Phoneme discrimination is believed to be less accurate in non-native languages compared to native ones. What remains unclear is whether differences in pre-attentive phonological processing emerge between the first foreign language (L2) and additional ones (L3/Ln), and whether they might be influenced by the acquisition setting (formal vs. naturalistic). We conducted an event-related brain potential oddball study with native Polish learners of English (L2) and Norwegian (L3/Ln). The results revealed a graded amplitude of the mismatch negativity (MMN) effect, which was largest in L1, smaller in L2, and smallest in L3/Ln. Considering the previously obtained results for naturalistic/mixed learners with the same language combination, we believe that the acquisition setting is an important factor influencing the perception of phonemic contrasts. In the naturalistic group, no difference was observed between L1 and L2, while the instructed group exhibited more fine-grained distinctions between all tested languages.
