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Abstract
When two parallel gratings moving at the same speed are presented simultaneously,
the lower-contrast grating appears slower. This misperception is evident across a
wide range of contrasts (2.5-50%) and does not appear to saturate (e.g. a 50% contrast
grating appears slower than a 70% contrast grating moving at the same speed). On average,
a 70% contrast grating must be slowed by 35% to match a 10% contrast grating moving
at 2 degrees/sec (N = 6). Furthermore, the effect is largely independent of the absolute
contrast level and is a quasi-linear function of log contrast ratio. A preliminary
parametric study shows that, although spatial frequency has little effect, relative
orientation is important. Finally, the misperception of relative speed appears lessened
when the stimuli to be matched are presented sequentially.