Role of two-dimensional surface characteristics in pictorial depth perception.

The purpose of the present experiment was to test the hypothesis that flat surface information for the plane of projection is the essential difference between ordinary and pictorial perception. Adults were asked to make relative size judgments of pairs of squares and triangles placed and pictured at various distances. The conditions were: real scene controls, life-size slides and prints, and real scenes viewed through clear glass, textured glass, a screen and a 50-mm lens. The error rate was significantly lower with real scenes than with either slides or prints which did not differ. The control data for real scenes were used for comparison to test for the effects of interposed flat surfaces on size judgments of real scenes. Viewing real scenes through either a clear glass pane or a 50-mm lens increased the error rate two and one-half times that of the controls for real scenes. Neither textured glass nor a screen significantly affected error rate. Results were interpreted as supporting the hypothesis that information about a flat surface for the plane of projection is the critical variable determining the special character of picture perception.