The retinal image of a static object undergoes significant changes during egomotion. Under most conditions, humans have the ability to perceive that object correctly as stationary, despite the retinal changes. The English painter Patrick Hughes has created a class of artworks ("reverspectives") that defeat this ability, since his artworks appear to turn as observers move in front of them. The simplest reverspective is a convex truncated square pyramid jutting from the wall toward the viewer with its small (frontoparallel) base closer to the viewer. The artist painted the small base to appear as the far wall of a room. The floor, ceiling, and left- and right- walls are painted on the bottom, top, and side faces of the pyramid, respectively. Thus the pictorial cues, which suggest a concave room, compete with the perception of the actual convex object. This competition is present in reverspectives that depict more complex scenes. Under a wide variety of viewing conditions, this competition causes reverspectives to appear in false depth, and to turn vividly as viewers move in front of them, violating the rigidity constraint. To quantify the effect of the pictorial cues, I measured the relative frequency of obtaining the false depth with and without the pictorial cues, using the same sculptured surface in both cases. Observers pressed one of two buttons, depending on whether they perceived the real or the false depth, under both monocular and binocular viewing. The role of pictorial cues was significant. The false depth was obtained 95% and 68% of the time, respectively, with and without pictorial cues under monocular viewing; the corresponding figures were 67% and 40% under binocular viewing. Similar results were obtained with the method of first-obtained percept. A model is presented to account for the illusory motion as a consequence of the false depth percept. This model is easily extended to account for the illusory motion of stereograms and of hollow masks.
All Science Journal Classification (ASJC) codes
- Sensory Systems