How many times have you encountered the following expressions: ‘This soup is rather flat. Pass me the salt, will you?’ Or, ‘D Minor is so blue, it makes me sad like nothing else’. Of course, every language is replete with cross sensory metaphors we use them all the time to describe anything ranging from food and drink to song and dance. But suppose D Minor didn’t evoke blue merely in your imagination and instead rendered a rich temporally varying texture in indigo and shades of blue (akin to media player visualizations) right before your eyes? In other words, if you saw blue every time D Minor was played and red every time you heard F# major? Well, then you suffer from (or are privileged to enjoy) a rare neuro-psychological phenomenon called synesthesia. Unless you are on mescal, peyote or LSD.
Synesthesia (Greek, syn = together + aesthesis = perception) is the involuntary physical experience of a cross-modal association. That is, the stimulation of one sensory modality reliably causes a perception in one or more different senses. Its phenomenology clearly distinguishes it from metaphor, literary tropes, sound symbolism, and deliberate artistic contrivances that sometimes employ the term "synesthesia" to describe their multisensory joinings.
As you can imagine, artists and writers are greatly aided by this gift of perception. Some synesthetes are also observed to have amazing memories, almost photographic. This is because almost every event in their lives is rich with conjoined sensation that influences their process of learning concepts and facts in a manner not dissimilar to associative learning.
Vladimir Nabokov, the Russian-American novelist and writer describes his synesthesia in his autobiography Speak Memory where he recalls his early childhood experiences of playing with colored wooden blocks of alphabet. The wooden blocks had a red ‘A’ and to him, ‘A’ was blue! So, he asked his mother how anybody could be so stupid to get the colours all wrong! But his mother understood of course, because she also suffered from same common form of synesthesia in which letters of the alphabet appear coloured. Nabokov’s son Dimitri inherited the trait as well.
Richard Cytowic, a leading neurologist in the field and author of the popular-science book ‘The Man who Tasted Shapes’ shares his inspiration to study the phenomenon. I quote from the transcripts:
…How did you get interested in it in the first place yourself?
Oh a complete accident, absolutely an accident. I was at a medical centre in North Carolina, and I lived next to the Conservatory, the School of the Arts, and my neighbour who taught at the School of the Arts, was kind enough to invite me to dinner and there was a bunch of us there and he'd made roast chickens and he delayed us sitting down to table with the admonition that there aren't enough points on the chicken. And he turned beet red and said, 'Oh my god, I shouldn't have said that, but well you're a neurologist, maybe you understand. I taste according to shape and I wanted the taste of this chicken to be a pointed, prickly shape, and it came out all round. I can't possibly serve this, I've got to fix it up.' And everybody else thought that he was just being silly, and I asked a few more questions and he told me that he'd had it all his life, nobody seemed to understand what he was talking about, and I said, 'Oh Michael, you've got synesthesia.' And he said, 'You mean there's a name for this?' And I said, 'Well yes'. And the rest is history. So Michael Watson, the lighting designer of the School of the Arts, is in fact The Man Who Tasted Shapes of the book's title. And that began a ten year adventure that we had together of trying to explain what was going on in his brain…
Studies have revealed that one in about twenty five thousand persons are synesthetic, women are twice more likely to be synesthetic than men, and further, that it runs in families. Most synesthetes have a conjoining of two senses, vision and audition, vision and taste or vision and touch. (Vision is dominant because of the obvious reason that there are as many as 30 discrete centers in the brain that are involved in processing of visual stimuli.)
Okay, so freak value apart, what is the big deal about this LSD-like perceptual experience without LSD? In other words, what elevates the phenomenon beyond a mere medical curiosity? I quote from Vilanayur Ramachandran’s BBC Reith Lecture on Synesthesia in 2003.
I'm going to show all of you that synesthesia is not just a quirk in some people's brain. All of you here are synesthetes, and I'm going to do an experiment. I want all of you to imagine in front of you, to visualise in front of you a bulbous amoeboid shape which looks a bit, has lots of curves on it, undulating curves. And right next to it imagine a jagged, like a piece of shattered glass with jagged shapes. And just for fun, I'm going to tell you this is Martian alphabet. Just as in English alphabet, A is a, B is b, you've got each shape with the particular sound, this is Martian alphabet and one of these shapes is kiki and the other is booba, and I want you to tell me which is which. How many of you think the bulbous shape is the kiki, raise your hands? Well there's one mutation there. In fact what you find is if you do this experiment, 98% of people say the jagged shape, the shattered glass is kiki, and the bulbous amoeboid shape is a booba. Now why is that? You never learnt Martian and nobody here is a Martian. The answer is you're all synesthetes but you're in denial about it. And I'll explain. Look at the kiki and look at the sound kiki. They both share one property, the kiki visual shape has a sharp inflexion and the sound kiki represented in your auditory cortex, in the hearing centres in the brain also has a sharp sudden inflexion of the sound and the brain performs a cross-modal synesthetic abstraction saying the only thing they have in common is the property of jaggedness. Let me extract that property, that's why they're both kiki.
Now let us take this idea of sensory fusion to a higher level of abstraction. I propose (with a heavy heart, for I discovered just yesterday that Ramachandran beat me to it) that we can obtain a glimpse (however slight) into the neural basis of the uniquely human aptitude for metaphor, abstract thought and the ability to draw parallels between seemingly unrelated ideas. I propose that akin to synesthesia, there must exist a phenomenon I dare to call syn-cognesia which helps us unify (not involuntarily perceived stimuli) but learned concepts that seem dissimilar. For instance, syn-cognesists like