Anticipatory coarticulation facilitates word recognition in toddlers

Highlights

• We report a looking-while-listening eyetracking study with 18–24 month-olds.

• We manipulated the coarticulatory cues on the word “the”.

• Under facilitating coarticulation, the cues predicted the following noun.

• Looking patterns were compared for facilitating vs. neutral coarticulation.

• Toddlers looked to target sooner when “the” contained facilitating coarticulation.

Abstract

Children learn from their environments and their caregivers. To capitalize on learning opportunities, young children have to recognize familiar words efficiently by integrating contextual cues across word boundaries. Previous research has shown that adults can use phonetic cues from anticipatory coarticulation during word recognition. We asked whether 18–24 month-olds (n = 29) used coarticulatory cues on the word “the” when recognizing the following noun. We performed a looking-while-listening eyetracking experiment to examine word recognition in neutral vs. facilitating coarticulatory conditions. Participants looked to the target image significantly sooner when the determiner contained facilitating coarticulatory cues. These results provide the first evidence that novice word-learners can take advantage of anticipatory sub-phonemic cues during word recognition.

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.