This review discusses whether deficient inhibitory motor control is the core deficit of attention-deficit/hyperactivity disorder (ADHD). Inhibitory motor control is commonly assessed using the stop-signal paradigm. Since the last meta-analysis that was performed, 33 new studies have appeared. The current meta-analysis revealed a significant difference between ADHD patients and matched controls in stop latency (stop-signal reaction time) in both children and adults. Basic reaction time was significantly longer in children with ADHD, but not in adults, and there was a significant interaction between the elongation of the latency to stop and to respond in adults, but not in children. Deficient inhibitory motor control may be less crucial in children than in adults with ADHD.

Previous reviews and meta-analyses that addressed abnormal Stroop interference in attention-deficit/ hyperactivity disorder (ADHD) yielded mixed results. The authors of the present study argue that the inconsistencies may reflect the problematic nature of 2 frequently used methods to quantify Stroop interference-the difference score and Golden's method (C. J. Golden, 1978). Golden's method correction for base-word reading is inadequate, and the difference score is sensitive to the nature of the outcome variable. The latter can be remedied with a ratio score. Contrasting previous meta-analyses, this meta-analysis covers all age groups and all Stroop test variants, and it excludes studies using the Golden quantification method. Mean effect sizes for interference in ADHD as quantified by difference scores relative to control scores were 0.24 across all studies but 1.11 for time-per-item studies; outcome variable was a significant moderator variable, reflecting the sensitivity of the difference score to this variable. Consistency analysis of ratio scores across 19 studies reveals more interference for the ADHD groups relative to the control groups. It is concluded that interference control is consistently compromised in individuals with ADHD.Keywords: meta-analysis, Stroop interference, attention-deficit/hyperactivity disorder, Stroop color and word task Attention-deficit/hyperactivity disorder (ADHD) is defined by inappropriate degrees of inattention, hyperactivity, and impulsivity. Barkley (1997) suggested that behavioral disinhibition is the primary deficit in ADHD (predominantly hyperactive-impulsive type and combined type) and distinguished three interrelated forms of behavioral inhibition. The first form is inhibition of an initial prepotent response to an event, that is, a response for which immediate reinforcement is available or with which reinforcement has been previously associated. The second form is stopping an ongoing response or response pattern. This causes a delay in the decision to respond or to continue responding. The third form is interference control, defined as protecting the period of delay and self-directed responses that occur within it from disruption by competing events and responses.Continuous performance tests (CPTs) and stop-signal tasks can be used to assess both inhibition of prepotent responses and stopping of ongoing responses. Several reviews and meta-analyses (Corkum & Siegel, 1993;Lijffijt, Kenemans, Verbaten, & van Engeland, 2005;Losier, McGrath, & Klein, 1996;Oosterlaan, Logan, & Sergeant, 1998;Riccio, Reynolds, & Lowe, 2001) demonstrated that individuals with ADHD perform worse on a CPT and stop-signal task as compared with normal control participants, reflecting poor response inhibition in ADHD patients. The Stroop test (Stroop, 1935) can be used to quantify interference control. Inconsistent findings have been reported regarding deficient interference control in ADHD. Stroop Test and ADHDThree versions of the Stroop test have been used in ADHD research: the standard Stroop ...

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