Lexical tonal effects in code-switching: A comparative study of Cantonese, Mandarin, and Vietnamese switching with English

Previous research has revealed much about the syntactic and social variables conditioning code-switching (i.e., the alternation between two or more languages in a discourse or utterance); however, little is known about the phonological effects. Our work explores this area by asking two main questions: (1) Does lexical tone affect code-switching between a tonal language and a non-tonal language? and (2) Is this effect (or lack thereof) observable cross-linguistically? We examine natural code-switching production between Cantonese and English, Mandarin and English, and Vietnamese and English. We use a semi-automatic natural-language processing method to process and extract relevant variables, including tonal categories at switch points. Data include transcribed natural speech from three bilingual corpora: the HLVC corpus (Cantonese/English, 25 speakers), the SEAME corpus (Mandarin/English, 20 speakers), and the CanVEC corpus (Vietnamese/English, 45 speakers). We use logistic mixed-effects models to examine tonal effects, taking into account other factors such as frequency and grammatical category. We found a robust tonal effect in Cantonese/English, a less robust effect in Mandarin/English, and no effect in Vietnamese/English. This indicates there is a tonal effect in code-switching between a tonal and a non-tonal language, but this effect is language-dependent. We also found a specific T3 ‘step-up’ pattern at Cantonese-English switch points and offered some possible phonological explanations. This is the first study that systematically investigates tonal effects in code-switching across different language pairs, using comparable data and methods. Our finding of a Cantonese-English T3 ‘step-up’ pattern is also a novel discovery that hitherto has not been documented. Theoretically, our findings support Clyne’s ‘facilitation theory’ in code-switching at a prosodic level. Empirically, we nevertheless emphasised the complexity of different prosodic features and social variables in play, thereby rejecting the idea of ‘predicting’ code-switching solely based on linguistic factors.