Task complexity effects on L2 speech rhythm in spontaneous speech production

Task-based pronunciation teaching studies have shown that the cognitive complexity of a task affects different aspects of second language (L2) speech, such as vowel accuracy and comprehensibility. However, its impact on L2 speech rhythm is still under-researched, especially in spontaneous pronunciation-unfocused tasks. In this study, we first investigated how task complexity influences L2 speech rhythm, and we then explored how L2 speech rhythm metrics might predict global pronunciation proficiency (comprehensibility and accentedness). Eighty-two Spanish/Catalan bilingual learners of English and a control group of eight native speakers (NSs) completed a simple and a complex version of an adapted monologic decision-making task. Oral production data were analysed using well-established rhythm metrics (%V, VarcoV, nPVI-V, and VarcoC), novel distance measures (Euclidean and Mahalanobis distance scores) and ratings from 13 English NSs. Results showed differential task complexity effects on L2 speech rhythm depending on the rhythm metrics and distance measures considered. Additionally, the %V rhythm metric and the Mahalanobis distance measure accounted for a modest amount of variance in both comprehensibility and accentedness scores, with Mahalanobis distances having a more reliable predicting power. The outcomes of this study point to the importance of further examining the role of task complexity in L2 speech rhythm in spontaneous speech and to what extent L2 speech rhythm is related to global measures of L2 pronunciation proficiency. These findings also highlight the need for identifying which rhythm metrics are more suitable to depict L2 speech elicited through different methods, particularly spontaneous speech.