SIMILARITIES IN THE DETECTION OF STIMULUS SYMMETRY BY INDIVIDUALS WITH AND WITHOUT MENTAL-RETARDATION

Intelligence-related differences in the detection of stimulus organiza tion previously identified by Soraci, Carlin, Deckner, and Baumeister (1990) were examined further to determine whether they would (a) exten d to similar checkerboard stimuli varying solely with respect to symme try and (b) generalize to form-like polygon stimuli. Detection perform ances of 10 individuals with mild mental retardation, 10 CA-matched, a nd 10 MA-matched individuals were assessed on a rapid presentation a t wo-choice match-to-sample task. The organizations of the target and di stractor stimuli were varied across four levels of symmetry: double, v ertical, horizontal, and asymmetrical. Results indicated that detectio n rates for each group were highest when the target stimulus was verti cally symmetrical or when target-distractor structural disparity was m aximal. However, no significant main effects of subject group or stimu lus type (i.e., checkerboard vs. polygon) were found, thereby arguing for the robustness of the symmetry effect across groups differing in i ntelligence and physically dissimilar stimulus types.