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Abstract

Ambiguity, and the ''errors'' it creates, have long been used as probes into visual processing. Here I describe a new form of dynamic ambiguous stimuli - the chimeric point-light walker - which is created by superimposing the profile views of a left and right facing figure. When viewed in isolation, this figure - which is ambiguous as it simultaneously suggests motion in both directions - does not appear to walk, but rather to be performing some complex novel action. However, when the figure is presented in a mask of additional moving dots, 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. I will discuss several domains within the realm of biological motion processing where this simple stimuli may have an application.