Carlson and associates48 compared the effects of methylphenidate with those of placebo on the performance of ADHD boys following their success or failure at tasks assigned to them. They provided evidence for a "salutary" effect of methylphenidate on the boys' performance and perceptions after attempting to solve both solvable and unsolvable puzzles. Boys exposed to unsolvable puzzles demonstrated increased persistence on a subsequent generalization task when receiving methylphenidate as compared with placebo. No differences were found between placebo and a "no pill" condition on the Posner letter-matching task and four other measures of phonologic processing in an attempt to isolate the effects of methylphenidate to parameter estimates of selective attention, the basic cognitive process of retrieving name codes from permanent memory, and a constant term that represented nonspecific aspects of information processing. Responses to the lettermatching stimuli were found to be more rapid with methylphenidate than with placebo.49 It is important to note that this improvement in performance was isolated to the parameter estimate that reflected nonspecific aspects of information processing.