The interaction of coarticulation and prosody in sound change

Ohala (1974, 1981a) has proposed that sound changes can originate in hearers' misinterpretations of synchronic phonetic patterns. This paper applies this idea to sound changes that are conditioned by the prosodic environment, such as the voicing of voiceless fricatives in unstressed syllables in Proto-Germanic. Browman and Goldstein's (1989, 1990) "gestural score" suggests a representation of synchronic patterns in which extreme overlap between gestures of neighboring phoneme segments in casual speech can produce the appearance of a feature change or a segment deletion. Many of the sound changes that are conditioned by prosodic environment can be viewed as a diachronic reinterpretation of just such synchronic fast-speech processes. For example, vowel reduction in unstressed syllables can be viewed as a reinterpretation of undershoot that occurs when the vowel is overlapped to a great extent by the oral gestures for neighboring consonants. Phonetic data are reviewed that support analogous accounts of stop spirantization, voiceless obstruent voicing, and even the insertion of an intrusive stop in clusters such as /ns/ in some prosodic environments.