Background: The objective of this study is to identify intact and deficient cognitive processes in children with attention deficit hyperactivity disorder (ADHD) and children with high functioning autism (HFA). Method: Three rigorously diagnosed groups of children aged between 6 and 12 years (54 ADHD, 41 HFA, and 41 normal controls) were tested on a wide range of tasks related to five major domains of executive functioning (EF): inhibition, visual working memory, planning, cognitive flexibility, and verbal fluency. In addition, the role of comorbid oppositional defiant disorder (ODD) and comorbid conduct disorder (CD) in ADHD was investigated by directly comparing 20 children with ADHD and 34 children with comorbid ADHD + ODD/CD. Results: ADHD was associated with EF deficits in inhibiting a prepotent response and verbal fluency. Children with HFA demonstrated deficits in all EF domains, except interference control and working memory. The HFA group showed more difficulties than the ADHD group with planning and cognitive flexibility. The comorbid ADHD + ODD/CD group did not show a distinctive pattern of performance on the EF tests compared to the ADHD group. Conclusion: The present study indicates that children with HFA exhibit more generalised and profound problems with EF tasks compared to children with ADHD.

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Overall, siblings of children with HFA are not more susceptible to adaptation problems than siblings of children without a disorder. Implications for practice and further research are discussed.

The present study was designed to investigate the hypothesis that children with Attention Deficit Hyperactivity Disorder combined subtype (ADHD-C) have a generalized executive functioning (EF) [Barkley, R. A. (1997). Behavioural inhibition, sustained attention, and executive functions: Constructing a unifying theory of AD/HD. Psychological Bulletin, 121, 65-94; Barkley, R. A. (1997). ADHD and the nature of self-control. New York: The Guilford Press]. We tested whether ADHD-C and ADHD inattentive subtype (ADHD-I) can be differentiated from each other on EF measures. We compared 16 normally developing boys with 16 boys with ADHD-C and 16 with ADHD-I on five EF domains. The boys were all matched on age, IQ, and the presence of oppositional defiant disorder (ODD)/conduct disorder (CD). Despite carefully diagnosed groups and methodological controls, the results do not support the EF-hypothesis of ADHD-C. Children with ADHD-C differed from normal controls (NC) on tasks related to inhibition; they did not exhibit EF deficits on all EF tasks. Children with ADHD-C also exhibited deficits on non-EF tasks. Furthermore, the ADHD-C and ADHD-I subtypes did not differ from one another. Neuropsychological findings on the domains under study did not yield evidence for the distinctiveness of ADHD-C and ADHD-I subtypes.

Pragmatic difficulties do occur in both HFA and ADHD. The present studies indicate that the CCC is a useful instrument to obtain information concerning pragmatic language use in both a clinical and a research setting. Although the information of parents is more tightly linked to the diagnosis, combining the information of both parent and teacher slightly improves case identification.