Sleep and cortisol function are two physiological self-regulatory processes that codevelop during infancy. Dysregulation of each system is linked to enduring health problems, so it is critical to understand factors contributing to the development of physiological self-regulation. However, it is not clear how infant sleep and cortisol interact with each other or with the parenting context. This project examined (1) the interplay of infant sleep and cortisol; (2) how cortisol interacts with parent characteristics in relation to infant sleep; and (3) whether consistent parenting buffers infant cortisol dysregulation. Study 1 (86 parent-infant dyads) investigated whether average nighttime sleep onset and duration predicted cumulative cortisol exposure, indexed by hair cortisol concentration (HCC). As hypothesized, infants who fell asleep earlier at night had lower HCC regardless of their family income and household chaos. Additionally, I expected that sleep characteristics on one night would predict total salivary cortisol exposure (AUCg) the next day, and that salivary cortisol at bedtime would predict sleep the same night. Partially supporting expectations, time-based analyses revealed that infants with lower cortisol on a particular evening fell asleep earlier the same night. In Study 2 (84 parent-infant dyads), I hypothesized that the link between parent characteristics (i.e., bedtime parental involvement and parental sensitivity) and infant sleep would differ by AUCg. Falling asleep independently predicted earlier sleep onset only for infants with dysregulated cortisol, whereas bedtime parental involvement did not predict sleep for infants with well-regulated cortisol. Infants with emotionally warm and appropriately responsive parents fell asleep earlier at night only if their cortisol was well-regulated. Utilizing archival data of 82 mother-infant dyads, Study 3 assessed consistency in parenting behaviors (i.e., smiles and laughter, and positive vocalizations), cortisol, and socioeconomic status (SES). As hypothesized, higher-SES infants experienced consistency, whereas lower-SES infants experienced inconsistency, in maternal smiles and laughter across 6 to 12 months of infancy. Contrary to expectations, inconsistent parenting did not predict cortisol. Findings highlight the intricate relation between two vital physiological processes codeveloping in the first year of life – sleep and cortisol regulation – and the role cortisol plays in moderating how parenting characteristics contribute to infant sleep.

The primary goal of this study was to examine how infants' language and emotion development intersect around the end of the first year. Specifically, is learning enhanced when a speaker is happy vs. neutral? Eighteen 12-month-old infants were familiarized and tested on four word-object associations that varied in bimodal emotion (happy vs. neutral), which were presented on a Tobii© T60 eye-tracker. Familiarization trials comprised of actresses looking towards and labeling a target object while ignoring a non-target distractor object on the opposite side of the screen. It was expected that infants would demonstrate better learning of word-object associations during the test trials when the speaker was happy. This hypothesis was partially supported, in that infants demonstrated a novelty preference for the novel non-target object compared to the familiar target object in the happy test trials only. However, no difference in attention was seen in happy test trials with the familiar target object and a familiar non-target object or for either of the neutral test trials. A second goal of this study was to examine infant-parent correspondence in emotion processing. Both infants and parents were presented with a series of emotion pairs on the eye-tracker, and the correlations between their gaze patterns were examined. In general, infants and parents had little to no correspondence in first look tendencies or overall fixation duration to either face in the pair. They also fixated on different areas of the face (infants on mouth region, parents on eye region). Finally, parental sensitivity was examined using a free-play interaction task. Parents' sensitivity was analyzed with respect to measures of infants learning during the language task as well as other infant characteristics (e.g. temperament, vocabulary). Overall, these findings add to the relatively limited research examining the intersection of language and socioemotional development in infancy. / Ph. D.