Dynamics of caregiver speech acoustic features and infants’ emotion regulation

• In Event: The influence of maternal communication on infants’ biobehavioral state

Abstract

Infants’ bio-behavioral regulation relies on interactions with caregivers, which set the stage for the development of increasing self-regulation with age. The acoustic features of caregiver voices may be a key influence on infants’ behavioral and physiological states (Feldman, 2007; Tronick, 1989). However, the quantification of specific prosodic acoustic features that form the foundation of the emotional and affective components of vocalizations have received little attention. Infant directed speech (“motherese”) is marked by exaggerated frequency modulation and strong high frequency power. Frequency band and modulation features of prosody may provide physiological cues for mobilization or calming through functional linkages between vocalization production, listening, and neurophysiological state regulation systems, including the parasympathetic branch of the autonomic nervous system that promotes calm social interaction (Kolacz, Lewis, & Porges, 2018; Porges & Lewis, 2010). This study examined whether mothers’ prosody, indexed by speech frequency bands and modulation depth, positively predicted calming of infants’ biobehavioral state following the Still Face paradigm, a stressor in which the mother withdraws and reinstates social cues.

94 dyads participated in the study (infant age 4-8 months; 48% female). Infants’ respiratory sinus arrhythmia (measuring cardiac vagal tone, parasympathetic influence on the heart) and heart rate (a measure of overall cardiac output, including sympathetic and parasympathetic influences) were derived from an electrocardiogram (ECG). Infants’ behavioral distress was measured by negative vocalizations, facial expressions, and gaze aversion. Spectral analysis and spectro-temporal modulation using a two-dimensional fast Fourier transformation of the audio spectrogram were applied to measure mothers’ vocalizations during the reunion phase immediately following the stressor. Mothers with high prosody were quantified as having strong frequency power in the social communication band (500-5000Hz), lower power in the high frequency band (5000+ Hz), and strong frequency and temporal modulation.

Analyses were conducted using regression and cross-lagged panel modeling. High maternal prosody after the stressor was associated with decreases in infants’ heart rate (β=-.26, 95%CI: [-.46, -.05]), decreases in behavioral distress (β=- .20, 95%CI: [-.38, -.02]), and increases in cardiac vagal tone in infants whose vagal tone was low during the stressor (in those 1 SD below mean: β=.39, 95%CI: [.06, .73]; Figure 1). The examination of bi-directional associations after the stressor showed that high infant heart rate predicted increases in maternal prosody (β=.18, 95%CI: [.03, .33]) and, conversely, high maternal prosody predicted decreases in infant heart rate (β=-.11, 95%CI: [-.22, -.01]; Figure 2).

This study is the first to use a novel, theoretically-informed composite measure of prosody based on the frequency bands and modulation of voice to study the naturalistic dynamics of caregiver prosody and infant biobehavioral state. These results suggest that specific vocal acoustic features of speech associated with motherese are relevant for regulating infants’ emotions and demonstrate mother-infant bi-directional dynamics. Moreover, we show that the influence of maternal prosody interacts with infants’ physiological state, such that infants with low cardiac vagal tone (parasympathetic regulation) engaged in physiological calming if their mothers had stronger prosodic features. These findings expand the conceptualizations of the mechanism of dyadic emotional regulation in infants’ social interactions.

Authors

• Jacek Kolacz, Indiana University - Bloomington
  Presenting Author

• Elizabeth daSilva, Indiana University- Purdue University Columbus
  Non-Presenting Author

• Gregory Lewis, Indiana University
  Non-Presenting Author

• Bennett I Bertenthal, Indiana University - Bloomington
  Non-Presenting Author

• Stephen Porges, Indiana University
  Non-Presenting Author