Temporal dynamics and uncertainty in binaural hearing revealed by anticipatory eye movements.

Matthew B Winn,Alan Kan,Ruth Y Litovsky

doi:10.1121/1.5088591

Abstract

Accurate perception of binaural cues is essential for left-right sound localization. Much literature focuses on threshold measures of perceptual acuity and accuracy. This study focused on supra-threshold perception using an anticipatory eye movement (AEM) paradigm designed to capture subtle aspects of perception that might not emerge in behavioral-motor responses, such as the accumulation of certainty, and rapid revisions in decision-making. Participants heard interaural timing differences (ITDs) or interaural level differences in correlated or uncorrelated narrowband noises, respectively. A cartoon ball moved behind an occluder and then emerged from the left or right side, consistent with the binaural cue. Participants anticipated the correct answer (before it appeared) by looking where the ball would emerge. Results showed quicker and more steadfast gaze fixations for stimuli with larger cue magnitudes. More difficult stimuli elicited a wider distribution of saccade times and greater number of corrective saccades before final judgment, implying perceptual uncertainty or competition. Cue levels above threshold elicited some wrong-way saccades that were quickly corrected. Saccades to ITDs were earlier and more reliable for low-frequency noises. The AEM paradigm reveals the time course of uncertainty and changes in perceptual decision-making for supra-threshold binaural stimuli even when behavioral responses are consistently correct.

Highlights

Binaural hearing refers to an intricate set of mechanisms whereby the auditory system compares acoustic information arriving at the two ears, and uses that information to perform important tasks, including localizing sounds (e.g., Mills, 1960; Macpherson and Middlebrooks, 2002) and understanding speech when there is background noise (e.g., Bronkhorst and Plomp, 1988; Hawley et al, 2004)
For very perceptible cues such as 16 or 24 dB interaural level differences (ILDs), success rate increased rapidly starting at roughly 200 ms, which is as fast as could be expected, given that it is roughly the amount of time needed to program and execute a saccade
Eye tracking can be a sensitive way to assess temporal aspects of binaural hearing, including the rapid accumulation of certainty and incremental perceptual decision-making and revisions as a listener is exposed to an auditory stimulus

Summary

Introduction

Binaural hearing refers to an intricate set of mechanisms whereby the auditory system compares acoustic information arriving at the two ears, and uses that information to perform important tasks, including localizing sounds (e.g., Mills, 1960; Macpherson and Middlebrooks, 2002) and understanding speech when there is background noise (e.g., Bronkhorst and Plomp, 1988; Hawley et al, 2004). The absolute accuracy and acuity of the binaural system has been studied in numerous ways, using a variety of behavioral techniques. Precision, and acuity of the binaural system have been studied in a variety of ways, typically with behavioral responses like pointing, button-pressing, or neural response data in non-human animals. These are gold-standard measurements that have advanced the field and formed the bedrock of knowledge of the binaural system. It is reasonable to suspect that the granular sensitivity of eyetracked responses would exceed that of behavioral responses in psychoacoustic studies, given the plethora of speech perception studies where such a pattern has prevailed. There is surprisingly little application of eye-tracking methods in basic psychoacoustics but potentially much to gain

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