Impaired executive functioning (EF) has been proposed to underlie symptoms of autism spectrum disorders (ASD). However, insight in the EF profile of ASD individuals is hampered due to task impurity and inconsistent findings. To elucidate these inconsistencies, we investigated the influence of task and sample characteristics on EF in ASD, with an extended test battery designed to reduce task impurity. Additionally, we studied the relation between EF and ASD symptoms. EF (inhibition, cognitive flexibility, generativity, working memory and planning) was measured in open-ended versus structured assessment situations, while controlling for possible confounding EF and non-EF variables. The performance of 50 individuals with ASD was compared with that of 50 age, gender and IQ matched typically developing (TD) individuals. The effects of group (ASD versus TD), age (children versus adolescents) and gender were examined, as well as the correlation between age, IQ, ASD symptoms and EF. Individuals with ASD showed impairments in all EF domains, but deficits were more pronounced in open-ended compared to structured settings. Group differences did not depend on gender and only occasionally on participants' age. This suggests that inconsistencies between studies largely result from differences in task characteristics and less from differences in the investigated sample features. However, age and IQ strongly correlated with EF, indicating that group differences in these factors should be controlled for when studying EF. Finally, EF correlated with both social and non-social ASD symptoms, but further research is needed to clarify the nature of this relationship.
Keywords: Age; Autism spectrum disorders; Executive functioning; Gender; IQ; Symptom severity.