Dissociating global and local biological motion processing in the human brain

Abstract

It has long been assumed that the human brain contains dedicated machinery for processing biological motion. Behaviourally, biological motion perception has been shown to implicate mechanisms that are distinct: one that governs the retrieval of global structure (body form) and another purported to process “local” information that is particularly sensitive to the gravity-defined acceleration pattern conveyed by the feet. Here, we used fMRI to dissociate the neural underpinnings of these two mechanisms. We measured responses (N=16 participants) to point-light stimuli containing solely structural information (local horizontal directionality neutralized but global structure intact), solely local information (global structure destroyed, but local information intact), and perturbed local information, presented vertically- upright and inverted. Observers were asked to judge walking direction. Results from SVM (MVPA) analyses indicate widespread sensitivity to global structure from early cortex (V1-V3) extending to the inferior and superior parietal lobule, in contrast to comparatively weak sensitivity to local information in cortex. Strikingly, we found significant sensitivity to local information in subcortical ventral lateral nucleus, VLN, an area not sensitive to global structure. These data suggest that distinct networks are engaged for biological structure versus local motion processing, the latter of which may rely primarily on earlier, subcortical systems.