People are remarkably adept at recognizing the motion of biological entities in complex visual scenes, even when they are portrayed by a handful of point-lights attached to the head and major joints. It has been demonstrated that many characteristics such as identity, action, mental state and gender can be readily retrieved from the point-light walker. However, perception of biological motion is strongly impaired if the point-light displays are shown upside down. The inversion effect in biological motion has often been attributed to the impaired processing of global configural information. Notably, it has recently been shown that there is another inversion effect which relies on the local motion signals, indicating that local biological motion might contain some specific meaningful information. This research focuses on the processing advantage of upright compared with inverted local biological motion as well as the function of such processing, and aims to examine whether the brain mechanisms involved in local biological motion processing are “special” and can operate independent of any global configuration . Three studies were conducted to address these questions. 1. A robust visual search asymmetry effect was found for local biological motion processing. 2. A temporal dilation effect associated with biological motion signals was found, independent of global configuration and observer’s subjective awareness. 3. A reflexive attention orienting effect of local biological motion cues was found in both adults and preschool children. Moreover, local biological motion cues can trigger an early directing attention negativity (EDAN) in an early temporal window. In conclusion, the current study found the specificity of local biological motion processing in both spatial and temporal dimensions, and local biological motion can direct our attention as social cues. Moreover, the inversion effect for local biological motion found in our current study was task-irrelevant and independent of observer’s subjective awareness, in support of the “local biological motion specificity” notion. These findings shed new light on the mechanisms underlying biological motion perception as well as the specificity of visual processing.
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