Ramus, F. 1 & Wimmer, H. 2
1 CNRS - Laboratoire de Sciences Cognitives et Psycholinguistique, Institute of Cognitive Studies, Ecole Normale Supérieure, Paris, France
2 University of Salzburg, Austria
I will report findings from structural MRI analyses carried out on the brain images of a population of 32 dyslexic and 32 control children, as well as on separate groups of dyslexic and control children scanned by collaborators. Our analyses bear on gray matter volumes, cortical thickness, sulcal configurations (of the sylvian fissure and the central sulcus), dimensions and asymmetry of the planum temporale and of Heschl's gyrus, and the micro-structure of the arcuate fasciculus. I will also highlight all the effects published in the dyslexia literature that we have failed to replicate on the way to our results. I will then reflect on the limitations of most published studies, on the conditions necessary to produce replicable results, and on the importance of oft-overlooked variables such as age, sex, SES and IQ.
My contribution will examine the evidence for the position that the main hurdle for dyslexic children is to acquire self-reliant phonological word decoding in the early phase of learning to read and that this difficulty with phonological reading secondarily leads to deficient input to the visual orthographic word lexicon required for fast visual word recognition (and for correct spelling). In neurological terms, the primary phonological reading problem is attributed to a dysfunction of a left temporo-parietal brain region; the secondary orthographic deficit is seen as reflected in reduced engagement of a left ventral occipito-temporal region. In the examination of this account, imaging studies and meta-analyses from our lab will be presented and a revision of the theoretical account will be proposed.