Developmental dyslexia is a mutlifactor disorder : The neuropsychological approach

Although increasing evidence from heterogeneous studies supports a neurobiological basis for developmental dyslexia, the underlying causes of this multisensory deficit are still unknown. The aim of this study was to understand better the relation between phonological awareness, perception of transient stimuli, visuo-spatial attention and implicit learning. Thirty-one dyslexic children took part in this study. Phonological awareness was investigated with a verbal fluency test and a spoonerism task. Implicit learning strategies were evaluated with a modified serial reaction time test, by measuring reaction time and the percentage of errors. Visuo-spatial atten- tion was analysed with a test of everyday attention for children (TEA-Ch) subtest. A modified random-dot kinematogram test was used to study the perception of motion in different directions in terms of reaction time and accuracy. Significant correlations were found between phonological awareness, implicit learning strategies and visuo-spatial attention tasks. Motion perception was found to be related only to visual spatial attention tasks. Two different subtypes of dyslexia could be identified from the abilities investigated abilities: in one subtype, the dysfunction affects the phonological system, implicit learning development, and visuo-spatial attention; whereas, in the other subtype, only motion perception and visuo-spatial attention are affected.