Orientation and symmetry: effects of multiple, rotational, and near symmetries.

Time to detect bilateral symmetry in different orientations was studied for closed polygons with single, double, quadruple, rotational, and near symmetry. In Experiment 1, the orientation of the axis of symmetry was varied. Detection was fastest for vertical symmetry, next fastest for horizontal, and slowest for left- and right-diagonal symmetries. For corresponding orientations, responses were faster to quadruple than double symmetries, and faster to double than single symmetries. Negative responses to nearly symmetric figures produced an orientation effect similar to that for single symmetries. Rotational symmetries showed no orientation effect and took longer to reject than near symmetries. In Experiment 2, subjects looked only for vertical symmetry. Responses were twice as fast as in comparable conditions of Experiment 1. The effect of multiple symmetries was still present, but rotational symmetries were rejected faster than near symmetries. The results are interpreted as supporting a dual process model for detecting symmetry in multiple orientation channels: Observers first select potential axes of symmetry defined by mirror-similar parts and then evaluate specific axes sequentially in a detailed comparison for mirror-identity.