Differing Developmental Trajectories in Heart Rate Responses to Speech Stimuli in Infants at High and Low Risk for Autism Spectrum Disorder.

Bassett-Gunter et al. (2017) tracked heart-rate reactions to speech in two groups of babies. One group had a high chance of autism because an older sibling was diagnosed. The other group had low chance.

The team measured heart rate while the babies listened to speech sounds every few months from age 3 to 12 months.

Low-risk babies slowly increased their heart-rate orienting to speech across the first year. High-risk babies did the opposite: their heart-rate response to the same sounds dropped over time.

This split suggests the high-risk group tunes out speech earlier than typical babies.

Wagner et al. (2025) extends this finding. They scanned the same high-likelihood infants at 9 months and saw weaker neural speech signals and unusual left-brain lateralization. Heart and brain data line up: both show dampened speech reactions before the first birthday.

Zhang et al. (2022) also extends the story. At 5 months, high-likelihood infants already had over-connected local brain networks. The early network inefficiency may set the stage for the later heart-rate drop reported in 2017.

Older reviews by Tanguay et al. (1982) and Iwata (1993) looked at brainstem hearing responses in autism and found mixed results. Those studies used clicks, not natural speech, and measured tiny brainstem waves. Bassett-Gunter et al. (2017) used longer speech sounds and captured slower autonomic reactions, so the papers do not clash; they simply probe different levels of the auditory pathway.

If you assess babies who have an older sibling with ASD, watch for fading interest in speech sounds. A simple heart-rate monitor during babbling games can flag this drop. Pair this with parent coaching from Choi et al. (2020): keep utterances short and lively to re-engage the baby. Early physiological red flags can guide you to start language enrichment months before formal delays appear.