When we imagine a train snaking through a desert, does information about the train’s speed make it into our visual mental image? In this paper, we make use of the motion aftereffect illusion (MAE) to test whether the speed of imagined visual motion modulates transfer of adaptation to a subsequent visual motion discrimination task. We compared the effects of viewing slow, medium, and fast motion on the magnitude of the MAE (Experiment 1) with the effects of simply imagining the same motion stimuli (Experiment 2). In Experiment 1 we found that increasing the speed of real visual motion from slow to medium produced a corresponding increase in the magnitude of the MAE, but increasing speed from medium to fast did not. Likewise, imagining slow motion produced a smaller MAE than did imagining medium motion, but the effect leveled of between medium and fast motion. These findings suggest that our mental imagery of motion is specific to the speed of the moving objects, and highlight areas of overlap between mental imagery and visual perception.