CHARLESTON, W.Va. -- How would you define the taste of dark blue?

To a normal person, that would be a strange question. But to a lexical-gustatory synesthete, it would be as natural as breathing. To a music-color synesthete, a simple note played on a piano would have its own distinct color. This is the world of synesthesia, where otherwise ordinary people tread the thin line between fantasy and reality.

Synesthesia is a condition in which a person has difficulty distinguishing between sensory inputs. Two or more of the senses are blended together, and one triggers the other.

This phenomenon is almost certainly caused by genetics, though the origin of synesthesia is still a topic of debate. According to recent studies, it appears in families and is more common among women than men.

All real synesthetes have the condition from their earliest memories and are unaware when young that there is anything different about the way they sense things because they have never known otherwise.

For a long time, this condition was dismissed as a myth, but as knowledge about the brain increased, research concluded that synesthesia was real. Although it is rare to have a true form of synesthesia, scientists speculate that more than half of the human race experiences a basic form of synesthesia, in which we associate higher sounds with bright colors and lower sounds with dark colors.

Having synesthesia is not quite the same as smelling a pie and having a picture of a pie come into your head. That is normal memory work. To a sound-vision synesthete, the smell of a pie will be a mixture of abstract textures and colors, and they don't have to know what the scent is to have a picture to go along with it.

There are endless types of synesthesia. Touch, taste, smell, hearing and sight are all reported as either a cause or effect of the condition. Pain and emotions are also tangled in the complicated web of synesthesia.

A common form of synesthesia is grapheme-color, in which the synesthete sees letters as each having an individual, regular color - no matter the color of ink the words are printed in. The colors stay the same throughout the synesthete's life. For example, the letter "A" is generally red.

More rare types of the condition provide an interesting look at the way modern concepts of witchcraft and magic have evolved. In one case - personality-color synesthesia - a person's personality produces a color visible to the synesthete. This is likely the basis for auras. A lower percentage of synesthetes also reported that, to them, personalities have scents.

CHARLESTON, W.Va. -- How would you define the taste of dark blue?

To a normal person, that would be a strange question. But to a lexical-gustatory synesthete, it would be as natural as breathing. To a music-color synesthete, a simple note played on a piano would have its own distinct color. This is the world of synesthesia, where otherwise ordinary people tread the thin line between fantasy and reality.

Synesthesia is a condition in which a person has difficulty distinguishing between sensory inputs. Two or more of the senses are blended together, and one triggers the other.

This phenomenon is almost certainly caused by genetics, though the origin of synesthesia is still a topic of debate. According to recent studies, it appears in families and is more common among women than men.

All real synesthetes have the condition from their earliest memories and are unaware when young that there is anything different about the way they sense things because they have never known otherwise.

For a long time, this condition was dismissed as a myth, but as knowledge about the brain increased, research concluded that synesthesia was real. Although it is rare to have a true form of synesthesia, scientists speculate that more than half of the human race experiences a basic form of synesthesia, in which we associate higher sounds with bright colors and lower sounds with dark colors.

Having synesthesia is not quite the same as smelling a pie and having a picture of a pie come into your head. That is normal memory work. To a sound-vision synesthete, the smell of a pie will be a mixture of abstract textures and colors, and they don't have to know what the scent is to have a picture to go along with it.

There are endless types of synesthesia. Touch, taste, smell, hearing and sight are all reported as either a cause or effect of the condition. Pain and emotions are also tangled in the complicated web of synesthesia.

A common form of synesthesia is grapheme-color, in which the synesthete sees letters as each having an individual, regular color - no matter the color of ink the words are printed in. The colors stay the same throughout the synesthete's life. For example, the letter "A" is generally red.

More rare types of the condition provide an interesting look at the way modern concepts of witchcraft and magic have evolved. In one case - personality-color synesthesia - a person's personality produces a color visible to the synesthete. This is likely the basis for auras. A lower percentage of synesthetes also reported that, to them, personalities have scents.

For several types of synesthesia, various emotions may have color, smell or taste. Abstract concepts are not immune, either. Time, days of the week, months, letters and numbers can have very clear personalities to certain synesthetes. To them, the letter "K" may be shy, or the number 3 untrustworthy. This particular form of synesthesia is called ordinal-linguistic personification.

Music is intricately tied to synesthesia. Synesthetes experience music in different ways. They not only see the notes or instruments in color, but they also taste and smell the music. In this way, any of the senses can become irreversibly linked to one another.

Synesthesia is usually one-way. A letter may produce a color, but colors will not produce a letter in return. However, in rare cases the condition is bi-directional. Also, many synesthetes experience more than one form of the condition.

Now that scientists are beginning to take an interest in synesthesia, extensive research on its cause and effects has begun, although it's difficult to get an accurate estimate of the percentage of the human population affected. This research is leading neurology into a new frontier, giving brain experts insight into how the mind processes sensory inputs.

On one thing scientists agree: intensive use of drugs such as LSD or Ecstasy cannot give someone synesthesia. They only simulate the condition and the effects dissipate as soon as the drug wears off.

The only known way to get synesthesia without having it from birth is losing a limb, and even in this instance, the synesthesia is limited. The sensation, known as a "phantom limb," is a kind of synesthesia that appears in rare cases after amputations.

So far, synesthesia has been proven to have only good side effects on people. Synesthetes are naturally artistic and enjoy doing creative activities. They score high on cognitive assessment and memory tests. They are no more prone to mental illness than the average person, testing negative for diseases such as schizophrenia and psychosis.

Several famous musicians, artists and even scientists are said to have had synesthesia. Among them are Duke Ellington, Nikolai Rimsky-Korsakov, Eddie Van Halen, John Mayer and Richard Feynman, the winner of the 1965 Nobel Prize in Physics. Feynman saw letters and numbers in color, which made equations simple for him.

Aristotle is rumored to have been a flavor-color synesthete, and Sir Isaac Newton did research in music-color synesthesia.

This fascinating condition is very real and very incredible. With modern technology and knowledge, it is hoped that more will be unearthed about this hidden world of the senses.