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Abstract
The perception of the speed of moving objects and guiding motor reactions to them is a crucial task of the visuomotor system that has to be performed across dramatic changes in luminance in everyday life. In a series of studies we demonstrate that the perceived speed of motion is significantly (up to 30%) overestimated at low luminance. This speed overestimation is a result of lengthened motion smear that is caused by an increase in visual persistence at low luminance. However, we find next that this change in perceived speed does not affect other speed-dependent responses: neither motion-induced position shifts (the flash lag effect) nor speed-dependent motor responses (eye and hand movements) are affected by variations in luminance that have large and significant effects on perceived speed. In conclusion multiple cues, including motion smear, may contribute to the perception of speed, but not all of them contribute to determining the position of and guiding responses to moving targets. The cues that do participate appear to be invariant to wide ranges of luminance.