Occluded Motion in the Retina

Abstract

Occluded motion is a fundamental visual event that is implicated in the tracking of predators and prey. In psychology, occluded motion results in phenomena like the “tunnel effect” and object permanence, but psychological literature repeatedly suggests lower-level contributions to their development. Here, we study occluded motion in the retina—defined as an object moving behind an occluder and then re-emerging from it—in an effort to determine the retinal contribution to higher-order perceptions of occluded motion. We recorded retinal ganglion cell activity of whole-mount larval tiger salamander retina (Ambystoma tigrinum) in response to smooth motion and motion onset of a bar with and without an occluding object. We report that the occluded smooth motion response was qualitatively similar to that of motion onset and occluded motion onset—a delayed sharp peak in firing much larger than the smooth motion response—but had a latency ranging from 5 to 40 ms beyond the delay to peak firing of motion onset or occluded motion onset. This occluded motion response occurred in all ganglion cell types and is robust to changes in stimulus polarities (bright and dark bars), and occluder widths. Moreover, in a condition in which the emergence from the occluder was 50 or 100 ms too early or too late compared to the expected time of emergence based on object velocity, the peak firing rate increased linearly with the delay to emergence. Neurons in the visual system downstream of the retina may feasibly detect the difference in response latency between occluded and un-occluded objects, thus providing a plausible neural mechanism for the “tunnel effect” and object permanence.