L2 minus L1 difference in N400 amplitude reveals the L2 vocabulary size

• ¹ Jagiellonian University, Poland

An unspeeded lexical decision task has proven to be a very successful tool in a quick and accurate assessment of L2 proficiency (cf. LexTALE task, Lemhöfer & Broersma, 2011). In the present study, we explore if a difference between the ERPs to stimuli (words and wordlike nonwords) presented in L1 and L2 is a good predictor of individuals' L2 proficiency. To this end we presented 42 L2 learners with a list of 70 words and 35 nonwords in English and another one in Polish. A subset of English (L2) items (40 words and 20 nonwords) were taken from the LexTALE test, which enabled us to assess L2 vocabulary size of each participant. As an additional index of L2 proficiency we used language self-rating questionnaire and verbal fluency score. EEG was recorded while participants were making lexical decisions to words and nonwords presented in a random order and blocked by language. Two results replicated earlier findings from the literature: 1) nonwords (both in L1 and L2) elicited stronger N400s than words; 2) L1 words engendered stronger N400s than L2 words. L2 minus L1 difference in N400 amplitude for correctly classified words did not predict language proficiency (measured by LexTALE score), but the same difference measured for all nonwords did: the N400 amplitude for L2 nonwords was strongly correlated with L2 proficiency (r > 0.9 for participants split into 8 equal bins based on their LexTALE score). These results show that as L2 learners acquire more vocabulary, the L2-like nonwords require more effortful and thorough search through the lexico-semantic network, before a "no" response can be made in a lexical decision task. On the other hand, L2 words need much more time and language experience (than was attested by our unbalanced bilingual participants), before they get "entrenched" enough in the mental lexicon, to elicit N400s resembling N400s to L1 words. References: Lemhöfer, K. & Broersma, M. (2011). Introducing LexTALE: A quick and valid Lexical Test for Advanced Learners of English. Behavior Research Methods. DOI: 10.3758/s13428-011-0146-0.