Subcortical encoding of harmonicity and frequency in autism: Insights from frequency-following responses

Autistic individuals often exhibit atypical sound perception, yet the specific acoustic properties involved-beyond sound intensity-remain unclear. This study examined whether subcortical processing of harmonicity and frequency differs in autistic children, potentially contributing to altered auditory experiences. Frequency-following responses (FFRs) were recorded from 15 autistic boys (ages 7-14) and nine age-matched neurotypical (NT) boys. In Experiment 1, participants heard three complex tones varying in their degree of harmonicity. No group differences emerged in FFRs to either the envelope or fine structure, suggesting comparable subcortical encoding of harmonicity. In Experiment 2, participants were presented with complex tones differing in the frequency of partials and/or fundamental frequency. Autistic children showed significantly weaker envelope responses across all stimuli and reduced fine structure responses around 500 Hz, while responses at lower and higher frequencies matched NT peers. These findings suggest that atypical subcortical encoding of frequency-specific information may contribute to altered sound perception in autism. Larger-scale studies are needed to confirm these results and connect them to behavioral measures.