Spatial cues alone produce inaccurate sound segregation: The effect of interaural time differences

Abstract

To clarify the role of spatial cues in sound segregation, this study explored whether interaural time differences (ITDs) are sufficient to allow listeners to identify a novel sound source from a mixture of sources. Listeners heard mixtures of two synthetic sounds, a target and distractor, each of which possessed naturalistic spectrotemporal correlations but otherwise lacked strong grouping cues, and which contained either the same or different ITDs. When the task was to judge whether a probe sound matched a source in the preceding mixture, performance improved greatly when the same target was presented repeatedly across distinct distractors, consistent with previous results. In contrast, performance improved only slightly with ITD separation of target and distractor, even when spectrotemporal overlap between target and distractor was reduced. However, when subjects localized, rather than identified, the sources in the mixture, sources with different ITDs were reported as two sources at distinct and accurately identified locations. ITDs alone thus enable listeners to perceptually segregate mixtures of sources, but the perceived content of these sources is inaccurate when other segregation cues, such as harmonicity and common onsets and offsets, do not also promote proper source separation.

Six Degrees of Auditory Spatial Separation

“…Later work has demonstrated, however, that the weighting of ILD and ITD cues is a more complex function of stimulus characteristics such as spectrum, interaural coherence, and onset characteristics (e.g., Stecker 2013;Stecker et al 2013). Our use of two concurrent stimuli, however, may have acted to decorrelate to some extent, the timing information at each ear, making the extraction of ITD cues for each stimulus unreliable (see Lee et al 2009;Rakerd and Hartmann 2010, but see also Schwartz et al 2012) and causing a down-weighting of the ITD cue relative to the ILD cue. This would be consistent with recent models of optimal cue integration in a variety of sensory systems which embody a Bayesian or BKalman filter^approach to optimize fusion of multiple cues that may vary in reliability (Ley et al 2009;Wozny and Shams 2011).…”

Cortical and Sensory Causes of Individual Differences in Selective Attention Ability Among Listeners With Normal Hearing Thresholds

“…Indeed, in typical English speech, syllabic rates are in this range, typically below 10 Hz (Greenberg, Carvey, Hitchcock, & Chang, 2003). Interestingly, although people have an intuitive sense that we should group together sound elements that have spatial cues consistent with the same source location, spatial cues have a relatively weak impact on perceptual grouping of brief sound elements (Darwin & Hukin, 1997); spatial cues generally only influence perceptual grouping at this level when other spectrotemporal cues are ambiguous (e.g., Schwartz, McDermott, & Shinn-Cunningham, 2012;Shinn-Cunningham, Lee, & Oxenham, 2007). Sounds that are harmonically related also tend to be perceived as having a common source, whereas inharmonicity can cause grouping to break down (Culling & Darwin, 1993a;Darwin, Hukin, & al-Khatib, 1995;.…”

Effects of dynamic range compression on spatial selective auditory attention in normal-hearing listeners

“…While intuitively sound localization is related to the ability to attend to sounds based on their location, accurate localization is neither necessary nor sufficient for predicting the importance of spatial cues in understanding a signal in a mixture of sounds (Noble et al, 1997;Gallun et al, 2008;Schwartz et al, 2012). How dynamic range compression affects this ability cannot be easily predicted by how it affects localization.…”

“…Given this, the reduction of ILDs caused by compression may in fact restore "normal" neural representations of ILDs in many individuals with hearing loss, leading us to overestimate the effects of compression by testing normal-hearing listeners. However, even if the restoration of normal ILDs improved sound localization accuracy, it would not necessarily improve the ability to use spatial cues to direct attention (Noble et al, 1997;Gallun et al, 2008;Schwartz et al, 2012). We argue that in order to correctly select a target talker using spatial cues (or any other cues), listeners only need to be able to distinguish the target from the maskers using one or more perceptual features, such as location.…”