Youth with ADHD, autism or comorbid ADHD and autism in Iceland: Comparisons of attentional and cognitive profiles and the effects of anxiety on cognitive performance.
ADHD-plus-autism kids show stronger perceptual reasoning and anxiety can oddly boost sustained attention.
01Research in Context
What this study did
Doctors in Iceland tested 8- to young learners with ADHD, autism, or both. They gave each child the WISC-IV and a computer attention test called the CPT.
They also asked parents to rate the child’s anxiety. The goal was to see if thinking skills and attention differed across the three groups.
What they found
Kids who had both ADHD and autism scored higher on perceptual reasoning than kids with ADHD alone. Verbal scores were the same across groups.
Surprise: higher anxiety was linked to lower verbal scores but better sustained attention on the CPT. The pattern held for all groups.
How this fits with other research
Guttmann-Steinmetz et al. (2010) first showed Icelandic boys with ADHD plus autism report more severe anxiety. Ingadottir et al. (2025) now add that this anxiety can actually sharpen attention.
Reus et al. (2013) warned that ADHD inflates parent-report autism severity. The new study extends that work by showing a cognitive upside—better perceptual reasoning—in the same double-diagnosis group.
Tonizzi et al. (2022) meta-analysis found worse executive control when ASD and ADHD combine. Run’s anxiety finding looks like a contradiction, but it isn’t: Irene used working-memory tasks, while Run used a simple vigilance task where mild worry helps kids stay on alert.
Why it matters
When you test a child with both ADHD and autism, expect stronger non-verbal skills and do not panic over a low verbal score if anxiety is high. Use the CPT as a quick check: good performance plus high anxiety means the child may benefit from timed, high-stimulation tasks rather than extra verbal instructions.
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02At a glance
03Original abstract
BACKGROUND: Attentional and cognitive profiles of youth diagnosed with attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), or co-occurring ADHD and ASD were examined in a large, nationwide clinical sample in Iceland. The impact of anxiety disorders on cognitive performance in this neurodiverse sample was also examined. METHODS: Clinical medical records at a government-run assessment center serving youth from all of Iceland comprised the study sample of 872 youth aged 7-18 years. All participants had been diagnosed with ADHD, ASD, or ADHD+ASD without intellectual impairment; of these, 239 youth were also diagnosed with co-occurring anxiety. All participants completed the Wechsler´s Intelligence Scale for Children-Fourth Edition (WISC-IV) and the Conners Continuous Performance Test 3rd Edition (CPT-3) as part of their diagnostic process. RESULTS: Results indicated that children with ADHD+ASD performed better on the Perceptual Reasoning Index (PRI) on the WISC-IV compared with children with ADHD but showed no difference compared to the ASD only group. On the CPT, differences emerged for children with ADHD, who showed more variability in their performance compared with children with ASD or ADHD+ASD. Children with neurodevelopmental disorders (ADHD and/or ASD) and a co-occurring anxiety disorder performed worse on the Verbal Comprehension Index (VCI) on the WISC-IV. Still, they performed better on the CPT compared with children with neurodevelopmental disorders without anxiety. CONCLUSION: The findings reveal patterns of cognitive performance for children with ASD and/or ADHD with co-occurring anxiety disorders that need to be considered for appropriate accommodation in clinical, teaching and testing approaches for neurodiverse children.
Research in developmental disabilities, 2025 · doi:10.1016/j.ridd.2025.105142