Tom tells me that my voice is yellow when he speaks to me in person, but is a bright green on the phone.  I’m not sure what I think about having a yellow voice, or even a bright green one.  While I hear voices as lighter or darker, throaty, wispy, husky, gravelly, etc., and I may think conceptually of a color when I hear a voice, I do not actually see the color.  But Tom, a wonderful tenor, good pianist and also former student of mine, has synesthesia, the condition in which a stimulus in one sense triggers a response in another.  And he actually sees yellow when he hears my voice.

Even as recently as a few years ago, people who experienced colored sounds or colored letters were not taken seriously so many of them didn’t talk about it.  In Musicophilia, Oliver Sacks relates the story of a songwriter with synesthesia who recalls that when questioned by his first-grade teacher about why he was staring into space, said that he was “counting the colors till Friday.”  The entire class laughed at him and he never again brought up seeing the days of the week as colors (known as time units – color synesthesia).

But research into many aspects of synesthesia has expanded exponentially in just the past few years, and theories about synesthesia that were considered probable just a decade ago have been replaced by new information and new theories.  Over the years, the number of people with synesthesia has been estimated by researchers as 1 in 10,000, 1 in 2000, 1 in 200, but the latest and most reliable estimate is 1 in 23, which is about 4.4% of the population.  Why the difference?  Many of the previous studies were based on self-reporting, or on response to a newspaper or internet ad.  The 1 in 23 figure comes from a study* using random samples from Edinburgh and Glasgow Universities and from visitors to London’s Science Museum.  The University study tested for several types of synesthesia; the Museum Study for just grapheme-color. (A grapheme is the smallest unit of a written language, such as letters of the alphabet or numerical digits.)

Previously, researchers thought there was a 6 – 1 female-male ratio in synesthesia, but the Edinburgh-Glasgow study showed that the male-female ratio is fairly equal.  Why the difference?  They concluded that in the previous studies involving self-reporting, women were more likely than men to talk about having synesthesia, so the samples were probably skewed.

There have been estimates of 60 to over 100 kinds of synesthesia and in 2004, the American Synesthesia Association reported 152 recorded forms of synesthesia.  Synesthesia is usually referred to as cross-sensory pairings, but a wide variety of non-sensory traits, such as personality and emotions, can also trigger a sensory response, which is why it is possible to have 152 kinds.  Color is by far the most prevalent response.  Graphemes, time units such as days of the week, and sounds are the most common triggers.  Synesthesia almost always goes in one direction only, as in sound triggering colors.  Rarely does color trigger sound, although apparently the synesthesia experienced by artist Wassily Kandinsky went in both directions:  sound to color and color to sound.   (Researchers believe that Kandinsky combined four senses synesthetically:  color, sound, touch, and smell.)  Most research has focused on sound-color or grapheme-color synesthesia.

Synesthesia is genetic and tends to run in families.  My former student Anissa (another wonderful singer and good pianist) is synesthetic and so is her cousin Kelly, and we’ll talk about their experience of synesthesia next time.  Synesthesia is involuntary, you can’t develop it through practice.  It is automatic, you have no control over whether or not it occurs, and it is stable over time.  For example, tests given at an interval of several years show that the true sound-color synesthete, for example, will experience the same colors in response to the same sounds, no matter how much time has elapsed.  If you want to find out if you are a synesthete, go to The Synesthesia Battery, a site run by David Eagleman, neuroscientist at Baylor College of Medicine.

All individuals who experience a certain kind of synesthesia (e.g. grapheme-color) do not experience it in the same way.  Anissa always sees A as pink; her cousin Kelly sees A as reddish orange.  Synesthete X may always see letters as black with the color as a sort of “aura.”  Synesthete Y may actually see the individual letters as different colors.

Neuroimaging has shown that there is increased cross-talk between sensory areas of the brain in people with synesthesia, and there are two basic theories about why that happens.  The fetus makes trillions of synaptic connections between brain areas, but all of them will not be needed, so in the first few months after birth, many of these connections are pruned as others become stronger. The first theory suggests that in someone with synesthesia, some of that pruning doesn’t occur and there are simply more connections left between sensory areas of the brain.  So the structure of the brain is different in a synesthete.

A second theory proposes that the same amount of cross-wiring exists in everyone, but the cross activation between sensory areas occurs when the balance of chemicals travelling between these areas is somehow skewed, allowing activity in one sensory area to cause simultaneous activity in another.  This theory is supported by the fact that non-synesthetes sometimes report synesthetic experiences during meditation, and LSD and other hallucinogenics can induce synesthetic experiences in nonsynesthetes so the cross-wiring must already be there.  If that’s the case, then the connections exist in everyone’s brain, but they only function in the synesthete’s brain.

Next time, we’ll explore sound-color synesthesia, including the possible relationship between absolute pitch and synesthesia, we’ll talk about Tom, Anissa, and Kelly’s music-color synesthesia, and – what difference does it make to a musician if he/she is synesthetic?

If you are reading this and you are a synesthete, it would be extremely interesting if you would share your experiences, either online or in a private e-mail to me.  Thanks.

*  Simner, et.al. (2006).  Synesthesia: The prevalence of atypical cross-modal experiences.  Perception 35: 1024-1033.