Inaudible components of the human infant cry influence haemodynamic responses in the breast region of mothers
Distress vocalizations are fundamental for survival, and both sonic and ultrasonic components of such vocalizations are preserved phylogenetically among many mammals. On this basis, we hypothesized that ultrasonic inaudible components of the acoustic signal might play a heretofore hidden role in humans as well. By investigating the human distress vocalization (infant cry), here we show that, similar to other species, the human infant cry contains ultrasonic components that modulate haemodynamic responses in mothers, without the mother being consciously aware of those modulations. In two studies, we measured the haemodynamic activity in the breasts of mothers while they were exposed to the ultrasonic components of infant cries. Although mothers were not aware of ultrasounds, the presence of the ultrasounds in combination with the audible components increased oxygenated haemoglobin concentration in the mothers’ breast region. This modulation was observed only when the body surface was exposed to the ultrasonic components. These findings provide the first evidence indicating that the ultrasonic components of the acoustic signal play a role in human mother–infant interaction.
KeywordsParenting Cry Mother Infant Ultrasonic
We thank Wakako Horita and Eriko Yamada for their help in participant recruitment and data collection. Without their help, this study would have been feasible. Yuichiro Kikuno also assisted participant recruitment. We also thank Paola Rigo and Tommaso Sega for their help with editing figures.
This research was supported by the Intramural Research Program of the NIH/NICHD, USA, and an International Research Fellowship at the Institute for Fiscal Studies (IFS), London, UK, funded by the European Research Council (ERC) under the Horizon 2020 research and innovation programme (Grant Agreement No. 695300-HKADeCERC-2015-AdG). This study was partly supported by Grant-in-Aid for Scientific Research on Innovative Areas (Chronogenesis: how the mind generates time; Grant No. 19H05315) to HD.
Compliance with ethical standards
Conflict of interest
We declare no conflict of interest.
The experimental protocol was approved by the ethical committee of Nagasaki University (No. 08102894-5). The participants were given information about the research and gave written informed consent.
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