An ELT Glossary : L1 Interference

• Definition : The negative influence of the learner's L1 on his/her use of the target language. 

• Examples :  a) Italian learners may say "I have seen him yesterday" because of the existence of a similar pattern in Italian; b) Spanish learners may insert an /e/ sound before words that start with a consonant cluster beginning with /s/ as this always happens in Spanish. For example: Espagna (Spain),  escuela (school), estrella (star).  The English words may therefore be pronounced as /espeɪn/, /esku:l/, /estɑ:/.

• The term is associated with audiolingualism, which saw L1 interference as detrimental to learning, and therefore attempted to exclude all use of the L1 from the learning process.  Later, it was recognised that L1 influence could also be positive (eg: recognition of cognates can help learners understand words they have never met before) and the alternative term "transfer" was proposed.