ADHD Reflects Impaired Externally Directed and Enhanced Internally Directed Attention in the Immediate Free-Recall Task

摘要

Previous attempts to understand the neurocognitive mechanisms underlying attention-deficit/hyperactivity disorder (ADHD) may be limited by the tendency to focus exclusively on "externally directed cognition" (EDC) while ignoring "internally directed cognition" (IDC; Dixon, Fox, & Christoff, 2014. There is clear evidence that ADHD reflects deficiencies in EDC because of weaknesses in modulatory, motivational, and cognitive control constructs, but little is currently known about the integrity of IDC in ADHD. In the present study, we used a verbal episodic memory task involving immediate free recall to assess the integrity of EDC and IDC in a sample of 111 adolescents, 50 with study-confirmed diagnoses of ADHD and 61 without. The ADHD group was found to have significantly worse scores on outcomes that depend on EDC during encoding (serial position), and significantly better scores on outcomes that depend on IDC during retrieval (lag-conditional response probabilities). In addition, model parameters estimating the contribution of EDC and IDC processes were fit to these data using the retrieved context model of memory search. The model suggested that, during encoding, the ADHD group had slower mental context drift, indicative of weaker externally directed attention to the list items, as well as deficiencies in their ability to allocate and sustain attention when the study list first appeared. During retrieval, in contrast, the model suggested that the ADHD group had faster mental context drift indicative of stronger internally directed attention to retrieved context. These findings provide novel evidence that ADHD reflects impaired EDC and enhanced IDC, and they reinforce the clinical relevance of distinguishing EDC and IDC in future studies.