Imagine a world where the sound of music would make you see colors. Where the note B is sparkling silver and D flat is a wondrous, pure periwinkle. Where the taste of food has a distinctive shape and where the sound of words can leave a bad taste. Even the calendar -- days, months and years -- can generate specific 3-D images.
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That's the world of Laura Rosser, 24, and others who have synesthesia, in which one sense -- taste, sight, hearing, touch or smell -- gets jumbled with another, creating what Dr. Richard Cytowic, a neurologist, describes as a blending of the senses.
"My voice, for example, is not only something that you hear but also something that you might see or taste or feel as a physical touch," Cytowic said.
Rosser sees every note of the piano she plays as a distinct color. "E flat is turquoise. Very warm turquoise," Rosser said. "F sharp is yellow-green." When Rosser plays many notes together, she said the colors "sort of merge into each other."
Synesthesia isn't just people getting a bit poetic about their world. The brains of people with the condition are actually wired differently.
Cytowic said people with synesthesia have a "different texture of reality."
Rosser sees numbers as colors, too. To her, "Twos are orange and [fives] are red." Another woman who has synesthesia, Crista Kostenko,27, sees the same numbers but in different colors. "My fives are red and my twos are yellow."
Rosser and sisters Evin Linn, 24, and Kostenko see more than just black letters. Since they were children, they've had cross talk going on in their brains, meaning every letter is associated with a distinct, unchanging color.
"What this shows is that synesthesia is both automatic and involuntary," Cytowic said. "So they can't really control it. It's just there. It's something that happens to you. You don't do anything to make it happen."
They see colored numbers, too, and the colors are very specific. When ABC News asked Rosser, Linn and Kostenko to show us how they see the number eight by selecting from hundreds of paint samples, they had a hard time finding a match.
"It's between gentle violet and exotic purple," Rosser said. "It's like majestic violet. But it's midnight navy, more between [the two]," Kostenko said. "It's more of a pink. Sort of a combination between rosy blush and spring tulips," Linn said.
The colors are always the same from the day they're born till the day they die. In case you don't believe them, there's scientific proof.
"It's a real color experience that's as vivid and real as the colors that you and I see ordinarily in the world -- it's just that it's being evoked in a highly unusual way," said Randolph Blake, an ABC News consultant, who, along with a team at Vanderbilt University, is researching Rosser's brain.
As black letters flash before her eyes, Rosser records the colors she sees. Amazingly, images of her brain show the color areas are active. These are areas that would not light up in other people's brains.
"The hypothesis is that there's some unusually strong connections between areas of her brain that aren't so strongly connected in our brains -- so strong, that when she's looking at a letter, it actually automatically activates that color area," Blake said.