The frequency and level dependence of across-frequency binaural interference for interaural time differences

Abstract

Binaural hearing enables listeners to localize sound in the horizontal plane, even when dealing with intricate speech-like signals characterized by distributed energy across a broad range of frequencies and varying sound pressure levels. Low-frequency interaural time differences (ITDs) are the most important cue for human horizontal-plane sound localization. Across-frequency binaural interference tasks (where changes in ITD discrimination thresholds of a target signal are measured in the presence of a remote interferer signal) can be used to measure how a listener weighs different frequency regions for ITD. While it is known that low-frequency (0.5 kHz) targets experience less binaural interference from higher-frequency (4 kHz) interferers than vice versa, the impact of the relative level of the two signals has remained mostly unexplored. ITD discrimination thresholds were measured in normal-hearing listeners with target/interferer intensities of 35, 55, and 75 dB-A and frequencies of 0.5, 4, and 8 kHz. Besides the expected frequency effects, data to date show binaural interference increases with increasing interferer level. These results help better understand how sound level variation and more realistic complex sounds like speech are localized.