Archival Report
Memory for Action Rules and Reaction Time Variability in Attention-Deficit/Hyperactivity Disorder

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Background

Patients with attention-deficit/hyperactivity disorder (ADHD) exhibit increased reaction time (RT) variability. This finding is consistent across various choice RT tasks and is considered a core ADHD phenotype, often interpreted as expressing occasional attention lapses. This study explores the selective contribution of perceptual and working memory (WM) processes to increased RT variability in ADHD.

Methods

Low and high WM demands were manipulated in a battery of choice RT tasks administered to two groups of college students (subjects with ADHD vs. healthy control subjects).

Results

Ex-Gaussian distribution fitting revealed an increased rate of exceptionally slow RTs (i.e., higher τ values) in subjects with ADHD under all conditions. These group differences interacted with WM demands, showing the largest group differences when WM processing was most demanding (ηp2 = .32). Under demanding WM conditions, evidence accumulation modeling demonstrated that increased RT variability in ADHD is not associated with either momentary or constant deficits in perceptual processing of the target. Rather, results favored a model associating increased RT variability in ADHD with reduced rate of WM retrieval.

Conclusions

These results suggest a pivotal contribution for the retrieval of action rules from WM to increased RT variability in ADHD.

Section snippets

Participants

Participants were 56 college students (Table 1), either with ADHD or with no clinical disorder. Participants with ADHD were asked to provide a history of ADHD diagnosis performed by a clinical psychologist or psychiatrist. The diagnosis was confirmed with a structured clinical interview for DSM-IV, including confirmation of the diagnosis with collateral contact when available. Participants completed a computerized version of the Conners’ Adult ADHD Rating Scales (58) to measure symptom severity,

Choice Task Performance

Ex-Gaussian parameters were estimated for each participant, at each condition. Repeated measures analyses of variance were performed separately for each ex-Gaussian parameter (µ, σ, τ) as dependent variables, with mapping (arbitrary or nonarbitrary), set size (two-choice or six-choice), task type (letters, digits, or shapes), and group (ADHD vs. HC) as independent variables (Figure 3; Supplement 1).

Discussion

The present study sought to explore the distinct contributions of perceptual processing and WM retrieval processes to increased RT variability in ADHD. Two groups of college undergraduates (subjects with ADHD vs. HC subjects) performed a battery of choice RT tasks under low and high WM load conditions. WM load was manipulated by means of set size (two-choice vs. six-choice) and mapping (arbitrary vs. nonarbitrary), with WM demands assumed to increase with the number of arbitrary rules.

Acknowledgments and Disclosures

This work was supported by the Israel Science Foundation Grant No. 1939/12 (to NM) and Fulbright Scholar Program (to ART).

We thank Gal Eblagon, Danielle Dotan, Ayala Barak, Sonia Rogachev, Shir Bekhor, and Eyal Eilat for their help in running the experiments.

The authors report no biomedical financial interests or potential conflicts of interest.

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