Effect of Reverberation on Directional Sensitivity of Auditory Neurons: Central and Peripheral Factors

Abstract

In Advances in Auditory Research: Physiology, Psychophysics and Models, edited by E. Lopez-Poveda and R. Meddis, Springer INTRODUCTION Indoors and in nature alike, the auditory scenes that we perceive unfold in reverberant environments. In a reverberant sound field, reflected acoustic waves reach the listener from all directions, interfering with the direct sound and distorting the binaural cues for sound localization such as interaural time and level differences (ITD and ILD). In previous work (Devore et al., 2009), we showed that reverberation degrades the directional sensitivity of low frequency, ITD-sensitive neurons in the inferior colliculus (IC) of anesthetized cats, although not as much as predicted by an interaural crosscorrelation model. Here, we extend this work by characterizing directional sensitivity in neurons across a wide range of the tonotopic axis in an awake rabbit preparation, while maintaining our focus on neurons that are sensitive to ITD.Low frequency IC neurons are typically sensitive to ITD in the waveform fine structure while high frequency IC neurons are sensitive to ITD in the amplitude envelopes (Batra et al., 1993;Joris, 2003; Griffin et al., 2005; Yin et al., 1984). At all characteristic frequencies (CF), the rate responses of IC neurons can be altered by imposing ILDs (Batra et al., 1993;Palmer et al., 2007); however, for stimuli with naturally co-occurring binaural cues, ILDs may be a more potent directional cue than envelope ITDs in high frequency neurons (Delgutte et al., 1995).We investigated the effects of reverberation on directional sensitivity of ITDsensitive neurons in the IC of awake rabbits using virtual auditory space (VAS) stimuli containing different binaural cues (ITD-only and ITD+ILD). We find that reverberation degrades the directional sensitivity of single neurons, although the amount of degradation depends on both the CF and the type of binaural cues available. We also compared results from IC neurons with measures of directional information extracted from coincidence analysis of spike trains recorded from auditory nerve (AN) fibers in anesthetized cats. Together our results suggest that the frequency-dependent degradation in ITD-based directional sensitivity partly originates in the auditory periphery and can be attributed to differential degradation of interaural envelopes and fine-time structure in reverberation.

Reverberation impairs brainstem temporal representations of voiced vowel sounds: challenging “periodicity-tagged” segregation of competing speech in rooms

“…The azimuth-difference benefit is decreased in reverberant environments compared to anechoic conditions (Plomp, 1976 ; Bronkhorst and Plomp, 1990 ; Culling et al, 2003 ; Lavandier and Culling, 2007 ; Ruggles and Shinn-Cunningham, 2011 ). Decreased interaural coherence (degrading spatial segregation cues) and decreased temporal-envelope modulation both contribute to increased speech-reception thresholds in reverberant environments (Hartmann, 1983 ; Rakerd and Hartmann, 1985 , 2005 ; Lavandier and Culling, 2007 , 2008 ; Devore et al, 2009 , 2010 ; Devore and Delgutte, 2010 ; Ihlefeld and Shinn-Cunningham, 2011 ; Monaghan et al, 2013 ). Consistent with theories of binaural unmasking such as equalization-cancelation (Durlach, 1972 ), decreased interaural coherence would increase the masking effect of interfering sounds.…”