Exemplar dynamics: Word frequency, lenition and contrast

Over the last decades, a considerable body of evidence has accumulated that speakers have detailed phonetic knowledge of a type which is not readily modelled using the categories and categorical rules of phonological theory. One line of evidence is systematic differences between languages in fine details of pronunciation. For example, it is known that Spanish and English differ systematically in the exact formant patterns typical of their point vowels (Bradlow 1995). Canadian French differs from both Canadian English and European French in the distribution of VOT times of voiced and voiceless stops (Caramazza and Yeni-Komshian, 1974). These are just two of many examples, with more reviewed in Pierrehumbert (in press) and Pierrehumbert et al. (in press); at this point, it is not possible to point to a single case in which analogous phonemes in two different languages display exactly the same phonetic targets and the same pattern of phonetic variation in different contexts. Exact phonetic targets and patterns of variation must accordingly be learned during the course of language acquisition. The usage-based framework readily accomodates such findings by proposing that mental representations of phonological targets and patterns are gradually built up through experience with speech. A particularly interesting and challenging result is the discovery that learned phonetic detail may be associated not just with languages or dialects, but even with specific words in the lexicon of a given dialect. This observation is made most convincingly in a series of studies by Bybee which explore the relationship of word frequency to lenition. Bybee (Hooper 1976) explored the process of schwa reduction and desyllabification which applies variably before sonorants such as /r/ and /n/ in English. She found that in high frequency words, such as every and the noun evening , the schwa was completely absent and the syllable it originally projected had vanished. In mid-frequency words, such as memory and salary , the modal outcome is a syllabic /r/. In rare words, such as