The main aim of this study was to test whether mothers' (n = 116) and fathers' (n = 116) mind-mindedness predicts infants' physiological emotion regulation (heart rate variability; HRV) across the first year of life. Three hypotheses were examined: (a) parents' mind-mindedness at 4 and 12 months predicts infants' HRV at 12 months over and above infants' initial HRV levels at 4 months, (b) mothers' and fathers' mind-mindedness independently predict infant HRV, and (c) the effects of mind-mindedness on infant HRV (partially) operate via parenting behaviour. Infants' HRV was assessed during rest and a stranger approach. Mind-mindedness was assessed by calculating the proportions of appropriate and non-attuned mind-related comments during free-play interactions, and parenting quality was observed at 4 and 12 months in the same interactions. Path analyses showed that mothers' appropriate mind-related comments at 4 and 12 months predicted higher baseline HRV at 12 months, whereas mothers' non-attuned comments predicted lower baseline HRV at 12 months. Similar, but concurrent, relations were found for fathers' appropriate and non-attuned mind-related comments and infant baseline HRV at 12 months. In addition, fathers' appropriate mind-related comments showed an indirect association with infant baseline HRV at 12 months via fathers' parenting quality. With regard to infant HRV reactivity during the stranger approach, mothers' appropriate mind-related comments at 4 months and fathers' non-attuned mind-related comments at 12 months predicted a larger HRV decline during the stranger approach at 12 months. Infants' HRV at 4 months did not predict parents' later mind-mindedness. The results indicate that mothers' and fathers' appropriate and non-attuned mind-related speech uniquely impacts the development of infants' physiological emotion regulation.
© 2018 The Authors. Developmental Science Published by John Wiley & Sons Ltd.