The Role of Head Movements and Signal Spectrum in an Auditory Front/Back Illusion

W Owen Brimijoin,Michael A Akeroyd

doi:10.1068/i7173sas

W Owen Brimijoin, Michael A Akeroyd

Open Access

https://doi.org/10.1068/i7173sas

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Abstract

We used a dynamic auditory spatial illusion to investigate the role of self-motion and acoustics in shaping our spatial percept of the environment. Using motion capture, we smoothly moved a sound source around listeners as a function of their own head movements. A lowpass filtered sound behind a listener that moved in the direction it would have moved if it had been located in the front was perceived as statically located in front. The contrariwise effect occurred if the sound was in front but moved as if it were behind. The illusion was strongest for sounds lowpass filtered at 500 Hz and weakened as a function of increasing lowpass cut-off frequency. The signals with the most high frequency energy were often associated with an unstable location percept that flickered from front to back as self-motion cues and spectral cues for location came into conflict with one another.

Highlights

The term “front/back confusion” refers to a common error in sound localization: a mistaken percept of a sound source being behind you when it is in front, or vice versa
It is thought that head movements contribute to our ability to resolve this problem (Wightman and Kistler 1999): if a listener turns 10o to the right, from the perspective of the listener a sound source that was in the front will move 10o to the left, whereas a sound source that was really behind will move 10o to the right
The geometry is shown in Figure 1: if a listener turns Θ degrees and the sound source is rotated by 2Θ degrees relative to the 180° loudspeaker, the listener perceives the sound to be stationary and located at 0°

Summary

Introduction

The term “front/back confusion” refers to a common error in sound localization: a mistaken percept of a sound source being behind you when it is in front, or vice versa. If a sound source is located either directly ahead or directly behind, in both cases the interaural time difference between the two sounds is zero, so creating a fundamental ambiguity. This ambiguity happens for any pair of front and back sound locations that share the same subtended angle off the listener’s midline.

Results

Conclusion