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Effects of pedagogical interventions with visual input enhancement on grammar learning have been investigated by a number of researchers during the past decade and a half. The present review delineates this research domain via a systematic synthesis of 16 primary studies (comprising 20 unique study samples) retrieved through an exhaustive literature search. The overall magnitude of visual input enhancement was addressed by calculating and aggregating effect size d values. The results indicate that second language readers provided with enhancement-embedded texts barely outperformed those who were exposed to unenhanced texts with the same target forms flooded in them ( d = 0.22). A theoretical tension between form and meaning was indicated by a small but negative effect size value for learners' meaning processing ( d = −0.26). The importance of improving methodological practices in this research domain, including the reporting of statistical and treatment-related information and the counteracting of a possible publication bias, was also revealed by the synthetic analyses and is further discussed.
Lee et al. (Wed,) studied this question.