The objective of the proposed research continues to be a comprehensive, systematic and parametric evaluation of the roles that spectral locus and temporal variation play in selected binaural experiments. By being able to produce interaural temporal disparities within selected aspects of narrow bands of noise, we hope to extend great knowledge of how the human's ability to lateralize, to discriminate and to detect is affected by the spectral region and spectral composition of sounds that are processed via binaural interactions. One large subset of experiments concerns lateralization and is directed toward the specific aim of evaluating, as a function of spectral locus and temporal variations, the relative potency of (1) interaural temporal delays (ITDs) of only the envelope of a narrow band of noise; (2) ITDs of only the phase-modulated component of a narrow band of noise; (3) ITDs present in combinations of envelope, carrier and/or phase-modulated components of narrow bands of noise. Another subset of experiments will be directed toward measuring lateralization while varying the putative pattern of activity along the frequency vs. internal delay plane that is a major (physiologically supported) feature of all modern theories and models of binaural hearing. To do so, we propose to measure extent of laterality both with an """"""""acoustic pointer"""""""" and by having listeners indicate with a light-pen/computer terminal where on a caricature of a human head they hear sounds within their own heads. We also proposed experiments concerning detection of interaural delays as a function of the spectral locus of the delay when the subject is presented stimuli that are composed of either broadband noises or several bands of noise which span a large range of frequencies. The purpose of these experiments is to evaluate exactly which regions of interfering sound make difficult the binaural processing of delays which occur only at high spectral frequencies. In addition to contributing to our understanding of normal hearing, this program of research should also help us being to understand how people with sensorineural hearing losses process sounds binaurally.
