Influence of Sound Source Location on the Behavior and Physiology of the Precedence Effect in Cats

Abstract

Dent ML, Tollin DJ, Yin TC. Influence of sound source location on the behavior and physiology of the precedence effect in cats. J Neurophysiol 102: 724 -734, 2009. First published May 13, 2009 doi:10.1152/jn.00129.2009. Psychophysical experiments on the precedence effect (PE) in cats have shown that they localize pairs of auditory stimuli presented from different locations in space based on the spatial position of the stimuli and the interstimulus delay (ISD) between the stimuli in a manner similar to humans. Cats exhibit localization dominance for pairs of transient stimuli with ͉ISDs͉ from ϳ0.4 to 10 ms, summing localization for ͉ISDs͉ Ͻ 0.4 ms and breakdown of fusion for ͉ISDs͉ Ͼ 10 ms, which is the approximate echo threshold. The neural correlates to the PE have been described in both anesthetized and unanesthetized animals at many levels from auditory nerve to cortex. Single-unit recordings from the inferior colliculus (IC) and auditory cortex of cats demonstrate that neurons respond to both lead and lag sounds at ISDs above behavioral echo thresholds, but the response to the lag is reduced at shorter ISDs, consistent with localization dominance. Here the influence of the relative locations of the leading and lagging sources on the PE was measured behaviorally in a psychophysical task and physiologically in the IC of awake behaving cats. At all configurations of lead-lag stimulus locations, the cats behaviorally exhibited summing localization, localization dominance, and breakdown of fusion. Recordings from the IC of awake behaving cats show neural responses paralleling behavioral measurements. Both behavioral and physiological results suggest systematically shorter echo thresholds when stimuli are further apart in space. I N T R O D U C T I O NThe precedence effect (PE) is an auditory illusion thought to be responsible for a listener's ability to localize sounds accurately in the presence of echoes in reverberant environments. Laboratory studies on the PE typically mimic a somewhat simplified version of a natural listening situation where a sound (lead) and its echo (lag) are delivered from loudspeakers positioned at different spatial locations, times, or intensities to the listener's ears. Three perceptual phases of the PE have been mapped out by a number of studies. At a 0-ms lead-lag delay, the listener perceives only one fused sound at a position midway between the locations of the lead and the lag. As lead-lag delays increase, the perceived location of the fused auditory image moves toward the leading source until ϳ1 ms when it is perceived at the actual location of the leading source. This phase of the PE is known as summing localization. In the phase known as localization dominance, a single fused auditory image is perceived only at the location of the leading stimulus, as if the spatial information about the lagging source location had been suppressed. Depending on a number of characteristics, this phase lasts for lead-lag interstimulus delays (ISDs) ranging from 1 to ϳ10 ms . The upper end of loc...

Physiological and Psychophysical Modeling of the Precedence Effect

“…Moreover, due to the fact that model SMAX cells generate the strongest suppression of the lag when the lead and lag locations are close together, the model predicted that precedence was stronger when the lead and lag were relatively near one another in space than when they were from opposite hemifields. In contrast, if the neural population consisted only of SMIN units that generate the strongest suppression when the lead and lag are from opposite hemifield, the predicted localization dominance would be stronger when two stimuli were further apart in space, which is inconsistent with psychophysical results (Litovsky and Shinn-Cunningham 2001;Dent et al 2009). …”

Using Virtual Acoustic Space to Investigate Sound Localisation

“…In contrast, many mammals may move their eyes and pinnae. This allows for example cats or monkeys to locate sound sources even with restrained head to a certain extent (Dent et al, 2009;Populin, 2006;Populin & Yin, 1998). The owl's saccadic head-turn response allows to use the owls' head-turn angle as a measure for the perceived sound source location (Knudsen & Konishi, 1978).…”

Behavior and modeling of two-dimensional precedence effect in head-unrestrained cats

“…Localization dominance can happen over a large range of ISDs. Typically, for shorter ISDs such as ISDs Յ0.4 ms in cats (Dent et al 2009) or Ͻ0.8 ms in humans (Blauert 1997), a different type of behavior can be observed. Summing localization, sometimes referred to as fusion, describes the perception of a fused sound in between the two actual target locations.…”

“…However, this scenario presumably happens infrequently in real life with single sound sources, because if the echo comes quickly after the direct sound (i.e., a small ISD), the echo location, as well as the perceived location, is likely to be close to the direct sound location. When the ISD exceeds a certain value, such as 8Ϫ10 ms for humans (Stecker and Hafter 2002;Agaeva 2011) and cats (Tollin and Yin 2003b;Dent et al 2009), both the direct sound and its echoes can be perceived. Because it is difficult for animal subjects to indicate that two separate sounds are perceived, one way to behaviorally measure the echo threshold is to examine whether the lagging sound can be localized on a significant number of occasions (Blauert 1997;Tollin and Yin 2003b).…”

“…Physiological recordings using paired sound sources have been conducted to examine the suppressive effect of the leading sound on the neural responses to the lagging sound (Yin 1994;Fitzpatrick et al 1995;Yin 1998a, 1998b;Mickey and Middlebrooks 2001;Spitzer et al 2004;Tollin et al 2004;Dent et al 2005Dent et al , 2009). Those recordings were typically obtained from low-frequency neurons that are sensitive to ITDs in the inferior colliculus (IC) or the auditory cortex.…”