Executive functions in Asperger's disorder: An empirical investigation of verbal and nonverbal skills

Researchers have investigated the specific strengths and weaknesses of individuals with Asperger's Disorder (AD). One construct used in this effort is Executive Functioning (EF). Whereas research has shown that this population performs more poorly than typically-developing matched controls on many EF tasks, there is a lack of consistency in these results. This is likely due to the use of inconsistent diagnostic criteria leading to incomparable studies. The present study investigated EF in AD using a bottom-up method whereby several EF tasks were administered to 33 adolescents with AD and 33 age- and gender-matched controls. Two-step cluster analysis was then used to derive subgroups. Diagnostic composition of these subgroups was examined to provide empirical evidence of a performance bias towards verbal EF for the AD group. Based on research demonstrating differential performance of modality on measures of cognitive intelligence and executive functioning, it was expected that a subgroup demonstrating high verbal and low non-verbal EF performance would be derived and that the majority of participants with AD would fall within this group. Results indicated that a two cluster solution best fit the data with 73% of the AD participants being classified into one cluster and 64% of the control participants classified into another. Investigation of the performance characteristics of the participants in cluster 1 indicated that assignment into this cluster was based primarily upon poor performance on the four visual EF tasks whereas assignment into cluster 2 was based primarily upon good performance on the four visual EF tasks and one verbal EF task. Further analysis of the data indicated that only two EF tasks demonstrated significant specificity, leading to the conclusion that these EF tasks are not adequate for diagnostic assessment of AD by themselves although they can provide insight into the current EF abilities of individuals with AD.