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Abstract
Both cognitive and motivational deficits are thought to give rise to the problems in the combined (ADHD-C) and inattentive subtype (ADHD-I) of attention-deficit hyperactivity disorder (ADHD). In both subtypes one of the most prominent cognitive weaknesses appears to be in visuospatial working memory (WM), which is composed of short-term memory (STM) and a central executive (CE). In children with ADHD-C, both STM and the CE seem impaired, and together with motivational impairments, give rise to their deficits in visuospatial WM. In children with ADHD-I, no studies investigated these WM components and their interplay with motivational impairments. Effects of a standard (feedback only) and a high level of reinforcement (feedback + 10 euros) on visuospatial WM-, STM-, and CE performance were examined in 27 children with ADHD-I (restrictive-subtype), 70 children with ADHD-C, and 40 typically developing controls (aged 9–12). In both ADHD-subtypes CE and WM performance was worse than in controls. STM performance of children with ADHD-I was, in contrast to that of children with ADHD-C, not different from controls. STM and WM performance was worse in ADHD-C than in ADHD-I, whereas CE-related performance did not differ. High reinforcement improved STM and WM performance in both subtypes but not in controls. This improvement was equally pronounced in both subtypes. High reinforcement did not improve CE-related performance. Both subtypes have equally pronounced motivational deficits, which have detrimental effects on their visuospatial STM and WM performance. In contrast to children with ADHD-C, children with ADHD-I seem unimpaired on visuospatial STM; only an impaired CE and motivational impairments give rise to their deficits in visuospatial WM.
Notes
1For comparison, 50% of the studies that were examined in Willcutt et al. (Citation2012) found a difference between ADHD-C and controls on short-term memory, and 80% found a difference on working memory.
2Meta-analytic findings suggest that children with ADHD show much more impairment on tasks that measure visuospatial working memory or short-term memory than on tasks measuring phonological working memory or short-term memory (Martinussen et al., Citation2005; Nigg, Citation2006; Willcutt et al., Citation2005). Therefore, in this study we focus on visuospatial working memory and its components.
3Operationalizing central executive performance by using the difference between working memory performance and short-term memory performance is based upon the theorem of Engle, Tuholski, Laughlin, and Conway (Citation1999)—which is consistent with other influential working memory models like those of Cowan (Citation1995) and Baddeley and Hitch (Citation1974)—that the working memory system consists of the contents of short-term memory plus the central executive. According to Engle et al., “working memory capacity = short-term memory capacity + central executive + the error of measurement” (p. 313).
4CD was excluded because it seems independently associated with motivational impairment (possibly caused by different underlying processes than in ADHD; Rubia et al., Citation2009).
5This relative difference between the ADHD groups in medication use was significant, χ2(1) = 11.168, p = .001. However, including medication use as a covariate in analyses where the ADHD groups were compared did not change the results.
6Orders of presentation used in counterbalancing:
7CE FO = STM FO – WM FO; CE 10 euros = STM 10 euros – WM 10 euros (CE = central executive performance, WM = mean score on working memory task; STM = mean score on short-term memory task; FO = feedback-only condition; 10 euros = 10 euros condition).
8With covarying for ODD and CD, the pattern of the results was the same. Further, these covariables did not significantly interact with task version, and only parent-rated CD interacted significantly with reinforcement condition, F(1, 91) = 5.23, p = .025, . Covarying for IQ or Inattention also did not change the pattern of the results.
9Covarying did not change the pattern of the results.
10Here we assume that the TD group was highly motivated in both reinforcement conditions, whereas the ADHD groups were highly motivated only in the 10 euros condition. This assumption is substantiated by participants' reports: After both reinforcement conditions were administered, children were asked what they thought of the task with FO and of the task with 10 euros. In line with our assumption, children in both ADHD groups were less positive about the task in the FO condition (40% reported that the FO task was fun) than about the task in 10 euros condition (80% reported that the 10 euros task was fun), whereas TD children were positive about the tasks in both reinforcement conditions (72.5% reported that the FO task was fun, and 80% reported that the 10 euros task was fun; for more details, see Appendix B).