Open Access

Sara Boxhoorn, Nico Bast, Hans Supèr, Leonie Polzer, Hannah Cholemkery, Christine M. Freitag

• Background: Previous research demonstrated atypical attention in children with attention‐deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Regarding visual orienting, findings suggest a differential impairment: Atypical orienting to relatively unexpected targets in ASD, and atypical processing of alerting cues in ADHD. The locus coeruleus‐norepinephrine (LC‐NE) system plays an important role in exploiting alerting cues to increase attention and task performance. The present study’s aim was to examine differential subcortical processes underlying visual orienting in ASD and ADHD with pupil dilation (PD) as index of LC activity. Methods: Pupil dilation (PD) progression metrics during visual orienting were calculated for task‐evoked PD locked to cue, stimulus onset, and behavioral response. Group differences in PD and reaction time (RT) were compared between children with ASD without ADHD (ASD‐) (N = 18), ADHD without ASD (ADHD‐) (N = 28), both disorders (ASD + ADHD) (N = 14), and typically developing children (TD) (N = 31) using linear mixed models (LMM). To further explore the modulatory role of the LC‐NE system group differences in the effect of task‐evoked PD metrics on RT were examined exploratively. Results: ASD (+ADHD) showed slower orienting responses to relatively unexpected spatial target stimuli as compared to TD, which was accompanied by higher PD amplitudes relative to ADHD− and TD. In ADHD−, shorter cue‐evoked PD latencies relative to ASD−, ASD + ADHD, and TD were found. Group differences in the effect of cue‐ and stimulus‐evoked PD amplitudes on RT were found in ASD− relative to TD. Conclusions: Study findings provide new evidence for a specific role of the LC‐NE system in impaired reflexive orienting responses in ASD, and atypical visual processing of alerting cues in ADHD.