Similarity in motion binds and bends judgments of aspect ratio

We investigated whether the visual system quickly shifts between attractive and repulsive distortions when the grouping state between a pair of shapes changes on a moment-to-moment basis. Observers viewed a pair of ellipses that differed in terms of how flat or tall they were and reported the aspect ratio of one ellipse from the pair. Each ellipse was defined by a cloud of coherently moving dots, and the dots within the two ellipses had either the same or different directions of motion, varying from trial to trial. We found that reports of the cued ellipse’s aspect ratio were repelled from the aspect ratio of the uncued ellipse when the shapes had different directions of motion compared to when they had the same direction of motion.