Neural correlates of intra-sentential code-switching in the auditory modality

Code-switching, the interchangeable use of two languages, is a hallmark of bilingual language processing. Although code-switching occurs most often in spoken communication, studies examining the neural mechanisms of code-switching typically present code-switched materials visually, using reading paradigms. The present study examined intra-sentential code-switching in the auditory modality in Spanish-English bilinguals, using Event-Related Potential (ERP) and Time Frequency Representation (TFR) analyses. Specifically, this study examined whether listening to code-switched sentences is associated with lexical-semantic integration (indexed by an N400 effect) or sentence-level reanalysis (indexed by an LPC effect), and the extent to which neural patterns associated with listening to code-switched speech are modulated by switching direction (from the dominant language to the weaker language, or vice versa). ERP results showed that listening to a switch from the dominant to the weaker language elicits N400 and LPC effects, while TFR results showed a power decrease in the upper beta frequency band. In contrast, listening to a switch from the weaker to the dominant language elicited only an N400 effect, while TFR results showed a power increase in the alpha frequency band. The findings indicate that cognitive processes involved in listening to intra-sentential code-switches vary by switching direction. More specifically, we propose that listening to dominant-to-weaker language switches engages lexical processes in addition to sentence-level reanalysis to integrate the weaker language into the sentence frame, whereas weaker-to-dominant switches engages lexical-semantic integration accompanied by inhibition processes (i.e., listeners inhibit their dominant language as the sentence unfolds in their weaker language, and this inhibition must be released upon hearing a switch into the dominant language).