Form information modulates the temporal dynamics of walking direction and body orientation processing in biological motion perception

Biological motion (BM) perception is crucial for survival and social interaction. Previous studies have shown that form structure influences the perception of walking direction and body orientation. However, the neural mechanisms underlying how form modulates the processing of these features remain unclear. To investigate how form is encoded and its interaction with the processing of walking direction and body orientation, we combined EEG and multivariate pattern analyses. Participants viewed classic point-light displays with different forms, walking directions, and body orientations. The decoding results revealed that form information was significantly decoded starting around 85 ms, peaking at 275 ms. The time generalization analysis revealed that the neural representation of form was transient before ~ 200 ms, and became stable thereafter. Importantly, decoding accuracy became significant at 100 ms for both body orientation and walking direction when form was intact, but remained at chance level for walking direction and was reduced for body orientation when form was scrambled. These results indicate that form structure influences the time course of body orientation and walking direction processing. These findings shed light on the encoding of form structure and its role in shaping the neural representation of other BM features.