Theories of developmental dyslexia



European Commission
Medical Research Council
Uta Frith, Stuart Rosen, and other collaborators from University College London.
Sarah White, Elizabeth Milne, Elizabeth Pidgeon, and other students and research assistants.

During my postdoc as a Marie Curie fellow at University College London in 2000-2001, in collaboration with Uta Frith, Stuart Rosen and others, I have attempted to produce decisive data that might allow us to adjudicate between competing theories of developmental dyslexia (phonological, auditory/temporal processing, visual/magnocellular, motor/cerebellar...). Our initial results on dyslexic adults favoured the idea that sensorimotor disorders are present in only a fraction of dyslexics, and that a specific phonological deficit seems sufficient to cause dyslexia: 

Ramus, F., Rosen, S., Dakin, S. C., Day, B. L., Castellote, J. M., White, S., & Frith, U. (2003). Theories of developmental dyslexia: Insights from a multiple case study of dyslexic adults. Brain, 126, 841-865. reprint (supplementary material)

This work has been extended by graduate students Liz Pidgeon and Sarah White in related studies, leading to similar conclusions:

Ramus, F., Pidgeon, E., & Frith, U. (2003). The relationship between motor control and phonology in dyslexic children. Journal of Child Psychology and Psychiatry, 44 (5), 712-722reprint

White, S., Milne, E., Rosen, S., Hansen, P. C., Swettenham, J., Frith, U., & Ramus, F. (2006). The role of sensorimotor impairments in dyslexia: A multiple case study of dyslexic children. Developmental Science, 9(3), 237-255. reprint
Followed by commentaries by Bishop, Goswami, Nicolson & Fawcett, and Tallal.
Followed by our reply: Ramus, F., White, S., & Frith, U. (2006). Weighing the evidence between competing theories of dyslexia. Developmental Science, 9(3), 265-269.

The latest developments in this line of research have investigated similar questions in autistic children (in collaboration with Liz Milne and John Swettenham, also at UCL) and systematically compared dyslexic and autistic children on language and sensorimotor measures. The latter study suggests that sensorimotor impairments are neither necessary nor sufficient to cause phonological and reading difficulties:

Milne, E., White, S., Campbell, R., Swettenham, J., Hansen, P. C., & Ramus, F. (2006). Motion and form coherence detection in autistic spectrum disorder: Relationship to motor control and 2:4 digit ratio. Journal of Autism and Developmental Disorders, 36(2), 225-237. reprint

White, S., Frith, U., Milne, E., Rosen, S., Swettenham, J., & Ramus, F. (2006). A double dissociation between sensorimotor impairments and reading disability: A comparison of autistic and dyslexic children.  Cognitive Neuropsychology, 23(5), 748-761. reprint

I have also carried out a review of the dyslexia literature, which have converged with the results from my own studies:

Ramus, F. (2003). Developmental dyslexia: specific phonological deficit or general sensorimotor dysfunction? Current Opinion in Neurobiology, 13(2), 212-218. reprint

The conclusion is that my research strongly supports the phonological theory of dyslexia. However the phonological theory in its current state is unable to explain why a significant proportion of dyslexics also have sensorimotor deficits (and does not much care about it). I have most recently tried to fill this gap with a new neurological model:

Ramus, F. (2002). Evidence for a domain-specific deficit in developmental dyslexia. Behavioral and Brain Sciences, 25(6), 767-768. (Commentary on Thomas & Karmiloff-Smith 2002reprint

Ramus, F. (2004). Neurobiology of dyslexia: A reinterpretation of the data. Trends in Neurosciences, 27(12), 720-726. reprint

Ramus, F. (2005). Motion perception deficit: risk factor or non-specific marker for neuro-developmental disorders? Cahiers de Psychologie Cognitive/Current Psychology of Cognition, 23(1-2), 180-188. reprint (Commentary on Milne et al. 2005)

Ramus, F. (2006). A neurological model of dyslexia and other domain-specific developmental disorders with an associated sensorimotor syndrome. In G. D. Rosen (Ed.), The Dyslexic Brain: New Pathways in Neuroscience Discovery (pp. 75-101). Mahwah, NJ: Lawrence Erlbaum Associates. reprint

More recent work has further confirmed the limited involvement of auditory perceptual deficits in dyslexia:

Soroli, E., Szenkovits, G., & Ramus, F. (2010). Exploring dyslexics' phonological deficit III: Foreign speech perception and production. Dyslexia, 16, 318-340. preprint

Ramus, F., & Ahissar, M. (2012). Developmental dyslexia: the difficulties of interpreting poor performance, and the importance of normal performance. Cognitive Neuropsychology, 29(1-2), 104-122.

Agus, T. R., Carrión Castillo, A., Pressnitzer, D., & Ramus, F. (in press). Perceptual learning of acoustic noise by dyslexic individuals. Journal of Speech, Language and Hearing Research.