Anne Fleur Kortekaas-Rijlaarsdam

105 REINFORCEMENT LEARNING IN ADHD: EFFECTS OF MPH 5 the most difficult EF pair (70-30% reward rate) was significantly lower ( p <.001 for both comparisons) than performance for the AB (100-0% reward rate) and CD pairs (85-15% reward rate), which did not differ significantly from each other ( p >.05). The main effect of group was not significant ( F (123)=.123, p =.727), nor was the interaction between group and stimulus pair ( F (246)=.25, p =.779). Effect of MPH treatment on learning task performance For the ADHD group, the main effect of treatment was significant ( F (308.34)=5.99, p =.015, d =.025) with higher learning task performance in the MPH condition compared to placebo. There was a trend effect of pair ( F (307.2)=2.52, p =.082 see Figure 5.2), but no interaction between treatment and pair ( F (307.2)=.27, p =.763). Table 5.1 Group Characteristics of the ADHD and TD Group ADHD (N=63) TD (N=62) ADHD v TD Percentage boys ( N ) 68.3( 43 ) 58.1( 36 ) χ 2 =1.40 M SD M SD Age (years) 10.49 1.24 10.23 1.32 t =-1.1 Estimated IQ 106.09 12.81 97.68 13.82 t =3.51** DBD parents Inattention 17.46 4.40 3.82 2.99 U =3876** Hyperactivity/Impulsivity 13.21 5.32 3.00 2.55 t =-13.64** ODD 7.21 4.28 CD 1.68 2.43 DBD teacher Inattention 16.40 4.88 Hyperactivity/Impulsivity 11.89 6.91 ODD 4.92 4.82 CD 1.14 2.24 DISC parents Inattention 7.83 1.16 Hyperactivity/Impulsivity 6.22 2.40 ODD 2.95 2.29 CD 0.46 1.08 Note . ADHD Attention-deficit hyperactivity disorder; TD Typically developing controls; DBD Disruptive Behavior Disorder rating scale; DISC Diagnostic Interview Schedule for Children, ODD Oppositional defiant disorder; CD Conduct disorder; U = Mann-Whitney U-test statistic **p<.01