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Peter Thompson; The transition from monocular to binocular vision: An eye-opening illusion of speed. Journal of Vision 2006;6(6):1087. doi: 10.1167/6.6.1087.
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It has been observed casually that when observing moving traffic from a high building the perceived speed of vehicles increases transiently (and dramatically) when viewing changes from being monocular to binocular. We have attempted to examine this effect in a series of experiments. We have determined that: (1) the illusion is apparent when observing objects moving from a horizontal as well as a vertical view-point; (2) the illusion is seen strongly when vision goes from monocular to binocular - but there is minimal perceived slowing when one eye is closed; (3) the effects are significantly bigger when viewing is initially with the non-dominant eye and then with both eyes; (4) the stronger the eye dominance, the bigger the effect; (5) the effect is of similar size for both left-to-right and right-to-left directions of motion; (6) generally faster speeds give larger effects; (7) although present in foveal vision, it is stronger with peripheral viewing.
Speed matching experiments measuring the PSE (by PEST staircase) of pairs of vertical sinusoidal gratings drifting horizontally, one viewed monocularly, the other binocularly, indicate no difference between the perceived speed of monocularly and binocularly viewed grating stimuli over a wide range of speeds. Therefore a difference in speed perception between monocular and binocular viewing does not account for the illusion.
Possible explanations of the effect and its similarity to aspects of the flash-lag effect will be discussed.
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