Do EF Deficits Ameliorate with Age in Individuals High Functioning Autism? Examining Cognitive Flexibility, Planning, and Working Memory Across Childhood and Adolescence

Background:  Deficits in Executive Functioning (EF) are notable features in Autism Spectrum Disorder. While, cognitive flexibility and planning have been found to be consistently impaired, the results regarding working memory have been mixed. Few studies have examined age-related performances on EF. Some of the recent studies have reported improvements with age on EF tasks for ASD (Happe, Booth, Charlton, and Hughes, 2006; McGovern & Sigman, 2005; Howlin, Mawhood, & Rutter, 2000).

Objectives:  The study aimed to (1) Examine Cognitive Flexibility, Planning, and Working Memory in individuals with HFA in comparison to typical controls (2) Investigate whether there are any age related improvements in EF.

Methods:  In this study, children with High Functioning Autism (N=28) aged 8-16 years were compared with age and IQ matched typically developing controls (N=28) on a battery of EF tests. The Number-Letter Switching test and the Tower Test of the Delis-Kaplan Executive Function System (D-KEFS) was used as a measure of cognitive flexibility and Planning Ability respectively. The digit span backward test of WISC-IV was used to assess the working memory of the participants.

Results:  A two-way ANOVA (group by age) analysis for the completion time for trail making test (Cognitive Flexibility), total correct for digit span backward task (Working Memory) and total achievement score for the Tower test (Planning) were conducted. All three variables showed significant group and age effects. Interaction of group and age were non-significant for all three tests. Post hoc comparisons showed that in comparison to the TD group, significant differences were found in performances on the cognitive flexibility and planning tests but not on the test of Working Memory, which was found deficit in younger, but not in older children with HFA. Older performed better than the younger subgroups on the Trail Making Test for the HFA group indicating improved cognitive flexibility. Performance on the digit span test fell just short of significance for the HFA group.

Conclusions:  Consistent with the Executive Dysfunction theory of ASD, impairments in EF in have been found. However, the findings are contradictory to the reports that profound and generalized impairments in Executive functioning are present throughout development in ASD. While all three EF domains: cognitive flexibility, working memory, and planning were found impaired in younger children with HFA; only cognitive flexibility and planning. Older HFA children when compared with younger HFA children performed better on the cognitive flexibility test. Though significant improvement has been reported on only on the test of cognitive flexibility findings present an encouraging picture suggesting improvements in cognitive flexibility with age in high functioning individuals with autism. They are consistent with the more recent findings that are suggestive of improved adaptation with age in individuals with ASD. Careful comparison of the sample characteristics (gender, verbal IQ, and non-verbal IQ) the younger and older HFA groups did not indicate differential sampling between the subgroups. Future studies that are longitudinal in nature can confirm the present findings and explore the developmental trajectory of EF across different domains and different age groups of ASD.