A quarterly publication of the Autism Research Institute

The Autism Research Review International is quarterly publication of the Autism Research Institute

Fall, 2021 | Number 4, Volume 35

Pupil responses to non-social stimuli: an early clue to ASD?

Infants who later develop autism spectrum disorders (ASD) show a strong “alerting” response to certain nonsocial sounds, according to a new study. 

Maja Rudling and colleagues studied 99 ten-month-old infants, 68 of whom were at elevated risk for ASD due to having a sibling with ASD. At follow-up at 36 months of age, 18 children in the elevated-risk group were diagnosed with autism. 

Using pupil dilation as a measure of attentional alerting, the researchers measured the infants’ responses to two stimuli: speech directed toward them, and the sound of running water. “Compared to infants without diagnosis,” the researchers found, “the infants who were subsequently diagnosed with autism had larger pupil dilation when listening to nonsocial sounds, while reactivity to speech was strikingly similar between groups. In the total sample, more pupil dilation to the nonsocial sound was associated with higher levels of autistic symptoms.” 

The researchers note that at the neural level, pupil size is considered to be a marker of activity in the locus coeruleus (LC), a key structure for regulating the neurotransmitter norepinephrine. “In turn,” they say, “LC activity has been associated with psychological processes related to attention orienting, sensory processing, and selectivity. These processes have been implicated in autism, and atypical LC activity has been proposed as one underlying mechanism of autistic development.” 

The researchers say their findings suggest that certain nonsocial sounds may cause atypical norepinephrine activity in infants who subsequently develop ASD. “If these atypical responses generalize to other environmental stimuli,” they say, “it could have cascading consequences for learning and development.” 

They conclude, “These findings may have important theoretical and clinical implications.” In particular, they say, “our results suggest that during social interaction with infants with an elevated likelihood of autism, one may promote development by minimizing task-irrelevant background sounds. This principle is well known in intervention for older children with autism, but to our knowledge it has not been emphasized in [prediagnostic] intervention trials so far.” 

The researchers note that their results need to be replicated because their study was small, involved children already at risk for ASD, and tested only one type of nonsocial sound.


“Larger pupil dilation to nonsocial sounds in infants with subsequent autism diagnosis,” Maja Rudling, Pär Nyström, Sven Bölte, and Terje Falck-Ytter, Journal of Child Psychology and Psychiatry, September 13, 2021 (free online). Address: Maja Rudling, Department of Psychology, Uppsala University, Box 1225, 751 42 Uppsala, Sweden, [email protected].