Verbal Memory and ADHD Symptoms in Higher Functioning School-Aged Students with ASD

Background: Studies of memory in higher functioning children with ASD (HFASD) have yielded inconsistent evidence of impairment (Luna et al. 2007; Ozonoff et al. 2009). In addition, most studies have focused on spatial memory rather than verbal memory, and many have not controlled for possible confounds of diagnostic group differences in IQ or the presence of ADHD symptoms. The latter is especially important because working memory impairments are associated with ADHD (Kofler et al. 2010; Sinzig et al. 2009) and research indicates that ADHD is comorbid with ASD at a rate of 50% or higher (Goldstein & Schwebach 2004).

Objectives: To examine whether there are verbal memory deficits specific to children with HFASD, and whether the nature of these deficits are related to individual differences in comorbid ADHD symptoms in these children

Methods: The study consisted of 144 participants (109 male; 35 female) ranging in age from 7.9 to 16.1 years (M = 11.40, SD= 2.19): 31 with HFASD, 43 HFASD + ADHD Combined, 25 with ADHD, and 40 TD.  ASD diagnosis was assessed with the ADOS-G, Connors-3 Parent Report total t-scores > 70 were used to assign children to the ADHD subgroups. The TD group had a significantly higher full-scale IQ (114.59) than the HFASD (101.91), Combined (99.16), and ADHD (99.15) groups. Verbal memory was assessed with the WRAML-2 “Story Memory” recall subtest and the “Verbal Working Memory” (WM) subtest.

Results: MANCOVA for Story Memory and Verbal WM with IQ as a covariate revealed a significant effect for Diagnostic Group, Wilks’ Λ = .75, F(6, 266) = 6.81, p < .001, h² = 0.13.  Univariate tests revealed Diagnostic Group effects for both variables: Story Memory (F(3, 134) = 7.74, p < 0.001, η2 = .15) and Verbal WM subtests, (F(3, 134) = 9.60, p < 0.001, η2 = .18). Follow-up tests for Story Memory revealed that the HFASD group and HFASD-ADHD combined group did not differ from each other but scored significantly lower than the TD group, and the combined group also scored significantly lower than the ADHD group (Bonferroni, ps < .001).  All three diagnostic groups scored lower than the TD group on Verbal WM (Bonferroni, ps< .01).

Conclusions: Our findings indicate that the HFASD group, irrespective of ADHD symptoms, was impaired on verbal WM relative to TD children. In addition, the HFASD group and HFASD-ADHD combined group did not differ on story memory but had significantly poorer story recall than the TD group, and the HFASD-ADHD Combined group was distinguished from the ADHD group by impairments in story recall.  The Story Memory task may reflect executive control in Verbal WM (Baddeley & Wison, 2002). If so, the data suggest that children with HFASD, especially those who have elevated ADHD symptoms, may be particularly vulnerable to impairments in this component of Verbal WM. Other observations in our research group suggest HFASD verbal memory impairment is not affected by anxiety symptoms, but does negatively impact academic communication development (Swain et al. 2014; Zajic et al. 2014).