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INTRODUCTION
The past decade has seen an increased number of pronunciation instruction (PI) empirical studies with promising findings and review articles recognizing a paradigm shift, indicating that explicit PI can help second-language (L2) learners achieve comprehensible pronunciation (e.g., Derwing et al., 2014; Lee et al., 2015; Saito, 2011; Thomson & Derwing, 2015; Trofimovich et al., 2017). However, most review articles have noted that the results of existing empirical studies are far from conclusive, as they contradict one another on a set of crucial issues related to designing interventions for improving L2 pronunciation: the focus of instruction, treatment context, and outcome measures (e.g., Lee et al., 2015; Thomson & Derwing, 2015).
Many studies discuss the relative effectiveness of PI for either segmental elements (isolated vowels and consonants, i.e., phonemes) or suprasegmental features (e.g., stress, rhythm, and intonation). Levis (2005) and Saito (2014) indicated that segmental phonemes may be easier for teachers to teach and learners to learn; in other studies, suprasegmentals have been found to play a very important role in comprehensibility (e.g., Hahn, 2004; Isaacs & Trofimovich, 2012; Kang et al., 2010; Saito & Saito, 2017). However, few empirical studies have investigated the relative effectiveness of PI on both feature types. Derwing et al. (1998) separated segmental from suprasegmental features in training (Sereno et al., 2016), examining the effects of two types of PI (segmental- and suprasegmental-based) compared with no PI and finding that explicit PI on suprasegmentals is more effective than that on segmentals when it comes to comprehensibility. Yet to what extent suprasegmental instruction is superior to segmental instruction remains unclear. Gordon and Darcy (2012) more clearly established that the effect of explicit PI on suprasegmentals is almost twice that of the effect on segmentals; however, as this paper was presented at the American Association for Applied Linguistics, it is difficult to clearly trace the procedure and data. Therefore, to what extent one type of explicit PI is superior to the other requires further empirical investigation.
The treatment context is another crucial feature that can greatly influence the impact of a pedagogical intervention (e.g., Plonsky & Oswald, 2014). Empirical studies centering on the effects of explicit PI on L2 pronunciation development have shown a general improvement in learners’ pronunciation after explicit instruction in...