Spatial layout, orientation relative to the observer, and perceived projection in pictures viewed at an angle.

Judgments of the spatial layout of a three-dimensional array of pictured dowels remain relatively constant as viewing angle changes, whereas judgments of their orientation relative to the observer (perceived orientation) vary. These changes in perceived orientation as viewing angle changes, called the differential rotation effect (DRE), also occur for stimuli such as the eyes in portraits, which are not extended in pictorial space. Thus, the mechanism for the DRE does not depend on the extension of pictured objects in depth. The DRE is decreased when back-illuminated pictures are viewed in the dark so that the picture plane is not visible. This result suggests that the DRE depends on information that defines a pictured object's direction relative to the picture plane. The difference in the way spatial layout and perceived orientation are affected by changes in viewing angle suggests that it is important to distinguish between these two attributes of pictures. In addition, another attribute, the picture's projection, should be distinguished from spatial layout and perceived orientation. When these distinctions are not made, the result is confusion, particularly when discussing whether or not pictures viewed at an angle appear distorted.