This continuing grant for three years is on auditory perception. The two ears must be used together, binaurally, for localizing a sound source in space. The difference for the two ears in arrival time of a signal is the interaural time delay (ITD), and the difference for the sound intensity is the interaural intensity difference (IID). The auditory system is very sensitive to small changes in these cues, and there has been a lot of theoretical interest in how such cues are used to construct the perception of sound localization. Models to account for binaural phenomena usually involve a display of interaural cross- correlation of auditory nerve activity, after some peripheral analy- sis. But it remains important to know whether the auditory system can extract such interaural differences when the stimulus is not a simple constant relatively low-frequency tone pulse, but more complex sounds such as amplitude-modulated tones or narrowband noise, which have a characteristic "envelope" of frequency or intensity with time. This project will extend theories of binaural interaction to desribe and predict results of experiments using complex binaural stimuli, and using pure tones over a very wide range of frequencies. Two models will be handled. One will be developed that considers the peaks of crosscorrelation functions, and how those vary with frequency. A second will reformulate a model initially designed only for low-frequency stimuli, using an approach relating auditory nerve fiber responses to high-frequency tones and broadband noise. The model predictions will be tested by psychoacoustical experiments, which will be used to distinguish alternative interpretations of sound lateralization phenomena, and better understand intersubject variability. This work is an unusually quantitative approach that will have substantial impact on an important issue in auditory perception. The models dealing with responses to complex stimuli are likely to influence current research in several sensory systems where complex stimuli are now being addressed in a quantitiative way. This work also may lead to potential application for auditory prosthesis or auditory displays for the blind.
