Using mechanical soothing to comfort crying babies? [Reader Comment to: Infant crying and the calming response.]

In this paper the authors respond to a study by Möller, De Vente and Rodenburg (2019) [1] in which the calming effect of ‘mechanical soothing’ was compared to that of parental soothing. We question the conclusions drawn by Möller et al. about mechanical soothing as an appropriate alternative to parental soothing. We argue that mechanical soothing is undesirable as it is insensitive to the child’s cues and the longterm effects on child development are unclear.

Keywords: infant crying; mechanical soothing; sensitivity

Babies cry. It is one of the few ways (next to looking cute) they have to elicit the care they need to survive the vulnerable period in which they are completely dependent upon adult care [2]. Caregivers are in turn provoked by the intense sound of crying. From an evolutionary perspective, it makes sense to calm a crying baby rapidly as not to attract the unwelcome attention of wild animals. But even in modern society, adults react strongly to crying: they perform worse on cognitive tests when they listen to cry sounds compared to when they listen to other, similarly loud sounds [3], and infant crying may be a risk factor for child maltreatment [4]. In typically developing infants, the amount of crying rises from birth onwards, peaks around the age of six weeks, and then diminishes [5]. Importantly, crying in early infancy can occur in spite of excellent parental care [6] and does not usually predict long-term problems [7].

In the study of Möller, De Vente and Rodenburg (2019) [1], the calming effect of ‘mechanical soothing’ was compared to that of parental soothing. To assess this, the soothing abilities of a ‘smart crib’ [a device developed to calm infants using swaddling, shushing via white noise, and swinging] were compared to the soothing abilities of a parent instructed to soothe according to a strict protocol [infant swaddled by experimenter, then held by mother horizontally and facing away from her]. Infant distress was triggered by eliciting the Moro reflex and placing the infant two meters away from its mother without eye contact or vocalization. Assessments of fussiness and heart rate showed a calming response in infants during both parental and mechanical soothing. When heart rate variability was assessed, no calming response was observed. When the strength of the calming response was compared between parental and mechanical soothing, the calming response was stronger for mechanical soothing when assessed through heart rate, and stronger for parental soothing when assessed through heart rate variability and fussiness. From this, the authors conclude that both soothing techniques result in a calming response, but that ‘it remains unclear whether parental or mechanical soothing is more effective for calming infants’ (p. 11). The study evokes many questions, but our main concern is two-fold. Firstly, we question whether it is justified to conclude that mechanical soothing can be considered an alternative to parental soothing, based on these results. It appears that the study only uses mechanical soothing, either by a machine (the smart crib), or by mothers instructed to behave like a machine. Secondly, we argue that mechanical soothing is undesirable; we argue that it is insensitive by definition and that it may have dire consequences for child development.