group. It is hypothesized that independent competences are present for these three behaviors and that this may account for dissociations among learning disorders. On the other hand, association among learning disorders may be due to an acquisition factor and particularly on the "ability to consolidate instances" which is responsible for automatized behavior.
Much research on learning disabilities has focused on a single-deficit approach (for a discussion see Pennington, 2006). However, most children actually present overlapping disorders. Thus, a large majority a children with reading deficits also show writing disorders (but also isolated disorders have been reported); moreover, many children with dyslexia (about 30-40%) show also calculations deficits. This proportion is much higher than that in the general population (ca. 4-5%) but, at the same time, indicates only a partial overlap between these disorders. Thus, by definition, focusing on single deficits only explains part of the phenomenology of these disorders but fails to account for the reasons underlying the frequent comorbidities. In this project, we aim to account for both the dissociations and associations among learning disorders thus contributing to a much more in-depth knowledge of these learning disabilities. In the last years, some studies have moved in this direction. However, identification of the cognitive factors accounting for the overlap among disorders has proven elusive (eg Wilson et al., 2015). We propose here that much of the overlap among disorders (or comorbidity) may be explained by the presence of a domain-independent factor ("ability to consolidate instances"). Accordingly, some children may be selectively impaired in automatizing reading as well as writing and doing maths. In this view, the ability to automatize is a factor that contributes to efficient performance. Conversely, poor ability in forming instances does not make the behavior impossible but rather has the more specific effect of preventing fast and fluid reading, efficient writing and fast and efficient calculation. As stated above, children (and even more so adults) with dyslexia are not unable to read but their reading is cumbersome, inefficient and ultimately tiring, characteristics which indicate a controlled, voluntary mode of processing (Schneider & Chein, 2003). This contrasts with the smooth and efficient decoding of the typically developing peers, which marks their pre-attentive, automatic processing (Schneider & Chein, 2003). Thus, lack of automaticity does not necessarily indicate an impaired core reading competence (which of course may also be present), but would indicate a deficit in a component necessary for fluent reading, and one that can be a source of at least partial associations.
Overall, we propose that the present proposal can shed a new perspective on our understanding of developmental learning disabilities.
References
Pennington, B. F. (2006). From single to multiple deficit models of developmental disorders. Cognition, 101(2), 385-413.
Schneider, W., & Chein, J. M. (2003). Controlled & automatic processing: behavior, theory, and biological mechanisms. Cognitive Science, 27(3), 525-559.
Wilson, A. J., Andrewes, S. G., Struthers, H., Rowe, V. M., Bogdanovic, R., & Waldie, K. E. (2015). Dyscalculia and dyslexia in adults: cognitive bases of comorbidity. Learning and Individual Differences, 37, 118-132.