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Astrid M.L. Kappers, Susan F. Pas; Perceived local velocity within a moving element is strongly influenced by its global motion. Journal of Vision 2002;2(7):394. doi: https://doi.org/10.1167/2.7.394.
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© ARVO (1962-2015); The Authors (2016-present)
We investigate whether the global motion of an object influences the perceived local motion of structures inside the object. To test this, we did the following psychophysical experiment: Two Gabor patches moved downwards along straight paths on a computer monitor. In addition to moving vertically, they could also move horizontally, either towards or away from each other. The sinusoidal patterns of the Gabor patches could also move relative to their boundaries, either inwards or outwards. Subjects were instructed to detect whether the sinusoidal patterns of the Gabor patches within their boundaries were moving inwards or outwards.
When the global velocity of the Gabor patches was exactly vertical, subjects showed no bias for the perceived direction of the motion within the Gabor patch. However, when the global motion of the Gabor patch contained a horizontal component, subjects showed large biases. These biases depend solely on the horizontal component of the global motion; they do not depend on the vertical motion component. When the Gabor patches are moving inwards globally, the motion within the Gabor patches relative to the boundaries needs to be outwards in order to appear stationary, and vice versa.
Although they were specifically instructed to look at the motion within the Gabor patches relative to their boundaries, subjects appear to track the absolute global movement of simple features of the Gabor patch.
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