Methods for investigation of L2 speech rhythm: Insights from the production of English speech rhythm by L2 Arabic learners

Rhythm metrics can detect second language development of target-like speech rhythm but interpretation of the results from metrics in learners’ speech is problematic because the mapping of metrics to underpinning phonological features is indirect. We investigate speech rhythm in first language (L1) Arabic / second language (L2) English, which differ in key properties contributing to the percept of rhythm: unstressed vowel reduction and syllable structure. Our production data are interpreted using additional measures, of stressed and unstressed vowels and of consonant cluster realization, alongside standard rhythm metrics; this combination facilitates disambiguation of competing interpretations of the metric results. The findings confirm the importance of using multiple rhythm metrics to study L2 speech rhythm and demonstrate how simple additional measures can guide interpretation of their results. In this study the metrics results showed that the speech produced by the L2 speakers, regardless of their length of residence in the UK, exhibited lower vocalic durational variability than the speech produced by the native Arabic and English speakers. However, closer inspection of the degree of vowel reduction by the native and nonnative groups confirms that no single metric captures the complex nature of the observed L2 rhythm patterns. Future L2 studies are advised not to draw firm conclusions about the degree of vowel reduction and consonant cluster realization in L2 speech based solely on the results of the rhythm metrics.