Adult learners acquire second language (L2) allophones with experience. We examine two mechanisms which may support the acquisition of allophonic variants in second language acquisition. One of the mechanisms is based on the distribution of phones with respect to their phonological context (i.e. phonological distribution). The other is based on the role the phones play in contrasting words (i.e. lexical contrast). Experiment 1 established adult native English speakers' baseline sensitivity to the novel [b]-[[voiced bilabial fricative]] auditory contrast. In Experiment 2 we examined whether adult native English speakers infer the phonological status of [b] and [[voiced bilabial fricative]] in an artificial language based only on their distributions to phonological contexts. We observed no evidence that these participants were able to do so. In Experiment 3 we investigated whether learners infer the phonological status of [b] and [[voiced bilabial fricative]] from the role they play in lexical contrast and observed both perceptual and lexical processing evidence to suggest that adults may use meaning-based cues to the lack of contrast to learn that two phones are allophones of the same phoneme. Together our findings suggest that adult L2 learners may prioritize information about function (in this case, lexical contrast) over the phonological distribution of phones as they determine the phonological status of L2 sounds.