Components of Optical Information for Depth Induce a Picture-Surface Angle Illusion

Perception of angles in two-dimensional (2D) shapes on a picture surface may be subject to error when the 2D shapes depict three-dimensional (3D) forms (Arnheim, 1954; Hammad et al., 2008a). This thesis tests the hypothesis that pictorial components of optical information for depth, available in the normal environment, cause an illusion in the perception of 2D shapes such as quadrilaterals on picture surfaces. Drawings of quadrilateral cube-tops were presented to participants as parts of 2D forms (1) depicting 3D parallelepipeds with long and short sides, shown by converging lines; (2) depicting cubes in parallel projection, with sides shown by parallel lines; (3) depicting asymmetric square-top pyramids, with wide bases shown by diverging lines; (4) depicting asymmetric triangle-top pyramids, with wide bases shown by diverging lines. In addition, tops of 3D objects will be drawn as (5) ellipses on 2D forms depicting cylindrical forms. Quadrilaterals will also be shown (6) depicting cubes with object-surface texture; (7) depicting cubes in apparent motion and (8) depicting cubes on a picture-surface that is itself depicted as highly textured - the latter is expected to reduce the illusion. Components of optical information for depth resulted in viewers overestimating the acute internal angles of the quadrilaterals. The theory tested here is that 2D features that provide optical information for slant-in-depth affect the perception of 2D shapes on the picture surface. The 3D information may make 2D shapes, including angles, appear closer to depicted 3D forms, and their angles, than is correct.Ph.D