Fluency is one of the most noticeable differences between native and nonnative speech and constitutes an essential component of second language proficiency; however, the concept has not been well understood by researchers. In order to deepen understanding of the multidimensional construct of fluency, the current dissertation investigated the production and perception of second language fluency from all three aspects--utterance, cognitive, and perceived fluency.Study 1 investigated utterance fluency and cognitive fluency of English speakers and Korean learners of English by comparing temporal measures and stimulated recall responses. The first language (L1) and second language (L2) speech were different in speed, length of run, repairs, and silent pauses. In particular, a striking group difference was found in the frequency of silent pauses within a clause, which is consistent with the claim that pauses within clauses reflect processing difficulties in speech production such as lexical retrieval. Stimulated recall responses showed that lower proficiency learners remembered more issues regarding L2 declarative knowledge on grammar and vocabulary than higher proficiency learners, which was compatible with the declarative/procedural model and studies on automaticity.Study 2 examined the relationship between utterance fluency and perceived fluency using two experiments. Experiment 1 investigated the relative contributions of frequency, length, and distribution of silent pauses to perceived fluency of L2 speech. Experiment 2 tested causal effects of pause location on perceived fluency of L1 and L2 speech. Findings of both Experiment 1 and Experiment 2 suggest a significant role of pause location in L2 perceived fluency. In Experiment 1, pause distribution demonstrated the strongest correlation with fluency ratings, and in Experiment 2, perceived fluency of L2 speech was influenced by pause location more than that of L1 speech. The findings are consistent with L1 literature on pause phenomena which has shown that silent pauses are one of the acoustic cues to clausal units, and silent pauses between clauses can facilitate speech perception and recall, whereas pauses within clauses can interfere with them in cognitively demanding contexts.One of the most novel and important findings of the current dissertation is the close relationship between L2 fluency and pauses within clauses. L1 and L2 speech exhibited a striking difference in the frequency of pauses within clauses, which is considered to reflect difficulties in speech production processing. Pauses within clauses also had a crucial impact on perceived fluency of L2 speech.
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