Buildup and breakdown of echo suppression for stimuli presented over headphones—the effects of interaural time and level differences

Abstract

The current study investigates buildup and breakdown of echo suppression for stimuli presented over headphones. The stimuli consisted of pairs of 120-micros clicks. The leading click (lead) and the lagging click (lag) in each pair were lateralized on opposite sides of the midline by means of interaural level differences (ILDs) of +/-10 dB or interaural time differences (ITDs) of +/-300 micros. Echo threshold was measured with an adaptive one-interval, two-alternative, forced-choice procedure with a subjective decision criterion, in which listeners had to report whether they heard a single, fused auditory event on one side of the midline, or two separate events on both sides. In the control conditions, referred to as the "single" conditions, echo threshold was measured for a single click pair, the test pair, presented in isolation. In addition to the control conditions, two kinds of test conditions were investigated, in which the test pair was preceded by 12 identical conditioning pairs: in the "same" conditions, the interaural configuration (ILDs or ITDs) of the conditioning pairs was identical to that of the test pair; in the "switch" conditions, the interaural configuration of lead and lag was reversed between the conditioning pairs and the test pair, in order to produce a switch in the lateralizations of the stimuli between the conditioning train and the test pair. No matter whether the lateralization of the clicks was produced by ILDs or by ITDs, most listeners experienced a buildup of echo suppression in the "same" conditions, manifested by a prolongation of echo threshold relative to the respective "single" conditions. However, the breakdown of echo suppression was much stronger in the ILD-switch than in the ITD-switch conditions. In five out of six listeners, the ITD switch had hardly any effect on echo threshold, although the ITDs (+/-300 micros) produced roughly the same degree of lateral displacement as the ILDs (+/-10 dB). These results suggest that the dynamic processes in echo suppression operate differentially in pathways responsible for the processing of interaural time and level differences.

Temporal weighting functions for interaural time and level differences. II. The effect of binaurally synchronous temporal jitter

“…Brown and Stecker, 2010;Stecker and Brown, 2010 . This result suggests that the mechanism of jitter-reduced onset weighting may be separate from the mechanism facilitating greater cue-averaging for ILD, an interpretation consistent with similar time courses of ITD and ILD sensitivity evidenced in some paradigms (e.g., studies of binaural adaptation, and different time courses of sensitivity evidenced in others (e.g., studies of the precedence effect, Krumbholz and Nobbe, 2002;Saberi et al, 2004;cf. Stecker and Brown, 2010).…”

“…Additionally, TWFs for lateralization suggest that onset dominance is reduced for ILD relative to ITD in both bilateral CI users (van Hoesel, 2008a,b) and normal-hearing listeners . Suggestive of further differences in the time courses of ITD and ILD processing, Krumbholz and Nobbe (2002) demonstrated a striking disparity between ITD-and ILD-based "echo thresholds" in the buildup and breakdown of the precedence effect, with buildup more robust for click pairs carrying ITD than ILD and breakdown much more robust for click pairs carrying ILD than ITD. In the present investigation (and the previous, Brown and Stecker, 2010) we have operationally defined onset dominance as the salience of onset information over longterm average information (AUC 1 À AUC mean ) after Saberi and Perrott (1995).…”

“…The nature of differences in the time courses of ITD versus ILD sensitivity, including the common finding of significant individual differences in sensitivity across listeners, remains an area of great interest to us and others at present (cf. McFadden et al, 1973;Krumbholz and Nobbe, 2002;Saberi and Antonio, 2003;Saberi et al, 2004;van Hoesel, 2008a,b;Litovsky et al, 2010;Stecker and Brown, 2010;Brown and Stecker, 2010;see Sec. IV B).…”

Onset- and offset-specific effects in interaural level difference discrimination

“…Keen and Freyman, 2009) for stimuli presented in the free field. Krumbholz and Nobbe (2002) demonstrated such breakdown to also occur during headphone presentation but only when the stimuli were lateralized by ILD and not when lateralized by ITD alone. That result is generally consistent with the maintained sensitivity to post-onset ILD demonstrated in the current study.…”

Mechanisms determining the salience of coloration in echoed sound: Influence of interaural time and level differences

“…It has been suggested that the strength of the perceptual suppression of echoes ͑''precedence effect''͒ varies with the spatial separation between the primary sound and the reflections ͑Litovsky et al, 1999; see also Shinn-Cunningham et al, 1993;Krumbholz and Nobbe, 2002͒. In Zurek's dichotic condition, the primary sound and the reflection had different ITDs ͑0 and 500 s͒, so, when sounded separately, they would be perceived in different lateral positions, and it may be that the salience of coloration decreases with increasing lateral displacement between primary sound and reflection.…”