摘要:AbstractAccording to Vygotsky, language serves not only as a tool for communication but also as a psychological tool in developing an individual's cognitive process. From this perspective, the use of language (i.e. L1) provides learners with additional cognitive support in solving second language (L2) linguistic tasks in an attempt to achieve the desired L2 learning goal. Grounded within the Vygotskian Sociocultural theory of mind (SCT), this paper reports on an investigation of the use of L1 (i.e. Malay language) as a semiotic mechanism in mediating learners’ understanding of the English tense-aspect system. The study involved 8 L1 Malay university-level learners of L2 English as they attempted to verbalize their understanding of target tense-aspect concept. Data was drawn from the verbalization protocols obtained by transcribing individual (self-explaining) and dyadic (collaborative interaction) activity during a CBI session. Our findings revealed that L1, manifested through learners’ metalanguage, act as a mediational tool to structure and organise thought in helping learners gain a deeper understanding of the target grammatical concept. Analysis of the findings not only supports the Vygotskian view regarding the role of L1 as a regulatory tool in L2 learning but also provide further evidence of the positive role and value of L1 in enabling learners to explore and gain insights of the relationship between form and meaning of the L2.