Degree

Doctor of Philosophy (PhD)

Department

Psychology

Document Type

Dissertation

Abstract

Children learn language more effectively from infant-directed speech (IDS) than adult-directed speech (ADS). Three experiments were run (a pilot and two full experiments) testing the effects of pitch and pitch variability on segmenting a target word out of the speech stream and then associating it to an object. Visual prosody via eyebrow movements and lip contours were added as additional cues after the Pilot Study. Additional factors included after the Pilot Study were shortened sentences from 10 syllables each to seven syllables each, shortened target words from three syllables to two syllables, consistent syllable onset of target words, and two different carrier phrases (utterances surrounding the target word) for each item rather than one carrier phrase presented twice. Target words were placed in the middle of the sentence (utterance-medial) in the Pilot Study and Experiment 2; target words were place at the end of the sentence (utterance-final) in Experiment 1. The results of the Pilot Study supported our hypothesis that contrasting the mean pitch and pitch variability of the target word from the carrier phrase benefits initial association task performance. The results of Experiment 1 did not support our hypothesis that contrasting the mean pitch and pitch variability of the target word from the carrier phrase facilitates segmentation and association, but the findings did indicate that utterance-final placement of target words yields successful segmentation and association performance, regardless of whether visual prosody was present. The results of Experiment 2 supported our hypothesis that the contrast between the carrier phrase and the target word facilitates initial and delay association task performance, especially when visual prosody was present, however regular IDS promoted successful association task performance regardless of whether visual cues were present or absent. Overall, we concluded that manipulating specific factors of speech may not be lucrative in the context of naturalistic speech and that the benefit of IDS exists as a result of the combination of its exaggerated acoustic and visual factors.

Date

11-12-2025

Committee Chair

McDonald, Janet L.

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