Neural correlates of audiovisual speech processing in a second language

• Audiovisual integration in posterior superior temporal sulci is true for L1 and L2.
• L2 audiovisual integration involves both unisensory and heteromodal regions.
• L2 audiovisual integration is biased toward visual input.

Neuroimaging studies of audiovisual speech processing have exclusively addressed listeners’ native language (L1). Yet, several behavioural studies now show that AV processing plays an important role in non-native (L2) speech perception. The current fMRI study measured brain activity during auditory, visual, audiovisual congruent and audiovisual incongruent utterances in L1 and L2. BOLD responses to congruent AV speech in the pSTS were stronger than in either unimodal condition in both L1 and L2. Yet no differences in AV processing were expressed according to the language background in this area. Instead, the regions in the bilateral occipital lobe had a stronger congruency effect on the BOLD response (congruent higher than incongruent) in L2 as compared to L1. According to these results, language background differences are predominantly expressed in these unimodal regions, whereas the pSTS is similarly involved in AV integration regardless of language dominance.