Executive Functions In Asperger's Syndrome: Evidence for a Modality Bias

Background: Investigations of deficits in executive functions (EF) in individuals with Asperger's syndrome (AS) have yielded mixed results.  A possible reason for this inconsistency may be the use of specific, often single, EF tasks, an approach that does not provide a structure by which commonalities in performance among tasks can be examined.  As well, much of the past research has utilized a heterogeneous sample comprised of individuals with AS and High-Functioning Autism, leading to potentially unrepresentative findings for AS specifically.

Objectives:  To understand the nature of executive functions in adolescents and young adults with AS.  Specifically, to determine if a modality bias exists.

Methods:  Seven subtests of the Delis-Kaplan Executive Function System (DKEFS) were administered to 33 individuals with AS and 33 age-and gender-matched controls (M = 18.85 years, SD = 1.56; 78.8% male).  Three of these tasks are verbally-mediated while four are nonverbally-mediated.

Results:  Initial exploratory factor analysis yielded a two-factor solution, with verbally-mediated EF tasks classified into one factor and nonverbally-mediated tasks classified into another.  Cluster analysis yielded a two cluster solution, with 78% of AS participants classified into Cluster A and 67% of control participants classified into Cluster B.  Investigation of the performance characteristics indicated that assignment into Cluster A was made predominantly on the basis of poor performance on the nonverbally-mediated EF tasks whereas assignment into Cluster B was done on the basis of good performance on the nonverbal tasks. 

Conclusions:  This study provides initial evidence supporting the notion that modality of EF should be further examined in AS.  Specifically, the majority of EF tasks previously used in research are nonverbally-mediated, resulting in findings that are potentially unrepresentative of EF abilities in this population.  Individuals with AS in this study demonstrated a deficit in nonverbally-mediated EF tasks, but not in verbally-mediated tasks.  This finding provides clarification to the research literature and a structure by which to better understand EF in this population.