Intensive language learning has been found to modulate attentional functions even in short language courses - for instance, in a one-week course of Scottish Gaelic (Bak et al., 2016). Other evidence suggests that a second language (L2) may be learnt more successfully by those who experience higher degrees of first language (L1) ‘attrition’ - that is, selective and reversible changes in their L1 (cf. Zingaretti, forthcoming). However, no study to date has sought to investigate whether, after only one week of intensive L2 learning, L1 changes of such kind may also occur alongside cognitive changes. The present study therefore aims to examine potential linguistic changes (in L2 Italian and L1 English) together with cognitive changes (in attentional inhibition and switching) following a one-week course of Italian. This study also scrutinises whether any of the (linguistic and/or cognitive) changes found following the course will remain three weeks after the end of the course. A group of second- and third-year students of Italian from different UK Universities enrolled on a one-week course taught by L1-speaker teachers of Italian online (due to the ongoing COVID-19 pandemic at the time). The course consisted of a daily 2-hour morning session, introducing a different topic each day and focusing on the development of lexical and morphosyntactic knowledge, and a 1-hour discussion-based session in the afternoon, focused on developing listening and speaking skills. Lexical access was examined through a verbal-fluency task (Ardila et al., 1994) in the L1/L2 and a translation-recognition task (Zingaretti, forthcoming; Sunderman & Kroll, 2006). The Test of Everyday Attention (Robertson et al., 1994) was used to test participants’ cognitive skills. Background measures were gathered through the use of the Language Experience and Proficiency Questionnaire (LEAP-Q), and L2 proficiency was assessed via LexITA (Amenta et al., 2020). Participants were tested before and after taking part in the course, as well as three weeks later. The results of mixed-effects Poisson regression analyses showed, on the one hand, that participants were significantly more likely to produce a higher number of words in L2 Italian following the course, while this was not the case in L1 English. Furthermore, no negative correlation was found between L1 and L2 verbal fluency scores in each testing phase. On the other hand, the results of mixed-effects logistic models showed that participants’ accuracy was more likely to be higher on the Test of Everyday Attention with distraction (measuring attentional inhibition) at the end of the course, while this was not the case on the Test of Everyday Attention with reversal (measuring attentional switching). Importantly, both the linguistic and cognitive changes found were maintained three weeks after the end of the course. Data from the translation-recognition task still need to be analysed, along with further sub-analyses needing to be carried out for the verbal-fluency tasks. Still, these initial results can be taken to suggest that one week of intensive L2 learning may be enough to yield at least some linguistic changes (i.e., in terms of L2 lexical access) as well as some cognitive enhancements (i.e., on attentional inhibition) lasting up to three weeks following the end of the course. Keywords: second language acquisition, first language attrition, lexical retrieval, attentional functions, intensive language course References Amenta, S., Badan, L., & Brysbaert, M. (2020). LexITA: A quick and reliable assessment tool for Italian L2 receptive vocabulary size. Applied Linguistics. Ardila, A., Rosselli, M., & Puente, A. E. (1994). Neuropsychological evaluation of the Spanish speaker. Plenum Press. https://doi.org/10.1007/978-1-4899-1453-8 Bak, T. H., Long, M. R., Vega-Mendoza, M., & Sorace, A. (2016). Novelty, challenge, and practice: The impact of intensive language learning on attentional functions. PloS one, 11(4), e0153485. Sunderman, G., & Kroll, J. F. (2006). First language activation during second language lexical processing: An investigation of lexical form, meaning, and grammatical class. Studies in second language acquisition, 28(3), 387-422. Marian, V., Blumenfeld, H. K., & Kaushanskaya, M. (2007). The Language Experience and Proficiency Questionnaire (LEAP-Q): Assessing language profiles in bilinguals and multilinguals. Robertson I. H., Ward T., Ridgeway V., & Nimmo-Smith I. (1994). The test of everyday attention: TEA: Thames Valley Test Company Bury St. Edmunds, UK. Zingaretti, M. (Forthcoming). First language attrition in late bilingualism: Lexical, syntactic and prosodic changes in English-Italian bilinguals. Doctoral dissertation, Edinburgh, Scotland: University of Edinburgh. The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. Is e buidheann carthannais a th’ ann an Oilthigh Dhùn Èideann, clàraichte an Alba, àireamh clàraidh SC005336.