BINAURAL INFORMATION PROCESSING

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The purpose of the proposed research is to gain a broader understanding of the manner in which interaural temporal disparities (ITD's) and interaural intensitive disparities (IID's) ar processed within high- frequency, complex waveforms. One subset of experiments concerns the evaluation of the degree to which ITD's and/or IID's account for the rather large release from masking which can be obtained when dichotic as compared to diotic signals are employed (the high-frequency MLD). "Natural" as well as specially constructed digital stimuli will be employed which will allow for the variation and measurement of the interaural parameters in a controlled and predictable fashion. In addition, listeners' absolute sensitivities to the presence of such cues within high-frequency, complex waveforms will be measured. A second subset of experiments involves a parametric investigation of the conditions under which listeners' use of interaural disparities within a (target) stimulus at one spectral locus is affected by the presence of (interfering) stimuli at different spectral loci. The manner in which these interfering stimuli affect the lateral position (measured via an acoustic "pointing" task) of the target, sensitivity to the presence of interaural disparities within the target and detection of targets within a background of noise (the MLD) will be investigated. A third subset of experiments will assess to what degree processing of ITD's within the envelopes of high-frequency stimuli is analogous to the processing of ITD's within the fine-structure of low-frequency stimuli. Detection of ITD's and extent of laterality will be measured for bands of noise and sinusoidally amplitude modulated tones (SAM) with center frequencies between 4 kHz and 15 kHz. In addition, an investigation of the conditions under which an envelope-based "binaural beat" occurs with SAM tones and two-tone complexes will be conducted.