VISUAL SELECTIVE ATTENTION AND MENTAL-RETARDATION

Two experiments are reported that examined differences in the control of visual attention exhibited by two groups of subjects with mental re tardation (Down syndrome versus non-Down subjects) and subjects withou t mental retardation. Subjects took part in a response competition tas k to examine their ability to restrict attentional focus to a narrow r ange of the visual field and to see if this ability is sensitive to to p-down operations associated with category variables (letter versus nu mber). Subjects saw targets flanked by distractors. The distractors co uld be identical to targets (2 2 2 or K K K), from the same category a s targets (3 2 3 or L K L), or from a different category to targets (L 2 L or 3 K 3). We also manipulated the separation between target and flankers from 0.06 to 2.5 degrees of visual angle. In Experiment 1, su bjects responded to either the number 2 or the letter K. Results indic ated that both groups of subjects with mental retardation exhibited gr eater interference at wider separation than did the non-retarded subje cts. In addition, the non-retarded subjects exhibited a category effec t (greater interference at wider separations for same than for differe nt category stimuli), whereas the subjects with mental retardation did not. Experiment 2 confirmed that this second difference was likely to be the result of searching for a particular category. The implication of these results for the application of cognitive neuroscience to the study of attentional processes of persons with mental retardation is discussed.