Face viewing behavior predicts multisensory gain during speech perception.

Visual information from the face of an interlocutor complements auditory information from their voice, enhancing intelligibility. However, there are large individual differences in the ability to comprehend noisy audiovisual speech. Another axis of individual variability is the extent to which humans fixate the mouth or the eyes of a viewed face. We speculated that across a lifetime of face viewing, individuals who prefer to fixate the mouth of a viewed face might accumulate stronger associations between visual and auditory speech, resulting in improved comprehension of noisy audiovisual speech. To test this idea, we assessed interindividual variability in two tasks. Participants (n = 102) varied greatly in their ability to understand noisy audiovisual sentences (accuracy from 2-58%) and in the time they spent fixating the mouth of a talker enunciating clear audiovisual syllables (3-98% of total time). These two variables were positively correlated: a 10% increase in time spent fixating the mouth equated to a 5.6% increase in multisensory gain. This finding demonstrates an unexpected link, mediated by histories of visual exposure, between two fundamental human abilities: processing faces and understanding speech.