How do we perceive and interpret the movements of other people? Previous research has demonstrated that, under a variety of conditions, the visual analysis of human movement differs from the visual analysis of object movement (Shiffrar, 2001). What accounts for this difference? One possibility is that the visual analysis of human movement differs from other motion analyses because humans have extensive visual experience with the movements of other people (e.g., Johansson, 1973). Another possibility is that the visual processes underlying the visual perception of human movement benefit from motor system input in a manner that fundamentally differs from all other visual motion analyses (e.g., Stevens et al., 2000). The first aim of this proposal is to examine these alternatives by determining the extent to which, and the conditions under which, visual and motor experience influence the visual analysis of human movement. Secondly, numerous researchers have proposed that the visual system can be understood as containing two independent and interdependent processing streams; namely, a ventral system dedicated to the explicit or conscious recognition of objects and a dorsal stream subserving the implicit or unconscious control of visually guided action (e.g., Creem & Proffitt, 2001; Milner & Goodale, 1995; Rossetti & Revonsuo, 2000). How does the visual perception of other peoples' movements depend upon these two subsystems? Amazingly, no data exist to answer this question. Because researchers have never systematically examined the relationships between implicit and explicit measures, stimuli, and experimental conditions used in studies of the visual analysis of human movement, it is not currently possible to define visual sensitivity to human movement. Nor is it currently possible to coherently connect neurophysiological data with behavioral measures of visual sensitivity to human movement. To resolve this impasse, we propose to examine the implicit and explicit visual perception of human movement across systematic variations in experimental conditions and stimuli. Thus, the second major aim of this proposal is to determine when and how implicit and explicit processes contribute to the ability of human observers to perceive, interpret, and interact with other moving humans. The results of these experiments will have important implications for the diagnosis and treatment of disorders associated with the inability to interpret the actions of others, such as autism, and for models of complex motion analyses