Active versus passive processing of biological motion.

Johansson's point-light walker figures remain one of the most powerful and convincing examples of the role that motion can play in the perception of form (Johansson, 1973 Perception & Psychophysics 14 201 - 211; 1975 Scientific American 232(6) 76 - 88). In the current work, we use a dual-task paradigm to explore the role of attention in the processing of such stimuli. In two experiments we find striking differences in the degree to which direction-discrimination performance in point-light walker displays appears to rely on attention. Specifically, we find that performance in displays thought to involve top-down processing, either in time (experiment 1) or space (experiment 2) is adversely affected by dividing attention. In contrast, dividing attention has little effect on performance in displays that allow low-level, bottom-up computations to be carried out. We interpret these results using the active/passive motion distinction introduced by Cavanagh (1991 Spatial Vision 5 303-309).