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Anna Hughes, Martha Fawcett, David Tolhurst; Measuring the effect of internal motion of a moving Gabor on speed perception and smooth pursuit. Journal of Vision 2015;15(12):281. doi: 10.1167/15.12.281.
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© ARVO (1962-2015); The Authors (2016-present)
We have previously shown that internal motion of the vertical stripes within a laterally moving Gabor patch can cause subjective biases in overall speed perception in an occlusion paradigm (Hughes, Stevens and Tolhurst, 2012). Here, we extend this result with a two-alternative-forced-choice paradigm, where observers chose which of two stimulus intervals contained the faster moving Gabor patch; the patches in the two intervals differed in the internal movement of the stripes. A Gabor patch with drifting stripes is perceived to move faster than a non drifting standard if the stripes drift in the same direction as the overall direction of movement. Conversely, if the stripes drift in the opposite direction to the overall direction of movement, the patch is perceived to move slower. We show that this speed effect depends on the relationship between the stripe motion and the direction travelled; when the stripe motion is orthogonal to the overall patch movement, no directional speed bias is seen. Similarly, adding non-directional temporal flicker to the patch does not affect speed judgements. Finally, we show that there are differences in eye movements made to the different types of stimuli, with smooth pursuit being faster on average if the stripes are drifting in the same direction as the overall direction of movement compared to if the stripes are drifting in the opposite direction, which may be related to the differences in speed perception seen.
Meeting abstract presented at VSS 2015
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