Infants' localization of sounds within hemifields: estimates of minimum audible angle.

Infants' acuity in localizing sounds within hemifields was examined by determining the smallest sound shift off 60 degrees and along the horizontal axis that infants could discriminate reliably, that is, minimum audible angle (MAA). Infants 6, 12, and 18 months of age were tested using a Go/No-Go conditioned head-turn procedure in which infants received an equal number of no-change (control) trials and sound-shift (experimental) trials. A correct response (i.e., a head turn toward the loud-speakers) on an experimental trial resulted in visual reinforcement. Localization acuity for sounds within hemifields was fairly poor and improved systematically with increasing age. MAA estimates at each age were significantly higher, indicating poorer localization acuity, in comparison to those obtained previously in research examining infants' resolution of auditory space near midline. These findings are consistent with adult data and demonstrate a finer partitioning of auditory space near midline than within hemifields. The implications of these findings for our understanding of the development of auditory processing mechanisms in sound localization are discussed.