The Role of Vocabulary Knowledge in Second Language Speaking Fluency: A Mixed-Methods Study

The present study examined the relationship between L2 learners’ task-related lexical access and their utterance fluency. Two groups of American learners of Chinese participated in the study. The first group of learners (N = 15) took part in a vocabulary test requiring them to translate 198 words related to four speaking tasks from L1 to L2. Learners’ accuracy and reaction time were recorded. Learners then completed four speaking tasks. Six features of their utterance fluency were measured. The second group of learners (N = 13) participated in a stimulated recall interview, which was conducted to obtain additional details regarding how lexical access affects utterance fluency in L2 speech. According to the results, significant correlations were found among vocabulary size and all three facets of utterance fluency: speed fluency (speech rate, mean length of runs), breakdown fluency (mean length of silent pauses, number of silent pauses), and repair fluency (number of disfluencies), excluding the number of filled pauses. However, among all fluency measures, only speech rate was significantly correlated to lexical retrieval speed. Moreover, stimulated recall responses revealed that around two-third of the disfluencies were reported to be caused by vocabulary-related issues. The findings confirmed that efficient task-related lexical access was crucial for producing fluent speech in second language.