Anne Fleur Kortekaas-Rijlaarsdam

87 MPH EFFECTS ON MATH PERFORMANCE: INFLUENCE OF COGNITION, MOTIVATION AND PERCEIVED COMPETENCE 4 ADHD (Placebo) Versus TD The ADHD group on placebo showed worse performance on the visuospatial working memory task and more lapses of attention than the TD group ( t (128) = 3.52, p = .001, d = .63 and t (125) = 3.74, p <.001, d = .67, respectively). Differences between the ADHD and TD group were not significant for performance on the Digit Span backwards, RT speed and interference control. In addition, children with ADHD on placebo rated their intrinsic motivation for math on the CAIMI as significantly lower than TD children ( t (127) = 2.61, p = .01, d = .46), whereas group differences in intrinsic motivation for schoolwork in general and for reading were not significant. Children with ADHD on placebo also showed higher reward responsivity and higher sensitivity to punishment on the SPSRQ-C ( t (125) = -3.73, p <.001, d = .67 and t (125) = 1.90, p = .06, d = .34, respectively) although the latter just escaped conventional levels of significance. Children with ADHD on placebo perceived their own academic competence (SPPC) as significantly lower than TD children, a finding that was corroborated by competence ratings of both parents and teachers ( t (128) = 3.96, p <.001, d = .70 and t (125) = 7.18, p <.001, d = 1.28 and t (126) = 5.80, p <.001, d = 1.03, respectively). MPH Effects on Cognition, Motivation and Competence MPH failed to result in any significant beneficial effects on the performance on Digit Span backwards, the visuospatial working memory task, RT speed, lapses of attention and interference control (see Table 4.2). GLMM analysis showed that the effect of MPH on self-rated competence according to parents (SPPC) was significant with a medium effect (t(60.60) = 2.93, β = -1.05, p = .005, d = .53). MPH did not affect academic competence rated by the child or teacher, intrinsic academic motivation (CAIMI General, Math and Reading) or sensitivity to punishment or reward (SPSRQ-C) (see Table 2). Mediation Analysis For parent-rated self-perceived competence, the first two criteria for mediation (Baron & Kenny, 1986) were met as MPH positively influenced math productivity and accuracy, as well as parent-rated self-perceived competence. To investigate whether the third criterion for mediation was met, GLMM was used to test whether parent-rated self- perceived competence affected math productivity and accuracy. Parent-rated self- perceived competence significantly affected math productivity but not accuracy when entered in a model with medication treatment: t (74.1) = 3.30, β = .53, p = .001 and t (114.4) = 1.67, β = 1.34, p = .097, respectively. The addition of parent-rated self- perceived competence to the model of the effects of MPH on math productivity reduced