Recognition of Human Body Movements: View-dependency, Inverse effect and biomechanical constraints.

Human body is represented multimodally as visual and motor in the brain. We reported that visual recognition of static body posture was affected by biomechanical constraints (Kitazaki and Inoue, VSS 2004), and action of the observer modulated the visual recognition of body posture (Inoue and Kitazaki, IMRF 2005). In this study, we investigated the effects of biomechanical constraints of human body on visual recognition of body movements, view-dependency and its inversion effects. First, we made twenty-seven different body movements with a three-dimensional computer modeling software. They were all biomechanically possible movements. Then, twenty-seven impossible movements were made by modifying possible ones. A pair of movements across viewpoints (0-180deg) was presented sequentially, and subjects were asked if they were identical or different movements regardless of the view difference. We found that recognition performance of possible movements was better and more view-independent than that of impossible ones. These effects decreased with using inverted bodies. Thus, recognition of human body movements was affected by biomechanical relationship of body parts and movements, and it was specific to upright body representation. These results suggest that the brain processing for human-body recognition is multimodal and utilizes both visual and motor information. [Supported by Nissan-Science-Foundation and MEXT-Japan]