Illusory spatial offset of a flash relative to a moving stimulus is caused by differential latencies for moving and flashed stimuli.
A flash that is presented adjacent to a continuously moving bar is perceived to lag behind the bar. One explanation for this phenomenon is that there is a difference in the persistence of the flash and the bar. Another explanation is that the visual system compensates for the neural delays of processing visual motion information, such as the moving bar, by spatially extrapolating the bar's perceived location forward in space along its expected trajectory. Two experiments demonstrate that neither of these models is tenable. The first experiment masked the flash one video frame after its presentation. The flash was still perceived to lag behind the bar, suggesting that a difference in the persistence of the flash and bar, does not cause the apparent offset. The second experiment employed unpredictable changes in the velocity of the bar including an abrupt reversal, disappearance, acceleration, and deceleration. If the extrapolation model held, the bar would continue to be extrapolated in accordance with its initial velocity until the moment of an abrupt velocity change. The results were inconsistent with this prediction, suggesting that there is little or no spatial compensation for the neural delays of processing moving objects. The results support a new model of temporal facilitation for moving objects whereby the apparent flash lag is due to a latency advantage for moving over flashed stimuli.
Whitney
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D
Vision Sciences Laboratory, Harvard University, Cambridge, MA 02138, USA. whitney@wjh.harvard.edu
Murakami
I
I
Cavanagh
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P
D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D009903:Optical Illusions / Q000502:physiology*; D010469:Perceptual Distortion / Q000502:physiology; D010775:Photic Stimulation; D011930:Reaction Time