NPR logo What's He Saying? 'Bahh' Or 'Fahh'? A Brain Mystery

What's He Saying? 'Bahh' Or 'Fahh'? A Brain Mystery

I love illusions, where your brain makes weird things happen. Those of you who come here often have seen some doozies, but this one ... oooh, this is one of the strangest.

The question is: Which is more powerful, your eyes or your ears? Watch this clip and experience "The McGurk Effect." Your ears will feel ashamed.

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The McGurk Effect is named for a psychologist from Scotland, Harry McGurk, working with John MacDonald. The experiment shows that while our senses seem separate — you wouldn't think what you see should affect what you hear — it turns out, that's totally wrong. If our eyes see one thing and our ears hear a different thing, when sight and sound grapple in our brains, the eyes win. Eyes tell ears what to hear. Or so it seems.

Not only that, even if your brain knows this is an illusion, you still can't hear the truth unless you close your eyes. The illusion is that powerful.

Why Does This Happen?

Does sight always beat sound? Professor Lawrence Rosenblum in the video seems to suggest that experimental results may vary depending on which sense is "more salient." I'm not sure what that means. Nosing around, I found some experiments where you see lips saying "gah" while the sound is saying "bah" and my brain chooses neither of them, and settles for a middle-of-the-road "dah." But nowhere could I find an explanation for why my ears keep surrendering to my eyes.

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Does anybody know?