Internal Brain damage Both
hemispheres of the brain make a contribution to the McGurk effect. They work together to integrate speech information that is received through the auditory and visual senses. A McGurk response is more likely to occur in right-handed individuals for whom the face has privileged access to the right hemisphere and words to the left hemisphere. In people with right hemisphere damage, impairment on both visual-only and audio-visual integration tasks is exhibited, although they are still able to integrate the information to produce a McGurk effect. People with dyslexia particularly differed for combination responses, not fusion responses. They use less visual information in speech perception, or have a reduced attention to
articulatory gestures, but have no trouble perceiving auditory-only cues. However, if the stimulus was nonhuman (for example bouncing a tennis ball to the sound of a bouncing beach ball) then they scored similarly to children without ASD. It has been suggested that the weakened McGurk effect seen in people with ASD is due to deficits in identifying both the auditory and visual components of speech rather than in the integration of said components (although distinguishing speech components as speech components may be isomorphic to integrating them).
Language-learning disabilities Adults with language-learning disabilities exhibit a much smaller McGurk effect than other adults. These people are not as influenced by visual input as most people. Often a reduced size of the
corpus callosum produces a hemisphere disconnection process. Schizophrenia slows down the development of audiovisual integration and does not allow it to reach its developmental peak. However, no degradation is observed. The greatest difficulty for aphasics is in the visual-only condition showing that they use more auditory stimuli in speech perception.
External Cross-dubbing Discrepancy in vowel category significantly reduced the magnitude of the McGurk effect for fusion responses. Auditory /a/ tokens dubbed onto visual /i/ articulations were more compatible than the reverse.
Mouth visibility The McGurk effect is stronger when the right side of the speaker's mouth (on the viewer's left) is visible. People tend to get more visual information from the right side of a speaker's mouth than the left or even the whole mouth. Visual attention modulates audiovisual speech perception.
Syllable structure A strong McGurk effect can be seen for click-vowel syllables compared to weak effects for isolated clicks. This shows that the McGurk effect can happen in a non-speech environment. If a male face is dubbed with a female voice, or vice versa, there is still no difference in strength of the McGurk effect. The effect is experienced more often and rated as clearer in the semantically congruent condition relative to the incongruent condition. While looking at oneself in the mirror and articulating visual stimuli while listening to another auditory stimulus, a strong McGurk effect can be observed. Subjects are still strongly influenced by auditory stimuli even when it lagged the visual stimuli by 180 milliseconds (point at which McGurk effect begins to weaken). Touch is a sensory perception like vision and audition, therefore increasing attention to touch, decreases the attention to auditory and visual senses.
Gaze The eyes do not need to
fixate in order to integrate audio and visual information in speech perception. There was no difference in the McGurk effect when the listener was focusing anywhere on the speaker's face. The effect does not appear if the listener focuses beyond the speaker's face. In order for the McGurk effect to become insignificant, the listener's gaze must deviate from the speaker's mouth by at least 60 degrees. ==Other languages==