Bilinguals automatically access both languages based on “irrelevant” acoustic detail: Evidence from lexical tone

Bilinguals simultaneously activate words from both languages that are consistent with the input, even in contexts/tasks which emphasise only one language. However, it is unknown whether/how the speech perception system integrates or ignores “irrelevant” acoustic cues which might constrain bilingual parallel activation. We leverage the opportunity of Mandarin-English bilinguals in which Mandarin uses an acoustic cue to contrast words (lexical tone) that is not relevant in English. For example, Mandarin distinguishes /bei/ with a high tone ( cup ) from the same word with a falling tone ( quilt ). Thus, when a bilingual hears bay with a falling prosody, do they use the prosodic information embedded in ‘bay’ to preferentially activate /bei4/ or do they simply ignore this cue because it is irrelevant in identifying ‘bay’? Using the Visual World Paradigm, Experiment 1 tested this hypothesis with English words of naturally falling prosody and Mandarin competitors that either matched the prosodic form (Tone 4) or did not (Tones 1–3). Participants fixated competitors more frequently than control distractors only when the target words contained the prosodic forms matched with the Mandarin competitors. Experiment 2 replicated this finding with English words superimposed with Tones 1–3 but only found the effect when English stimuli were strongly Mandarin-like. Experiment 3 replicated Experiment 1 by showing no difference between natural tokens and tone-synthesized ones. Together, these results demonstrate that bilingual parallel activation is automatic and that lexical tone, irrelevant to the present language and task, is obligatorily interpreted in real-time processing.