Self- and Social-Touch: Effects on Subjective Pleasantness and the Posterior Auricular Muscle Reflex

Abstract

Assessing the pleasantness of social touch experiences typically relies on subjective self-report measures, which are prone to biases. To address this limitation, we explored the sound-elicited posterior auricular muscle reflex (PAR). This reflex exhibits a potentiated reflexive response to primary rewards and was therefore considered as a potential objective marker of touch pleasantness. This paper examined whether the PAR can be modulated by different touch contexts of CT-optimal touch (3cm/s), by measuring the PAR of 75 participants receiving social touch (administered by the experimenter to the participant) and applying self-touch. Also, the effect of two different touch tools, the bare hand or a cosmetic brush, was investigated. Additionally, participants provided subjective ratings of pleasantness derived from each touch experience. In the control condition, participants observed touch being applied to a fake arm or applied touch to the fake arm themselves. Unexpectedly, the prediction that the PAR would exhibit greater responses to the primary reward of social touch was not met. Instead, results revealed that self-initiated touch, wherein the participant touched their own arm or the fake arm, resulted in greater PAR potentiation than receiving social touch. Contrastingly, subjective ratings found social touch to be rated as more pleasant than self-touch, and touch applied to the fake arm to be less pleasant than touch applied to the participant’s real arm. No significant evidence to suggest a relationship between subjective pleasantness ratings and the PAR was found, diminishing the validity of this measure as an objective complement to current self-report measures.