The reason ventriloquists seem able to “throw” their voices to the mouths of their dummies is because an area of the brain of onlookers that processes sounds handles vision too, say scientists.

By studying monkeys, researchers at the Duke University Medical Centre, North Carolina, found that auditory and visual information is processed together before the combined signals make it to the brain’s cortex, the analytical portion of the brain that assembles stimuli from the senses into coherent thoughts.

“The prevailing wisdom among brain scientists has been that each of the five senses — sight, hearing, smell, touch and taste — is governed by its own corresponding region of the brain,” said Jennifer Groh, neurobiologist. “Now, we are beginning to appreciate that it’s not that simple,” said Groh, whose findings were recently published in the Proceedings of the National Academy of Sciences. Her team focused on a tiny round structure in the brain known as the inferior colliculus, one of several early stops for signals leaving the ear.

“We found that this structure, which had been assumed to mainly process auditory information, actually responds to visual information as well,” Groh explained. “This means that visual and auditory information gets combined quite early, and before the ‘thinking part’ of the brain can make sense of it.”

That is why ventriloquism seems to work, she said. The association between the voice and the moving mouth of the dummy is made before the viewer consciously thinks about it.

The same process may also explain why the words being spoken by a talking head on television appear to be coming out of the mouth, even though the TV’s speakers are located to the side of the set. “The eyes see the lips moving and the ears hear the sound and the brain immediately jumps to the conclusion about the origin of the voice,” Groh said.

And the work could explain why at a noisy party it is easier to understand someone if you can see them too. “Our work does suggest a possible neural mechanism for the ‘cocktail party effect’ — basically, the presence of visual signals in the auditory pathway could contribute to how the brain identifies where a sound is coming from.”