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Dylan R. Nieman, Bhavin R. Sheth, Shinsuke Shimojo; Mutually contradictory percepts in motion processing. Journal of Vision 2006;6(6):554. doi: 10.1167/6.6.554.
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Studies of thinking and reasoning processes have shown that people can maintain multiple, fundamentally incompatible beliefs, particularly if attention is not drawn to the incompatibility. Recent work suggests the same may be true for multiple low-level visual percepts: Whitney and Cavanagh (2000) inferred that while a target's perceived position is shifted by an inducer, there is no accompanying percept of target motion. A more explicit perceptual paradox can be shown if the motion and position percepts of a target stimulus are each tested and found to be inconsistent under conditions without an inducer. Observers (n=12) watched a small, circular target move diagonally at constant speed (21.2 deg/s) on a screen for 200 ms, then make an abrupt 90 degree turn and continue at the same speed for 200 ms. Observers fixated a small dot outside the target's path and judged the position of the turn-point relative to nearby horizontal or vertical hash marks. The two-dimensional position of the turn was systematically mislocalized to a position outside the object's motion trajectory. Our control data indicates that known effects like Frohlich, flash-lag, representational momentum, and onset repulsion are unable to explain the shift. Specific probing of the target's trajectory suggests that observers maintain no less than three percepts that are mutually inconsistent: the position of the pre-turn path, the position of the post-turn path, and the position of the turn-point itself. Our findings support the idea that lower-level sensory processing can be mutually contradictory, suggesting some module-like structure.
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