The two-process theory of biological motion processing

Perception, identification, and understanding of others' actions from motion information are vital for our survival in the social world. A breakthrough in the understanding of action perception was the discovery that our visual system is sensitive to human action from the sparse motion input of only a dozen point lights, a phenomenon known as biological motion (BM) processing. Previous psychological and computational models cannot fully explain the emerging evidence for the existence of BM processing during early ontogeny. Here, we propose a two-process model of the mechanisms underlying BM processing. We hypothesize that the first system, the 'Step Detector,' rapidly processes the local foot motion and feet-below-the-body information that is specific to vertebrates, is less dependent on postnatal learning, and involves subcortical networks. The second system, the 'Bodily Action Evaluator,' slowly processes the fine global structure-from-motion, is specific to conspecific, and dependent on gradual learning processed in cortical networks. This proposed model provides new insight into research on the development of BM processing.