Display symmetry affects positional specificity in same-different judgmentof pairs of novel visual patterns

Deciding whether a novel visual pattern is the same as or different from a previously seen reference is easier if both stimuli are presented to the sa me rather than to different locations in the field of view (Foster & Kahn ( 1985). Biological Cybernetics, 51, 305-312; Dill & Fable (1998). Perception and Psychophysics, 60, 65-81). We investigated whether pattern symmetry in teracts with the effect of translation. Patterns were small dot-clouds whic h could be mirror-symmetric or asymmetric. Translations were displacements of the visual pattern symmetrically across the fovea, either left-right or above-below. We found that same-different discriminations were worse (less accurate and slower) for translated patterns, to an extent which in general was not influenced by pattern symmetry, or pattern orientation, or directi on of displacement. However, if the displaced pattern was a mirror image of the original one (along the trajectory of the displacement), then performa nce was largely invariant to translation. Both positional specificity and i ts reduction in symmetric displays may be explained by location-specific pr e-processing of the visual input. (C) 1999 Elsevier Science Ltd. All rights reserved.