This study examines the production of Italian /t/ by native English participants who began acquiring Italian as adults. It investigates the extent of phonetic learning in Italian /t/ for individuals who have been living in Italy for many years (late bilinguals) and the effect of quantity of native speaker input on phonetic learning in Italian /t/ for the late bilinguals and three groups of students who differ in terms of amount of received exposure to native Italian speech.
In addition, it investigates whether phonetic learning in Italian /t/ coincides with modifications to the way in which English /t/ is produced. Voice-onset time (VOT), burst amplitude and closure duration were measured in English and Italian monolingual productions of /t/ in order to establish phonetic norms. Only VOT exhibited enough variation to be used as an indicator of phonetic learning. Late bilinguals showed partial phonetic learning in the form of compromise values which were intermediate to English and Italian monolingual VOT. Phonetic learning in student realisations of Italian /t/ increased in line with amount of received native speaker input. Contrastingly, the late bilinguals did not display the most phonetic learning, despite having received the most native speaker input. It was proposed that native speaker input influences phonetic learning in the early stages of acquisition, but that phonetic learning for the late bilinguals had fossilised. In the later stages of acquisition, age of learning (AOL) was deemed to be a more accurate predictor of phonetic learning than input. Neither the late bilinguals, nor the students exhibited modifications to VOT in their English realisations of /t/ which may have occurred as a result of a lack of plasticity in the L1 phonetic system, or a high level of L1 use in participants’ daily lives.