Abstract
This paper argues that people with more than one language have different knowledge of their Lis than do monolingual people, and this difference can mainly be due to the effect of subsequent languages on the development and use of the LI skills. In order to investigate the state of the L1 in foreign language learners a longitudinal experiment was conducted with native speakers of Hungarian studying English, French or Russian as a foreign language in different classroom settings. The L2 effect on the LI was analyzed from three aspects: (1) structural well-formedness; (2) use of linguistic and visual memory; and (3) metaphorical density. This study will focus only on issues concerning structural well- formedness.1 The participants of the experiment were tested three times during a two year period. Findings demonstrated that intensive and successful foreign language learning can have a beneficial effect on the development and use of mother tongue skills.