“…Each index might reflect activity of a different psychophysiological system with its own characteristics, including the speed of responses to external circumstances (e.g., fast response for heart rate vs. slow response for salivary cortisol), underlying rhythms (e.g., oscillations for respiration vs. a marked diurnal pattern of a morning decrease and subsequent increase for salivary α-amylase), relevant confounding factors (e.g., temperature for skin-conductance levels vs. intake of caffeine for cortisol), and types of psychosocial contexts they respond to (e.g., socioevaluative threat for cortisol). Consequently, markers of the sympathetic nervous system, parasympathetic nervous system, and hypothalamic pituitary adrenal axis activity might behave differently when it comes to couple synchrony (Coutinho et al, 2021; Nelson et al, 2017; Palumbo et al, 2017; for evidence from parent–child synchrony, see Davis et al, 2018; DePasquale, 2020).…”