摘要:Because the Japanese language does not have a robust plural morpheme system, it is morphologically incongruent with English. As such, L1 Japanese learners of L2 English are argued to be unable to fully acquire English plural morphemes. While previous studies have revealed limitations in L2 processing, recent studies have revealed that advanced-learners are sensitive to incongruent morphology. However, these studies have largely investigated processing within English as a second language context. As such, the present study investigated the sensitivity to inflectional number agreement in English by Japanese learners of English in Japan using the Lexical Maze Task. The results revealed that these learners were sensitive to violations in number agreement for both plural (this *dogs) and null (these *cat) morphemes. However, further analysis revealed that this was modulated by English proficiency. While participants with higher English ability were found to reveal greater sensitivity to ungrammatical morphemes, it was found that this was only the case for the ungrammatical plural (this *dogs). The ungrammatical null (these *cat) was instead revealed to evoke longer responses times by low proficiency learners, and high proficiency learners showed no sensitivity. This might be explained by a greater lexical variability among more advanced learners. Accordingly, this study demonstrates that despite morphological incongruence, non-advanced Japanese learners of English in Japan can acquire the English plural -S morpheme.