Testing the role of vertical symmetry in letter matching

A series of experiments tested a recent suggestion that vertical symmetry of a stimulus display can serve as a visual diagnostic for responding "same" in a letter-matching task. The data of chief interest were same reaction times to vertically symmetric (e.g., AA) and asymmetric (e.g., LL) displays, each composed of two side-by-side uppercase letters. Overall, the data argue against subjects' use of vertical symmetry as a diagnostic in dealing with letter pairs. The results were interpreted within the context of recent work on symmetry. In particular, it was suggested that the importance of structural diagnostics in a matching task may be inversely related to the codability of the stimulus elements being compared.