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Perception of a camouflaged point-light walker: a differential priming effect


Bülthoff,  I
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Pavlova, M., Bülthoff, I., & Sokolov, A. (1998). Perception of a camouflaged point-light walker: a differential priming effect. Poster presented at 21st European Conference on Visual Perception, Oxford, UK.

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Recently, we showed that recovery of a priori known structure from biological motion leveled off with changing display orientation (eg Pavlova and Sokolov, 1997 Perception 26 Supplement, 92). How does image-plane rotation of a prime affect detection of a camouflaged point-light walker? At each of five randomly presented display orientations between upright and inverted (0°, 45°, 90°, 135°, and 180°), viewers saw a sequence of displays (each display for 1 s). Half of them comprised a camouflaged point-light walker, and half a 'scrambled-walker' mask. In a confidence-rating procedure, observers judged whether a walker was present. Prior to each experimental sequence, they were primed (for 10 s) either with an upright-, 45°-, 90°-, or 180°-oriented sample of the walker. Pronounced priming effects were found only with an upright-oriented prime: it improved detectability for the same-oriented displays, and to a lesser extent for 45°. With 45°-prime, sensitivity for 0°-, 45°-, and 90°-oriented displays was higher than for 135° and 180°. However, with 90°- and 180°-primes ROC curves for all orientations were situated close to one another. These findings indicate that the priming effect in biological motion is partly independent of the relative orientation of priming and primed displays. Moreover, it occurs only if a prime corresponds to a limited range of deviations from upright orientation within which display is spontaneously recognisable despite a discrepancy between event kinematics and dynamics (Pavlova, 1996 Perception 25 Supplement, 6). The primacy of dynamic constraints in the perception of structure from biological motion is discussed.