Facts of the Matter Richard Brill

Sensory overload

Millions of people hear color and see sound

WHAT COLOR is B-flat? What does it taste like? These would be bizarre questions to most of us, but if you are among the 260 million people worldwide who are synesthetes the questions make perfect sense.

Synesthesia (from Greek: syn = together + aisthesis = perception) is the ability to hear colors, taste shapes, or experience other startling sensory crossovers.

One man experiences a vivid bitter taste in his mouth when he shapes hamburger patties with his hands. Another sees printed black numbers in color, each numeral a different hue. Another finds a food tastes good, but has colors that clash sickeningly.

A woman sees blue when she listens to the note C sharp played on the piano. Other notes evoke different hues such that the piano keys appear color-coded, making it easier for her to remember and play musical scales.

Synesthetes may describe the color, shape, or taste of someone's voice, or music that looks like a scintillation of jagged, colored triangles.

Seeing the color yellow, a synesthete might experience a scent of yellow as well.

No one knows for sure how many people are affected, but the best estimate is it is about one out of every 23 people (4.3%). At that rate, 13 million Americans experience a crossover perception in one or more different senses.

For any individual synesthete there is consistency from one instance to another, and two individuals do not usually share the same specific sensations from the same stimuli, even when the involved senses are the same.

More than 99 percent of synesthetic sensations involve mapping one or more of taste, touch, sound, or smell to color.

Many synesthetes report that they are moderately offended if another synesthete's perceptions do not agree with their own, and may feel that "my color is right and yours is wrong."

Many synesthetes do not see the colors floating out in space but instead describe it as a strong mental association, as if it is just self-evidently true that a "B" is blue. In some cases it is as if the colors were being projected on a screen in space.

The most common type of synesthesia is letter or number-to-color mapping in which numerals or letters of the alphabet are associated with a particular color.

In one study, nearly two-thirds of all synesthetes fell into this category, but in the same study one-half reported more than one crossover mapping to color.

Tasting or feeling sound are also common crossovers.

There are rather distinct groups in which synesthesia is common.

In the United States, three times as many women as men are synesthetes, but in the United Kingdom the ration is 8-1. The reason for the difference is not known.

Synesthetes are more likely to be left-handed than the overall population.

Children are more synesthetic than adults. Some children apparently lost their synesthesia around the time of puberty. Adult synesthetes have always had it, from their earliest recollections, and it lasts throughout life.

Synesthetes are of normal intelligence and have normal results on neurological exams.

Synesthesia does tend to run in families. Indications are that it is a dominant trait that is carried on the X-chromosome, and thus cannot be traced genetically to either mother or father.

In one study, synesthetes scored significantly higher on tests of cognitive creativity than non-synesthetes. Another study suggested that synesthesia is seven times as common in creative people as in the general population.

There is a close relationship between synesthesia and metaphor.

Synesthesia involves arbitrary links between seemingly unrelated perceptual entities such as colors and numbers, metaphor involves links between seemingly unrelated conceptual realms.

The similarity of synesthesic sensations and metaphor seems to be more than just coincidence, and that makes it more than just a curiosity.

Neuroscientists are interested in synesthesia because of what it may tell us about consciousness, the nature of reality, and the relationship between reason and emotion.

Research is now finding clues to some of the most mysterious aspects of the human mind, such as the emergence of abstract thought, language and metaphor.

One of the biggest mysteries is the "binding problem." No one knows exactly how we bind our perceptions together into a concept such as "flower."

A flower has a color, a shape, a scent and a texture. Somehow the brain manages to bind all of these perceptions together into one concept of a flower.

A cat feels fluffy, we hear it meow and purr. It has a certain appearance and odor, all of which are activated simultaneously by the memory of a cat or the sound of the word "cat."

The largest part of our brain is devoted to sight, and the amount of visual information it can process is astounding.

The procession power goes into changing electrical signals coming from the retina into colorful, moving, three-dimensional pictures.

When electrical waves traveling through the optic nerve reach the occipital lobe at the back of the brain, it is processed. Visual information is classified based on attributes such as color, motion, form and depth. Then the processed information about these attributes is distributed to adjacent regions in the temporal and parietal lobes.

Color information travels to the temporal lobe and up through a hierarchy of color centers. One of these lies near a patch of cortex at the junction of the temporal, parietal and occipital lobes, which are concerned with more sophisticated aspects of color processing, such as our internal white balance.

Neighboring brain regions often inhibit one another's activity in order to minimize cross talk. Reducing this inhibition by blocking the action of an inhibitory neurotransmitter or failing to produce an inhibitor causes activity in one area to induce activity in a neighboring lobe. Cross activation may also occur between widely separated areas and could account for some of the less common forms of synesthesia.

One researcher described it metaphorically as neighboring countries with porous borders.

It appears that we all have some degree of synesthesia, but it may not be strong enough for us to distinguish the metaphor of a musical interval "feeling" blue from the synesthetic reality of it actually appearing blue.