Binaural Hearing with Temporally Complex Signals

Spatial hearing in real-world scenes involves stimuli that are both spectrally and temporally complex. That is, they consist of multiple frequency components that change over time. Temporal complexity results from motion of sound sources, acoustical effects resulting from interaction with the environment (e.g., reverberation), and intrinsic modulations of the sounds themselves. These factors introduce dynamic fluctuations in the binaural acoustic cues responsible for spatial hearing, and in the overall features of the waveform, such as its amplitude envelope, that affect how the brain processes those cues. Although temporal complexity adds challenge to the problem of spatial hearing, brain mechanisms seem to have evolved to manage and even exploit temporal complexity to support robust spatial hearing in complex scenes. This chapter explores research on five interrelated aspects of temporal complexity with profound impacts on binaural hearing: (1) the importance of binaural information that co-occurs with envelope fluctuations; (2) the superior sensitivity to binaural cues carried by steep versus shallow envelope slopes; (3) the apparent insensitivity to binaural information conveyed by rapidly fluctuating envelopes; (4) the dependence of binaural integration (sensitivity over time) on the specific cues available; and (5) the role of stimulus similarity across the two ears in the form of interaural coherence or interaural correlation as an important mediating factor and as a direct cue to the binaural configuration of the auditory scene. The overall results suggest that robust spatial representations of acoustically complex scenes are facilitated by the binaural system exploiting temporal complexity, for example by utilizing binaural information conveyed by relatively large, infrequently occurring, positive-going envelope fluctuations.