Relative sound localisation abilities in human listeners

Abstract

Spatial acuity varies with sound-source azimuth, signal-to-noise ratio, and the spectral characteristics of the sound source. Here, the spatial localisation abilities of listeners were assessed using a relative localisation task. This task tested localisation ability at fixed angular separations throughout space using a two-alternative forced-choice design across a variety of listening conditions. Subjects were required to determine whether a target sound originated to the left or right of a preceding reference in the presence of a multi-source noise background. Experiment 1 demonstrated that subjects' ability to determine the relative location of two sources declined with less favourable signal-to-noise ratios and at peripheral locations. Experiment 2 assessed performance with both broadband and spectrally restricted stimuli designed to limit localisation cues to predominantly interaural level differences or interaural timing differences (ITDs). Predictions generated from topographic, modified topographic, and two-channel models of sound localisation suggest that for low-pass stimuli, where ITD cues were dominant, the two-channel model provides an adequate description of the experimental data, whereas for broadband and high frequency bandpass stimuli none of the models was able to fully account for performance. Experiment 3 demonstrated that relative localisation performance was uninfluenced by shifts in gaze direction.

Multisensory stimuli improve relative localisation judgments compared to unisensory auditory or visual stimuli

“…1(E)]. Stimulus pulses were identical to those used in Wood and Bizley (2015): 15 ms in duration, cosine ramped with 5 ms duration at the onset and offset of each pulse. Pulses were presented at a rate of 10 Hz with a 185 ms delay between the end of the final pulse at the reference speaker and the first pulse at the target speaker in order to aid perceptual segregation of the reference and the target.…”

“…The pulses were embedded in a noisy background comprised of independently generated auditory and visual noise from each speaker/LED. The amplitude of the noise was varied independently at each location every 15 ms with amplitude values drawn from a distribution whose mean and variance could be controlled (as in Wood and Bizley, 2015). Values were drawn from a Gaussian distribution with a mean level at each speaker of 49 dB sound pressure level (SPL) and a standard deviation of 1.5 dB SPL giving a mean noise level across all speakers of 63 dB SPL (calibrated using a Bruel and Kjær 3110–003 measuring amplifier placed at the centre of the speaker ring).…”

“…It was hypothesised that when comparing the ability to make auditory and visual relative localisation judgments with perceptually matched stimuli, visual performance would exceed auditory in central locations (i.e., at the fovea). However, visual localisation acuity declines linearly with eccentricity (Michel and Geisler, 2011), whereas the decline in auditory localisation cues is more modest with cues remaining robust across a range of eccentricities (Macpherson and Middlebrooks, 2002; Wood and Bizley, 2015). We therefore predicted that at more peripheral locations auditory relative localisation judgments might be more accurate than visual.…”

“…Both auditory (Mills, 1958; Makous and Middlebrooks, 1990; Charbonneau et al , 2013; Wood and Bizley, 2015; Carlile et al , 2016) and visual localisation acuity declines with eccentricity (Mateeff and Gourevich, 1984; Perrott et al , 1993; Charbonneau et al , 2013). Few studies have attempted to directly compare spatial acuity for auditory and visual stimuli throughout the visual field and focus instead on the spatial capture observed when spatially separated auditory-visual signals are presented (Howard and Templeton, 1966; Bertelson and Radeau, 1981).…”

“…Since both visual contrast (Kanai et al , 2004) and auditory signal-to-noise ratio impact upon localisation accuracy (Wood and Bizley 2015) our goal was to present perceptually matched stimuli so that localisation acuity could be directly compared across modalities. The aims of this study were therefore to determine (i) how relative localisation judgments vary throughout frontal space for equally detectable auditory and visual signals and (ii) whether an auditory-visual signal conferred a processing advantage over the most effective unisensory stimulus.…”