Brief articleAnticipatory coarticulation facilitates word recognition in toddlers
Introduction
To learn from their environment, young children must be able to process familiar words efficiently. Word recognition mediates toddlers’ ability to learn words from caregivers (Weisleder & Fernald, 2013), and efficiency of lexical processing during the first two years predicts vocabulary and working memory later in childhood (Marchman & Fernald, 2008). Grammatical, pragmatic and phonetic contextual cues can constrain word recognition by simplifying the search space, but many such cues to word identification are not word-internal. Therefore, integrating contextual cues across word boundaries is essential for efficient word recognition.
One of the most well established context-sensitive phenomena in phonetics is coarticulation: the overlap of articulatory gestures in neighboring sounds. Coarticulation influences the production of sound patterns both within and across word boundaries. Typical English examples include coronal place assimilation (e.g., saying in case with a velar nasal consonant) and fronting of /k/ in keep (cf. backing and lip-rounding on /k/ in coop). A coarticulated sound carries acoustic information about neighboring sounds, introducing redundant and locally coherent information into the speech signal. In this respect, coarticulation provides regularity or “lawful variability” that can support speech perception (Elman & McClelland, 1986).
Indeed, adult listeners access and exploit coarticulatory cues during speech perception and word recognition (Gow, 2002, Gow and McMurray, 2007). Adults are slower to recognize words when there is a mismatch between coarticulatory cues in a vowel and the following consonant (e.g., Dahan et al., 2001, McQueen et al., 1999, Tobin et al., 2010). Conversely, appropriate coarticulation can facilitate spoken word recognition (e.g., Mattys, White, & Melhorn, 2005). For example, adult English listeners are faster to recognize a noun when the preceding determiner the carries information about the onset of the noun (Salverda, Kleinschmidt, & Tanenhaus, 2014).
It is not known whether young children can take advantage of coarticulatory cues during word recognition. Toddlers encode subsegmental details in their lexical representations (Fisher, Church, & Chambers, 2004), so coarticulatory cues should be accessible to these listeners in principle. In addition, toddlers recognize spoken words incrementally, using acoustic cues as they become available as a word unfolds over the speech signal (e.g., Fernald et al., 2001, Swingley et al., 1999). Moreover, toddlers rely on contextual cues when recognizing words produced in fluent speech (Plunkett, 2006). These findings raise an important question: Can young listeners use coarticulatory cues to facilitate recognition of a following word?
This question is important given the longstanding debate concerning the nature of early phonological representations. One point of view holds that these representations are under-specified and that children differentiate between words using relatively holistic phonological representations (Charles-Luce and Luce, 1990, Charles-Luce and Luce, 1995, Jusczyk, 1993). Based on a corpus analysis, Charles-Luce and Luce argued that young children do not need the same phonological detail in their lexical representations as adults do because children’s phonological neighborhoods are much sparser. Researchers supporting this point of view have hypothesized that children’s phonological representations gradually become more detailed as vocabulary size increases (Edwards et al., 2004, Metsala, 1999, Werker and Curtin, 2005, Werker et al., 2002). An opposing point of view posits that children’s phonological representations are segmental from very early in development (Dollaghan, 1994, Magnuson et al., 2003). This view is supported by studies showing that infants are sensitive to one-feature mispronunciations of familiar words (e.g., Swingley and Aslin, 2000, Swingley and Aslin, 2002, White and Morgan, 2008; see also review in Mayor & Plunkett, 2014). If toddlers use anticipatory coarticulation for word recognition, this finding would provide additional support for the viewpoint that children’s phonological representations are well specified even when their vocabularies are relatively small.
In the present study, we investigated whether toddlers took advantage of sub-phonemic anticipatory coarticulatory cues between words. Specifically, we asked whether coarticulatory acoustic cues on the determiner the facilitate recognition of the following word. We used a looking-while-listening task (Fernald, Zangl, Portillo, & Marchman, 2008) to determine whether toddlers looked more quickly to a named image in facilitating vs. neutral coarticulatory contexts (manipulated within subjects). Crucially, all of the items were cross-spliced to ensure that the recordings were otherwise comparable. We hypothesized that if toddlers are sensitive to coarticulation, we should see earlier recognition of the target noun in facilitating contexts relative to neutral contexts.
Section snippets
Participants
Twenty-nine 18–24-month-olds (M = 20.8, range = 18.1–23.8, 13 male) participated in this study. An additional 11 toddlers were excluded from the analyses due to inattentiveness (10) or having more than 50% missing data during non-filler trials (1). Caregivers completed the short version of the Words and Sentences Form of the MacArthur–Bates Communicative Development Inventory (MBCDI; Fenson et al., 2007).
Materials and stimuli
We selected target words that are familiar to toddlers in this age group. For the facilitating
Results
Overall looking patterns are presented in Fig. 2. Accuracy hovers around chance performance over the course of the determiner and approximately 250 ms into the target word. Accuracy increases from 250 to 1000 ms, and after 1000 ms accuracy begins to plateau then decline. Time clearly predicts accuracy; the probability of looking to target increases as the word unfolds. Importantly, coarticulatory information also predicts accuracy because participants have a noticeable head-start on the
Discussion
The present study provides the first evidence that toddlers take advantage of coarticulatory cues across word boundaries when recognizing familiar words. Participants on average looked to a named image approximately 100 ms earlier when the determiner the contained coarticulatory cues about the onset of the following noun. These results indicate that novice word-learners can take advantage of anticipatory coarticulatory information across word boundaries to support recognition of familiar words.
Acknowledgements
This research was supported by NIDCD Grant R01 DC012513 to Susan Ellis Weismer, Jan Edwards, and Jenny R. Saffran, NICHD Grant R37-HD037466 to Jenny R. Saffran, a grant from the James F. McDonnell Foundation to Jenny R. Saffran, NIDCD Grant R01-02932 to Jan Edwards, Mary E. Beckman, and Benjamin Munson, NICHD Grant 2-T32-HD049899 to Maryellen MacDonald, and NICHD Grant P30-HD03352 to the Waisman Center. We thank Eileen Haebig, Franzo Law II, Erin Long, Courtney Venker, and Matt Winn for help
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