When and where to listen?

Abstract

In natural listening environments, humans hear multiple concurrent sounds arriving from different locations. In order to attend to a single source, concurrent sounds must be separated into individual sound objects, a process that relies on binaural hearing. However, the fluctuating binaural cues that arise when sounds from multiple sources merge at each ear generate fluctuating binaural cues that may be unreliable as to source location. This reliability can be quantified in terms of the interaural coherence (IAC). To overcome unreliable binaural cues, it is suggested that the brain monitors IAC and extracts spatial information from sound energy during epochs where IAC is high. To test this hypothesis, we designed a stimulus allowing us to modulate IAC over time and frequency. Our data indicate that IAC weighting plays a relatively minor role in source separation. Rather, binaural cues only contribute to source localization during rising sound energy. Binaural cues in later epochs of a modulated sound waveform are completely ignored even when IAC is high and spans a wide frequency range. The data do not support weighting based on IAC but, rather, suggest a fast, “non-sluggish” processing of binaural cues to extract information only during the rising energy envelope.