The Effect of Background Babble on Speech Perception for Monolingual and Bilingual Speakers : An ERP Study

Behavioral research has documented that background noise impacts speech perception for non-native speakers more than for native speakers, even when the non-native language is acquired at an early age and is currently the dominant language of use. Neurophysiological studies comparing language processing in quiet for the bilingual and monolingual brain are plentiful; however the impact of noise on neural markers associated with semantic processing (i.e. PN/N400) for these groups has not been compared. The present study measured auditory event-related potentials (ERPs) to English words using a semantic priming paradigm for two groups of young adults: monolingual speakers of English and highly proficient bilingual speakers of Spanish/English. Participants listened to English word triplets (S1, S2, S3); they were instructed to decide if the third word was semantically related to either of the preceding words. Analyses of ERP waveforms time-locked to S1 and S2 provided an opportunity to evaluate how the brain processes semantic relationships between words without interference from a simultaneous overt response. Results confirmed essentially equivalent neural patterns of semantic processing of word triplets between groups under ideal listening conditions. In the presence of background babble, distinct differences between group activation patterns were evident at posterior electrode sites, however results also indicated widespread similarities between monolingual and bilingual listeners. In particular, both groups evoked interesting changes in anterior neural activity when processing target words (related or unrelated to a preceding word) compared to when processing the initial prime words. The noise condition also elicited significant interaction effects of listening condition and group, suggesting that background babble impacts neural responses associated with semantic processing differently for monolinguals versus highly proficient bilingual speakers. Implications of these findings are discussed in relationship to existing literature and the need for further study