The study compared the attention-deficit/hyperactivity disorder (ADHD) related clinical symptoms and a wide-ranging attention performance in 216 youths with autistic disorder (autism), 138 youths with Asperger's disorder (AD) and 255 typically-developing youths. The diagnosis of autism and AD were made based on the clinical assessments according to the DSM-IV criteria and confirmed by the Autism Diagnostic Interview-Revised. All the participants were assessed with the Conners’ Continuous Performance Test (CCPT) and the questionnaires about ADHD, oppositional, and autistic symptoms. All indices of the CCPT were analyzed based on a recently developed factor structure, including focused attention, cognitive impulsivity, sustained attention, and vigilance. We found that compared with typically-developing youths, youths with autism and AD showed more inattentive, hyperactive/impulsive, and oppositional symptoms, and performed worse in focused attention and sustained attention as assessed by the CCPT. Youths with AD also showed more oppositional symptoms than youths with autism. Moreover, youths with autism had poorer focused attention than youths with AD; but, youths with AD had more impaired sustained attention. Our results validate different manifestations of ADHD-related symptoms and attention performance between youths with autism and youths with AD and suggest intervention for youths with autism spectrum disorders should consider these specific measures.
Autism spectrum disorders (ASDs), characterized by different degree of impaired social interaction, communication deficits, and restricted interests, are a group of complex neurodevelopmental disorders that include autistic disorder (autism), Asperger's disorder (AD), and pervasive developmental disorder not otherwise specified (American Psychiatric Association, 1994). Beyond the core symptoms, attention difficulties and hyperactive behaviors are frequently reported in some individuals with ASD (Wing, 1997). It has been theorized that impairments in attention may underlie some of the primary neuropathological functions in autism (Cornblatt and Malhotra, 2001 and Courchesne et al., 1989), based on various experiments (e.g., Garretson et al., 1990 and Pascualvaca et al., 1998).
Early investigation by Gillberg (1989) showed that 21% of the ASD youths met the diagnostic criteria of both ADHD and ASD. This early observation was supported by studies based on either structured psychiatric interview (Ghaziuddin, Weidmer-Mikhail, & Ghaziuddin, 1998), or questionnaires (e.g., Fombonne, Simmons, Ford, Meltzer, & Goodman, 2001), showing that a substantial proportion (29–83%) of individuals with ASD have ADHD symptoms. Recent work (sample sizes ranging from 27 to 483) documented that about half (52–78%) of the ASD population also met the diagnostic criteria for ADHD (e.g., Lee and Ousley, 2006, Sinzig et al., 2009 and Yoshida and Uchiyama, 2004), despite exclusion of comorbid diagnoses in the DSM-IV-TR. These ADHD symptoms in children with ASD may persist into adolescence (Lee & Ousley, 2006), correlate with autistic symptoms (Sinzig et al., 2009), and may exacerbate executive dysfunction, impaired verbal working memory, and maladaptive behaviors (Murray, 2010), resulting in more severe autistic traits, and externalizing symptoms (Yerys et al., 2009). Despite the high co-occurrence of ADHD and ASD and its impact, few studies have investigated the differential severity of ADHD symptoms between different ASD subtypes (Thede & Coolidge, 2007). In addition, higher prevalence of oppositional defiant disorder, up to 27%, was also noted in children with ASD than typically-developing (TD) children (Gadow et al., 2004 and Gadow et al., 2005). Yet, the severity of oppositional symptoms between children with autism and those with AD were controversial (Thede and Coolidge, 2007 and Tonge et al., 1999).
Several studies have linked executive function (EF) deficits to ASD with probably different EF patterns between autism and AD. For example, individuals with AD, but not those with autism, had an impaired set-shifting performance (Ozonoff, South, & Miller, 2000), while deficits in response inhibition were found in individuals with high-functioning autism (HFA) but not in individuals with AD (Rinehart, Bradshaw, Brereton, & Tonge, 2002). Other studies, however, did not show such EF deficits either in autism or AD (e.g., Thede & Coolidge, 2007). Whether a more fundamental neurocognitive function, attention performance, differs between autism and AD is largely unknown. Although earlier studies (n = 10–23) have shown impaired attention as assessed by one or two indices of the Continuous Performance Test (CPT) in autism (e.g., Garretson et al., 1990 and Pascualvaca et al., 1998), no study has compared the CPT performance between autism and AD.
Previous studies of attention research in ASD have mainly recruited Caucasian but not Asian populations. Moreover, the evidence to differentiate autism from AD is lacking with regards to ADHD-related symptoms and a wide range of attention performance (Thede & Coolidge, 2007). Hence, we conducted this study to compare the severity of inattentive, hyperactive/impulsive, and oppositional symptoms, and the attention profiles (focused attention, cognitive impulsivity, sustained attention, and vigilance) as assessed by the Conners’ CPT (CCPT) among youths with autism, youths with AD, and TD youths and to examine the correlations between the CCPT performance and autistic and ADHD symptoms among ethnic Chinese youths with ASD in Taiwan.
We hypothesized that youths with ASD may have more ADHD-related symptoms and deficits in several attention dimensions than TD youths but the patterns of attention deficits may not be the same between youths with autism and youths with AD, and may not be compatible with the findings documented in ADHD, in terms of attention profiles as well as the correlations with ADHD and ASD symptoms.
