What you see isn't always what you get: Auditory word signals trump consciously perceived words in lexical access.

Human speech perception often includes both an auditory and visual component. A conflict in these signals can result in the McGurk illusion, in which the listener perceives a fusion of the two streams, implying that information from both has been integrated. We report two experiments investigating whether auditory-visual integration of speech occurs before or after lexical access, and whether the visual signal influences lexical access at all. Subjects were presented with McGurk or Congruent primes and performed a lexical decision task on related or unrelated targets. Although subjects perceived the McGurk illusion, McGurk and Congruent primes with matching real-word auditory signals equivalently primed targets that were semantically related to the auditory signal, but not targets related to the McGurk percept. We conclude that the time course of auditory-visual integration is dependent on the lexicality of the auditory and visual input signals, and that listeners can lexically access one word and yet consciously perceive another.