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Synesthesia: Cross-sensory Experiences

Sep 2008

Written by Dr. Frederic B. Tate

Sensory "cross-talk" more common than once thought

Imagine that each time you hear a car horn you get the taste of blackberries in your mouth. Or when a red traffic light turns green, you smell smoke. You could have synesthesia (also spelled synaesthesia), a term from the Greek root meaning "with sensation." People with synesthesia may, for example, see numbers and letters in color, "taste" sounds or "hear" shapes. The sensation can occur between any two senses or perceptual modes. The Russian painter Wassily Kandinsky and the composer Franz Liszt both had synesthesia. But what was once thought to be a rare neurological phenomenon may actually be fairly common. Research varies as to estimated occurrences, but the most liberal estimates report that one in every 30 people may have this ability.

The most common form of synesthesia, called "grapheme/color synesthesia," is when numbers as well as individual letters of the alphabet are seen as shaded or tinged with a color. One synesthete (a person with synesthesia) may state that she sees the letter "P" as red, but when she adds a line and turns the letter into an "R," the letter changes from red to yellow! For her a page of black print is a rainbow of colors. Probably one of the rarest forms of this experience is lexical/gustatory synesthesia, whereby spoken words evoke the sensation of taste. These individuals have very specific, fixed tastes associated with words, and usually for as long as the synesthete can remember, he or she has experienced the tastes with those words.

Knowledge of synesthesia is not new and was actually investigated as early as the 1800s. Only recently, however, has scientific research been collected on the topic. This is due in part to advances in the field of neuropsychology. Synesthesia is not a neurological disorder; it does not interfere with daily activities, and most people with this ability consider it a gift. In fact, there is a strong correlation between art, creativity and synesthesia. Most synesthetes say that they did not know their ability was unusual until discovering, usually in childhood, that other people did not perceive the world as they did.

Theories of the neurological genesis of synesthesia are varied. Most researchers assert that this condition is caused by "cross-talk" between different regions of the brain. For example, regions involved in naming letters are adjacent to the area involved in color processing; synesthesia may be the result of cross-activation between these two areas. Recent research shows marked differences in the brains of synesthetes and the general population. Synesthetes have higher levels of connectivity between the fusiform gyrus (part of the temporal lobe, the area that controls processing and color information as well as word and number recognition) and the frontal cortex. Scientists hypothesize that this "cross-wiring" occurs when the nerve wiring that is usually contained within one sensory system crosses into another system.

Researchers are studying synesthesia not just because it is interesting, but also in hopes that results will offer new insights into brain functioning and multisensory integration. One of the mysteries in the study of consciousness is called the "binding" problem. We are still not sure how the human mind manages to bind perceptions into a whole. When we see a flower we see color and shape, feel texture, and possibly smell its scent. Our brain manages to bind all of these perceptions together into one concept-a flower. Studying synesthetes may afford answers to mysteries such as binding and someday help us better understand how our minds function.

For further information on this topic, visit these Web sites:
• American Synesthesia Association
• A community of synesthetes on (http://community.

Try this simple synesthesia experiment with a group:

1. Read a list of random numbers between 0 and 9 out loud at a rate of about one every three seconds.

2. After each number is read, ask people to write down the number and what COLOR they associate with each number.

3. Collect the answers. These are answers A.

4. Two to three weeks later, repeat the experiment but change the order of the numbers first used.

5. Collect the answers. These are answers B.

6. Compare answers A and B. People with synesthesia will have all or most of the same number-color pairs on both sets of answers.


Dr. Frederic Tate is a member of the psychology department at Eastern State Hospital. He can be contacted at