Mind & EverydayFact
Your eyes can decide which syllable you hear.
Harry McGurk and John MacDonald showed in Nature in 1976: hear "ba-ba" while watching lips form "ga-ga" and you perceive "da-da". Your brain fuses image and sound into a single percept. Even researchers who have studied it for decades still experience it.
Useful: It explains why watching someone's mouth makes bad audio suddenly intelligible.
Source: en.wikipedia.org