Objectives: The aim of the present study was to investigate the electrophysiological correlates of voice processing in 4- to 12-year-old children with ASD compared to typically developing children. Voice processing was evaluated by comparing cortical auditory evoked potentials (AEPs) to vocal sounds vs. environmental sounds (non-vocal) of everyday life. Pattern of response were assessed according to verbal abilities in children with ASD.
Methods: Participants were 50 typically-developing (TD) children and 12 children with ASD, all aged 4 to 12 years. The stimuli used were extracted from the sequences used in Belin et al.s’block-design fMRI studies with stimulus duration adjusted to 500 ms. AEPs were analyzed topographically (scalp potential and current density mapping). Mean (± sem) verbal and non-verbal IQ scores of children with ASD were 69 ± 14 and 87 ± 11 respectively.
Results: A specific response to voice was found in TD children as a positive deflection localized over right fronto-temporal sites, which we termed Fronto-Temporal Positivity to Voice (FTPV), with maximal amplitude in the 100-250 ms latency range. This response was very robust throughout childhood. It was identical in the 4 age-groups: 4-5, 6-7, 8-9, 10-12 year-olds. Compared to age-matched TD children, FTPV amplitude was significantly smaller in children with ASD who had concomitant language impairment whereas it was greater in children whose verbal abilities were less affected.
Conclusions: The fronto-temporal positivity to voice (FTPV) recorded in TD children may constitute the electrophysiological counterpart of the activation of the temporal voice areas previously described in neuroimaging studies. Results in children with ASD indicated atypical responses to voice. Moreover the relationship between voice processing and verbal abilities lead us to hypothesize that cortical response to voice is a putative predictive marker of language development in ASD.