Date of Degree


Document Type


Degree Name



Speech-Language-Hearing Sciences


John L. Locke

Committee Members

Martin R. Gitterman

Glenis R. Long

Sethu Karthikeyan

Valerie L. Shafer

Subject Categories

Biological Psychology | Communication | Linguistics | Other Linguistics | Other Psychology | Other Social and Behavioral Sciences | Psychology | Social and Behavioral Sciences


Infant vocalizations, evolution of speech and language, biolinguistics, evolutionary developmental linguistics


The effect of variability in infant vocalizations on potential caregivers’ heart rate variability (HRV), facial expressions, and subjective ratings on emotional reactions and desire to approach the baby was examined in an evolutionary context. Recordings of non-canonical, canonical, fussing, and crying vocalizations were utilized to elicit physiological and self-reported reactions from sixty participants. Breastfeeding mothers, non-mothers at high estradiol point in menstrual cycle, non-mothers at low estradiol point in menstrual cycle, fathers, and non-fathers were included in the study. Participants wore Polar RS800 heart rate monitors, were video recorded for facial expression analysis, and filled out 11 point self-rating forms on emotional reactions to the infant vocal stimuli. It was expected that participants would show higher HRV for the canonical vocalizations as compared to non-canonical, fussing and crying vocal stimuli. Overall HRV as measured by SDNN (standard deviation of NN, or “normal-to-normal” interbeat intervals), was highest for the recorded babbling, however these differences were not significant. Most raters considered crying and fussing to be strong indicators of a need for interaction. Participants showed the greatest percentage of happy facial expressions (evaluated via analysis of video recordings) and also self-reported the babbling vocalizations high on “happiness” and “most liked”, as predicted. Although the predicted directions for the differences between mothers and non-mothers at two different assumed estradiol levels in menstrual cycle were not significant, breastfeeding mothers did show higher facial expressions of happiness while listening to the babbling stimuli, gave higher scores of self-rated sadness when listening to crying, and rated their irritation levels lower and the desire to pick up the baby higher for the fussing stimuli.

The square root of the mean squared difference of successive NN intervals were significantly higher in fathers than non-fathers while listening to the babbling stimuli. Fathers had significantly higher self-reported happiness levels and higher scores towards the “most liked” end of the rating scale for the babbling stimuli. The results are discussed within an evolutionary framework considering the potential influence of parental selection of vocal behaviors, an attraction to complexity of sounds across species, as well as the possible influence of hormones on potential caregivers’ responses to infant needs.