The less you see it, the faster it moves: shortening the "on-time" speeds up apparent motion.
The apparent motion (AM) created by two spots illuminated in alteration looks faster when there is dark temporal interval (ISI) between the offset of one spot and the onset of the other than when the spots are presented immediately after one another (no ISI), even though the temporal frequency and the spatial separation between spots are held constant. AMISI looks 18.6% faster than AMnoISI at temporal frequencies between 1.5 and 4.5 Hz. Reducing the duty cycle from 0.5 to 0.05 increases the apparent speedup to 30%. This difference in subjective speed is not due to differential saturation of velocity detectors, nor to the apparent spatial separation between spots, nor to differences in the time-averaged luminance of the stimuli. It is the "on-time", the time for which the spot is visible in one position, that determines the subjective speed. The longer the on-time, the slower the spot appears to move.
Giaschi
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Department of Psychology, York University, Ontario, Canada.
Anstis
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S
D005260:Female; D005425:Flicker Fusion / Q000502:physiology; D005583:Fourier Analysis; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009903:Optical Illusions / Q000502:physiology*; D010783:Photometry; D013997:Time Factors