However, if integration does not occur, the observer can perceive the components separately and may choose to respond either according to what he heard or according to what he saw. The real McGurk effect arises due to multisensory integration, resulting in an altered auditory percept. One challenge with this interpretation of the McGurk effect is that it is impossible to be certain that the responses the observer gives correspond to the actual percepts. Thus, when the McGurk effect occurs, the observer has the subjective experience of hearing a certain utterance, even though another utterance is presented acoustically. When integration takes place, it results in a unified percept, without access to the individual components that contributed to the percept. The different variants of the McGurk effect represent the outcome of audiovisual integration. This definition includes all variants of the illusion, and it has been used by MacDonald and McGurk (1978) themselves, as well as by several others (e.g., Rosenblum and SaldaГ±a, 1996 Brancazio et al., 2003). Here my first claim is that the definition of the McGurk effect should be that an acoustic utterance is heard as another utterance when presented with discrepant visual articulation. There are other pairings, which result in hearing according to the visual component, e.g., acoustic presented with visual is heard as. For example, a reverse combination of these consonants, AV, is heard as, i.e., the visual and auditory components one after the other. This definition ignores the fact that other incongruent audiovisual stimuli produce different types of percepts. Many researchers have defined the McGurk effect exclusively as the fusion effect because here integration results in the perception of a third consonant, obviously merging information from audition and vision ( van Wassenhove et al., 2007 Keil et al., 2012 Setti et al., 2013).

This is called the fusion effect since the percept differs from the acoustic and visual components. The best-known case is when dubbing a voice saying onto a face articulating results in hearing. There are many variants of the McGurk effect ( McGurk and MacDonald, 1976 MacDonald and McGurk, 1978) 1. Second, when interpreting the McGurk effect, it is crucial to take into account the perception of the unisensory acoustic and visual stimulus components. First, the McGurk effect should be defined as a categorical change in auditory perception induced by incongruent visual speech, resulting in a single percept of hearing something other than what the voice is saying. Here I shall make two main claims regarding the definition and interpretation of the McGurk effect since they bear relevance to its use as a measure of multisensory integration.

It is a very useful research tool since the strength of the McGurk effect can be taken to reflect the strength of audiovisual integration. It shows that auditory and visual information is merged into a unified, integrated percept. The reason for the great impact is that this is a striking demonstration of multisensory integration. It has been replicated many times, and it has sparked an abundance of research. The illusion has been termed the McGurk effect. Even though the acoustic speech signal was well recognized alone, it was heard as another consonant after dubbing with incongruent visual speech. They recorded a voice articulating a consonant and dubbed it with a face articulating another consonant. McGurk and MacDonald (1976) reported a powerful multisensory illusion occurring with audiovisual speech.

Define auditory