This study investigates the effects of individual bilingualism and long-term language contact on monophthongal vowel productions in English and Welsh.

To this end, we recorded the Welsh and English vowel productions of two sets of Welsh-English bilinguals differing in home language use, as well as the English vowel productions of English monolinguals.

The data were analysed acoustically, with a focus on spectral and temporal properties. Comparisons were then made within each language and cross-linguistically.

The results of a cross-linguistic acoustic comparison revealed a high degree of convergence in the monophthong systems of Welsh and English, but also some language-specific categories. Interestingly, at the individual level we found no effect of linguistic experience on vowel production: the two sets of bilinguals and the English monolinguals did not differ in their realisation of English vowels, and the two sets of bilinguals did not differ in their realisation of Welsh vowels.

This is one of few studies to examine the effect of linguistic background on variation in Welsh and English bilingual speech, and the first to compare the speech of Welsh-English bilinguals and English monolinguals. More specifically, it investigates the extent to which a speaker’s home language can affect phonetic variation in a close-knit community of speakers and in a situation characterised by long-term language contact.

The findings demonstrate pervasive phonetic convergence in a language contact situation with a historical substrate. They also indicate that a homogeneous peer group with shared values can override the effects of individual linguistic experience.