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Amelia Hunt, Fred Halper; Replacing point lights with complex dissimilar elements disrupts biological motion perception. Journal of Vision 2007;7(9):479. doi: 10.1167/7.9.479.
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The rapid and seemingly effortless extraction of detailed information from visually impoverished point-light displays of humans walking is often held up as a compelling example of the perception of form from motion. Here we show that motion information is actually not sufficient for the impression of a human walker to be extracted from a point-light display. We manipulated the 13 small dots out of which the typical point-light walker is constructed. Attempts to use size, color, or shape changes to disrupt walker perception had only modest impact on its robustness. But when all the local elements of the walker were replaced with complex unique objects*, such as animals and food items, perception of the walker was severely disrupted. Of thirty-five naïve observers presented with this array for one full gait cycle (3667ms), none perceived a human walker, even though movement paths were unchanged. A new group of ten observers' ratings of how much the display resembled a human walking confirmed this finding, with a mean rating of 6.75/7 for the standard point-light walker, and 2.60/7 for the walker made from objects. Ratings of walkers constructed from simple but dissimilar elements (letters) and from complex but identical elements (an alarm clock) differed significantly from the standard walker and from the object walker, but not from each other. This pattern suggests that the Gestalt principles of simplicity and similarity play an important role in the extraction of human form information from the motion of the elements. We conclude that the spontaneous perception of a human walking is not an inevitable consequence of the motion of the points in a point-light walker, but depends on the points themselves being relatively simple and uniform.
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