A cyclopean visual saltation illusion reveals perceptual grouping in three-dimensional space

When a number of visual elements are presented briefly one after the other at two separate locations, mislocalization occurs with elements perceived "jumping" evenly across the space between locations. This is the visual saltation illusion. We investigated whether saltation occurs in three-dimensional (3D) space. In separate experiments, observers judged the perceived positions of the first, second, and last elements for a sequence in which the first two elements were presented at one location, and the third was presented at a second location. If saltation occurred, only the second element was mislocalized to a position between the first and second locations. In Experiment 1, we observed 3D saltation, but only for conditions in which the stimulus was located away from the point of fixation. This effect was also observed when the two locations in depth have no lateral 2D separation (Experiment 2). In Experiment 3, we showed that a locally generated motion aftereffect between the two locations distorts the perceived position in depth of only the second element, which perceptually overlaps with the adapted region. Our results demonstrate the appearance of 3D saltation, and that the illusion represents a process in which higher cortical areas feed back to activate lower level inputs to achieve 3D perceptual "filling in."