Development of phonetic variants (allophones) in 2-year-olds learning American English: A study of alveolar stop /t, d/ codas

This study examined the emergence of the phonetic variants (often called allophones) of alveolar phonemes in the speech production of 2-year-olds. Our specific question was: Does the child start by producing a “canonical” form of a phoneme (e.g., /t/ with a clear closure and a release burst), only later learning to produce its other phonetic variants (e.g., unreleased stop, flap, and glottal stop)? Or, does the child start by producing the appropriate phonetic variants in the appropriate contexts and only later learn that they are phonetic variants of the same phoneme? In order to address this question, we investigated the production of three phonetic variants (unreleased stop, flap, and glottal stop) of the alveolar stop codas /t, d/ in the spontaneous speech of 6 American-English-speaking mother-child dyads, using both acoustic and perceptual coding. The results showed that 2-year-old children produced all three variants significantly less often than their mothers, and produced acoustic cues to canonical /t, d/ more often. This supports the view that young children start out by producing a fully articulated canonical variant of a phoneme in contexts where an adult would produce non-canonical forms. The implications of these findings for early phonological representations are discussed.