The covariation of acoustic features of infant cries and autonomic state

Abstract

The evolution of the autonomic nervous system provides an organizing principle to interpret the adaptive significance of physiological systems in promoting social behavior and responding to social challenges. This phylogenetic shift in neural regulation of the autonomic nervous system in mammals has produced a neuroanatomically integrated social engagement system, including neural mechanisms that regulate both cardiac vagal tone and muscles involved in vocalization. Mammalian vocalizations are part of a conspecific social communication system, with several mammalian species modulating acoustic features of vocalizations to signal affective state. Prosody, defined by variations in rhythm and pitch, is a feature of mammalian vocalizations that communicate emotion and affective state. While the covariation between physiological state and the acoustic frequencies of vocalizations is neurophysiologically based, few studies have investigated the covariation between vocal prosody and autonomic state. In response to this paucity of scientific evidence, the current study explored the utility of vocal prosody as a sensitive index of autonomic activity in human infants during the Still Face challenge. Overall, significant correlations were observed between several acoustic features of the infant vocalizations and autonomic state, demonstrating an association between shorter heart period and reductions in heart period and respiratory sinus arrhythmia following the challenge with the dampening of the modulation of acoustic features (fundamental frequency, variance, 50% bandwidth, and duration) that are perceived as prosody.

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“…An example of a graded signal is crying behavior in human infants: acoustically, crying is highly complex, and it can transfer important information about urgency and severity. Mothers can often identify the type of distress (hunger versus pain) expressed in their infant's cry (Gustafson and Harris, 1990), but by and large, the signal lies on a continuum (Stewart et al, 2013). On the other hand, categorical signals are characterized by a narrow or highly clustered distribution of features (Fig.…”

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“…The production of vocalisations that convey emotion (i.e., prosody) and the ability to detect these sounds evolved in parallel with the changes in the mammalian autonomic nervous system (Stewart et al, 2013(Stewart et al, , 2015. During the phylogenetic transition that produced the two vagal circuits in mammals, the uniquely mammalian vagal circuit evolved to provide a parallel output to laryngeal muscles that mediate vocal prosody.…”

“…Thus, mammals, not only had the ability to express bodily state in voice, but also had a uniquely mammalian middle ear that functionally dampened low-frequency background noise and enabled the processing of specific acoustic cues of social communication (Porges & Lewis, 2009;Porges et al, 2014;Stewart et al, 2013Stewart et al, , 2015.…”

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“…Cry is one of the earliest and most prominent social communicative signals (Stewart et al, 2013). Evolutionarily, cries index the presence of a problematic, possible threatening situation and, especially baby cries, arouse in individuals a specific set of physiological and emotional patterns which underlie a sense of alertness and promptness to address the cause (Venuti et al, 2012: Messina et al, 2016).…”