Non-native phonemes in adult word learning: evidence from the N400m

Newborns are equipped with a large phonemic inventory that becomes tuned to one's native language early in life. We review and add new data about how learning of a non-native phoneme can be accomplished in adults and how the efficiency of word learning can be assessed by neurophysiological measures. For this purpose, we studied the acquisition of the voiceless, bilabial fricative /Φ/ via a statistical-learning paradigm. Phonemes were embedded in minimal pairs of pseudowords, differing only with respect to the fricative (/aΦo/ versus /afo/). During learning, pseudowords were combined with pictures of objects with some combinations of pseudowords and pictures occurring more frequently than others. Behavioural data and the N400m component, as an index of lexical activation/semantic access, showed that participants had learned to associate the pseudowords with the pictures. However, they could not discriminate within the minimal pairs. Importantly, before learning, the novel words with the sound /Φ/ showed smaller N400 amplitudes than those with native phonemes, evidencing their non-word status. Learning abolished this difference indicating that /Φ/ had become integrated into the native category /f/, instead of establishing a novel category. Our data and review demonstrate that native phonemic categories are powerful attractors hampering the mastery of non-native contrasts.