Complex interactions between spatial, orientation, and motion cues for biological motion perception across visual space

Human observers are adept at perceiving complex actions in point-light biological motion displays that represent the human form with a sparse array of moving points. However, the neural computations supporting action perception remain unclear, particularly with regards to central versus peripheral vision. We created novel action stimuli comprised of Gabor patches to examine the contributions of various competing visual cues to action perception across the visual field. The Gabor action stimulus made it possible to pin down form processing at two levels: (a) local information about limb angle represented by Gabor orientations and (b) global body structure signaled by the spatial arrangement of Gabor patches. This stimulus also introduced two types of motion signals: (a) local velocity represented by Gabor drifting motion and (b) joint motion trajectories signaled by position changes of Gabor disks over time. In central vision, the computational analysis of global cues based on the spatial arrangement of joints and joint trajectories dominated processing, with minimal influence of local drifting motion and orientation cues. In the periphery we found that local drifting motion and orientation cues interacted with spatial cues in sophisticated ways depending on the particular discrimination task and location within the visual field to influence action perception. This dissociation was evident in several experiments showing phantom action percepts in the periphery that contradicted central vision. Our findings suggest a highly flexible and adaptive system for processing visual cues at multiple levels for biological motion and action perception.