S2-1: The Contribution of form and Motion to the Perception of Human Actions

The visual pathway for the processing of human actions involves a stream of regions along the lateral occipitotemporal cortex (LOTC), including regions defined by their selectivity to human body shape/form (e.g., EBA) or motion (e.g., MT/MST). As the perception of actions, especially biological motion, involves the integration of form and motion cues, an important question has been the relative contribution of these cues to the neural response to biological motion in LOTC regions. Understanding the contribution of form and motion to the neural response of regions within the LOTC will provide us with clues to where these cues become integrated. In this presentation I will propose that the neural response to biological motion in LOTC regions comprises the linear combination of the response of independent neural populations tuned to either the form or the motion cues, rather than an integrated response. Part of the difficulty in testing this proposal is that it is not trivial to manipulate form or motion cues of a biological motion stimulus independently. However, recent evidence suggests that we might be able to take advantage of differences in the retinotopy and/or contrast sensitivity between form and motion selective neural populations. I will present functional magnetic resonance imaging (fMRI) and behavioural studies showing that form and motion cues in biological motion differ in their sensitivity to contrast and spatial position, and that we can use this to manipulate the contribution of each to the neural response and perception of actions