Purpose: The classic motion aftereffect is motion illusion induced by adaptation to a moving stimulus. Last year at ARVO, we reported that adaptation to translational motion stimuli induced a bias in the perceived direction of motion (DOM) of subsequent motion stimuli. We hypothesized that a similar bias would occur in perceived speed. We have performed experiments to measure the full velocity bias induced by motion adaptation. Methods: Stimuli were presented in two circular patches, on either side of a fixation point. The adaptation stimulus was presented for 10 second intervals, and consisted of a patch of constant-velocity random dots (CVRDs) and a patch of dynamic random noise. The subject then simultaneously viewed a test stimulus at the location of the adapting dots, and a match stimulus at the location of the noise. Both test and match consisted of CVRDs. The subjects performed a matching task, in which they reported whether the test and match velocities appeared the same or different. The collected could thus be used to determine the point of subjective equality. Results: Adaptation produces notable biases in the perceived speed of test stimuli. Specifically, test stimuli that are moving slower than the adaptation speed are matched by stimuli moving slower than the actual speed of the test stimuli. Similarly, test stimuli that are moving faster than the adaptation speed are matched by stimuli that are moving faster than the test speed. Conclusions: These results are consistent with a motion mechanism which explicitly represents speed. They also lend support to the hypothesis that the two-dimensional quantity of velocity (i.e., speed and DOM) is explicitly represented by the visual system. Warning: Undefined array key 2 in /System/Volumes/Data/e/1.3/p1/lcv/html_public/pubs/makeAbs.php on line 304