The screen starts out black. Quietly, out of the darkness, the lonely sound of a solo bassoon emerges. With it, a faint glimmer of July-sky blue pops out, swirling and expanding as the melody gets louder. Soon, other instruments join in: oboes, clarinets, and flutes sound. Each contributes its own color. Dots of pink, cream, and indigo converge on the screen. They float like bubbles until, suddenly, an unexpected horn sounds. Its high pitch pierces the melody, ushering in a ball of orange flames. For now, the bubbles burst.

This is the opening of Igor Stravinsky’s score “The Rite of Spring,” as performed in the 1940 Disney film Fantasia. It is also considered one of the best representations of what it is like to experience synesthesia, an inherited brain phenomenon which alters the way some people perceive sounds and other sensory stimuli. Synesthesia, a term that comes from the Greek words syn, meaning union, and aisthaesis, meaning sensation, makes a person experience things like color, sound, or taste automatically when other sensory pathways are activated.

Some synesthetes consistently perceive numbers or letters of the alphabet in specific colors, while others associate sounds with a particular shape. Synesthetes may also be able to associate the timbre, or characteristic sound, of a specific musical instrument with a color, shape, or texture. When the sounds of instruments rub up against each other in Stravinsky’s dissonant ballet, a sound-color synesthete would perceive this clash of tones as a technicolor symphony.

Synesthetic responses are as diverse as the stimuli that produce them. To Katie Carrillo, a synesthete from San Antonio, Texas, many names come with a color association. She tells me that “Allison” is “orange with small yellow streaks.” But names aren’t the only things that color her world; she also perceives numbers and certain forms of music in specific shades. “When I hear Beethoven, I can see brown dancing across my vision,” she says. To her, the number one always appears “purplish-blue” while an eight is black. Perceiving color alongside certain numbers or letters, called color-grapheme synesthesia, is one of the most common types. Graphemes are symbols like numbers and letters that signify some meaning, colorful or otherwise, to those who read them.

A more unusual type of synesthesia, dubbed number-form, makes people perceive numbers in a distinct spatial arrangement. While you or I might sometimes think of numbers in a descending line, like a thermometer, or even a circle, as in a clock, synesthetes’ number-forms are more than intuitive patterns picked up from the environment. Some synesthetes visualize numbers in a sporadically bendy line where numbers like 46, 54 and 70, random to the rest of us, serve as turning points, according to Richard Cytowic and David Eagleman, authors of the book Wednesday is Indigo Blue. Others see the days of a month in a twisting, snakelike pattern, or in a stretched-out oval where some months inexplicably take up much more physical space than others.

Synesthetes may sound like a rare breed, but chances are, you know several. One out of every twenty-three people experiences some form of synesthesia, say neuroscientists Julia Simner at the University of Edinburgh and Jamie Ward at the University of Sussex, who conducted a landmark study in 2006 to pin down the phenomenon’s prevalence. They also found that synesthesia affects males and females at about the same rate.

Even if you know a synesthete, they may not know it themselves. Since synesthesia affects our most basic, everyday perceptions, many synesthetes don’t consider hearing shapes or seeing sounds atypical at all, until someone else tells them so. Carrie Firman, a graduate student in visual arts at the University at Buffalo, thought her synesthetic perceptions were common to everybody until about two years ago. A friend sent her a link to a dinosaur comic in which a T. rex describes the phenomenon and quips, “People with synesthesia basically have super powers.” Firman, who visualizes sounds in specific shapes, was surprised. “When I saw the comic, I thought—wait a second. That’s not normal?” she recalls. “I didn’t realize it was unique at all.”

For many synesthetes, hearing shapes or tasting colors is simply the way to experience the world, and there’s nothing special about it. In this way, synesthesia is an anomaly in the world of neuroscience. Other idiosyncrasies of the brain spur a researcher’s impulse to find prevention and treatment. People with attention deficit disorder are routinely medicated with Ritalin to suppress their tendencies, while there’s behavioral therapy for those on the autism spectrum. One in every twenty-three people walks around each day with another brain abnormality that’s recognized by scientists and researched the world over. But no one’s talking about treating it. Throughout its history, synesthesia has been met with awe, admiration and skepticism, but never with a widespread impulse to treat.

Georg Sachs, a German medical student, wrote the first scientific account of synesthesia. The year was 1812, and the subject was himself. Sachs focused most of his doctoral thesis on albinism, another trait he possessed, but managed to sneak in a few out-of-context sections on his unusual perceptions.

Sachs detailed his colored perception of letters, days of the week, musical intervals, and numbers. He saw the number one as “indefinitely white,” six as “indigo,” and nine as “nearly dark-green.” One of the critics who reviewed Sachs’s thesis praised his uncanny colored vision as something positive.

“It is strange that the author represents, in his own way, colored objects,” writes the anonymous critic, but his lofty conclusion reads: “This phenomenon speaks to an overall higher sense of vision in some humans.” Thanks to other positive accounts like this one, scientists stepped up to the plate of synesthesia research, which Cytowic and Eagleman note was a well-respected field.

In the mid-1800s, cultural ground was fertile for synesthesia to gain public popularity. Psychology was emerging as a discipline, bringing with it a focus on invisible matters of the mind. At the same time, French poets Arthur Rimbaud and Charles Baudelaire hit the literary scene in Europe. Although there’s no proof either poet was a synesthete, their work widely popularized the phenomenon. They made unusual interminglings of the senses appear valid, even artistic, in the public eye. In Rimbaud’s poem “Voyelles,” he assigns each vowel a color. For instance, he writes that “I” is the crimson of “sang craché, rire des lèvres belles”—spat blood and pretty, laughing lips.

But by the 1930s, the scientific community began to have doubts that synesthesia was a legitimate phenomenon worthy of scientific attention. After Sigmund Freud’s death in 1939, many psychologists awoke hungover on dreams, the superego, and other ideas of the mind’s invisible workings. Instead, they craved observable explanations.

And so, behaviorism was born. Rejecting a focus on internal mental life, behaviorism prized only that which could be observed outwardly. Ivan Pavlov’s salivating dogs exemplify mid-1900s behaviorism: concrete measurements and hands-on observation with meat, bells, and spit. As for synesthesia, a self-reported phenomenon nearly impossible to prove, interest and research began to wane. Like hysteria or hypochondria, Cytowic and Eagleman point out, synesthesia came to be considered an illegitimate affliction, “no longer a respectable topic of inquiry.”

In the 1980s, a shift toward cognitive psychology brought invisible sciences of the mind back into vogue. With tools like computer imaging and a better knowledge of genetics, neuroscientists were ready to tackle synesthesia once again. Even so, some stigma against synesthesia existed—and continues to persist—in the general population. Wendy Mass, author of A Mango-Shaped Space, focuses a large part of her book on synesthesia’s stigma. Mass writes about a young grapheme-color synesthete named Mia, who recalls being asked to complete a math problem on the blackboard at school. Mia protests about the white chalk, asking: “But isn’t it better to use the right colors?” After going on about which hue would suit each digit, Mia is met with a whisper—“freak”—from the back of the classroom. Mia’s teacher dismisses the idea that there are any “right” colors, and sends her to the principal’s office for disruptive behavior.

Many people with synesthesia say they are met with stares, disbelief, or other socially undesirable attention when people learn about their perceptions. “You have to learn to try to keep it in the box,” says Firman. “In life, they teach you that sound isn’t visual.” Sometimes, people think synesthesia is the result of a runaway imagination—something dreamed up for attention, rather than a basic cornerstone of some people’s perception. In her book, Mass writes about a mother left confused and embarrassed by her young son’s synesthetic perceptions. The mother, unfamiliar with synesthesia, would divert attention from her son in public by saying, “Don’t pay any attention…he has an overactive imagination.” Firman, who is working with the theme of synesthesia in her fine arts master’s thesis, recalls being met with a similar kind of stigma in the initial stages of her project. “I’ve had a lot of trouble getting some of my faculty on board, trying to express I’m really not making this up,” she says.

The American Synesthesia Association (ASA) was founded in 1995, and the advent of the internet has helped to make the synesthetic community more cohesive and publicly visible. Using these tools to dispel whatever stigma exists is important to members of the synesthetic community for their identity, but also because of its larger message about different perceptions. Firman concluded her presentation at this year’s ASA conference by saying, “If we can’t accept that our neighbor sees green triangles when a dog barks across the street, how can we accept that they may eat, speak, dress, worship, and live differently than ourselves?”

Sean Day, a professor of English and journalism at Trident Technical College in South Carolina, who also conducts synesthesia research, recalls being met with undesired awe or disbelief upon sharing his synesthetic view of the world. Day thinks his unusual perceptions themselves aren’t particularly noteworthy—“It’s more about how other people act and treat you.”

Day has a type of synesthesia that causes him to see the timbres of different musical instruments each in their own specific color, a trait he noticed was unique at a young age. “As a child, I used to pick records to play based on the colors I wanted to see,” he says. “I knew my perceptions were different. Nobody else was talking about the colors.” He also perceives color in relation to most flavors of food, as well as some odors. If you ask him what he thinks of violin music, he’ll tell you it’s light tan with a texture of polished wood. Strawberries, to him, are particularly complex; when he tastes them, they appear very light blue with streaks of pink. But to Day, observations like these are wholly unexciting.

“It just is,” he says. “This is how I perceive the world.”

Then he asks me an important question.

“Can you smell roses?”

I answer yes.

“Cookies?”

Another yes.

“Your favorite home-cooked meal?”

Before I can answer, he surprises me. “What about public restrooms?”

Therein lies the ordinariness of synesthesia. Just as our normal sense of smell pleases us sometimes and displeases us at others, synesthetic perceptions do the same. “There are things you like and things you don’t,” says Day, “but it’s all part of the way you perceive.”

As it turns out, Carrie Firman’s dinosaur comic was wrong. Synesthetes don’t have superpowers. They also don’t have a disease. They simply stumble around like the rest of us, trying to make sense of the world.

Professionals in the field seem to agree that when it comes to synesthesia, there’s nothing to fix. Veronica Gross, a visiting assistant professor of psychology at Emmanuel College in Boston, wrote her Ph.D. dissertation on synesthesia. She says that synesthesia may be atypical, but that’s no reason to single it out as something problematic.

“Neurologically, there’s no loss of function,” she says, adding that trying to treat synesthesia would be about as illogical as trying to treat ambidexterity or perfect pitch. Synesthetes aren’t likely to feel especially overwhelmed by the experience of many senses at once, she says, and so there’s really no drawback to being a synesthete.

“For the most part, they learn how to cope with synesthesia just as we learn to cope with our sensory information,” she says. “A deaf person might ask if we find hearing overwhelming, but this is something we just learn how to deal with.”

Gross also explains that synesthesia is not a hallucinatory disorder, even though synesthetic perceptions may seem to verge on the same territory as descriptions of psychedelic drug use. Mass’s book, A Mango-Shaped Space, mentions the synesthete Mia’s psychotherapist, who asked if she had been using drugs, thinking this might be the cause of her color vision. But there’s little proof that synesthesia and drug-induced hallucination act in the same way, says Gross.

People who take hallucinogenic drugs, such as LSD, do activate some of the same brain regions as synesthesia, but that’s as far as the comparison goes. “When you have visual stimuli, there are only so many parts of the brain that are going to be activated,” explains Gross, adding that the primary visual cortex has been shown to be active during all of synesthetic perceptions, hallucinations, and normal vision. So has a different sensory-integration area of the brain, called the posterior parietal lobe. “What is causing that activation, though, is different pathways,” she notes.

Real synesthesia is notoriously hard to verify. Unlike conditions that are diagnosed to be treated, synesthesia has no exhaustive list of characteristics, because nobody would fit the bill exactly. Synesthetes are like snowflakes: no two have the exact same associations, even identical twins.

Cytowic and Eagleman point out that there are, however, some basic requirements. If a synesthete perceives the number three in magenta today, he should have the same perception tomorrow. In other words, associations should remain stable through life. Synesthetic associations must also be automatic and involuntary, not dreamed-up figments of the imagination. Synesthesia is memorable, meaning a person’s pairings register consciously. Finally, synesthesia usually only goes one way; if someone hears crickets every time he chews spearmint gum, he won’t spontaneously taste spearmint if he hears bugs chirping on a camping trip.

As it stands now, researchers have two hypotheses on how synesthesia comes to be. According to the first idea, synesthetes have extra connections between sensory areas in their brains, leading to a lot of crosstalk. Imaging studies have shown that grapheme-color synesthetes have more white matter, or message-conducting zones, between the neighboring areas in the brain’s fusiform gyrus that recognize graphemes and colors.

In normal neural development, the brain begins like an overgrown tree much in need of a gardener. Connections between brain cells, called neurons, are plentiful. As we grow and develop, many of these connections naturally die, a process neuroscientists refer to as “pruning.”

“We’re all born with multisensory pathways everywhere,” says Michelle Jarick, a Ph.D. student in cognitive neuroscience at the University of Waterloo. “During neural pruning, connections become fewer and fewer between the areas we don’t use.” Jarick, who conducts research on synesthesia, says synesthetes’ brains might be like secret gardens, with connections left unkempt. “In synesthetes, many of the extra connections linking these brain areas are preserved, when we’ve already had ours pruned off long ago,” she says. In other words, maybe we’re all born synesthetes.

A second theory proposes that we all retain these extra, un-pruned brain connections typical of synesthetes, but non-synesthetes are better able to keep them in check. “It could be that most people just have extra neurons to inhibit these connections,” Jarick says. “In people with synesthesia, those inhibitory neurons aren’t there.”

Even with two theories pointing the way to how synesthesia might work, and active research being conducted on both of them, “Not enough is going wrong to make this classified as a disorder,” says Gross. “It’s just an interesting bend in evolution.”

In synesthesia research, then, treatment is not the objective. Instead, the field is focused on a different goal: learning how synethesia works, simply to understand it. Scientists point out that understanding the synesthetic brain could inform studies of normal neuroscience. For instance, the mechanism that makes separate sensory brain areas interact more than usual in synesthesia could shed light on what happens when other, non-sensory areas of the brain interact in excess. Extra crosstalk between brain zones for memory and planning, for example, could be the basis of intelligence, creativity, or madness, Cytowic and Eagleman hypothesize.

Even without a goal of treatment on the horizon, there is still much to be gained from studying synesthesia. Understanding one of nature’s sensory mysteries, raising awareness of varieties of human perception, or further cementing synesthesia’s scientific basis are all reasons that scientists head to their lab benches every day to study the taste of shapes.

Scientists have long understood that synesthesia is passed down genetically, since it recurs at a very high rate in families. Researchers don’t know how many genes interact to confer synesthesia. It could be one, or it could be several. Gross explains that genes behind synesthesia could signal more crosstalk than usual between different sensory brain areas, causing perception in overdrive.

Cytowic and Eaglman point out that a synesthesia gene might affect an area called the inferior parietal lobule. This area is a junction important for the crossover of input highways that have to do with hearing, feeling, and seeing. In his work with the Center for Synesthesia Research at Baylor College of Medicine, Eagleman has done studies that suggest a place for a synesthesia gene on chromosome 16. But with 400 genes and 23 million base pairs to wade through on that single chromosome, it might be a long haul yet.

Most quests to find a gene are motivated by health risk or the shiny promise of therapy, but synesthesia is a beautiful anomaly. Most synesthetes are pleased with the way they perceive. To some synesthetes, for example, such extra sensory perception makes math easier. Jarick tells of one grapheme-color synesthete who uses her colors to do her accounting. “At the end of the day, if the colors are correct, she knows she has done her math properly,” notes Jarick.

To others, synesthesia can serve as a useful memory tool. Katie Carrillo reveals that perceiving a word over and over again in the same color easily helps her to memorize the association. “Then, when asked to write it, it’s like you have an automatic spelling check in your brain,” she says. If the colors are wrong, so is the spelling.

Still others say their synesthesia is useful when trying to remember people’s names or identify musical intervals. One of Cytowic and Eagleman’s subjects associates each interval with a distinct scent; to her, a minor fourth smells like freshly mown grass.

For now and maybe for always, synesthesia is unavoidable for those who inherit and express it. Although she doesn’t routinely make a point of telling her friends about her synesthesia, which she calls “super vision,” Carrillo wouldn’t trade it if given the choice. “I haven’t heard of a working treatment, but even if there was, I wouldn’t take it,” she says. “I am more proud of my condition than embarrassed.”

Many synesthetes embrace their unusual perceptions and use them to create original art. Some researchers believe synesthesia is more common among artists. A recent study suggests synesthesia crops up in about seven per cent of artists and just two per cent of non-artists, but more research is needed to confirm this link. It may be that certain famous artist/synesthetes, such as composer Franz Liszt and novelist Vladimir Nabokov, skew our perceptions, making the link seem stronger than it is.

As an artist, Firman uses various media to translate her perceptions into something a non-synesthetic audience can interpret. “We get so frustrated trying to explain exactly what our reactions are, because it sounds so foreign,” says Firman, who recently designed an interactive online exhibit called The Synesthetic Library where viewers can click on shapes to hear what sound they signal for her. A pink wave-like shape sounds like a bow over viola strings, while a blue thought bubble puffs like a gentle breath of air.

In addition to hearing sound for shapes, Firman sees pain in color. “Aches and pains I see as red, whereas stabbing pains are amber,” she says, adding that experiencing colored pain is one of the only times she regrets having synesthesia. “I really wish I could turn those colors off,” she says. “I don’t need to be reminded I’m in pain.”

While colored pain happens in about six per cent of synesthetes, others experience different challenges. “Synesthesia does not help me in math,” states Carrillo. When multiplying 9 by 9, she says, 81 is not a logical result because its digits are different colors. “They don’t agree,” she says. To some who visualize numbers in forms like a counter-clockwise circle, it can be difficult to tell time on a conventional clock. To others, it can be disconcerting to read text printed in color, because letters appear in the “wrong” hues.

Despite the difficulties, Firman points out that living with synesthesia isn’t especially taxing compared to chronic illness or disability. “It’s so different from real health conditions,” she says, adding that it frustrates her when people think of her synesthesia as an impairment. “Sometimes I’ll fight back and say, this is something my body does right.”

Current research is exploring the links between synesthesia and several other, more harmful neurological abnormalities, such as autism and schizophrenia. Most of these links rely on genes: if the region of a gene where the synesthesia trait resides is close to schizophrenia’s region, for example, the two are more likely to be inherited together. “More researchers are looking at connections to asperger’s, autism, or other neurological things. There are genes we think are related,” Gross points out. Clinical reports have shown synesthesia occurs more commonly in people on the autism spectrum, but so far, much of this research is only anecdotal. “There’s tons of speculation, but not enough proof,” says Gross.

Without clear links to neurological conditions, synesthesia remains simply a spot on the spectrum of normal. This embracing attitude has practical implications, Jarick points out, such as in the classroom. “There might be a lot of kids out there who don’t have learning disabilities, they’re just synesthetic. Their math or their reading times might be slower,” she suggests. “Educating teachers on this might help to get away from some kids being stigmatized.”

Synesthetes and experts alike echo the idea that continuing to tear down synesthesia’s stigma, however subtle, is a far more important goal than treating or curing the phenomenon. Sean Day puts it this way: “If you take a pair of dice, it’s really easy to roll a five, six, or seven. But there’s only one way to get to 12,” he says, using the laws of simple probability. “Synesthesia is like rolling a 12. It’s rare, but every once in awhile it’s going to happen. But because rolling a 12 is so rare, a lot of people treat it as if it’s rolling a 13.” A 13, Day notes, would be something completely outside the predictable realm of things, like glow-in-the-dark mice.

“It’s important to see synesthesia as a 12,” he urges. To him and some 300 million other people around the world, synesthesia is simply normal reality, nothing short of ordinary. In a world of neuroscience preoccupied with fixing abnormalities, Day’s blithe acceptance stands out. It colors things a little differently, but as a vantage point, it’s refreshing.