Somatosensory-visual effects in visual biological motion perception.

Pierre Progin,Lars Schwabe,Wenwen Chang,Olaf Blanke,Kim Q Do,Manuel Mercier,Anna Brooks,Nathan Faivre

doi:10.1371/journal.pone.0234026

Abstract

Social cognition is dependent on the ability to extract information from human stimuli. Of those, patterns of biological motion (BM) and in particular walking patterns of other humans, are prime examples. Although most often tested in isolation, BM outside the laboratory is often associated with multisensory cues (i.e. we often hear and see someone walking) and there is evidence that vision-based judgments of BM stimuli are systematically influenced by motor signals. Furthermore, cross-modal visuo-tactile mechanisms have been shown to influence perception of bodily stimuli. Based on these observations, we here investigated if somatosensory inputs would affect visual BM perception. In two experiments, we asked healthy participants to perform a speed discrimination task on two point light walkers (PLW) presented one after the other. In the first experiment, we quantified somatosensory-visual interactions by presenting PLW together with tactile stimuli either on the participants' forearms or feet soles. In the second experiment, we assessed the specificity of these interactions by presenting tactile stimuli either synchronously or asynchronously with upright or inverted PLW. Our results confirm that somatosensory input in the form of tactile foot stimulation influences visual BM perception. When presented with a seen walker's footsteps, additional tactile cues enhanced sensitivity on a speed discrimination task, but only if the tactile stimuli were presented on the relevant body-part (under the feet) and when the tactile stimuli were presented synchronously with the seen footsteps of the PLW, whether upright or inverted. Based on these findings we discuss potential mechanisms of somatosensory-visual interactions in BM perception.

Highlights

Actions of other individuals are a fundamental source of information for social agents and as such, the ability to exploit the sensory information they generate is important for social cognition
This indicates that visuotactile cues delivered to the feet, but not the upper limbs, improves the discrimination of biological motion (BM) perception
We designed Experiment 1 to compare the discriminability of visual BM when tactile stimulation was applied to the participants’ feet (ET) or forearms (CT), or when no tactile stimulation was applied (V)

Summary

Introduction

Actions of other individuals are a fundamental source of information for social agents and as such, the ability to exploit the sensory information they generate is important for social cognition. A seminal study by Gunnar Johansson (1973) reported that actors defined solely by point lights attached to the major joints of an otherwise invisible body are, once set in motion, highly perceivable Since these so-called point light walkers (hereafter PLWs) have been considered a classic ‘form-from-motion’ stimulus, and have been deployed as the gold standard tool used to further understand the perceptual and neural mechanisms supporting BM perception. These so-called point light walkers (hereafter PLWs) have been considered a classic ‘form-from-motion’ stimulus, and have been deployed as the gold standard tool used to further understand the perceptual and neural mechanisms supporting BM perception Perception of such PLW patterns survives information degradation, as when PLWs are embedded in ‘noise’ that mimics the motion of ‘signal’ point lights [1,2], and when the number of point lights is reduced to represent the major bodily joints only [3,4]

Methods

Results

Conclusion