The role of onsets and envelope fluctuations in binaural cue use

Abstract

Effective localization of real sound sources requires neural mechanisms to accurately extract and represent binaural cues, including interaural time and level differences (ITD and ILD) in the sound arriving at the ears. Many studies have explored the relative effectiveness of these cues, and how that effectiveness varies with the acoustical features of a sound such as spectral frequency and modulation characteristics. In particular, several classic and recent studies have demonstrated relatively greater sensitivity to ITD and ILD present at sound onsets and other positive-going fluctuations of the sound envelope. The results of those studies have clear implications for how spatial cues are extracted from naturally fluctuating sounds such as human speech, and how that process is altered by echoes, reverberation, and competing sources in real auditory scenes. Here, we review the results of several recent studies to summarize and critique the evidence for envelope-triggered extraction of ITD and ILD across a wide range of spectral frequencies. A number of competing models for cue extraction in fluctuating envelopes are also considered in light of this evidence. [Work supported by NIH R01-DC011548.]