[Speech perception in the first two years].

The development of speech perception relies upon early auditory capacities (i.e. discrimination, segmentation and representation). Infants are able to discriminate most of the phonetic contrasts occurring in natural languages, and at the end of the first year, this universal ability starts to narrow down to the contrasts used in the environmental language. During the second year, this specialization is characterized by the development of comprehension, lexical organization and word production. That process appears now as the result of multiple interactions between perceptual, cognitive and social developing abilities. Distinct factors like word acquisition, sensitivity to the statistical properties of the input, or even the nature of the social interactions, might play a role at one time or another during the acquisition of phonological patterns. Experience with the native language is necessary for phonetic segments to be functional units of perception and for speech sound representations (words, syllables) to be more specified and phonetically organized. This evolution goes on beyond 24 months of age in a learning context characterized from the early stages by the interaction with other developing (linguistic and non-linguistic) capacities.