This study probed set-shifting abilities in high-functioning children with ASD by assessing both stage completion and errors on the ID/ED shift test. Consistent with previous reports, children with ASD completed as many stages as TD children; however, children with ASD made significantly more errors than TD children during the ED reversal stage.We did not observe group differences in the number of errors made during the ED shift stage. We also examined errors within a large subset of children who at least attempted all nine stages. This subset analysis was consistent with the full sample analysis in that children with ASD made significantly more errors during the ED reversal stage than did TD controls. Correlation analyses revealed a significant positive relationship between restricted interest/repetitive behavior symptoms on the ADI/ADI–R and errors completed during ED reversal shifting, but not during ED shifting.
The current investigation not only documents ED reversal shifting deficits but also, for the first time, links these deficits with restricted interest/repetitive behavior symptoms among high-functioning children with ASD. Our finding of an ED reversal shifting deficit for high-functioning children in the full and subset analyses supports the two previous studies which have reported on ED reversal shifting in ASD. The present study extends findings from a study of low-functioning children with ASDs (Hughes et al., 1994
) and a study including a combined group of children and adults with high-functioning ASDs (Ozonoff et al., 2004
). Our findings are consistent with, and expand on, previous investigations of high-functioning primary school age children with ASD, which reported intact ED shifting but did not report on ED reversal shift performance.
ED reversal involves reversing a valence assignment, switching the reward value from positive to negative for a stimulus, and the orbitofrontal cortex plays a key role in stimulus–reward assignments (Loveland et al., 2008
). Associating a stimulus and reward within a social interaction (i.e. reward is meted out by a person) is impaired in young children with ASDs (Dawson et al., 2002
). Loveland and colleagues reduced the level of social demands and still reported reversal deficits in primary school aged children (Loveland et al., 2008
). The present findings extend this line of investigation by demonstrating ED reversal deficits in a computerized task that has no social demands, suggesting that the orbitofrontal-limbic network may also underlie non-social reversal learning deficits.
The correlation between ED reversal errors and restricted interest/repetitive behavior symptoms highlights the utility of reversal set-shifting as a potential intermediate phenotype for ASDs. As discussed above, intermediate cognitive phenotypes serve as a link between behavioral symptoms and brain and genetic assays. In line with past studies, the present findings confirm the relationship between set-shifting difficulties and restricted interest/repetitive behavior symptoms in children with ASDs (Kenworthy et al., 2008; Lopez et al., 2005
; South et al., 2007
). Further investigation of ED reversal shifts might include other groups of children with developmental disorders, however, in order to determine the specificity of these findings to ASDs alone. In addition, it would be important to investigate whether this relationship occurs across all ages and functioning levels of individuals with ASDs. Previous studies investigating ED reversal shifts did not investigate the relationship between ED reversal shifting performance and ASD symptoms (Hughes et al., 1994
; Ozonoff et al., 2004
One puzzling aspect of the current findings is the relatively unimpaired ED shifting but deficient ED reversal shifting in our high-functioning ASD group. Past studies of individuals with ASDs of similar ages and functioning levels also report successful ED shifting (Edgin and Pennington, 2005
; Goldberg et al., 2005
; Happé et al., 2006
; Landa and Goldberg, 2005
), but the one study probing ED reversal shifting found deficits in both ED shifting and ED reversal shifting (Ozonoff et al., 2004
). Two potential interacting confounds may explain this apparent discrepancy of findings: (1) the inclusion of a substitution score of 25 errors for stages not attempted, and (2) the age groups tested in previous studies. The substitution score inflates variance and this may obscure group differences of modest effect size in the ED shift stage. Studies reporting no ED shifting deficits for ASD groups tested mostly primary school aged samples. Primary school aged samples may require a higher number of substitution scores for both ASD and TD groups during the ED shift stage than an older, particularly TD, sample. This discrepancy in the utilization of substitution scores may lead to reduced variability in the older sample which increases the power to detect differences of moderate effect size.
While the present study provides novel insights into the set-shifting abilities of high-functioning children with ASDs, several unanswered questions remain for future investigations. Examination of the relationship between these deficits and restricted interest/repetitive behavior symptoms was coarse due to utilization of a summary score (i.e. the restricted interest/repetitive behavior symptoms scale from the ADI/ADI–R), and would be better investigated using a continuous measure, such as the Social Responsiveness Scale (Constantino and Gruber, 2005
). Future investigations of ED reversal shift deficits may also elect to segregate this behavioral symptom construct and probe whether ED reversal shifting deficits relate to higher-order cognitive rigidity, reflected in resistance to change, insistence on sameness, and rituals, or to lower-order repetitive and sensory behaviors, reflected in stereotypies and self-stimulation. Additionally, the high average IQ of our ASD group may limit generalizing the current results to lower-functioning children with ASDs.
Strengths of the study include the large, well-characterized ASD sample within a narrow age range, which provided adequate power to detect group differences and significant correlations. Children with ASDs were well matched group-wise (with a two-to-one ratio) for age, IQ, and gender ratio; this matching was sustained on the subset analysis. The current investigation also presents ID/ED data on the largest exclusively pediatric ASD sample published to date (n
= 42), which allowed matching the ASD and TD groups on performance. While the correlation analysis was conducted on a subset of the total sample (n
= 27), raising issues of power or sample stability, this sample size was equal to or larger than full samples reported earlier (Edgin and Pennington, 2005
; Goldberg et al., 2005
; Landa and Goldberg, 2005
). Furthermore, the significant correlation observed between the number of ED reversal shift errors and restricted interest/repetitive behavior symptoms was robust and immune to the influence of outliers because we used non-parametric (Spearman’s rho) correlations. Thus, we avoided limitations of previous investigations by recruiting a large group of high-functioning children with ASDs over a narrow age range when dynamic developmental gains in set-shifting skills are observed (Luciana and Nelson, 2002
), and by examining group differences in performance on both the ED shift and ED reversal shift tasks.
The present study documents inefficient ED reversal shifting among high-functioning children with ASDs, and reinforces the utility of the ID/ED test in parsing specific components of set-shifting difficulty among individuals with ASD. Furthermore, the current investigation establishes a link between ED reversal shifting and restricted interest/repetitive behavior symptoms used to diagnose ASDs. This finding strengthens the case for utilizing set-shifting as a potential intermediate phenotype for informing gene–brain–behavior models of ASDs.