In the late 19th century, synesthesia, that strange and magical condition where the sense are intertwined, was the subject of much research all over Europe and America. The fact that some unspecified number of people experienced sensory crossover was fascinating, but attempting to design tests that would satisfactorily prove its existence, not to mention why it happened, was difficult. With the advent of behaviorism in the 1930s, a field which disallowed any usefulness in internal experience, interest in synesthesia waned, and it became a forgotten science. Then in the 1980s, with the cognitive revolution, science began once again to pay attention to internal states. Lo! Synesthesia slowly crept back into fashion.
We all know stereotypical synesthesia from movies and TV: the idiot savant who sees colors when he or she hears music, or perhaps the brilliant cryptographer whose different letters and/or numbers in different colors move about to solve a mystery. Because I first heard about it as a child, I had a bunch of really wild ideas about the condition, based on a description of a condition where the so-called sufferers' "senses were mixed up". I had imagined people who could taste sound, or see smells; people who felt color or pattern on their skin, or perhaps people who smelled their way through life, instead of looking.
Some of the above are actually documented, but others are (at the moment anyway) merely fancies of mine. When I started reading around in preparation of this post, though, I found a fascinating array of different perceptual issues under the same heading. In fact, as I started reading, I began to realize that I was synesthetic myself.
Drawing of the neural circuitry of a rodent hippocampus
Strangely, I had often thought how cool it would be to be synesthetic, but had assumed, like narcolepsy, that it was relatively rare and rather unmistakable. When someone I knew said she was synesthetic I figured it was a bid for attention, a way of making herself more interesting. I knew that I had some perceptual quirks, but simply put it down to being highly imaginative, or perhaps merely the leftovers of some childhood way of teaching myself things.
For example, when I was first learning my alphabet, I saw the letters as having distinct personalities. I didn't seem to have any choice about what their personalities were, but they were clearly there. Putting together words was much like putting together little conversation groups at a party: the dynamics were different if you forgot one, or put it between the wrong two letters (thus my spelling was always excellent). To this day, I still see the letters as having these same personalities (with some odd effects due to fonts - some fonts I don't like because they warp the poor letters' personalities in uncomfortable ways); however, now I gloss over it. Like so many things when we grow up, we begin to take things for granted, like the motions of driving or the walk to the mailbox. We say to ourselves, there's the oak tree, or oh, it's sunny today, but we say it in shorthand. We don't really look at the oak tree, and we certainly don't stop long enough to actually look at the way the sun is hitting the grass.
So I have been living with these little characters [sic] all my life, without really noticing them much. But if you asked me about them I could tell you all about how the "a" and the "y" don't really like each other - but that might be because the "y" is kind of stuck up, and the "a" is really very down-to-earth. And so on.
It turns out this is called Ordinal Linguistic Personification, and can be identified as true synesthesia by a test they use for many synesthetic expressions, ie. a test where the quality of the picture shown is in contrast with the automatically perceived quality as seen by the synesthete. So, for example, if the synesthete sees a "b" as female, then making a male figure out of "b"s will slow their recognition time.
This form of synesthesia often goes hand-in-hand with Grapheme-Color Synesthesia, which is the most common form: seeing letters and numbers as colored. I don't personally have this form of it, but like many forms of the condition it can be seen as actually colored, or can simply have a strong, automatic color association in the mind of the perceiver. Which makes it difficult to put a finger on, except that tests have proven that people can be confused because of the strength of their perceptions. As one person says, of her grapheme-color perceptions, "I thought this was caused by me over-thinking things." Apparently this is actually quite common, for people (like me) to simply believe they are being imaginative, or making up systems to help themselves (as I did), in school or elsewhere.
A picture of one person's number-form synesthesia, ie. the mental mapping of numbers, from Francis Galton's study, The Visions of Sane Persons
One of my favorite forms is lexical-gustatory synesthesia, where people experience phonemes as different tastes in their mouth. Can you imagine? It would be like the fairy tale of the two sisters who have jewels, frogs, etc. falling from their mouths, except all mixed together, depending on what you were saying. It might be enough to turn one into a seriously laconic individual.
What about people who "see" music, or sounds? This is another common form of synesthesia, to have colors associated with specific tones, so that listening to music becomes a more intense and complex experience. I always thought that the little thing I did, where I "imagined" the music as colored ribbons which twined above, and slightly to the left, of my vision, was a sort of game I played with myself, because like a page on a computer desktop I could minimize it if needed. But it was always there, even if I wasn't specifically thinking about it. Apparently, this is not an unusual type of synesthesia for musicians to have.
In fact, it seems to be fairly common for synesthetes to be creative people. "Some studies have suggested that synesthetes are unusually sensitive to external stimuli. Other possible associated cognitive traits include left-right confusion, difficulties with math, and difficulties with writing." [wiki]
Carol Steen's painting of a synesthetic experience of acupuncture
I find this interesting, because I have all of those traits (except writing), and am terrible with numerals. Conceptually, I'm all over math, but when I have to deal with the visual symbols I get lost. On thinking about it, I realize that seeing letters as interesting social groups actually helps me to spell, but it doesn't help with math. The personalities of the numbers confuse me when I'm trying to work with their numeric values.
This human ability to make up stories, to find systems so as to make sense of a chaotic universe, is inherent in everyone, reaching right down to some of our most basic ways of interacting with the world. Like face recognition, storytelling is one of the deep ways we recognize things and organize our world. But synesthesia lies even deeper, right down to the molecular levels of the brain. It is beginning to emerge that the characteristic is X-chromosome-linked, and there is some evidence that some of its effect (though not all) is associated with the hippocampus, a part of the limbic system of the brain which is crucial for spatial memory and navigation, and which is affected by many kinds of altered states of consciousness. LSD, for example, is said to induce synesthesia sometimes, and its effect is connected to the hippocampus. Interestingly, the limbic system is also where many emotional associations are made.
There is some researchers who believe that neonatal brains have minimal sensory differentiation, ie, that we "learn" to differentiate between the five senses; and therefore synesthetes may be people for whom these differentiations have not developed into such specifically walled-off areas. A common conception is that when sensory stimulation comes in from one area, such as the ears, there is a sort of cross-stimulation that takes place where neurons in the sight area of the cerebral cortex are activated as well, causing a visual response.
As Mr Cytowic (see below) says, "Mechanistic explanations have been plentiful throughout synesthesia's history. The notion of crossed wires turns up repeatedly. As early as 1704, Sir Isaac Newton struggled to devise mathematical formulae to equate the vibration of sound waves to a corresponding wavelength of light. Goethe noted color correspondences in his 1810 work, Zur Farbenlehre. The nineteenth century saw an alchemical zeal in the search for universal correspondences and a presumed algorithm for translating one sense into another. This mechanistic approach was consistent with the then-common view of a clockwork universe based on Newton's uniform laws of motion."
There are other aspects to it, which haven't been explored so much, which don't fit in so well with the scientific community's penchant for following single ideas down to their roots. For example, synesthetes generally have very good memory, recalling things such as conversations, directions, and verbal instructions with surprising accuracy. They are very often amazingly good at spatial location "such as the precise location of kitchen utensils, furniture arrangements and floor plans, books on shelves, or text blocks in a specific book. Perhaps related to this observation is a tendency to prefer order, neatness, symmetry, and balance. Work cannot commence until the desk is arranged just so, or everything in the kitchen is put away in its proper place. Synesthetes perform in the superior range of the Wechsler Memory Scale." [Cytowik again]
It is interesting to note how the term "synesthesia" has been used for many years in the world of literature, art and music, not as an experiential condition but as a metaphoric edifice, a sort of symbolic way of expressing things. The metaphors (that storytelling urge, again) which pervade our senses, the smell of green cut grass or the clarity of wetness, are a cultural construct, a direct connection to the arts. Despite this, there are many famous creative synesthetes, who have made their mark, directly or indirectly, on our lives. Vasily Kandinski, a well-known synesthete himself, is quoted many times in scientific literature. His desire to bring the immediacy of his perception to audiences, his exhortation to "stop thinking!" has endeared him to those people fascinated by the wild individuality of the condition, the repercussive echos that it brings to the study of the brain. For synesthesia is, at heart, that most ineffible of things: a creative experience of the world, immediate and unquantifiable, having an everlasting impact on our culture through its artists. It brings to mind what Kandinski said, back in 1910:
"Lend your ears to music, open your eyes to painting, and . . . stop thinking! Just ask yourself whether the work has enabled you to 'walk about' into a hitherto unknown world. If the answer is yes, what more do you want?"
Richard E. Cytowic's very interesting and absorbing review of the subject from 1995, very worth taking a look at for a more detailed and sensory description.
His book, The Man Who Tasted Shapes, can be found on Amazon.
Wired Magazine's 2005 take on the phenomenon.
(Thanks to Violinist.com for the image at the top of the post)