Cerebellar Tasks do not Distinguish Between Children with Developmental Dyslexia and Children with Intellectual Disability

This paper explored the claim that only children with developmental dyslexia, whose reading ability is discrepant from their average general reasoning ability show specific deficits in motor tasks assessing cerebellar functioning (Fawcett et al., 2001 Fawcett, A. J. and Nicolson, R. I. 2001. “Dyslexia: The role of the cerebellum”. In Dyslexia: Theory and good practice, Edited by: Fawcett, A. J. 89–105. London: Whurr.  Google Scholar], Cerebellar tests differentiate between groups of poor readers with and without IQ discrepancy. J. Learning Disabilities, 34, 119) and rapid serial naming (RAN, Wolf & Bowers, 1999 Wolf, M. and Bowers, P. 1999. The double deficit hypothesis for the developmental dyslexias. Journal of Educational Psychology, 91: 1–24. Crossref], Web of Science ®] , Google Scholar], The double deficit hypothesis for the developmental dyslexias. J. Educ. Psychol., 91, 1). All available children between the ages of 11 and 14 were recruited from two special schools for children with either (a) formally-diagnosed intellectual disabilities (N?=?18); or (b) formal diagnoses of developmental dyslexia (N?=?25). These two groups of children did not differ on gender, age, pseudoword decoding abilities, or on 7 of 8 literacy measures, but did differ significantly, as expected on verbal and non-verbal reasoning tasks. Importantly, there were no deficits in bead threading ability or postural stability in the children with developmental dyslexia compared to the children with intellectual disabilities. There were also no between-group differences in rapid naming measures. The present results therefore provide no support for the claim that cerebellar deficits or RAN distinguish between children with dyslexia and children with intellectual disabilities that include reading.