The proposed research seeks (1) to explore the development of auditory perceptual abilities, specifically pitch and timbre perception, during infancy, and (2) to delineate some of the acoustic cues infants can employ in those tasks. Both pitch and timbre perception appear to require the integration or synthesis of information gleaned from a peripheral analysis of the spectral characteristics of sound, whereas spectral analysis alone permits simple discrimination of sounds. On the basis of the animal literature, adult psychoacoustics work, and the available infancy research, it can be hypothesized that the synthesis of acoustic information will show dramatic developmental changes during early life. Furthermore, it appears that the ability to analyze sounds into their spectral components precedes the ability to integrate that information in the service of perception. The studies of pitch perception will attempt to establish the emergence of pitch for complex harmonic and inharmonic sounds, including the perception of the missing fundamental. Specifically, these studies will (1) evaluate pitch extraction from harmonic tonal complexes in 3 month olds, and (2) from inharmonic tonal complexes in 7 month olds; (3) determine whether 7 month olds can use spectral information to categorize tonal complexes, when they are unable to integrate that information; (4) determine whether 7 month old infants can use high frequency energy to extract pitch from tonal complexes; and (5) employ a psychophysical technique to assess the extent of the dominance region for pitch in 7 month olds, and (6) in adults. Since very little is known about timbre perception in infancy, an initial study will investigate infants' categorization of sounds on the basis of timbre, but in the presence of irrelevant variations in pitch. Infants from 3 to 8 months of age will be tested in an operant conditioning procedure. Since the proposed research will investigate both analytic and synthetic processing of sound, it is hoped that the general pattern of auditory development and the mechanisms underlying it can be uncovered. In doing so, the proposed research will provide a necessary preliminary step toward the formulation of a general model of auditory development. Furthermore, the brain-behavior relations uncovered will contribute to our understanding of the behavioral consequences of brain damage in human adults and children.
