It is well known that objects similar in appearance become bound, or grouped, in perceptual organization. Less well-known is that this relationship works in the opposite direction--grouping (or un-grouping) can make objects look more similar (or dissimilar) to each other. Yet examinations of this latter kind of effect tend to focus on distortions in one direction only (from grouping or un-grouping) that build up over time, across many trials. Here we focus on the flexibility of this process, namely, can the visual system leverage transient cues about objects’ similarity in motion so that they look more like each other in shape, on a trial-by-trial basis? On each trial, observers viewed a pair of briefly presented ellipses that differed in terms of how flat or tall they were, and they reported the aspect ratio of one shape from the pair, cued by an arrow after they disappeared. Crucially, each shape was defined by a cloud of coherently-moving dots on a background of dots with random motion vectors. We manipulated the dots within the two shapes so that they had either the same or different vectors in order to facilitate or disrupt grouping. We found that when the two shapes were grouped by similar motion, the aspect ratio of the cued shape was attracted to the aspect ratio of the uncued shape. We found the opposite pattern when the two shapes had dissimilar motion. In summary, observers reported that the shapes looked more (or less) like each other based on their shared or unshared motion within a brief perceptual moment. We conclude that the visual system can adaptively alter visual experience based on grouping, quickly imposing the appearance of similarity or distinctiveness to fit a perceiver’s belief that objects do or do not belong together.