Depth perception in simple line drawings

Three-dimensional interpretation of simple line drawings, composed of two triangles with a common side, was studied through the quantitative measurement of perceived orientation of the surface indicated by a stimulus figure. In a single triangle, depth perception is ambiguous and is not stable even if perceived. In two triangles with a common side, however, depth is stably perceived. Depth effect, defined as the magnitude of the angle formed by the two perceived surfaces, increased linearly as the magnitude of an angle at a vertex facing the common side became larger. The depth effect did not vary significantly for the change of a triangular from when the magnitude of the angle at the vertex facing the common side was constant. These results suggest that the depth effect changes systematically with variation in the triangle's form.