Using acoustic features of mothers’ infant-directed speech to predict changes in infant biobehavioral state

Abstract

Infant directed speech is marked by exaggerated frequency modulation and strong high frequency power, features that may provide physiological cues for mobilization or calming (Porges and Lewis, 2010; Kolacz et al., 2018). We examined whether these features predicted changes in infant biobehavioral state during the Still Face Paradigm, a stressor in which the mother withdraws and reinstates social cues. 98 mother-infant dyads participated when infants were 4-8 months old. Infant heart rate and respiratory sinus arrhythmia (a measure of cardiac parasympathetic control) were derived from an electrocardiogram (ECG). Infant behavioral distress was measured by vocal, facial, and body movement distress. Mothers’ vocalizations were measured using spectral analysis within designated frequency bands and modulation using a 2-dimensional fast Fourier transform of the audio spectrogram. Maternal frequency modulation predicted decreases in infant heart rate (p = .030), mid-frequency acoustic power (500–5000 Hz) predicted increases in cardiac parasympathetic regulation in infants with low parasympathetic tone (p = .024), and high frequency power predicted increases in infant behavioral distress in infants who were not initially distressed (p = .011). These results suggest that mothers’ vocal frequency band power and modulation may be aspects of infant-directed speech that are relevant for regulating infant biobehavioral state.