How would it feel when you read a newspaper and the words glow like brilliant jewels? Imagine the sound of a piano conjuring up the colour pink. And when you feel pain, your world goes orange, as if you've put on a pair of tinted glasses.
For some people, this is everyday life. A condition called synesthesia, which causes the senses to fuse together, leads to unusual perceptions. The melding can take many forms, from hearing colours to tasting sounds.
The world in multimedia
"It's like experiencing the world in multimedia," says Carol Steen, an artist who lives in New York City. "Synesthesia doesn't obscure anything. It simply enhances it."
Steen is co-founder of the American Synesthesia Association. The group is holding its second annual meeting this weekend at the University of California, San Diego, where synesthetes and scientists are discussing the latest research into the condition.
Among those scheduled to attend are Dr Richard Cytowic, a neurologist and one of the foremost synesthesia researchers. He believes understanding synesthesia may unlock some of the mysteries of more ordinary perceptions.
For instance, when we see a red apple, Cytowic says, we don't see round in one place in our mind, red in another place, and the concept of an apple elsewhere.
"All the senses come together and we say, 'Oh. There's an apple,'" Cytowic says. "How that binding happens is the million-dollar question. Because synesthetes bind sensory qualities in unusual ways, understanding how their minds work may provide some answers."
Synesthesia is derived from the Greek word meaning "joined sensation." It can take many forms, Cytowic explains.
One woman felt guitar music tickling her ankles, violin music brushing against her face and trumpets on the back of her neck. Another man felt he could reach out and touch smooth, cool columns when he ate spearmint.
Cytowic estimates about one in 2 000 people have synesthesia. The most common form is seeing colours in printed words and numbers.
Why does it occur?
Researchers are unsure why synesthesia occurs. At the conference, scientists will present the results of studies using magnetic resonance brain imaging.
What is known is that the phenomenon is unlearned and involuntary. Synesthesia appears to be inherited, and is more common among women than men. People with synesthesia tend to have better than average memories and slight deficiencies in math and spatial navigation.
Famous synesthetes include the artist David Hockney, the writer Vladimir Nabokov and the composer Franz Lizst.
There is no treatment, and few synesthetes would want it anyway, Cytowic says.
"Synesthesia is abnormal only in it being rare," Cytowic says. "And people who have it often view it as a gift."
How to recognise synesthesia
Here's how you know if you have synesthesia, researchers say:
- It's involuntary, and begins in childhood.
- There's a spatial element to the perceptions. For example, some people for whom sounds trigger colours describe the colour as appearing on a screen a few inches in front of their face rather than in their head.
- The joined senses are elemental. For example, a sound may trigger a sour taste, but it would not trigger the sensation of eating a gourmet meal. A sound might trigger seeing a colour, but it would not trigger viewing a landscape with sheep and hills and a sunset.
- Synesthetes tend to have very good memories, and the extra perceptions help their recollections.
- The perceptions are laden with feeling and emotion, often positive but sometimes negative.