Comparisons of Binaural Processing at Low & High Frequencies

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DESCRIPTION (provided by applicant): The objectives of the proposed research continue to be an evaluation, characterization, and comparison of how the binaural auditory system processes interaural temporal disparities (ITDs), a major cue for the localization of sound. The program of research flows directly from our findings that the use of special "transposed" high-frequency stimuli can overcome the typically poor ability of listeners to process ITDs within high-frequency channels. Not only do transposed stimuli lead to more efficient ITD-processing, they also appear to be relatively "immune" to the degrading effects observed with conventional high-frequency stimuli, when other, "jamming" or "interfering," low-frequency information is present. The proposed program of research seeks to reveal and understand what specific aspects of the envelopes of high-frequency temporal waveforms are sufficient for the processing of ITDs to be enhanced and for "resistance" to binaural "interference" to occur. In order to provide answers, we propose to employ a multi-faceted, convergent, and, we believe, innovative approach that exploits the combination of 1) a number of sophisticated computer- based techniques for controlling and quantifying via specific metrics the temporal characteristics of the envelopes of high-frequency stimuli; 2) highly precise and repeatable behavioral measures of threshold-ITDs and ITD-based laterality; 3) a type of theoretical approach that yields specific quantitative predictions about the patterning of the behavioral data in terms of either variations in the external stimulus, per se, or in terms of variations in the stimuli as processed by both peripheral and central stages of auditory processing. The relevance of the proposed research to public health includes potential health benefits stemming from a better understanding of how the ear and brain process envelope-based information. The results of our investigations promise to provide direction to others about how they can manipulate specific temporal aspects of the envelopes of high-frequency waveforms to convey more efficiently monaural as well as binaural timing information via prosthetic devices such as cochlear implants and/or digital hearing aids..