Abstract
When an object rapidly disappears from view, the event requires some cognitively consistent explanation. We report a new phenomenon, the Object Disappearance Effect (ODE), in which static, suddenly disappearing stimuli are seen to move backward in depth when they are in a stereoscopic context. The target was a row of disks switching off/on in a static background of similar rows of disks. In the context of the normal flat display, the target seemed to simply switch off/on. When the context was changed to a stereoscopic view of a 3D surface, the observers unexpectedly saw depth-motion despite the lack of disparity change in either the target or the surround. Thus, the 3D-context activated the heuristic of backward motion to explain the object disappearance. How will this phenomenon be affected (i) by the spatial target/surround configuration and/or (ii) by introducing stereomotion in the surround? Five configurations were studied in (i) a static and (ii) a stereomoving environment. The stereomotion was either with or against the direction of the illusory motion. The direction and speed of both target and surround were judged. The data indicate that the target was perceived to move backward as it switched off, forward when switched on again. It appeared to go to the same specific depth location, regardless of the disparity of the starting point. We propose the operation of a Destination-Capture Principle determining the perceived speed and trajectory. Introducing stereomotion in the surround did not significantly affect the illusory depth-motion in the target. Surprisingly, the illusory target motion reduced the disparity-defined surround motion, but only when the motions were in the same direction. Thus, the ODE reveals how the basic strategy of the visual system is to use heuristics in interpreting object behavior (events) in dynamic scenes. The new phenomenon reveals the dominance of cognitive factors in associating 3D motion perception and object-level processing.