Gravity Cues Embedded in the Kinematics of Human Motion Are Detected in Form-from-Motion Areas of the Visual System and in Motor-Related Areas.

Fabien Cignetti,Christine Assaiante,Christina Schmitz,Pierre-Yves Chabeauti,Marianne Vaugoyeau,Jasmine Menant,Jean-Luc J J Anton

doi:10.3389/fpsyg.2017.01396

Abstract

The present study investigated the cortical areas engaged in the perception of graviceptive information embedded in biological motion (BM). To this end, functional magnetic resonance imaging was used to assess the cortical areas active during the observation of human movements performed under normogravity and microgravity (parabolic flight). Movements were defined by motion cues alone using point-light displays. We found that gravity modulated the activation of a restricted set of regions of the network subtending BM perception, including form-from-motion areas of the visual system (kinetic occipital region, lingual gyrus, cuneus) and motor-related areas (primary motor and somatosensory cortices). These findings suggest that compliance of observed movements with normal gravity was carried out by mapping them onto the observer’s motor system and by extracting their overall form from local motion of the moving light points. We propose that judgment on graviceptive information embedded in BM can be established based on motor resonance and visual familiarity mechanisms and not necessarily by accessing the internal model of gravitational motion stored in the vestibular cortex.

Highlights

Earth’s gravity is an important factor that influences visual perception
Based on the fact that the visual system is quite poor at estimating image accelerations (Werkhoven et al, 1992), the above predictive behaviors in visual perception and interceptive responses involving knowledge about gravity were in favor of the existence of an internal model of gravitational motion internalized in the human brain
A first analysis of the Functional magnetic resonance imaging (fMRI) data consisted in identifying brain regions that were activated during the observation of point light displays independently of whether the movements were performed under normogravity or microgravity

Summary

INTRODUCTION

Earth’s gravity is an important factor that influences visual perception. Psychophysical experiments demonstrated that several spatiotemporal characteristics of a visual scene are estimated employing implicit knowledge about the effects of gravity on moving objects in the physical world. It can only be argued that these regions are commonly involved during the execution and the observation of movements (Rizzolatti and Craighero, 2004; Dinstein et al, 2007; Kilner et al, 2007; Chong et al, 2008; Kilner et al, 2009; Saygin et al, 2012), or otherwise are core nodes of the mirror-neuron system (MNS) whose activation is often interpreted within the framework of motor resonance, whereby an observed action is understood through mapping onto the observer’s own motor representation In this framework, interpreting gravitational cues embedded in BM would rely on a mechanism that ‘judges’ the compliance of the observed BM with naturalistic (Earth-based) BM stored in the observer sensorimotor repertoire, that is a sort of implicit coding of gravity effects that may not require a predictive code from the internal model of gravity. We expected that coding of gravitational content in BM displays engages motor resonance, which should be reflected in a larger activity in regions of the MNS (i.e., a larger motor resonance) for normogravity BM displays given the closer match between the observed action and the observers’ own sensorimotor representations

Participants

RESULTS

DISCUSSION