Psychoacoustic evidence for stronger discrimination suppression of spatial information conveyed by lag-click interaural time than interaural level differences

Mats E Nilsson,Carlos Tirado,Malina Szychowska

doi:10.1121/1.5087707

Mats E Nilsson, Carlos Tirado + Show 1 more

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https://doi.org/10.1121/1.5087707

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Abstract

Listeners have limited access to spatial information in lagging sound, a phenomenon known as discrimination suppression. It is unclear whether discrimination suppression works differently for interaural time differences (ITDs) and interaural level differences (ILDs). To explore this, three listeners assessed the lateralization (left or right) and detection (present or not) of lag clicks with a large fixed ITD (350 μs) or ILD (10 dB) following a diotic lead click, with inter-click intervals (ICIs) of 0.125-256 ms. Performance was measured on a common scale for both cues: the lag-lead amplitude ratio [dB] at 75% correct answers. The main finding was that the lateralization thresholds, but not detection thresholds, were more strongly elevated for ITD-only than ILD-only clicks at intermediate ICIs (1-8 ms) in which previous research has found the strongest discrimination suppression effects. Altogether, these findings suggest that discrimination suppression involves mechanisms that make spatial information conveyed by lag-click ITDs less accessible to listeners than spatial information conveyed by lag-click ILDs.

Highlights

Some blind people have learned to echolocate, i.e., to detect and localize objects by listening to how self-generated sounds are reflected from nearby surfaces (Kolarik et al, 2014)
A key feature of this study was that its design allowed comparison of interaural time differences (ITDs) and interaural level differences (ILDs) lag-click lateralization thresholds on a common scale, lead peak amplitude ratio (LLR) [dB], and the same measure was used to quantify lag-click detection thresholds to disentangle audibility from the lateralization of lag clicks
The main finding was the elevated lateralization thresholds for ITD-only lag clicks at intermediate inter-click intervals (ICIs) (1–8 ms), at which discrimination suppression is typically observed. This pattern was specific to lateralization thresholds, and detection thresholds for ITD-only stimuli were no higher than for stimuli containing ILDs. This is consistent with the notion that the discrimination suppression of transient stimuli with intermediate ICIs involves mechanisms that make it harder to access spatial information conveyed by lag-click ITDs than by lagclick ILDs

Summary

Introduction

Some blind people have learned to echolocate, i.e., to detect and localize objects by listening to how self-generated sounds are reflected from nearby surfaces (Kolarik et al, 2014). For localization (but not detection), this would seem to require an ability to overcome the precedence-effect phenomenon discrimination suppression, i.e., the auditory system’s tendency to suppress spatial information in reflected (lagging) sound in favor of spatial information in direct (leading) sound (Nilsson and Schenkman, 2016; Wallmeier et al, 2013). This apparent conflict between human echolocation and discrimination suppression was the starting point of the present research. In this article, “lateralization” will refer to whether a sound is heard to the left or the right, irrespective of the degree of the perceived displacement

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