The Role of Objecthood and Animacy in Apparent Movement Processing

Although the ability to detect the actions of other living beings is key for adaptive social behavior, it is still unclear if biological motion perception is specific to human stimuli. Biological motion perception involves both bottom-up processing of movement kinematics (‘motion pathway) and top-down reconstruction of movement from changes in body posture (‘form pathway’). Previous research using point-light displays has shown that processing in the motion pathway depends on the presence of a well-defined, recognizable shape (objecthood) but not necessarily on whether that shape depicts a living being (animacy). Here, we focused on the form pathway. Specifically, we combined EEG frequency tagging with apparent motion to study how objecthood and animacy influence posture processing and the integration of postures into movements. By measuring brain responses to repeating sequences of well-defined or pixelated images (objecthood), depicting human or corkscrew agents (animacy), performing either fluent or non-fluent movements (movement fluency), we found that movement processing was sensitive to objecthood but not animacy. In contrast, posture processing was sensitive to both. Together, these results indicate that reconstructing biological movement from apparent motion sequences requires a well-defined, but not necessarily an animate shape. Instead, stimulus animacy appears to be relevant only for posture processing.