Allophonic Variation and the Acquisition of Phoneme Categories

One of the first tasks infants have to accomplish in order to acquire their native language consists of segmenting the continuous signal into discrete categories that represent the vowels and consonants used in their language. Experimental research has shown that this segmentation is acquired during the first year of life. In particular, vowel categories are established at around 6 months (Kuhl et al. 1992; Polka & Werker 1994), and consonant categories at around 10-12 months (Werker & Tees 1984a). Recently, it was argued that a statistical analysis of the acoustic space and the formation of prototypes might be used by infants to acquire these categories (Kuhl et al. 1997; Maye, Werker & Gerken 2002). Within a language’s segment inventory, a distinction is made between phonemes, i.e. those segments that are used to make lexical distinctions, and allophones, i.e. phonetic variants of phonemes that appear in certain phonological contexts. Consider, for instance, the following segments occurring in English: [t, d, t ̇]. The distinction between [t] and [d] is phonemic (witness the minimal pair hat had), whereas [t ̇] is an allophone of the phoneme /t/ that occurs at the beginning of stressed syllables (Kahn 1976). The distinction between phonemes and allophones is to a large extent arbitrary. For instance, Korean has a phonemic distinction between [t] and [t ̇] and an allophonic one between [t] and [d] (Kim 1990). To the extent that allophones are realized as distinct acoustic prototypes, a statistical algorithm like the one proposed by Maye, Werker & Gerken (2002) yields the acquisition of segmental categories, not of more abstract phoneme categories. Thus, it predicts that both English and Korean infants acquire three separate categories for [t], [d], and [t ̇]. Several articles, though, have shown that adults do not process allophonic contrasts in the same way as phonemic contrasts, suggesting that at one point they have acquired the distinction between