Anne Fleur Kortekaas-Rijlaarsdam

119 EFFECTS OF MPH AND REWARD ON MATH PERFORMANCE 6 the absence of ADHD, children in the TD group were required to obtain scores ≤ 90 th percentile on both the Inattentive and Hyperactive/Impulsive scale of the parent version of the DBDRS. TD children were excluded if reported to have ever been diagnosed with a psychiatric disorder (parental report). Medication Design and Procedure For the participants with ADHD, a randomized double-blind placebo-controlled crossover design was used to compare the direct effects of extended release MPH (Equasym XL®) with placebo. Treatment duration was 7 days with a 48-hour washout prior to the study and in between the treatment weeks. Children were tested on the last day of each treatment week at their own primary school. Doses were identical to those clinically titrated and currently prescribed by the treating physician. For details of the trial design, see Kortekaas-Rijlaarsdam et al. (2017b). The current study has been carried out in accordance with the Declaration of Helsinki and was approved by the local ethics committee. Informed consent was obtained from parents and children above the age of 11. Testing was completed at the child’s school. All measures were collected by the researchers using fully standardized instructions. All procedures and scoring were by two researchers independently. All researchers were blinded to medication condition. Testing of children with ADHD (placebo and MPH condition) occurred during expected plasma peak levels of methylphenidate, with testing commencing within 60-90 minutes after medication intake (Banaschewski et al., 2006). The TD group was assessed only once. Testing procedures were identical in the ADHD and TD group, with the exception that the testing of the TD group was preceded by a short version of the WISC-III-R to estimate TD children’s IQ as TD children were first seen on the day of the assessment. Participants with ADHD received a small gift independent of performance. Materials The Motivated Math Task (MMT) was developed specifically for this study. The objective of this task was to measure the ability to profit from ecologically valid, positive feedback coupled with reward (a smiling face combined with the sound of applause and earning of +1 point, which [if enough points were earned] could be exchanged for stickers) on a math (addition) task. Stickers were chosen by the child prior to the task. By comparing trials in which the child could receive rewarded feedback (in 85% of correct trials in the motivation condition) with neutral trials (trials in which the child receives no rewarded feedback), the influence of motivation on performance was measured. The task consisted of a practice and an experimental phase.