Numerical estimation in typical and atypical development : what is the core deficit?

(eng) The present thesis focused on those multiple explanations for dyscalculia assuming that this disability could be due to a) a basic numerical deficit affecting the representation and the manipulation of number magnitude (Butterworth, 1999, 2005; Wilson & Dehaene, 2007), b) an access deficit to that number magnitude from numerical symbols (Rousselle & Noël, 2007) or eventually due to c) a deficit affecting a larger magnitude system (Walsh, 2003). Several studies are presented and tested the different hypotheses by comparing children with mathematical learning disabilities (MLD) and typically achieving (TA) children’s abilities to provide approximate answers contrasting symbolic (Arabic numbers) and non-symbolic (pattern of dots) numerical magnitudes as well as continuous (quantity of liquid) magnitudes. Performances of TA adults and adults who had experienced MLD in childhood were also examined. The comparison between adults and children performances provides the characteristic and the longevity of mathematical difficulties and has implications for the diagnosis and rehabilitation of people with MLD.