Lexical inference is the most common strategy that L2 learners use when they encounter unfamiliar vocabulary while reading a text (Fraser, 1999). Whether vocabulary knowledge or grammar knowledge has more impact on lexical inference remains a debate, and several scholars point to text complexity as another factor that affects lexical inference. Therefore, this study aims to examine the impact that L2 proficiency and text complexity have on the lexical inference and reading comprehension of CSL learners. L2 proficiency concerns vocabulary knowledge and grammar knowledge, and text complexity concerns semantic transparency and the difficulty of grammar. We asked participants to use the "Think Aloud"method to highlight occurrences of specific knowledge source usage as they perform lexical inference on vocabulary with different levels of semantic transparency. Thirty-one CFL Japanese learners participated in this study. Four texts with different levels of text complexity were chosen with four target words identified in each text. The experimental procedure included: vocabulary knowledge test, reading the texts, think aloud, reading comprehension test, and grammar knowledge test. The research findings are as follows:(1)The correlation between L2 proficiency and lexical inference performance is significant (r =.522, p =.003). (2) Learners' performances in the reading of the four selected texts are significantly different in terms of text comprehension and lexical choice (F = 8.290, p =.000; F = 28.226, p =.000), but not in terms of reading comprehension. As for the results related to text comprehension, semantic transparency and the difficulty of grammar have an interaction effect (F = 11.307, p =.001). The main effect of semantic transparency is significant (F = 12.563, p =.000), while the main effect of the difficulty of grammar is nonsignificant. Regarding lexical choice, the interaction effect of semantic transparency and the difficulty of grammar is significant (F = 10.321, p =.001). The main effect that semantic transparency has on lexical choice is significant, and the main effect of the difficulty of grammar on lexical choice is likewise significant (F = 69.770, p =.000; F = 4.587, p =.034).(3)The correlation between reading comprehension and, respectively, L2 proficiency and lexical inference performance are both significant (r =.704, p =.000; r =.389, p =.030); 49.5% of variance in reading comprehension can be attributed to L2 proficiency. (4) Regardless of the level of semantic transparency, the most common knowledge source for lexical inference is textual clues.
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