Hearing lips in a second language: visual articulatory information enables the perception of second language sounds.

We investigated the effects of visual speech information (articulatory gestures) on the perception of second language (L2) sounds. Previous studies have demonstrated that listeners often fail to hear the difference between certain non-native phonemic contrasts, such as in the case of Spanish native speakers regarding the Catalan sounds /epsilon/ and /e/. Here, we tested whether adding visual information about the articulatory gestures (i.e., lip movements) could enhance this perceptual ability. We found that, for auditory-only presentations, Spanish-dominant bilinguals failed to show sensitivity to the /epsilon/-/e/ contrast, whereas Catalan-dominant bilinguals did. Yet, when the same speech events were presented audiovisually, Spanish-dominants (as well as Catalan-dominants) were sensitive to the phonemic contrast. Finally, when the stimuli were presented only visually (in the absence of sound), none of the two groups presented clear signs of discrimination. Our results suggest that visual speech gestures enhance second language perception at the level of phonological processing especially by way of multisensory integration.