Electrophysiological markers of biological motion and human form recognition.

Current models suggest that human form and motion information are initially processed through separate pathways, then integrated in action perception. Testing such a sequential model requires techniques with high temporal resolution. Prior work demonstrated sensitivity of a posterior temporal event-related potential (ERP) effect - the N2 - to biological motion, but did not test whether the N2 indexes biological motion perception specifically, or human form/action perception more generally. We recorded ERPs while participants viewed stimuli across 3 blocks: (1) static (non-moving) point-light displays of humans performing actions; (2) static stick figures with clear forms; and (3) point-light biological motion. A similar sequence of ERP components was elicited by human forms in all blocks (stationary and moving), and reliably discriminated between human and scrambled forms. The N2 showed similar scalp distribution and sensitivity to stimulus manipulations for both stick figures and biological motion, suggesting that it indexes integration of form and motion information, rather than biological motion perception exclusively - and that form and motion information are therefore integrated by approximately 200ms. We identified a component subsequent to the N2, which we label the medial parietal positivity/ventral-anterior negativity (MPP/VAN), that was also sensitive to both human form and motion information. We propose that the MPP/VAN reflects higher-order human action recognition that occurs subsequent to the integration of form and motion information reflected by the N2.