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The gentle sounds of a baby's early vocalizations are more than just expressions of joy for parents. They indicate a connection between the baby's heart rate and speech development, according to research by Jeremy I. Borjon, an assistant professor of psychology at the University of Houston. Published in the Proceedings of the National Academy of Sciences, Borjon's study suggests that these initial sounds and attempts at word formation are directly linked to heart rate.
Speech production in infants is not only a cognitive task but also a motor skill requiring coordination of various muscles. This coordination appears to be influenced by changes in heart rate. Borjon's research involved studying 24-month-old babies to determine if heart rate fluctuations align with vocal production. The findings revealed that these fluctuations do coincide with when infants make vocalizations and influence their duration and recognizability as words.
"Heart rate naturally fluctuates in all mammals, steadily increasing then decreasing in a rhythmic pattern," Borjon explained. "It turns out infants were most likely to make a vocalization when their heart rate fluctuation had reached a local peak (maximum) or local trough (minimum)."
The study found that vocalizations made at peak heart rates tended to be longer, while those made just before a trough were more likely to be recognized as words by listeners unfamiliar with the baby’s speech patterns.
Borjon's team analyzed 2,708 vocalizations from 34 infants aged 18 to 27 months during playtime with caregivers. While whole words are uncommon in this age group, about 10.3% of these sounds were identifiable as words by naive listeners. The study considered all types of sounds produced by the infants, including laughs, babbles, and coos.
"Every sound an infant makes helps their brain and body learn how to coordinate with each other, eventually leading to speech," said Borjon.
As children grow, their autonomic nervous system—which regulates functions like heart rate—also develops. Significant changes occur in the first few years regarding how the heart and lungs function.
The link between recognizable speech and decelerating heart rates suggests that successful speech development may depend on experiencing predictable autonomic activity ranges during growth stages.
"Understanding how the autonomic nervous system relates to infant vocalizations over development is a critical avenue of future research for understanding how language emerges, as well as risk factors for atypical language development," concluded Borjon.