Izard, C. E., Porges, S. W., Simons, R. F., Haynes, O. M., Hyde, C., Parisi, M., Cohen, B. (1991). Infant cardiac activity: Developmental changes and relations with attachment. Developmental Psychology, 27(3), 432-439.


In this study the stability over the first 13 months of life of measures of infant cardiac activity (heart period and heart-period variability), their relations with each other, and their relations with a continuous-variable index of infant-mother attachment were investigated. The indexes of cardiac activity changed in an orderly way with development (increasing heart-rate variability, decreasing heart rate). There were moderate to high intercorrelations among the cardiac measures, particularly those indexing heart-rate variability (i.e., vagal tone, heart-period variance, and heart-period range). Regression analyses showed that the measures of heart-rate variability at 3, 6, and 9 months were significant predictors of the continuous-variable index of security. The higher the infants' heart-rate variability the higher were their attachment insecurity scores. Analyses of whether the conventional secure/insecure classification was related to the early infant cardiac measures indicated that measures of heart-rate variability were significantly higher in the insecure children.

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