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Phonetic variation in consonants in infant-directed and adult-directed speech: the case of regressive place assimilation in word-final alveolar stops*



Pronunciation variation is under-studied in infant-directed speech, particularly for consonants. Regressive place assimilation involves a word-final alveolar stop taking the place of articulation of a following word-initial consonant. We investigated pronunciation variation in word-final alveolar stop consonants in storybooks read by forty-eight mothers in adult-directed or infant-directed style to infants aged approximately 0;3, 0;9, 1;1, or 1;8. We focused on phonological environments where regressive place assimilation could occur, i.e., when the stop preceded a word-initial labial or velar consonant. Spectrogram, waveform, and perceptual evidence was used to classify tokens into four pronunciation categories: canonical, assimilated, glottalized, or deleted. Results showed a reliable tendency for canonical variants to occur in infant-directed speech more often than in adult-directed speech. However, the otherwise very similar distributions of variants across addressee and age group suggested that infants largely experience statistical distributions of non-canonical consonantal pronunciation variants that mirror those experienced by adults.


Corresponding author

Address for correspondence: Dr Laura C. Dilley, Michigan State University, Department of Communicative Sciences and Disorders, 1026 Red Cedar Road, Rm. 116, Oyer Speech & Hearing Building, East Lansing, MI 48824-1220. tel: 517-884-2255; fax: 517-353-3176; e-mail:


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This research is supported by NIH-NIDCD R01DC008581 to T. Bergeson. We thank Claire Carpenter, Erin Dixon, Dana Flowerday, Shaina Selbig, Kellie Voss, and Zach Zells for their assistance with data analysis and coding. We also express our gratitude to Jessica Gamache and Evamarie Cropsey for assistance with figures and references, respectively. Moreover, we gratefully acknowledge Chris Heffner, Erin Dixon, Elizabeth Wieland, and Tuuli Morrill for their valuable feedback on an earlier draft of this manuscript.



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