Factors modulating cross-linguistic co-activation in bilinguals

•Activation of bilinguals’ languages is driven by phonemic but not phonetic overlap.•The pattern of activation is similar in both first and second language listeners.•Some phonemes may be more susceptible to co-activation than others. Activation of both of a bilingual’s languages during auditory word recognition has been widely documented. Here, we argue that if parallel activation in bilinguals is the result of a bottom-up process where phonetic features that overlap across two languages activate both linguistic systems, then the robustness of such parallel activation is in fact surprising. This is because phonemes across two different languages are rarely perfectly matched to each other in phonetic features. For instance, across Spanish and English, a “voiced” stop is realized in phonetically-distinct ways, and therefore, words that begin with voiced stops in English do not in fact fully overlap in phonetic features with words in Spanish. In two eye-tracking experiments using a visual world paradigm, we examined the effect of a phonemic match (English /b/ matched to Spanish /b/) vs. a phonetic match (English /b/ matched to Spanish /p/) on cross-linguistic co-activation (English words co-activating Spanish) in Spanish L1 and in Spanish L2 speakers. We found that while phonemic matching induced co-activation in both Spanish L1 and Spanish L2 speakers, phonetic matching did not. Together, these results indicate that co-activation of two languages in bilinguals may proceed through activation of categorical phonemic information rather than through activation of phonetic features.