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Recent discussions in the literature, along with the revision of the Diagnostic and Statistical Manual (DSM) (American Psychiatric Association 2013), suggest aetiological commonalities between the highly comorbid Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD). Addressing this discussion requires studying these disorders together by comparing constructs typical to each of them. In the present study, we investigate global processing, known to be difficult for participants with ASD, and Intra-Subject Variability (ISV), known to be consistently increased in participants with ADHD, in groups, aged 10–13 years, with ADHD (n = 25), ASD without comorbid ADHD (ASD-) (n = 13) and ASD with ADHD (ASD+) (n = 18) in comparison with a typically developing group (n = 22). A Copying task, typically requiring global processing and in this case particularly designed using equally complex stimuli to also measure ISV across trials, was selected. Oculomotor measures in this task proved to be particularly sensitive to group differences. While increased ISV was not observed in the present task in participants with ADHD, both ASD groups looked longer on the figure to be drawn, indicating that global processing takes longer in ASD. However, the ASD+ group fixated on the figure only between drawing movements, whereas the ASD- group did this throughout the drawing process. The present study provides evidence towards ASD and ADHD being separate, not-overlapping, disorders. Since the pure ASD- group was affected more by central coherence problems than the ASD+ group, it may suggest that neuropsychological constructs interact differently in different clinical groups and sub-groups. [ABSTRACT FROM AUTHOR]

Background: Endophenotypes are intermediate variables in the hypothetical causal chain from observed behavior of a clinical disorder to its underlying genotype. Recent literature trends point to the potential etiological overlap between Attention Deficit Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD). The present study aims to systematically compare these groups, by studying the potential endophenotypes of ASD (local-global processing; social cueing) and ADHD (Intra-Subject Variability (ISV)) in tandem. Methods: Three tasks, namely visual search, copying down and gaze cueing were administered to directly examine ASD- (ASD without co-morbid ADHD), ADHD and ASD+ (ASD with co-morbid ADHD) groups, in comparison to a typically developing (TD) group (N=100). Step-by-step process analysis and scan-path models were employed to analyze the oculomotor and behavioural data collected. Results: Results from the visual search task show that groups with ADHD symptoms (ADHD and ASD+) have increased intra-subject variability, whereas only the ASD- group showed signs of superior performance. Fixation durations during the copying down task can differentiate ASD- and ADHD groups on the strategies used. The gaze cueing task, shows the ASD+ group to use different strategies as compared to TD, and have slower and more variable saccadic RTs as compared to ADHD and ASD-. Conclusion: The present study gives evidence for a double dissociation between ADHD and ASD when no comorbid symptoms are present, on paradigms of local-global processing and social cueing. Oculomotor paradigms and analysis have successfully teased apart this interaction in the present study and can aid greatly in the quest for these endophenotypes. [ABSTRACT FROM AUTHOR]

• This oculomotor study examined social cueing, and intra-subject variability (ISV) in TD, ADHD, ASD- (without ADHD) and ASD+ (with ADHD) groups. • The ASD- group could follow social cues, indicating that social cueing is intact in the 'pure' ASD group when task expectations are clear. • The ADHD group showed faster saccadic reaction times and a pattern of viewing comparable to the TD group, although no ISV was observed in this task. • The ASD + group showed a different processing style for social cueing and ISV as compared to the TD and other clinical groups. • A secondary analysis gives evidence of non-additive effects of the ASD and ADHD factors, making it imperative to look for better models to explain the comorbid ASD + group. Recent trends in literature, along with the changes to the Diagnostic and Statistical Manual (DSM), make it imperative to study Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) together, in order to better understand potential aetiological commonalities between these highly comorbid disorders. The present study examines social cueing, a highly studied construct in ASD, and intra-subject variability (ISV), a potential endophenotype of ADHD, in four groups of typically developing (TD), ADHD, ASD- (ASD without ADHD), ASD+ (ASD with ADHD) participants (N = 85) aged 10–13 years. Results showed that social cueing is intact in the 'pure' ASD group when task expectations are clear. The ADHD group showed faster saccadic reaction times, no increased ISV and a pattern of viewing comparable to the TD group. However, the ASD + group showed a differences in processing style and ISV. A secondary analysis gives evidence of non-additive effects of the ASD and ADHD factors. [ABSTRACT FROM AUTHOR]