Abstract
When many dots group to form a rotating ring, color changes among them become unnoticed, changes otherwise salient when the ring remains stationary. This ‘Motion Silencing (MS)’ illusion is a striking failure of change perception. Why does MS occur? We sought to distinguish between the possibility that the illusion is caused by lower-level limitations on processing and the possibility that it reflects uncertainty among higher-level inferential mechanisms. In Experiment 1, we developed a search-inspired methodology to quantify the illusion. Participants saw two side-by-side rings of multicolored dots, in one of which the dots changed color rapidly. The task was to report which ring included the changes. When both rings were stationary, latency to respond was fast. When the rings rotated, latencies were longer and increased with rotation speed, thereby revealing the presence of MS: the rotating and changing ring seeming to observers like the one that rotates without changing. We employed this method to identify two conditions where MS does not obtain despite dot motion. In Experiment 2, dots were arranged in a hollow square. Significantly less silencing obtained when the dots translated around the square perimeter compared to when the square rotated around its center. In Experiment 3, dots were arranged in a column. When dots translated in opposite horizontal directions, the resulting impression of a rotating cylinder produced strong MS; but nearly none obtained when all the dots translated in one direction. These experiments imply limits to the motion conditions that produce MS, with strong silencing specifically for rotation. By contrasting stimuli with nearly identical lower-level properties, these experiments suggest that silencing cannot be the consequence of those properties or related processing limitations. We suggest that silencing arises in the process of visual inference, perhaps specifically during inferences about whole object rotation.