The Gradual Acquisition of English / l /

One of the fundamental issues in developmental phonology is why some speech sounds are acquired early whereas others are acquired much later (e.g. Prather, Hendrick, and Kern, 1975; Hare, 1983; Dyson, 1988; Smit, Hand, Freilinger, and Bernthal, 1990). We speculate that there are at least two issues at play: articulatory control and learning the phonology of the native language. With respect to the need for articulatory control, we posit that children must develop proper motor control over the primary speech organs, including the tongue, lips, vocal folds (required for voicing) and velum (required for nasal consonant and vowel contrasts). It is plausible that motor control for some organs takes longer to develop than others, either due to inherent physiological difficulty of manipulation, or due to frequency of use in non-speech contexts. Children must develop a phonology appropriate to their native language community. In particular, they must develop contrasts between speech sounds used by adults of their speech community, and lose contrasts that are not relevant to their speech community. Language users often contrast sounds that are acoustically similar, and it has been shown that these contrasts can take longer than others to develop (e.g., Narayan, Werker, and Beddor, 2010). In this study, we are primarily interested in children’s articulatory control over the tongue. One property common to many of the most protracted sounds in acquisition, such as the liquids /l/ and /ɹ/ and the affricates /tʃ/ and /dʒ/, is that they involve the coordination of multiple lingual gestures. That is, in the speech of adults, typical production of these sounds requires movement of the tongue to form more than one constriction against the palate. In contrast, some of the earliest acquired speech sounds, the nasal stops /m/ and /n/, and the labiovelar glide /w/, involve coordination of a single lingual gesture with another nonlingual gesture. In production of the nasal stops /n/ and /m/, speakers must simultaneously lower the velum, allowing airflow to be rerouted through the nasal cavity, and form an oral closure, provided by the lips in /m/ and by the tongue tip in /n/. The glide /w/ requires partial constriction of both the lips and of the tongue body with the palate (Ladefoged, 1993; Johnson, 2003). Laterals are particularly relevant, due to their articulatory complexity and protractedness of acquisition, with word-initial (onset) /l/ typically acquired