The usefulness of metrics in the quantification of speech rhythm

The performance of the rhythm metrics ΔC, %V, PVIs and Varcos, said to quantify rhythm class distinctions, was tested using English, German, Greek, Italian, Korean and Spanish. Eight participants per language produced speech using three elicitation methods, spontaneous speech, story reading and reading a set of sentences divided into “uncontrolled” sentences from original works of each language, and sentences devised to maximize or minimize syllable structure complexity (“stress-timed” and “syllable-timed” sets respectively). Rhythm classifications based on pooled data were inconsistent across metrics, while cross-linguistic differences in scores were often statistically non-significant even for comparisons between prototypical languages like English and Spanish. Metrics showed substantial inter-speaker variation and proved very sensitive to elicitation method and syllable complexity, so that the size of both effects was large and often comparable to that of language. These results suggest that any cross-linguistic differences captured by metrics are not robust; metric scores range substantially within a language and are readily affected by a variety of methodological decisions, making cross-linguistic comparisons and rhythmic classifications based on metrics unsafe at best.

► The performance of rhythm metrics, %V, ΔC, nPVI, rPVi, VarcoC and VarcoV, was tested. ► Large and varied samples of English, German, Greek, Italian, Korean and Spanish were used. ► Metrics showed substantial inter-speaker variation. ► Metrics proved very sensitive to elicitation method and syllable complexity. ► Timing features captured by metrics are unstable and overlap across languages.