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

Abstract

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.

Pronunciation Variation in Infant-Directed Speech: Phonetic Reduction of Two Highly Frequent Words

“…This is in line with results by Dilley et al (2013), who found similar distributions for non-canonical pronunciations in alveolar stops in infant-and adult-directed read speech. Bortfeld and Morgan (2010) speculate that variation in the input on dimensions that are not crucial for word identification (such as talker gender, pitch or emphatic stress) aids infants in distinguishing features that are lexically relevant from those that are not.…”

“…On the segmental level, caregivers also use exaggeration. In infant-directed speech, speakers tend to produce more extreme variants of vowels, thereby increasing the acoustic distance between these vowels (e. Seidl, 2013, for counterexamples), and have a greater tendency to produce canonical variants of consonants than in adult-directed speech, at least in read speech (Dilley, Millett, McAuley & Bergeson, 2013). In other words: in infant-directed speech, speakers appear to hyperarticulate segments to make them easier to distinguish, thereby accommodating to the needs of the listener (see Lindblom, 1990).…”

“…However, these reports on phonetic reduction in infant-and child-directed speech investigated either word duration or emphasis (Bortfeld & Morgan, 2010;Fisher & Tokura, 1995;Pate & Goldwater, 2011), mild reduction processes in speech directed at toddlers (Shockey & Bond, 1980), they did not provide quantitative data on reduction degree and frequency Anderson, 1983, 1994;Stoel-Gammon, 1984) or focused on read instead of spontaneous speech (Dilley et al, 2013). Hence, they did not study the occurrence of pronunciation variants that are so reduced when compared to their full form that they could be classified as different words by infants.…”

Lexically conditioned phonetic variation in motherese: age-of-acquisition and other word-specific factors in infant- and adult-directed speech

“…Other reported segment-level articulation effects in IDS include more canonical consonant allophones and less variable vowel allophones (Kuhl et al 1997;Dilley et al 2014;though cf. McMurray et al 2013).…”

“…Overall, mothers talking to their infants tend to produce slower rates of speech (Fernald 1992), higher and broader pitch ranges (Fernald 1984;Smith and Trainor 2008), hyperaticulated vowels (Kuhl et al 1997, Kuhl et al 2008Rattanasone et al 2013), and more canonical allophonic consonant variants (Dilley et al 2014), compared to speech directed toward adults. Such infant-directed effects have been found in a number of languages (Ferguson 1964;Fernald et al 1989), though the details of the effects are not always identical (e.g., Benders 2013;Igarashi et al 2013).…”