Wednesday, August 01, 2007

Harry McGurk

You've come across a zillion optical illusions on the web, but how many audible illusions have you found? OK, you could argue that the Harry McGurk Effect is also an optical one, since it requires you to watch at least half the time, but the real tricking is through the ears, and whichever way you look at it, it's a fascinating illusion.

Whenever you watch the movie linked here, you'll quite clearly hear him saying "Dada dada dada", but if you close your eyes, you'll quite clearly hear him saying "Baba baba baba" instead. Play the clip several times, alternating between looking while listening, and listening with your eyes shut. Try looking off to the side of the screen and then quickly looking straight at him in mid-sentence, and what you hear will change!

Most adults (98%) think they are hearing "Dada". In reality you are hearing the sound "Baba", while you are seeing the lip movements for "Gaga". The McGurk Effect was first described by Harry McGurk and John MacDonald in "Hearing lips and seeing voices", Nature 264, 746-748 (1976).

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