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Bettina Friedrich, Pascal Mamassian; Motion capture and motion after-effect. Journal of Vision 2004;4(8):549. doi: 10.1167/4.8.549.
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The position of a motion field can be misperceived in its direction of motion (Ramachandran & Anstis, 1990, Perception, 19: 611–616; De Valois & De Valois, 1991, Vision Research, 31: 1619–1626). Targets flashed in the vicinity are also mislocalized (Whitney & Cavanagh, 2000, Nature Neuroscience, 3: 954–959), an effect called motion capture. In this study, we measured motion capture at different locations around the motion field. Our method involved double-flashing the very same target, once during the motion and a second time immediately after the motion has stopped. If targets are affected by motion, then the first target should appear shifted in the direction of motion while the second target should be perceptually shifted in the opposite direction. The magnitude of the motion captures can therefore be measured by comparing the perceived position of the two targets' appearances. A first experiment tested the front and the back regions of the motion field. Most observers showed the expected difference between the perceived locations of the first and second appearence of the target. Furthermore the magnitude of the shift was usually different between the front and back regions. With our experiment we can measure motion capture at various locations around the motion field. Our results indicate that motion seems to induce different captures at different locations around the motion field, which might be due to attentional shifts induced by motion. Implications of these results for a general model of motion capture will be discussed.
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