Abstract
When we perceive others in everyday life, their bodies are often partially occluded. However, parts are perceived as belonging to the same person. High-level visual areas are known to automatically complete partially occluded objects, as revealed by classic "gestalt" phenomena. In contrast, body completion could rely on "embodied" processing in addition to visual processing. In other words, we suggest that humans use their own body repertoire to support visual perception in body completion. We developed a novel paradigm with largely occluded bodies to test if and how participants integrate faces and hands into a "body-gestalt" (BG) while imitating or observing finger movements. In 3 behavioural and 2 MEG experiments (+4 additional pilots), we consistently found that speed and accuracy of imitating a finger movement depended on the efficiency with which the stimulus configuration could be integrated into a BG. Moreover, our results revealed that BG completion was an "embodied" process and not purely visual, by showing that changing participants’ postures modulated response times (and accuracy) ‘online’. That is, body gestalt completion was shown to be most effective when the posture implied by the stimulus matched the participant’s posture. Finally, in the MEG studies, the time-frequency analysis revealed a significant power difference in the α and β ranges between BG and noBG. The source localization of 14Hz oscillations (+/- 6Hz) revealed different generators depending on the implied postures of the stimulus configurations. For visually frequent postures (1st study), a power decrease was localized in the occipital cortex, confirming a predominantly visual process of BG completion. However, when the implied visual postures were less familiar (2nd study), we observed a significantly different power increase in prefrontal and parietal motor/bodyschema/attention areas during observation, supporting the notion that posture and/or motor resonance were crucially involved in the completion of less visually familiar body gestalts.
Meeting abstract presented at VSS 2012