John R. Cook

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)




The effect of Methylphenidate (MPH) on the short-term memory scanning of boys with Attention Deficit Disorder (ADD) was examined from the perspectives of a linear stages model and a capacity model of information processing. A total of 36, six- to ten-year-old boys participated in three age- and IQ-matched groups. The boys with ADD were selected on the basis of a clinical diagnosis, meeting DSM-III criteria on the SNAP and a score of 15 or more on the Abbreviated Conners Rating Scale (ACRS). They received treatment with placebo and methylphenidate (MPH) for three weeks each in a double-blind, single crossover procedure that was counterbalanced with respect the order of treatment. Two comparison groups were comprised of boys who were normal achievers (NA) and boys who were reading disabled (RD) and who did not receive medication.

It was hypothesized that the administration of MPH to the boys with ADD would result in reductions in Sternberg reaction time and that this effect of medication would be restricted to the second half of the sessions. In partial support of the hypothesis, a significant effect of MPH administration on Sternberg reaction time was found in comparing reaction times obtained while the boys with ADD were receiving the active drug (MPH) with their reaction times at baseline. A similar drop in reaction from baseline was observed for boys with ADD who were administered placebo and for boys in the comparison groups after the first three week time period. This drop in reaction time was attributed to practice. The results of exploratory investigations using the additive factor method suggested that this practice effect involved an increased rate of serial comparison.

Other effects of MPH were found to occur as a significantly reduced reaction time in the MPH condition relative to the placebo condition and as an order of treatment or carry-over effect. The carry-over effect was seen as improved Sternberg reaction time in the placebo condition when it followed the MPH condition as opposed to when it preceded it.