A chimeric point-light walker

Ambiguity has long been used as a probe into visual processing. Here, we describe a new dynamic ambiguous figure - the chimeric point-light walker - which we hope will prove to be a useful tool for exploring biological motion. We begin by describing the construction of the stimulus and discussing the compelling finding that, when presented in a mask, observers consistently fail to notice anything odd about the walker, reporting instead that they are watching an unambiguous figure moving either to the left or right. Some observers report that the initial percept fluctuates, moving first to the left, then to the right, or vice versa; others always perceive a constant direction. All observers, when briefly shown the unmasked ambiguous figure, have no difficulty in perceiving the novel motion pattern once the mask is returned. These two findings - the initial report of unambiguous motion and the subsequent 'primed' perception of the ambiguity - are both consistent with an important role for top-down processing in biological motion. We conclude by suggesting several domains within the realm of biological-motion processing where this simple stimulus may prove to be useful.