What color are those letters? If you're a non-synesthete, you probably replied "blue." Even "neon blue" if you were feeling descriptive. For grapheme-color synesthetes, however, that question may have several very different answers.

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Introduction to How Synesthesia Works

By the end of this article, you will probably think you have synesthesia in some form. At the very least, you will probably hope you do.

Synesthesia is a phenomenon where experiencing one sense (or cognitive pathway) results in the experience of another one. So you might "see" the letter B (typically uppercase and lowercase) as red or hear a word that makes you taste a certain flavor [source: Ramachandran and Hubbard]. Music, too, might be perceived as colorful, where a C note is maroon and F sharp is yellow -- it might change by octaves, too. Or maybe you see dates spatially -- Tuesday is always a yard or two to your right, a fixed position in space.

So have you found yourself already racking your brain, trying to decide if 8 is purple or the letter Q tastes like bananas?

If you really strongly understand any of these sensations, you might just be a synesthete. (Or synesthesiac, a term that doesn't exist but I think should.) And although for a long time, researchers thought synesthesia was incredibly rare, it turns out that just asking someone if they experience these symptoms isn't entirely accurate. A 2006 study that gave objective tests to subjects found that synesthesia was 88 times more likely than previously thought, and it affected 2-4 percent of the general population [source: Simner et al.].

Not every synesthete experience is the same, either in people or between different synesthetic forms. For example, a small 2005 study found that while grapheme-color synesthetes (those who perceive letters, numbers or words as colors) almost always associate a word with a color, many lexical-gustatory synesthetes (those who link words with a certain taste) don't have a particular association with every word [source: Ward et al.].

Knowing that forms of synesthesia are not necessarily alike, let's take (or taste?) a look at the next page and get a primer on some more common forms of the condition.

Sweet Personalities, Sharp Laughter

So if synesthetes see the number five as red, does that mean red means five to them? Not necessarily. It seems that synesthesia is directional, meaning it only goes one way. If we were to just "evoke" the number five from red, it's less clear how it would behave -- would it be big? How would one "see" it? Our brain seems to have an easier time arousing the image of a red five than finding "five" in red, which makes scientists think synesthesia has to do with how senses (and not numbers) are mapped in our brain [source: Ramachandran and Hubbard].

Different Forms of Synesthesia

As a general rule, synesthesia can occur between just about any combination of senses or cognitive pathways.

The most common type of synesthesia is grapheme-color. Graphemes (letters or numbers) take on certain colors to the synesthete. This is almost always uniform for each person, but not among synesthetes in general. For instance, one person with synesthesia could always see the letter A as red, but that doesn't mean all synesthetes will experience the same color. (Although there are some studies that show certain combinations appearing more among synesthetes -- including A as inherently red [source: Ramachandran and Hubbard].)

Another synesthesia that is reported is sound-to-color synesthesia. This could indicate a few different things; it might mean that something as simple as a noise (a car horn, flushing toilet) takes on a color or shape in the mind's eye when it's heard. You might experience some sounds as a texture. Some lucky folks get to "see" music and associate a wide variety of musical notes with a rainbow of colors. Interestingly, a 2006 study did show that sound-to-color synesthetes associated a higher pitch to a lighter color -- which non-synesthetes also agreed on [source: Ward]. This led researchers to conclude that synesthesia might be using the same cross-modal pathways that most people use, rather than pathways special to the condition.

Next up is one of the rarer (and more delicious) forms of synesthesia, which is lexical-gustatory (or olfactory). This kind of synesthete might taste certain flavors (or even whole dishes or meals) based on a visual picture or word or sound. They might also associate smells with certain colors, or shapes -- let's say the smell of toast might be ochre. Some synesthetes even claim to taste the emotions of other people [source: Carlsen].

Some less common forms include mirror-touch synesthesia, which causes some people to experience a physical feeling when other people are touched (read Can people feel the pain of others? for more info on this particular twist). Ordinal-linguistic personification is where a person might give personality traits to individual items in ordinal lists. For instance, saying that the letter A appears egotistical, the letter B nurturing and the letter C brave -- it can happen with numbers, days of the week and so on. Number-form is where a person sees numbers as a very distinct map -- often, lower numbers (more commonly seen ones) are bunched up at one end (or the first 12 might imitate a clock face). They're not necessarily linear, but might curve in and out, or move up and down. However the map "looks," it stays uniform for the number-form synesthete.

So we got it: There are lots of synesthesia forms out there. But why in the world do they occur?

The Evolution of Disgust

Researchers studying synesthesia note with interest that we use terms like "disgusting" (and a matching facial expression) across cultures to denote something nasty tasting -- and morally reprehensible. One hypothesis is that as mammals evolved, the frontal lobes used to distinguish smell and taste were taken over when new social acts (that is, morality) needed to be defined, and some cross-wiring took place [source: Ramachandran and Hubbard]. Perhaps our reaction to a cheating spouse or slimy politician is just a form of synesthesia that became normalized.

I'm Sensing Some Confusion

So let's say you really want to taste purple or find a way to associate colors with numbers. How the heck does one get synesthesia? First, let's delve into the nitty-gritty of how scientists think (smell? hear?) how synesthesia works.

We don't know a ton about synesthesia, although it has become a popular field for study. Researchers do think the condition tends to be somewhat inherited or genetic, as about 40 percent of synesthetes report a first degree relative with synesthesia [source: Brang and Ramachandran]. Many synesthetes recall synesthesia as long as they can remember, and it can be discerned at an early age.

If you don't have synesthesia, you might be trying hard to make associations with colors or numbers related to memories. (You might decide the letter G is blue because you can recall a teal "G" on a poster in your childhood bedroom.) But synesthesia has been shown to be a sensory phenomenon, unrelated to memory. For example, if you are given a matrix mostly consisting of the number five all over the paper -- scattered with a few twos, which form the shape of a triangle -- you would have a hard time discerning the triangle. You'd have to look closely to search for the twos, and then discern the shape from there. A grapheme-color synesthete can see the triangle almost instantly. This has led researchers to conclude that synesthesia is quite real, and that it happens early in the perception process; your mind, in other words, doesn't spend time searching for a memory association [source: Ramachandran and Hubbard].

The more global theory of how it works is pretty straightforward: Researchers think that synesthesia is a kind of cross-wiring in the brain. In grapheme-color synesthetes, seeing a number simply stimulates your grapheme region and the area of your visual cortex that responds to color stimuli [source: Brang and Ramachandran]. One theory is that there are increased neural connections in the brain of synesthetes that could've been the result of less "neural pruning" while in utero [source: Brang and Ramachandran]. Even cooler is that there might be actual anatomical differences in the brains of synesthetes, like increased white and gray matter in the brain [source: Brang and Ramachandran].

Although one study did find that some exposure to color-letters built up their association, the effect didn't stick around [source: Colizoli]. So far, it doesn't appear one can "get" synesthesia.

Kanye West performs during the 2011 Essence Music Festival in New Orleans, La. West is one of numerous contemporary artists like Mary J. Blige, Aphex Twin, Billy Joel and Stevie Wonder who say they see music in color.

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What's Synesthesia Like?

Most discussions of synesthesia will include famous creative types. Vladimir Nabakov wrote about his synesthesia in his biography "Speak, Memory," and the composers Franz Liszt and Nikolai Rimsky-Korsakov apparently clashed over what colors certain musical keys were [source: Cytowic and Eagleman]. But if you're a non-synesthete and feeling bummed about how mundane your worldview appears, take heart: Although much has been said about synesthesia among artists, there is no evidence that having synesthesia makes one more creative [source: Brang and Ramachandran].

However, there just may be some secondary cognitive benefits for synesthetes. Memorization appears to be one of them. Some synesthetes can memorize a substantial list of numbers by recalling color associations, for example. And some color synesthetes have also demonstrated an impressive sensitivity to discerning extremely similar colors [source: Brang and Ramachandran]. (It remains to be seen whether synesthesia is the cause of this, or if it can be attributed to the broad and frequent experience synesthetes have with color.)

Alas, it's not all idyllic. Some synesthetes report their condition can be a little grating at times. It can be uncomfortable, for instance, for a grapheme-color synesthete to see a number in the "wrong" color. One lexical-gustatory synesthete also made the point that if a certain name doesn't taste right to him, he has a hard time liking the person it's attached to [source: Carlsen]. (One can only assume that's where nicknames come in handy.)

And while not everyone has synesthesia, we should point out that hallucinogenic drugs might be one way that synesthesia could be "manufactured." Several drugs can produce vivid synesthesia in otherwise non-synesthetes, which might be a key to understanding the condition. One researcher has posited that in non-synesthetes, information in a multisensory area travels back easily to its single-sense area, but in synesthetes it gets a bit mixed up along the way. Taking something like LSD might mean that the subsequent change in neurochemistry causes those existing connections to get confused for a while [source: Carpenter].

So we've still got a lot to learn about synesthesia, it seems. Read on to the next page to taste, touch, feel or just see a lot more information about it.

Lots More Information

Author's Note: How Synesthesia Works

I'll just say it: I'm disappointed to be a non-synesthete. But the more I learned about synesthesia, the less "outside" the phenomena I felt. Most of us have a very traditional, dependable relationship with our senses even though we can't ever be sure that, say, I perceive red like you do, or that pad thai tastes the same to both of us. So synesthesia doesn't just show how senses can cross; it shows that perhaps our senses aren't that reliable, period.

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