Abstract
Imagine that a 3D object is illuminated from behind, and its shadow is cast into a translucent screen viewed by an observer. When stationary, it looks like a flat 2D figure, but when rotated, it appears as a 3D rotating object (depth-from-rotation). The relative motion of the points of shadow gives depth information but perspective information is not present. So, the relative depth of points can be perceived but not their depth order. It is impossible to tell which is the front and which is the back of the objects. The 3D object is ambiguous with respect to its reflection in the projection plane. As a result the object appears to reverse in depth periodically as well as direction of rotation. This study investigated if manipulating intent of subject alters perception of depth-from-rotation display. In the experiment, the stimulus change was coincided with the rotation of a crank handle rotated rightward or leftward by the observer. The result showed that the perceived direction of rotation from the display coincided the manual control at a high rate. Prolonged viewing, however, made reverse the apparent rotation. We measured duration of initial rotation. The manual control extended the mean duration.