Lighting position and judgments of distance of shadow-casting objects

Participants recruited on the web performed in two experiments in which they viewed eight pictures of the same two rods in the exact same positions with shadows generated by a light source located at eight positions around the rods. In Exp. 1, participants judged how much shadows projected to the front, back, and sides of the rods facilitated the correct perception of the actual distance of the rods relative to each other. In Exp. 1 (n: 52), frontal lighting facilitated judgments more than lighting from the rear, but frontal and side lighting did not differ in facilitative effects. In Exp. 2 (n: 72), judgments of rods depicted with shadows were relative to a judgment of the rods depicted without shadows (raw scores were the value of the judgment of the shadowless rods subtracted from the value of the judgment of each of the eight sets of rods). Again, frontal lighting was more facilitative than rear lighting and frontal lighting did not differ from side lighting. However, when the average of each participant's backlighting judgments was compared with his judgment of the shadowless rods, shadows generated by backlighting were more facilitative than none.