07 Jun 2005

Laurence White & Sven Mattys (University of Bristol)

The rhythm of so-called "stress-timed" languages such as English and Dutch has long been contrasted with that of "syllable-timed" languages like Spanish and French, but quantifying this distinction has proved difficult. "Stress-timed" languages have stressed vowels that are substantially longer than (typically reduced) unstressed vowels, whereas, in "syllable-timed" languages, vowel duration varies less between stressed and unstressed syllables. Additionally, "stress-timed" languages allow greater complexity in syllable onsets and codas. Ramus, Nespor and Mehler (1999) and Grabe and Low (2002) have proposed rhythm metrics which exploit these patterns to quantify rhythmic distinctions between languages.

Subjective impressions suggest that rhythm contributes to the perception of a speaker's accent as being non-native. We examined English spoken as a second languages (L2) by native Spanish and Dutch speakers, and Spanish and Dutch spoken as L2s by native English speakers, and compared these L2s on a range of rhythm measures with Spanish, English and Dutch spoken as a first language (L1). We found that the influence of L1 was manifest primarily in measures of vocalic durational variation. The overall balance of vocalic and intervocalic measures also differed between L1s and L2s, but not necessarily in the direction of L2 speakers' first language. Metrics relating to variation in consonantal intervals showed strong language dependence, regardless of speakers' linguistic origins.

Differences in rhythmicity may also be observed between dialects of a given language, arising either from segmental or suprasegmental variation. Dialects such as Bristolian manifest less vowel reduction and less contrast between the length of tense and lax vowels; dialects with pitch-peak delay, such as Welsh Valleys and Orcadian, may show levelling of the duration contrast between stressed and post-stressed syllables. We recorded speakers of several British dialects— Bristolian, Welsh Valleys, Orcadian and Shetland (which lacks pitch-peak delay, in contrast with Orcadian)—together with standard Southern British English. We found that certain vocalic metrics successfully captured the impressionistic observation of more "syllable-timed" rhythm in, for example, Orcadian or Welsh Valleys English. In particular, the standard deviation of vocalic intervals, normalised for speech rate, provided a discriminant gradient index of dialect rhythmicity, as does a measure of the relative proportions of vocalic and consonantal intervals. These results suggest that rhythmic variation is continuous rather than categorical.

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