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Times Books

170 pages, $26

It sounds faintly schizophrenic, to see sounds or to taste shapes. And indeed, throughout history, people who claimed that words or music came in different colors were in danger of being misdiagnosed as psychotic -- or dismissed as speaking merely metaphorically.

But what they were experiencing is synesthesia, a neurological condition in which stimulating one sense fires off a reaction in a second sense. Synesthetes might say that a food tastes "pointy" and mean not a metaphor, but a sensation in the mouth.

Researchers disagree about how many people have some form of synesthesia; estimates vary from one in 10 to one in 25,000. But many researchers believe more children than adults and more women than men experience the phenomenon. The French poet Arthur Rimbaud wrote a sonnet, "Voyelles," about his experience of colored vowels. Novelist Vladimir Nabokov described his colored alphabet in his autobiography. Franz Liszt reportedly saw colored notes.

Journalist Patricia Lynne Duffy is another synesthete and her matter-of-fact descriptions of the phenomenon in "Blue Cats and Chartreuse Kittens" will go a long way to letting others enter into synesthetes' perceptions.

Duffy experiences a colored alphabet, one of the most common manifestations of the experience. Before she could read, she would see colored patterns when she heard words, a unique pattern for each set of sounds. She spent much of her childhood painting pictures of the designs, never realizing that other people didn't hear words in the same way.

When she learned the alphabet and began to read, her color perceptions transferred to letters and then to the words formed by the letters. In Duffy's mind, "c" is dark blue, which means that "cat" is a blue word, too. "K" is chartreuse, so "kitten" is chartreuse.

The mark of a true synesthete is that his or her perceptions don't shift. "It is important to understand that to a synesthete, the color of a letter is as intrinsic part of it as is its shape," Duffy writes. "To me, a red O seems as peculiar and wrong as the notion of a triangular O. An O is circular! And it is white!"

It's interesting, say researchers, that colored-language synesthetes don't necessarily agree on which colors go with which letters -- but that a remarkable number say that the letter "o" is white.

What's going on here?

Duffy devotes much of the book to what researchers think is going on in a synesthete's brain (something about lack of blood flow) and why they think it might have developed (an evolutionary trick to fix complex experiences).

But some of the most affecting passages are synesthetes' accounts of how they found others who could understand their perceptions, after years of feeling like freaks. "I felt I had to hide the way I was internalizing things," says one synesthete, who dazzlingly experiences numbers and units of time as being colored and three-dimensional. (That's similar to the synesthesia I experience, time as colored spaces. By the way, we're living in a trapezoidal lemon-yellow decade.)

To bridge the gap between synesthetes and others, Duffy includes several Web pages. A good starting point is web.mit.edu/synesthesia/www/synesthesia.html, which tries to reproduce some perceptions.

Meanwhile, Duffy's book is a thought-provoking glimpse at how much is lurking in other people's minds -- and how little we know about it.

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