Similarities in the detection of stimulus symmetry by individuals with and without mental retardation.

Intelligence-related differences in the detection of stimulus organization previously identified by Soraci, Carlin, Deckner, and Baumeister (1990) were examined further to determine whether they would (a) extend to similar checkerboard stimuli varying solely with respect to symmetry and (b) generalize to form-like polygon stimuli. Detection performances of 10 individuals with mild mental retardation, 10 CA-matched, and 10 MA-matched individuals were assessed on a rapid presentation a two-choice match-to-sample task. The organizations of the target and distractor stimuli were varied across four levels of symmetry: double, vertical, horizontal, and asymmetrical. Results indicated that detection rates for each group were highest when the target stimulus was vertically symmetrical or when target-distractor structural disparity was maximal. However, no significant main effects of subject group or stimulus type (i.e., checkerboard vs. polygon) were found, thereby arguing for the robustness of the symmetry effect across groups differing in intelligence and physically dissimilar stimulus types.