Effects of bilingualism on non-native phonetic contrasts.

Monolingual listeners often have difficulties discriminating non-native contrasts. The Perceptual Assimilation Model (PAM) [C. T. Best, G. W. McRoberts, and N. M. Sithole, JEP:HPP 14, 345–360 (1988)] predicts poor discrimination if two non-native sounds assimilated equally well to a single native category (SC), good discrimination if a category goodness (CG) difference is perceived, and excellent discrimination if sounds are assimilated to two different categories (TC). However, implications for bilingual listeners are uncertain. Do bilinguals maintain two separate phonological systems, or do the systems interact to enhance or inhibit non-native discrimination? In this study, monolingual English and bilingual Spanish/English listeners discriminated and categorized Spanish [b–p], English [b–ph], and three Xhosa bilabial stop contrasts. Both groups discriminated English [b–ph] excellently, as did bilinguals for Spanish [b–p], which monolinguals discriminated less well, consistent with CG assimilation. Compatible with PAM, monolinguals showed excellent TC performance on Xhosa unaspirated/aspirated stops; bilinguals’ lower discrimination indicated CG assimilation. On Xhosa implosive/pre-nasalized stops, monolinguals showed CG assimilation and greatly outperformed bilinguals, who showed an SC pattern. Conversely, on Xhosa implosive/plosive stops monolinguals showed SC assimilation; bilingual discrimination was higher, showing GC assimilation. [Work supported by NIH.]