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 retardation (Down syndrome versus non-Down subjects) and subjects without mental retardation. Subjects took part in a response competition task to examine their ability to restrict attentional focus to a narrow range of the visual field and to see if this ability is sensitive to top-down operations associated with category variables (letter versus number). Subjects saw targets flanked by distractors. The distractors could be identical to targets (2 2 2 or K K K), from the same category as 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, subjects responded to either the number 2 or the letter K. Results indicated that both groups of subjects with mental retardation exhibited greater interference at wider separation than did the non-retarded subjects. In addition, the non-retarded subjects exhibited a category effect (greater interference at wider separations for same than for different 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.