Sampson, Julia LaurenInfant-directed speech (IDS) contains many unique characteristics that may facilitate language development. One acoustic cue that may differ in IDS compared to adult-directed speech (ADS) is voice onset time (VOT). The present study examines the VOT of open- and closed-class words in speech to infants at 10/11, 18, and 24 months of age, as well as in speech to adults. This study also looks at correlations between clarification of VOT in speech to infants, and language outcomes at 2 years. Results show that VOT clarification in IDS did not differ significantly at any of the ages. Overlap between voicing categories for open class words was significantly less in ADS than IDS. The overlap for closed class words at 18 months was significantly related to language outcomes, with lower overlap relating to higher outcome scores. Possible explanations are discussed.ThesisBehavioral sciencesAcousticsSpeech therapyInfant-directed SpeechLanguage DevelopmentVoice onset time