McGurk effect
When humans perceive speech, they not only take in auditory information but also visual information as well in the form of reading lips, facial expression, and other body bodily cues. Usually, these two sources of information are consistent with each other so the brain simply combines them to form one unified perceived stimuli. When the McGurk effect is tested and the incoming information from the ears and eyes differ, the brian tries to make sense of the contradictory stimuli which ultimately results in a fusion of both. In humans, information received from the eyes dominates other sensory modalities, including audition, so for instance when 'ba' is heard and 'ga' is seen, the resulting stimuli is heard is 'da'. The resulting stimuli is what happens when the brain tries to make sense of the two different sets of information.