SOUND LOCALIZATION ACUITY IN VERY YOUNG INFANTS - AN OBSERVER-BASED TESTING PROCEDURE

Infants 8 to 28 weeks of age were tested to determine the smallest sound shift off midline and along the horizontal axis that could be reliably discriminated, that is, minimum audible angle. Both sound-shift and no-shift trials were presented. For each trial, an observer decided, based solely on the infant's behavior, whether the sound shifted location (i.e., an observer-based yes-no task). To isolate sensory from nonsensory factors, analyses were performed on d′ scores. The results indicated increasing localization acuity with age. The video records revealed numerous auditory orienting behaviors (e.g., alerting, quieting, and lateral head and eye movements) and highlighted the value of not requiring that specific behavioral responses be performed on sound-shift trials. Possible factors contributing to these developmental trends are discussed.