Human Versus Non-Human Action Sound Processing in Young Children with Autism

Background: Autism spectrum disorders (ASDs) are characterized by difficulties in communication and social interaction, including the comprehension of non-verbal behaviours such as other people’s actions and gestures. Behavioural and neuroimaging studies have revealed reduced attention to social cues, such as eye-gaze or gestures, as well as atypical visual perceptual processing of biological motion and human actions in this population. However, it is not known whether atypical neural activity is confined to the perceptual processing of visual social stimuli or, instead, extends to social perception in the auditory modality.

Objectives: The aim of the current study was to examine the perceptual processing of human and non-human action-related sounds in 4- to 6-year old high-functioning children with ASD compared with typically developing control children, matched for sex, chronological age, and verbal abilities.

Methods: An auditory-auditory repetition suppression event-related potentials (ERPs) paradigm was employed, whereby children with ASD (n=18) and typically developing controls (n=18) passively listened to repeated and non-repeated human action or environmental sound stimuli. More specifically, the ERP paradigm included a single block of trials, presenting two types of human action sounds (hands clapping, hands ripping paper) and two types of non-human action sounds (helicopter blades spinning, ocean waves). There were four different types of trials, which involved the immediate repetition or non-repetition of human and non-human action sound stimuli. Differences in neural activity elicited by repeated (suppression of brain mechanisms) and non-repeated (release of brain mechanisms) stimuli were examined. Behavioural measures, including the Mullen Scales of Early Learning and the Autism Diagnostic Observation Schedule, were also administered for the behavioural characterisation and matching of the participant groups.

Results: ERPs to both types of sounds included early sensory (P1, N1) and later cognitive processing components (N4, N600) over both frontal and temporal sites, which did not differ between the participant groups. However, children with ASD presented with enhanced cortical responses to the non-human action sounds over posterior parietal sites at an early stage of perceptual/cognitive processing (N2b), when compared with controls. In addition, children with autism exhibited less habituation to human action sounds relative to controls, at a later stage of cognitive processing (N4) over the same parietal electrode sites.

Conclusions: The current results provide evidence for atypical processing of both human and non-human action sounds in young children with autism.  These results are consistent with previous findings of atypical visual perceptual processing of objects in young children with autism, and suggest that similar atypicalities exist in the auditory and visual domains.  The finding of reduced habituation to human action sounds in the current study is also consistent with recent findings of both visual and auditory social processing in this population early in life.  Taken together, the current results provide further evidence for an imbalance between social and non-social processing mechanisms in young children with autism.