Human and Non-Human Action Sound Processing in Toddlers At Risk for Autism

Background:

Previous behavioural studies have revealed difficulties in the comprehension and production of body actions and gestures in children and adolescents with Autism Spectrum Disorders (ASD). In addition, decreased attention to other people as well as gestural communication delays have been observed in high-risk infant siblings of children with autism, including those later diagnosed with the disorder. The neural mechanisms underlying the perceptual processing of visual stimuli depicting human gestures and biological motion have also been found to be atypical in individuals with ASD. However, it is not currently known whether similar atypicalities characterise the perceptual processing of human action sounds (i.e., auditory gestures) in ASD.

Objectives:

The aim of the current study is to investigate the perceptual processing of human action sounds in toddlers at risk for autism, using a novel event-related potentials (ERP) auditory-auditory repetition-suppression paradigm.

Methods:

Twenty-one low-risk 2- and 3-year old toddlers and nine high-risk siblings of children with autism, matched for chronological and developmental age, have taken part in this study thus far. The auditory-auditory repetition suppression 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 (ocean waves, helicopter blades spinning). There were also four different types of trials, which involved the immediate repetition or non-repetition of both 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 two participant groups.

Results:

Results reveal two negative-going repetition suppression components, peaking at 300ms and 580ms respectively, over the frontal area in response to human action sounds in both groups. However, preliminary results indicate that the latter, N580, component’s amplitude was smaller over the right hemisphere in the high-risk toddlers. For non-human action sounds, a positive-going repetition suppression component peaking at 250ms was identified in both groups. However, the amplitude of this component was found to be smaller over the left hemisphere in high-risk toddlers. Finally, although no lateralisation differences were found for either human or non-human action sound processing in the low-risk toddlers, non-human action sound processing was right lateralised in the high-risk group.

Conclusions:

These results suggest that toddlers at risk for autism present with an atypical pattern of perceptual processing of both human and non-human action sounds. The reduced brain activity observed over right frontal channels in response to body action sounds in the high-risk group provides evidence for a dysfunctional auditory gesture processing mechanism at a late stage of cognitive-perceptual processing. Moreover, reduced activation over the left frontal cortex, in combination with the tendency for a greater right frontal activity, in response to non-human action sounds suggests an atypical neural mechanism associated with the early perceptual processing of non-human action sounds in toddlers at risk for autism.