Linguistic dimensions of comprehensibility and perceived fluency in L2 speech across tasks of varying complexity

This study investigated the effects of task complexity on the linguistic dimensions of comprehensibility and perceived fluency in L2 Japanese. 36 Chinese-speaking learners of Japanese performed two argumentative speech tasks with differing levels of complexity. These audio samples were judged by eight experienced native raters of Japanese for comprehensibility and perceived fluency and then analyzed in terms of complexity, accuracy, and fluency. The results showed that linguistic correlates of comprehensibility exhibit a task-specific effect, with additional linguistic dimensions (e.g., syntactic density, explicit grammatical marking) becoming increasingly relevant as task complexity rises. In contrast, perceived fluency also undergoes a task-specific shift but differently: rather than expanding the set of predictors, it changes the nature of primary cues, placing greater emphasis on syntactic sophistication alongside (but not replacing) temporal aspects. Findings underscore the unique role of Japanese linguistic system in shaping listeners’ judgments of L2 Japanese.