Interactions between form and motion cues in the visual perception of biological motion

The seminal work by Johansson (1973) illustrated how the interaction between form and motion cues conveyed by an array of point-lights could elicit rich perceptions of biological organisms. Much of the subsequent study of biological form from motion perception has employed direction discriminations of laterally-viewed point-light walkers as a measure of sensitivity. To date, however, those stimulus properties that convey cues to direction have not been formally identified. Furthermore, exactly how those cues interact to elicit perceptions of direction remains unknown. The main aim of the current research was to identify the cues to direction conveyed by a laterally-viewed point-light walker and to investigate how those cues interact to elicit perceptions of direction. Specifically, the point-light walker stimulus was deconstructed into the cues to direction conveyed by configural information, articulatory motions, local motion trajectory, and net translation. The stimulus was then systematically reconstructed and the individual cues to direction from each stimulus feature were manipulated. The results of these experiments indicate that direction-of-translation (DoT) is processed early in a processing hierarchy that feeds-forward, interacting with the subsequent processing of the directional information conveyed by configural information and articulatory motions, to be a significant contributor to the perception of direction of biological point-light stimuli. The cues to direction conveyed by configural information and articulatory motions appear to be processed in parallel, exhibiting bi-directional interactions and influences on perceptions of direction-of-facing (DoF) and direction-of-walking (DoW). The DoT of the stimuli employed here has also been shown to significantly influence perceptions of DoF and DoW, often becoming the most heavily weighted cue. This indicates a feed-forward interaction between low-level processing of translatory motion and higher-level processing of form and motion information that needs to be incorporated into current models of biological motion processing. No significant cues to direction were observed to be conveyed by the local motion trajectories of the point-lights. These results carry implications for the existing knowledge of the relative contributions of configural information and articulatory motions to perceptions of direction, and the models proposed to describe the mechanisms involved