Sounds that are contrastive in a language are rated by listeners as being more differentfrom each other than sounds that don’t occur in the language or sounds that areallophones of a single phoneme. The study reported in this paper replicates this findingand adds new data on the perceptual impact of learning a language with a new contrast.Two groups of speakers of the Nanjing dialect of Mandarin Chinese were tested. Onegroup was older and had not been required to learn standard Mandarin as school children,while the other younger group had learned standard Mandarin in school. Nanjing dialectdoes not contrast [n] and [l], while standard Mandarin does. Listeners rated the similarityof naturally produced non-words presented in pairs, where the only difference betweenthe tokens was the medial consonant. Pairs contrasting [n] and [l] were rated by olderNanjing speakers as if two [n] tokens or two [l] tokens had been presented, while thesesame pairs were rated by younger Nanjing speakers as noticeably different but not asdifferent as pairs that contrast in their native language.