When /b/ill with /g/ill becomes /d/ill: Evidence for a lexical effect in audiovisual speech perception

Although the McGurk Effect is a well researched illusory phenomenon arising from discrepant auditory and visual speech information little is known about the influence of lexical processes on this phenomenon. Thus, we investigated the McGurk Effect using three letter consonant-vowel-consonant real word and pseudoword pairs with an audiovisual discrepancy positioned at either stimulus onset or offset. The results demonstrated that the frequency of illusions was similar for real words and pseudowords when the discrepancy was at stimulus onset but was significantly lower for real words when the audiovisual discrepancy was positioned at stimulus offset. Positioning of audiovisual discrepancy was not important for accurate auditory perception of pseudowords. These results suggest that the McGurk illusion is the result of audiovisual integration that occurs early in perception prior to word identification and that these early audiovisual integrative processes are modulated by lexical knowledge.