Influence of envelope fluctuation on the lateralization of interaurally delayed low-frequency stimuli.

Jörg Encke,Mathias Dietz

doi:10.1121/10.0006571

Abstract

Disregarding onset and offset effects, interaurally delaying a 500 Hz tone by 1.5 ms is identical to advancing it by 0.5 ms. When presented over headphones, humans indeed perceive such a tone lateralized toward the side of the nominal lag. Any stimulus other than a tone has more than one frequency component and is thus unambiguous. It has been shown that phase ambiguity can be resolved when increasing the stimulus bandwidth. This has mostly been attributed to the integration of information across frequencies. Additionally, interaural timing information conveyed in the stimulus envelope within a single frequency channel is a second possible cue that could help to resolve phase ambiguity. This study employs stimuli designed to differ in the amount of envelope fluctuation while retaining the same power spectral density as well as interaural differences. Any difference in lateralization must thus be a result of the difference in envelope. The results show that stimuli with strong envelope fluctuation require significantly smaller bandwidths to resolve phase ambiguity when compared to stimuli with weak envelope fluctuation. This suggests that within-channel information is an important cue used to resolve phase ambiguity.

Highlights

26111 Oldenburg, Germany, ORCID: 0000-0002-1830-469X.for the external ITD
The results show that stimuli with strong envelope fluctuation require significantly smaller bandwidths to resolve phase ambiguity when compared to stimuli with weak envelope fluctuation
The band and complex group, stimuli with stronger envelope fluctuation resulted in significantly lower changeover bandwidth [see Fig. 3(b)] supporting the hypothesis that within-frequency channel information is used to resolve ambiguous phase differences

Summary

Introduction

26111 Oldenburg, Germany, ORCID: 0000-0002-1830-469X.for the external ITD. This arrangement would resemble a place coding of azimuthal direction similar to the visual system. Report that two stimuli with the same physical ITD and no interaural intensity difference can be perceived as either coming clearly from the left or from the right, depending on the bandwidth of the respective stimulus [Trahiotis and Stern, 1989; see Fig. 1(a)]. The effect of bandwidth-dependent lateralization of stimuli with the same ITD can be understood in light of the periodicity of a sinusoidal stimulus. Disregarding onset/ offset effects, delaying a 500 Hz sinusoid by 1.5 ms is equivalent to phase shifting it by 1:5p. The subjects perceived the noises lateralized to the nominal lag, consistent with an ITD of À0.5 ms. The change in lateralization suggests that subjects were able to resolve phase ambiguity in stimuli with larger bandwidth. Two different mechanisms that could underlie this effect have since been proposed

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