abstract: The current study delineated the developmental trajectories of early childhood externalizing and internalizing symptoms reported by mothers and fathers, and examined the role of the 18-month observed parenting quality × Respiratory Sinus Arrhythmia (RSA) interaction in predicting these trajectories. Child sex was tested as a covariate and moderator. It was found that children's low baseline RSA or high RSA reactivity , in comparison to high baseline RSA or low RSA reactivity , was more reactive as a function of early parenting quality when predicting the development of early childhood problem symptoms. Differential patterns of the interaction between parenting quality and RSA were detected for mothers' and fathers' reports. Mother-reported models showed a diathesis-stress pattern, whereas the father-reported model showed a vantage-sensitivity pattern, especially for internalizing symptoms. This may imply the potential benefit of fathers' active engagement in children's early development. In addition, the effect of the parenting quality × RSA interaction in predicting the mother-reported models was found to be further moderated by child sex. Specifically, the parenting quality × baseline RSA interaction was significantly predictive of girls' 54-month internalizing, and the parenting quality × RSA reactivity interaction significantly predicted boys' internalizing slope. Girls with low baseline RSA or boys with high RSA reactivity were vulnerable to the less positive parenting, exhibiting high levels of 54-month internalizing symptoms or slow decline in internalizing over time, respectively. Future research directions were discussed in terms of integrating the measures of SNS and PNS in psychopathology study, exploring the mechanisms underlying the sex difference in parenting quality × RSA interaction, and comparing the findings of children's typical and atypical development. / Dissertation/Thesis / Masters Thesis Psychology 2014