Noise reduction limits the McGurk Effect
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In the McGurk Effect (McGurk & MacDonald, 1976), a visual depiction of a speaker silently mouthing the syllable [ga]/[ka] is presented concurrently with the auditory input [ba]/[pa], resulting in “fused” [da]/[ta] being heard. Deonarine (2010) found that increasing the intensity (volume) of the auditory input changes the perception of the auditory input from [ga] (at quiet volume levels) to [da], and then to [ba] (at loud volume levels). The present experiments show that reducing both ambient noise (additional frequencies in the environment) and stimulus noise (excess frequencies in the sound wave which accompany the intended auditory signal) prevents the illusory percept. This suggests that noise is crucial to audiovisual integration and that the McGurk effect depends on the existence of auditory ambiguity.