Synesthesia is a neurological condition which affects perception. The word synesthesia is derived from the Greek rooy, syn meaning union and aisthaesis, meaning senses. Synesthesia is perceiving through the use of two senses. For synesthetes (what those who experience synesthesia are called), ordinary activities like vision, sound and touch are experienced perceptually through the senses as color, touch, taste or sound.
In their book, "Wednesday is Indigo Blue," neurologists Richard E. Cytowic and David M. Eagle described the symptoms of synesthesia. The condition causes one sense to heighten or trigger a response through another sense. For example, a certain smell will be accompanied by a particular color. A letter or number will be viewed or experienced as a color, or a word will elicit a taste. Cytowic and Eagle list five symptoms that are present in a diagnosis of synesthesia:
1. The experience is involuntary and automatic. That means a person must have no choice but to respond to an outside stimulus;
2. The condition must be spatially extended. Synesthetes believe their experiences are normal and within the bounds of reality. Children, in particular, do not see anything wrong with what they perceive. As people mature, they learn to use the gifts to help in memorizing letters, numbers, sequences or names;
3. Sensations must be durable and generic. Durable describes the experience of being present or innate from birth, lasting throughout one’s life. Generic refers to experiencing synesthesia not in a detailed or highly specific manner, but rather in a more diffuse manner. Color is sensed as a blotch or cloud of color. Tastes are experienced as a "sense" of sourness;
4. Sensations must be memorable. For example, if one experiences the number seven as the color purple, that person will always associate the same number with the same color. This holds true for a sound. Tests done to determine the validity of synesthesia describe patients' reporting the same results for their experiences years later;
5. Sensations are affect-laden. A synesthete’s experiences produce a sense of pleasure or discomfort, enjoyment or distaste. For example, dialing numbers on a phone might produce a pleasurable experience because certain numbers educe beautiful colors. In other cases, certain numbers may produce discordant sounds or repulsive colors.
There are different types of synesthesia, the most common being grapheme-color synesthesia. This type of synesthesia causes a person to associate colors with numbers and letters. About 10 percent of patients experience this type of grapheme-color synesthesia, actually projecting the color onto the external items;the other 90 percent “feel” or "sense" the color of the number internally. Grapheme synesthesia is not generally viewed by those who have this condition as a hindrance. In fact, many report using their condition to help them differentiate between objects and ideas. A synesthete might report experiencing the word "plane" quite differently from the word "plain," or the word "break" differently from "brake." Another perception experienced by someone with synesthesia is the color personification of a series like the days of the week or the months of the year. Each series evokes a type of color personality.
Synesthetes experience letters and numbers differently. For example, some see vowels in darker colors, while others see consonants as darker. For some, even numbers evoke pleasurable sounds or colors, while odd numbers evoke the opposite. Synesthesia is viewed as a gift by many who have it. Many synesthetes are able to memorize names and phone numbers, and are adept at doing mental arithmetic. They also use their gifts in the creative arts, music and artistic outlets.
Visual motion sound synesthesia occurs when light and motion evoke a sound response. For example, one might see a flashing red light and "hear" a bell ringing at the same time. Or the wind blowing fire might evoke the sound of a baby crying. The combination of sounds sets off an audio synesthesia experience.
Spatial sequence synesthesia is a different type of synesthesia. It occurs when some synesthetes are given a sequence of numbers. One number in the sequence will tend to appear farther away than the other. People with this type of synesthesia tend to have superior memories
Sound and color synesthesia (chromesthesia) occurs when a combination of sounds in the environment sets off a "fireworks-like" display of lights. For example, the sound of a tea kettle going off, music playing and a baby laughing in combination might set off this response. Some people visualize music, "seeing" the instruments, notes or lines of color moving and floating before their eyes.
A rare type of synesthesia is referred to as lexical-gustatory synesthesia. This happens when people taste words. According to the author of "Words on the Tip of Your Tongue," Julia Simner, a cognitive neuropsychologist and synaesthesia expert at the University of Edinburgh, this is a rare condition. Lexical-gustatories involuntarily "'taste' words when they hear them, or even try to recall them.” She has found only 10 such people in Europe and the United States.
In research reported in the New York Times, researchers reported that “Magnetic-resonance imaging indicates that they are not faking. The correct words light up the taste regions of their brains.”Synesthesia-like experiences occur to some who use psychedelic drugs, suffer a stroke, have an epileptic seizure or suffer deafness or blindness. The difference between the two types is that one type of synesthesia is congenital and present from birth and caused by heredity; the other type is brought on by a physiological or neurological event."
According to research from the University of Washington, synesthesia tends to affect: 1) women more than men; 2) left-handed people more than right-handed; 3) people of normal or above normal intelligence; and 4) people through inheritance, perhaps through a dominant trait and the X chromosome.