Coping with phonological variation in early lexical acquisition

Mapping word forms onto their corresponding meanings is one of the most complex tasks that young infants acquiring their native language have to perform. This is due to the fact that an utterance can refer to many different aspects of a scene, a problem known as referential ambiguity (Quine 1960). An even more basic problem, though, is that it is not easy to find word forms to start with. In fact, the speech waveform is continuous, and word boundaries are not readily available. Moreover, words often surface with different phonetic forms due to the application of postlexical phonological processes; that is, surface word forms exhibit what we call phonological variation. Most models of lexical acquisition assume that infants can somehow extract unique word forms out of the speech stream before they acquire the meaning of words (e.g. Siskind 1996). Hence, they propose a solution to the problem of referential ambiguity, thereby assuming that the problems of finding word boundaries and undoing phonological variation have already been solved. There is evidence that infants can indeed find word boundaries before they have a lexicon (Jusczyk & Aslin 1995). By contrast, virtually nothing is known concerning the question of how prelexical infants deal with phonological variation. In this paper, we will examine if and how infants that do not have a lexicon might undo phonological variation, i.e. deduce which phonological processes apply and infer unique underlying word forms that will constitute lexical entries. The various intricacies of phonological variation for lexical acquisition can be illustrated within a single language, i.e. Korean. First, consider the allophonic rule of obstruent voicing. This rule voices plain obstruents that occur between two voiced segments, as illustrated in (1); voiced obstruents do not otherwise occur in Korean.