Boys Town Natl. Res. Hospital, 555 N. 30th St., Omaha, NE 68131
Since the pioneering work of Eimas et al. [Science 171, 319--324], numerous experiments have shown that infants discriminate speech-relevant acoustic parameters in the same way adults do. Both infants and adults discriminate an acoustic difference if it places two stimuli on opposite sides of a phoneme boundary, but fail to discriminate a difference if it places two stimuli within the same phoneme category. Such results have led to the suggestion that the relation between acoustic and phonemic structure is innately recognized. However, studies of phoneme identification with preschool and young school-aged children call into question the intransigent nature of this proposed, innate mechanism. When two acoustic parameters are varied across stimuli, the contributions of each to phonemic decisions appear to differ for adults and children. Such results have led to the suggestion that the weights assigned to various acoustic properties of the speech signal are retuned as children gain experience with their native language, a proposal called the developmental weighting shift. Evidence for this proposal will be presented, as well as a discussion of its potential relation to developmental changes in auditory capacities and phonemic awareness.