Assimilation of L2 vowels to L1 phonemes governs L2 learning 94 in adulthood: a behavioral and ERP study

According to the Perceptual Assimilation Model (PAM), acoustic similarity/dissimilarity between sounds of the second language (L2) and the native language (L1) governs L2 learnability in adulthood and predicts L2 sound perception by naïve listeners. The study addressed two questions: (1) whether the discrimination patterns predicted by the PAM for L2 naïve listeners are also reflected in the modulation of Mismatch Negativity (MMN) component of the event-related response (ERP) and (2) whether L2 classroom learning is associated with the typology of L2 naïve listeners, as recently suggested by behavioral studies on cross-linguistic research. We measured the behavioral and ERP responses in two groups (10 subjects per group) of Salento Italian (SI) undergraduate students of British English (BE) attending the first the fifth year of the Foreign Languages and Literatures Faculty, compared with 10 inexperienced subjects of BE as L2 (only for the ERP experiment). An identification test examined the perceived phonetic distance between the L1 (/i, ɛ, a, ɔ, u/) and L2 (/iː, ɪ, ɛ, æ, ʌ, ɑː, ɒ, ɜː, ɔː, ʊ, uː/) vowel system. The contrasts /iː/-/uː/ and /æ/-/ʌ/ (for which the PAM’s framework predicted an excellent and a good discrimination, respectively) were selected for an oddity discrimination test and the ERP experiment. In the ERP experiment, using an oddball paradigm, the contrasts /iː/-/uː/ and /æ/ -/ʌ/ were tested while subjects watched a silent movie. As a control condition we introduced the L1 within-category contrast /ɛ/-[e] for which poor discrimination is predicted for all subjects. Following the PAM predictions, the two groups of students did not differ in their behavioral discrimination performance: they exhibited excellent discrimination of /iː/-/uː/ and moderate to good discrimination of /æ/-/ʌ/. MMN amplitudes confirmed that the L2 contrasts were well discriminated. Crucially, no difference was found between the groups of students and the inexperienced group for the L2 contrasts /iː/-/uː/ and /æ/-/ʌ/, and, as predicted, all the subjects showed poor discrimination for the L1 within-category contrast. MMN peak latencies were modulated by the contrast type: /i/-/u/ elicited a faster MMN than /æ/-/ʌ/ and /ɛ/-[e]; in turn, /æ/-/ʌ/ evoked a faster MMN than /ɛ/-[e], reflecting the acoustic distance between the stimuli. Furthermore, the MMN was right lateralized. In line with the PAM model, we extend the findings of previous behavioral studies showing that, at the psychophysiological level, classroom instruction in adulthood relies on assimilation of L2 vowels to L1 phoneme categories and does not trigger improvement in L2 phonetic discrimination.