Effects of orientation and speed on direction perception during occluded target motion A Hughes, D Tolhurst |
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Department of Physiology, University of Cambridge, United Kingdom
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| We have previously shown that visual predictions of the direction of a moving Gabor can be biased by the motion of the stripes within it (Hughes & Tolhurst, 2012, Perception, 41(12), 1519). Here we show that the orientation of static stripes can also cause perceptual biases. Observers viewed a Gabor target with oblique stripes moving across a CRT display with a linear trajectory randomly chosen within 18 degrees of the horizontal. After occlusion, they predicted where it would later cross a vertical line using a numerical scale bar. We show that speed of lateral movement has an important effect on direction perception; at high speeds, patches with oblique stripes that pointed upwards relative to the direction of lateral motion were perceived to cross higher than patches where the stripes pointed downwards relative to the direction of motion. This effect occurred only at speeds at or above the critical speed required for 'motion streaks' (Geisler, 1999, Nature, 6739, 65-69), suggesting that it may be caused by a similar orientation specific mechanism. However, at lower speeds, the pattern of perceived biases was reversed. We propose that the different patterns of results may reflect different motion detection processes that operate at different speeds. |
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