This study investigated the effect of phonological neighborhood density (PND) on the lexical encoding of perceptually confusable segmental contrasts and the extent to which the precision of encoding is modulated by phonetic categorization and vocabulary size. Korean learners of English and native speakers of American English completed an auditory lexical decision task that contained words and nonwords with /ɛ/, /æ/, /f/, and /p/ (/æ/ and /f/ do not exist in Korean), two phonetic categorization tasks (/ɛ/−/æ/ and /f/−/p/), and a vocabulary test. For the Korean group, participants’ categorization of /f/−/p/ was the only significant predictor of /f/−/p/ nonword rejection. For /ɛ/−/æ/, nonword versions of high PND words were rejected more accurately than low PND. Additionally, vocabulary size and phonetic categorization significantly interacted so that as perception abilities improve, the benefits that come from having a large vocabulary grow as well.

This study investigated the contribution of second-language (L2) phonetic categorization abilities and vocabulary size to the phonolexical encoding of challenging non-native phonological contrasts into the L2 lexicon. Two groups of German learners of English differing in L2 proficiency (advanced vs. intermediate) participated in an English lexical decision task including words and nonwords with /ɛ/ and /æ/ (/æ/ does not exist in German), an /ɛ/-/æ/ phonetic categorization task and an English vocabulary test. Results showed that the effects of phonetic categorization and vocabulary size on lexical decision performance were modulated by proficiency: categorization predicted /ɛ/-/æ/ nonword rejection accuracy for intermediate learners, whereas vocabulary did so for advanced learners. This suggests that sufficient phonetic identification ability is key for an accurate phonological representation of difficult L2 phones, but, for learners for whom robust phonetic identification is already in place, their ultimate success is tightly linked to their vocabulary size in the L2.