Our objective is to develop and validate objective electrophysiologic probes of cortical acoustic processing of complex sounds in the young infant. Cortical evoked responses to speech sounds differing across acoustic dimensions that are critical for the perception of speech exhibit characteristic waveforms and spatial distribution. It is hypothesized that deviant patterns of cortical responses index deviant auditory processing associated with some instances of abnormal speech and language development. The finding that cortical responses to infrequent changes in acoustic features elicit distinctive responses further enhances the potential for detection of impaired discriminative capacity in the infant. The integrity of the auditory system will be examined from ear to cortex employing frequency specific ABR, obligatory cortical responses to speech sounds and discriminative cortical responses to speech sound tokens along the dimensions of place of articulation (PLACE) and voicing (voice onset - time - VOT). Discriminative responses will be examined in response to stimuli that differ in acoustic properties within and across phonemic boundaries. The developmental pattern of cortical responses to these speech sound tokens will also be compared with complex tonal stimuli that elicit """"""""categorical"""""""" discriminative behavior to examine the possibility that different spatial and temporal patterns of cortical responses in secondary auditory cortical areas may specifically encode the speech sounds as """"""""phonetic"""""""" entities. The validity of the electrophysiologic indices will be evaluated by direct comparison to behavioral responses utilizing Visual Reinforcement Infant Speech Discrimination (VRISD) techniques in infants at six months of age. The predictive value of deviant electrophysiologic measures will be assessed in follow-up studies of speech and language development.
