Researchers stumble across people who 'hear' movement

Washington, Aug 7 : Individuals with synesthesia or 'cross activated senses' perceive the world in a different way and unlike any of us they can hear movement.

They perceive numbers or letters in terms of colours or days of the week as possessing personalities, even as they function normally in the world outside.

Now, California Institute of Technology researchers have discovered a type of synesthesia in which individuals hear sounds, such as tapping, beeping, or whirring, when they see things move or flash.

Surprisingly, the scientists said auditory synesthesia may not be unusual - and may simply represent an enhanced form of how the brain normally processes visual information.

Psychologists previously reported visual, tactile, and taste synesthesias, but auditory synesthesia had never been identified. Caltech lecturer in computation and neural systems Melissa Saenz discovered the phenomenon quite by accident.

"While I was running an experiment at the Caltech Brain Imaging Center, a group of students happened to pass by on a tour, and I volunteered to explain what I was doing," explained Saenz, who, along with Christof Koch, professor at Caltech, reports the finding.

"As part of the experiment, a moving display was running on my computer screen with dots rapidly expanding out, somewhat like the opening scene of Star Wars. Out of the blue, one of the students asked, 'Does anyone else hear something when you look at that?'

"After talking to him further, I realised that his experience had all the characteristics of a synesthesia: an automatic sensory cross-activation that he had experienced all of his life," she said.

A search of the synesthesia literature revealed that auditory synesthesia - of any kind - had never been reported. Intrigued, Saenz began to look for other individuals with the same ability, using the original movie seen by the student as a test.

"I queried a few hundred people and three more individuals turned up," she said. Having that specific example made it easy to find more people. That movie just happens to be quite "noisy" to the synesthetes and was a great screening tool.

"When asked if it made a sound, one of the individuals responded, 'how could it not?' I would have been less successful had I just generally asked, 'Do you hear sounds when you see things move or flash?' because in the real environment, things that move often really do make a sound, for example, a buzzing bee.

"These individuals have an enhanced soundtrack in life, rather than a dramatically different experience, compared to others," said Saenz. However, when asked, all of the synesthetes could name examples of daily visual events that caused sounds that they logically knew to be only in their minds, such as seeing a fluttering butterfly or watching television with the sound turned off.

Saenz and Koch found that the four synesthetes outperformed a group of nonsynesthetes on a simple test involving rhythmic patterns of flashes similar to visual Morse code.

However, with visual flashes synesthetes were much more accurate, responding correctly more than 75 percent of the time, compared to around 50 percent - the level predicted by chance - in the control group. "Synesthetes had an advantage because they not only saw but also heard the visual patterns," Saenz says.

Saenz and Koch suspect that as much as one percent of the population may experience auditory synesthesia. These findings were published in Tuesday's issue of Current Biology.