Dissertation Defense Announcement

School of Communication Sciences and Disorders announces the Final Dissertation Defense of

Hyunjoo Yoo

for the Degree of Doctor of Philosophy

June 14, 2018 at 11:00 AM in Community Health Building

Advisor: D. Kimbrough Oller

Reactions of adult listeners to infant distress vocalizations and protophones

ABSTRACT: Caregiver-infant interaction is critical for cognitive, social, emotional, and language development. This dissertation investigated adult responses to infant speech-like (i.e., protophones) and distress vocalizations in three individual projects. Study1 investigated different timing of caregiver responses to protophones and cries. In order for caregivers to respond differently to protophones and cries, they need to be able to differentiate these sounds. Study 2 and Study 3 projects addressed this issue. Infant recordings from a longitudinal study were used for the dissertation. For Study 1 and 3, all-day LENA home recordings were used, and for Study 2, both LENA and laboratory recordings were used. Adult listeners for Study 2 and 3 were students and/or staff in the School of Communication Sciences and Disorders. Pupillometry and reaction time were used in Study 2 to measure listeners' cognitive load when judging infant vocalizations. Study 1 found that caregivers tended to take turns with protophones, suggesting they viewed protophones as conversational material, while they tended to overlap with cries from the first months of life. This result is important because it suggests parents know that protophones are precursors to speech even in the first months of life, whereas cries express distress, and caregivers intuitively treat them as not being conversational material. Study 2 found that nonparent adult listeners were reliably able to identify high-distress wail cry and mid-distress whine. Listeners judged cry faster in a speech-babble noise condition than in a no-noise or a music-masking condition, a pattern consistent with the fast-guessing principle. Greater pupil dilation was found when listeners identified whine than when they identified cry in the noise condition, suggesting there was greater cognitive load in the noise condition. Study 3 documented the extent to which listeners agree with each other in perceiving the level of distress in infant vocalizations ranging from cries to protophones. The study also showed that duration, number of acoustic regimes, and low/high spectral ratio (cutoff:4kHz) were strong predictors of perception of the level of distress. In addition, regardless of experience in infant vocalization coding, listeners were not significantly different in perceiving the level of distress.