The Role of Predictability in Intonational Variability

Predictability is known to affect many properties of speech production. In particular, it has been observed that highly predictable elements (words, syllables) are produced with less phonetic prominence (shorter duration, less peripheral vowels) than less predictable elements. This tendency has been proposed to be a general property of language. This paper examines whether predictability is correlated with fundamental frequency (F0) production, through analysis of experimental corpora of American English. Predictability was variously defined as discourse mention, utterance probability, and semantic focus. The results revealed consistent effects of utterance probability and semantic focus on F0, in the expected direction: less predictable words were produced with a higher F0 than more predictable words. However, no effect of discourse mention was observed. These results provide further empirical support for the generalization that phonetic prominence is inversely related to linguistic predictability. In addition, the divergent results for different predictability measures suggests that the parameterization of predictability within a particular experimental design can have significant impact on the interpretation of results, and that it cannot be assumed that two measures necessarily reflect the same cognitive reality.