Recalibrating the body: visuotactile ventriloquism aftereffect.

Majed Samad,Ladan Shams

doi:10.7717/peerj.4504

Abstract

Visuotactile ventriloquism is a recently reported effect showing that somatotopic tactile representations (namely, representation of location along the surface of one’s arm) can be biased by simultaneous presentation of a visual stimulus in a spatial localization task along the surface of the skin. Here we investigated whether the exposure to discrepancy between tactile and visual stimuli on the skin can induce lasting changes in the somatotopic representations of space. We conducted an experiment investigating this question by asking participants to perform a localization task that included unisensory and bisensory trials, before and after exposure to spatially discrepant visuotactile stimuli. Participants localized brief flashes of light and brief vibrations that were presented along the surface of their forearms, and were presented either individually (unisensory conditions) or were presented simultaneously at the same location or different locations. We then compared the localization of tactile stimuli in unisensory tactile conditions before and after the exposure to discrepant bisensory stimuli. After exposure, participants exhibited a shift in their tactile localizations in the direction of the visual stimulus that was presented during the exposure block. These results demonstrate that the somatotopic spatial representations are capable of rapidly recalibrating after a very brief exposure to visually discrepant stimuli.

Highlights

The nervous system is at all times playing a guessing game with the aim of identifying which sensations should be integrated and which ought to be segregated
Consider what happens when a sound and sight are concurrently processed by the brain. If they originate from different sources, but the brain erroneously infers that they have a common cause, this can lead to an illusion known as the ventriloquist illusion, wherein the perceived location of the sound is captured by the location of the visual stimulus (Alais & Burr, 2004; Bischoff et al, 2007; Howard & Templeton, 1966)
These differences were coded so that they are positive when the tactile localization is shifted towards the elbow, which is where the visual stimulus would have been presented for the Vision-Left group

Summary

INTRODUCTION

The nervous system is at all times playing a guessing game with the aim of identifying which sensations should be integrated and which ought to be segregated. In the audiovisual ventriloquist illusion, prior work has uncovered evidence that there is an accompanying aftereffect that develops as a result of exposure to spatially discrepant audiovisual stimulus pairs such that subsequent auditory localizations are biased towards the position of the visual stimulus (Lewald, 2002; Recanzone, 1998) and that it emerges very rapidly (Frissen, Vroomen & Gelder, 2012), and can occur in the temporal domain when the discrepancy is an asynchrony (Burg, Orchard-Mills & Alais, 2015; Van der Burg, Alais & Cass, 2015; Orchard-Mills, Van der Burg & Alais, 2016) This effect is interpreted as a recalibration of the mapping between auditory and visual spatial representations. Given that our previous study (Samad & Shams, 2016) identified a vigorous interaction between visual and tactile stimuli in the somatotopic space, we hypothesized that an aftereffect would be observable such that tactile representations would be biased, dependent on the disparity between the visuotactile stimuli that were presented during the exposure phase

Participants

Procedure

RESULTS

DISCUSSION