Modeling Orientation Effects in Symmetry Detection: The Role of Visual Structure

Symmetry detection is a key part of human perception. One incompletely understood aspect of symmetry detection concerns orientation effects. The best-known orientation effect is the preference for vertical symmetry, where symmetry around a vertical axis is detected more quickly and accurately than symmetry at other orientations. Current symmetry detection models have difficulty explaining this effect. Using MAGI (Ferguson, 1994), we show how orientation effects may be caused by interactions between the perceived visual relations and the current reference frame. As evidence for this explanation, we simulate several orientation characteristics, including the preference for vertical symmetry and Wiser’s (1981) theory of "intrinsic axes". Finally, we successfully simulate the results of a classic study by Palmer and Hemenway (1978) which explores the relationship between the preference for vertical symmetry, multiple symmetries, and inexact symmetry. Collectively, these results show that orientation effects may be due to characteristics of detected visual relations rather than either exact point-to-point equivalencies or the bilateral symmetry of the visual system.