Side by side: Modeling dyadic physiological linkage in strangers.

Physiological linkage (PL) refers to coordinated physiological responses among interacting partners (Feldman, 2012a), thought to offer mammals evolutionary advantages by promoting survival through social groups. Although PL has been observed in dyads who are familiar or have close relationships (e.g., parent-infant interactions, romantic couples), less is known with regard to PL in stranger dyads. The current study used dynamic linear time series modeling to assess cardiac interbeat interval linkage in 26 same-gender stranger dyads (17 female and 9 male dyads; 18-22 years old) while they spoke or wrote about emotional or neutral life events. The estimated coefficients in bivariate regression models indicated small but statistically significant PL effects for both male and female dyads. The PL effect was stronger for female dyads, extending to a lag of 4 seconds. For male dyads, the effect was statistically significant but weaker than for female dyads, extending only to a lag of 1 second. No statistically significant differences in PL were noted for type of task (i.e., baseline, writing, speaking, listening) or with differing task emotional content. Frequency domain analysis based on the estimated dynamic models yielded similar results. Our results suggest that PL can be detected among strangers in this setting and appears to be stronger and longer-lasting in women. Our findings are discussed in terms of the importance of biological synchrony in humans, gender differences, and possible implications for objective measurement of social reciprocity at a physiological level. (PsycINFO Database Record