Preference for audiovisual speech congruency in superior temporal cortex

Auditory speech perception can be altered by concurrent visual information. The superior temporal cortex is an important combining site for this integration process. This area was previously found to be sensitive to audiovisual congruency. However, the direction of this congruency effect (i.e., stronger or weaker activity for congruent compared to incongruent stimulation) has been more equivocal. Here, we used fMRI to look at the neural responses of human participants during the McGurk illusion—in which auditory /aba/ and visual /aga/ inputs are fused to perceived /ada/—in a large homogenous sample of participants who consistently experienced this illusion. This enabled us to compare the neuronal responses during congruent audiovisual stimulation with incongruent audiovisual stimulation leading to the McGurk illusion while avoiding the possible confounding factor of sensory surprise that can occur when McGurk stimuli are only occasionally perceived. We found larger activity for congruent audiovisual stimuli than for incongruent (McGurk) stimuli in bilateral superior temporal cortex, extending into the primary auditory cortex. This finding suggests that superior temporal cortex prefers when auditory and visual input support the same representation.