Anne Fleur Kortekaas-Rijlaarsdam

135 SUMMARY AND DISCUSSION 7 how necessary improvements in specific cognitive and motivational deficits associated with ADHD are for medication-related academic improvement. T H I RD A I M Effects of MPH on Feedback Learning and on the Ability to Profit from Reward The third aim was to quantify the effects of MPH on two aspects of reinforcements processing in children with ADHD: Firstly, the effects of MPH on feedback learning were studied (Chapter 5) and secondly, the interaction between MPH and reward on math performance was investigated (Chapter 6). For both studies, data were obtained from the abovementioned RCT comparing performance of 63 children with ADHD while treated with MPH or placebo, and comparing their performance to that of 67 TD controls. To study the effects of MPH on feedback learning, a well validated associative learning test adapted for children was used: The task started with a learning phase during which novel stimulus-reward associations were learned, and was followed by a test phase during which the acquired knowledges had to be applied to novel stimulus pairs. The task ended with a reversal phase in which contingency values were reversed. Using this task, the effects of ADHD diagnosis and MPH treatment on the acquisition of stimulus-reward associations, generalization of this knowledge to novel contexts and reversal learning were studied. The results suggest that both the acquisition of stimulus-reward associations and reversal learning are intact in children with ADHD. However, children with ADHD showed impairments in generalization of acquired knowledge. Treatment with MPH improved the acquisition of novel stimulus-reward associations and there was a trend effect of MPH on generalization of knowledge. MPH normalized the ability of children with ADHD to generalize knowledge to the level of TD peers. In conclusion, these result reveal that the acquisition of knowledge with feedback learning is intact in children with ADHD but that they face difficulties when applying this knowledge to novel contexts. Medication has potentially beneficial effects on feedback learning in ADHD in a way that may lead to improvements of generalization of stimulus-reward associations. However, replication of these results is necessary. In Chapter 6 we compared the effects of reward and MPH, and the possible interaction between them, on an ecologically valid math performance task in children with ADHD. To this end, we developed a math task that required children with ADHD and TD controls to solve calculations (addition) of increasing difficulty level. Difficulty was adapted to performance and performance was either coupled to contingent reward (motivation condition: a smiling face; the sound of applause; +1 point which could be exchanged for stickers) or no feedback (neutral condition). Achieved difficulty level