I recently went to see a ventriloquist show – Jay Johnson’s, “The two and only“. While funny, the best part was the history and science woven into the show. However Jay Johnson hadn’t read a couple of fairly recent studies.
The mechanism for ventriloquism has been debated for centuries with theories from demon possesion, mental illness and the ability to “throw” one’s voice to a new location routinely suggested.
A couple of years ago two scientists (Alais and Burr) unlocked the secret and even discovered “reverse ventriloquism” .
Basically, we trust our eyes over our ears. Both your ears and your eyes can judge the location of something. A good ventriloquist moves his dummy in sync with his words. Your ears say the sound is coming from the ventriloquist, but your eyes tell you it’s coming from the dummy’s mouth. The eyes have it.
In experimental conditions , one researcher (Spence) used a loudspeaker playing a series of words and a video of someone’s lips mouthing a few of those words. Listeners heard the lip-synced words coming from the television, and the non lip-synced words coming from the loudspeaker – so long as the loudspeaker and the television were not too far apart.
Alais and Burr took this apparent reliance on the eyes a step further. By degrading an image (in their case turning a larget clear dot into a fuzzy blob) and thus reducing the accuracy of the visual cues, they found that people started to trust their ears over their eyes. When the blob was very fuzzy and thus it was hard to say exactly where the blob was observers would assume the location of the blob was at the location of an accompanying sound. They called this the “reverse ventriloquist effect”.
 Alais, D. & Burr, D. The ventriloquist effect results from near-optimal bimodal integration. Current Biology, 14, 257 – 262, (2004).
 Driver J (1996) Enhancement of selective listening by illusory mislocation of speech sounds due to lip-reading. Nature 381: 66-68