The present study was designed to investigate attentional processes and performance asymmetries in goal-directed aiming in individuals with Down syndrome (DS; n = 6 in each group). Using the right and left hands, young adults with and without DS completed rapid aiming movements to small targets in ipsilateral and contralateral space. On some trials, a visual distractor was present. As attention and action were assumed to be coupled, the impact of distractors on reaction time (RT) and movement kinematics was examined. The performance of individuals with DS was quantitatively and qualitatively different from nonaffected participants, suggesting that participants in the two groups used different strategies to complete the task. Individuals with DS exhibited movement time (MT) interference when a distractor was present. This finding is consistent with an action-centered framework of attention.

In the typical induction of the orientation-contingent color aftereffect (CCAE), the stimuli are composed of elements that differ in both color and luminance. Three experiments are reported that show that chromatic contrast between stimulus elements is insufficient for the induction of the orientation-CCAE and that luminance contrast is necessary. These experiments expand on previous research concerned with the role of luminance contrast in the induction of orientation-CCAEsby eliminating alternative explanations.The orientation-contingent color aftereffect (CCAE) typically is induced by alternating two complementarily colored and orthogonally oriented grids every few seconds for several minutes (McCollough, 1965). For example, a grid constructed of black-and-green horizontal bars might be alternated with a grid constructed ofblackand-red vertical bars. Following such induction, complementary color aftereffects contingent on grid orientation are noted-black-and-white assessment grids appear colored. In this example, the white space between the black horizontal bars appears pink and the white space between the black vertical bars appears green.The grids used in the induction of the orientation-CCAE are usually composed of chromatic and achromatic (black) bars that differ in luminance. A few studies have examined the role of the luminance contrast' between the chromatic and achromatic bars in the induction ofthe orientation-CCAE. Ellis (1977) and Mikaelian (1980) systematically varied luminance contrast by increasing the luminance of the achromatic bars from black to various shades of gray. They reported that the size of the orientation-CCAE decreased with decreasing luminance contrast and concluded that isoluminant grids were ineffective in inducing an orientation-CCAE. Allan, Siegel, Toppan, and Lockhead (1991) also reported that induction with grids composed of gray and colored isoluminant bars did not result in an orientation-CCAE. These studies are in agreement with Stromeyer's (1978) often-cited conclusion, based on unpublished data, that luminance contrast is necessary for the induction of the orientation-CCAE. ' Although the existing data suggest that luminance contrast is necessary for the induction ofthe orientation-CCAE, an examination of the published experiments reveals that the absence of the orientation-CCAE after isoluminant induction might be attributable to variables other than the luminance contrast of the induction grids. The three experiments reported in the present paper explore this possibility. GENERAL METHOD SubjectsA total of 59 subjects participated in the three experiments. The subjects had no previous experience in contingent aftereffect tasks, and each subject participated in only one of the three experiments. All but 2 of the subjects were students enrolled in introductory psychology at McMastcr University who received course credit for their participation. The remaining 2 subjects (Experiment 2) were 5th year engineering students who volunteered.