Working memory deficits in children: Contributions of executive control processes and symptoms of ADHD

The most empirically supported model of working memory contains four components: (a) the phonological loop, (b) the visuospatial sketchpad, (c) the episodic buffer, and (d) the central executive (Baddeley & Hitch, 1974; Baddeley, 2003). The central executive has been fractionated into four subprocesses: (a) sustained attention, (b) selective attention/inhibition (c) shifting attention, and (d) control of retrieval from long-term memory (Baddeley, 2003; Mirsky et al., 1991; Zoelch et al., 2005). Children with ADHD are known to have working memory deficits, though the role of each component of the working memory system in these deficits is not known. The purpose of the current study is to examine the relationships between (a) symptoms of ADHD and working memory performance, (b) central executive processes and working memory performance, and (c) the unique contributions of each fractionated central executive process to the relationship between symptoms of ADHD and working memory performance. Eighty-five children ages 8 to 16 from an outpatient clinical database were included in the study sample. Sustained attention was found to contribute unique variance to working memory performance after controlling for short-term memory. Selective attention/inhibition, shifting attention, and control of retrieval from long-term memory did not contribute unique variance to working memory, though limited power may have affected results. ADHD symptoms did not correlate with working memory, but they did correlate with short-term memory. Sustained attention was then examined as a mediator between ADHD hyperactivity symptoms and short-term memory. Though not a significant mediator, results of mediation procedures appear to indicate partial mediation. Results indicate that sustained attention may be a fractionated process of the central executive. They also suggest that ADHD symptoms may interfere with working memory at the short-term memory and executive levels. Further investigation is suggested to explain relationships between executive processes and working memory performance and between symptoms of ADHD and all components of the working memory system.