Towards a better understanding of ecologically valid parent-infant affective touch research

BACKGROUND. Affective touch is widely recognized as crucial for the healthy development of young infants, with an essential subclass of unmyelinated low-threshold mechano-sensitive skin fibres (i.e., C-Tactile afferents) that conduct affective information about interpersonal touch, occupying a far-reaching role. However, studying infants is challenging, and there exists debate regarding the appropriate methodology for conducting experimental touch research among this target group. Standardized laboratory studies are the norm in affective touch research with adult populations, while infant populations – inherently irritable and sensitive – require a more ecologically valid setting. With the latter, however, situational-dependent behaviours can cause metabolic changes which affect cardiorespiratory parameters, serving as a potentially significant confounding factor.

AIM. This study explored a golden mean in conducting ecologically valid yet standardized experimental affective touch research with infants.

METHODS. To test ecological validity, we replicated previous research measuring the effect of a 3-min stroking touch period on mother-infant physiological self-regulation, adding the use or omission of oil, and vanilla baselines pre- and post-stroking touch where the mother stroked a pillow to stabilize metabolic activity instead of using resting baselines. Electrocardiogram (ECG) and respiration of 21 mother-infant dyads (infants aged 5-15 weeks) were measured to calculate RR-intervals (RRI), respiration rates (fR) and respiratory sinus arrhythmia (RSA).

CONCLUSIONS. Infants’ RSA significantly increased during the post-stroking vanilla baseline, but not during the stroking touch period. This indicates a delayed effect of stroking touch on infant cardio respiration. We propose that this can be attributed to the disruption of the infants' ecological context within this standardized experimental setup, by including vanilla baselines and the use or omission of oil. This novel interactive context potentially required the infants to acclimate. Furthermore, the use or omission of oil did not influence infant cardio respiration, and overall no changes were observed in the mothers’ physiology. These findings highlight the importance of conducting ecologically valid and tailored experimental research when studying a vulnerable population of infants.