No symmetry advantage when object matching involves accidental viewpoints.

The presupposed advantage of symmetrical objects over asymmetrical objects was investigated in an object matching task, using accidental and non-accidental viewpoints. In addition, the accidental views could be symmetric or asymmetric. When two non-accidental views were presented, symmetrical objects were matched faster than asymmetrical objects. When an accidental view was presented first (followed by a non-accidental view), the matching of symmetrical objects was equal to that of asymmetrical objects. When a non-accidental view was presented first (followed by an accidental view), matching was again equal for the symmetrical and asymmetrical objects, although much faster compared with the opposite sequence of presented views. No effects of image symmetry in the accidental viewpoints were found. Apparently, the advantage of symmetrical objects over asymmetrical objects is only present in object matching when 3-D object structures are visible.