Based on recent studies that put into question the concepts of prototype and typicality, this study treats the processes of categorization by sufferers from Alzheimer's disease, in the light of two themes: clotting of the prototype into stereotype and distinction between, on the one hand, the representations of common objects developed by an individual in a very early stage of his development and, on the other hand, the socialized attainments acquired subsequently. We analyse the processes of categorization in five groups of subjects (English-speaking students, French-speaking students, sufferers from Alzheimer's disease and witnesses) paired by age, sex and level of studies. Our aim is to study two effects on the probability of categorical inclusion: the effect of constraints and categories (putting in contrast four types of categories - two "natural" ones and two "artefactual" or cultural ones), and the effect of typicality of examples, in the different groups of subjects. By this analysis, we aim to demonstrate specific behaviours shown by the group of sufferers.

It is a well known phenomenon that deaf children generally have many difficulties in acquiring reading and spelling in alphabetic orthographies. It is argued here that these difficulties mainly result from the fact that these children rely on lipreading to perceive spoken language and that their phonological representations are underspecified. Two lines of evidence are presented in support of this view: 1/ an analysis of how deaf children exposed to spoken language only and/or to signed language read and spell; 2/ an analysis of the effect of exposure to visual systems disambiguating lipreading on the development of phonological abilities. It is concludede that deaf children may develop reading and spelling along lines similar to those of hearing children, provided that they are exposed to a linguistic input in which all the phonological contrasts of spoken language are specified.

If dysphonia is clearly identified as a phonation disorder, dysarthria is often wrongly restricted to an arthric impairment. Actually, dysarthria is a motor speech disorder, whose origin is a lesion of the central or peripheral nervous system; it involves various possible deteriorations during the motor execution of speech, which influence respiratory, phonatory, resonatory, articulatory, and prosodic aspects of speech production. The distinction between dysphonia and dysarthria based on which anatomical level is lesioned does not accurately explain the duality between these terms; on the other hand, a distinction rather based on the neurological origin of the disorder would seem more adapted to describe as precisely as possible the multiple dysfunctions of voice and speech. In fact, the study of dysarthric and dysphonic speech for the better understanding of normal speech represents an original approach, which considers speech disorder as a model of its own for speech investigation.

The production of speech is a complex cognitive activity, whose elaboration may be disturbed in various ways. Our purpose here is to explore the continuum between normal and pathological speech production. There are similitudes between performance errors by average speakers and the paraphasias produced by aphasics in the same circumstances; both kinds of perturbations affect the same linguistic units and reveal similar psycholinguistic mechanisms. Yet, production in these two cases differ according to several criteria, such as the error rate, the way the erroneous item and the target item are connected, the speaker's awareness of inadequacy, the comments he makes and his need for justification. Those elements point out to the boundaries that may be defined between normal and pathological speech.