Do the Senses Make Sense?

      In his autobiography, Speak Memory, Vladimir Nabokov describes a rather curious experience: “I present a fine case of colored hearing” he writes. “Perhaps ‘hearing’ is not quite accurate, since the color sensation seems to be produced by the very act of my orally forming a given letter while I imagine its outline” [1] (Nabokov, 381) The  synesthetic experience described by the famed novelist, although unusual, is by no means unique. The phenomena was once thought to be quite rare and was often brushed aside by the scientific community who attributed it to hallucinations and drug use. Recently however, synesthesia has become the subject of much research among neurobiologists. Recent studies have shown that far from being a freak occurrence,  approximately one in twenty people have experienced one of the many different kinds of synesthesia [2][5] .

      Defined as the neurological coupling of two or more bodily senses, synethesia can vary significantly from person to person. Usually however the phenomenon can be classified into five common categories. These include: grapheme-color synesthesia where letters or numbers are perceived as colored, ordinal linguistic personification where letters, numbers or even days of the week can be associated with different personalities, spatial-sequence synesthesia where numbers or dates are perceived as having a characteristic shape, music and sound-color synesthesia where individuals associate colors and shapes with sound, and lexical-gustatory synesthesia, where words are associated with particular tastes [3] .

      What can the experience of synesthesia tell us about how we perceive reality? Do people with synesthesia perceive the world as more colored, vibrant and vivid than it really is? This web paper will focus on the possible causes of synesthesia and the implications these findings have on our understanding of some of the most unfathomable aspects of the human mind.

      In order to arrive at any conclusions regarding the implications of synesthesia we must first understand its causes. One apparently simple explanation is the theory that affected people exhibit very strong childhood associations. We have all played with refrigerator magnets for example. If the A on a person’s refrigerator was red than it is quite probable that for the rest of their life this person will tend to associate the letter A with that color [4].  This theory does not explain why some people retain more vivid memories than others or why many children can casually remark that this or that block or letter is the “wrong” color. 

      A simple test called the pop-out, or segregation test has been done on affected individuals in order to determine whether the effects of synesthesia are genuinely sensory. Subjects were shown a set of black 2’s arranged in a specific pattern amongst black 5’s. To a person who does not experience grapheme-color synesthesia the 2’s blend in with the 5’s and can only be distinguished under very close scrutiny. To a synesthete however, who perceives each number as colored, the 2’s immediately pop-out from the 5’s and the shape they make is easily discernible.  The results indicate that the experience of synesthesia is indeed due to sensory phenomena. It would seem that the explanation of synesthesia may be found by a closer examination of the sensory process [2].

 Scientists believe that the effects of synesthesia occur due to cross-wiring of the brain at one of the various places responsible for a different aspect of our perception [2]. Take, for example, the process of color perception. When we look at an object the wavelengths that strike our eye form an image on the back of the retina. This image however and the image in our brain are quite different. The brain fills in the picture, the dimensions and even the color of an object all on its own. While it would seem that the picture in our head is in one distinct place, following the optic nerve from the retina has shown us that this is not the case. On the contrary, different information from the optic nerve goes to various locations in the brain which all work together like a perceptual symphony to create what we think we see.

 Because so many places in the brain are responsible for creating the complete picture, the number of different cross-wiring scenarios is infinite. From the optic nerve of the retina, signals travel to area 17 in the occipital lobe of the brain. Here they can be broken up into simple characteristics such as color, shape and depth. Color information continues on to the V4 region of the temporal lobe. This region is also responsible for the visual appearance of numbers and therefore may account for a cross-linkage between color and number perception. The color signals then travel to the TPO junction, between the temporal, parietal and occipital lobes. Since more complex numerical computation is also located in this region cross linkage may result in synesthetes who link colors with abstract numerical concepts like the days of the week [2].

 While it is possible that the cross-wiring is physical, the linkage of senses can also be explained on a chemical level. Most neurons function as inhibitors of other neural pathways and entire brain regions are often responsible for inhibiting the activity of neighboring regions. “Disinherited feedback”, a reduction of inhibition, may result in the activation of cross-sensory input [5]. It follows therefore, that the cross-wiring of sensations could exist in everyone. The synesthetes in our society are just less inhibited than the rest of us.

 This brings us back to the ever elusive question: what is reality? Is the reality experienced by synesthetes somehow more real or is synethesia just a euphemism for psychic disturbance?

       It would seem that if the brain truly creates reality then everyone’s perception of the world must be a little different. We know that neither color nor sound are intrinsic properties of an object. A rose for example is not red by its nature, color is not one of its intrinsic properties. It merely gives off certain wavelengths of light that the brain can process into the experience of color. A color blind person and a person who can see color may be standing in the same garden, looking at the same rose that is still giving off the same wavelength of light. However the two people will experience this moment differently. To a synesthete who may experience a sweet taste in addition to the perception of color, that rose appears differently, but is still every bit as real. Reality then, is encompassed by the brain and the experience of a synesthete is every bit as valid as a more mundane picture the flower . The next question that arises is why synesthesia, which is thought to be an x-linked trait, should be passed along at all. Of what possible use is this ability to connect senses? What is its role in the human experience?

      Nabokov writes in his memoirs that “the confessions of a synesthete must sound tedious and pretentious to those who are protected from such leakings and drafts by more solid walls than mine are” (Nabokov 382). What he does not take into account is the fact that in our own way we are all synethetes. The ability to connect two senses can account for some of the most baffling and wondrous mysteries of the human mind and the human experience.

      From and evolutionary standpoint the synesthetic experiance may go a long way to explain the uniquely human ability to create complex language All humans possess an intrinsic capacity to associate certain sounds with certain shapes or things. Recent research has demonstrated this ability with an experiment called the Bouba/Kiki Effect. When subjects are shown two shapes, one jagged and angular and the other bulbous and with smooth edges they almost always associate the former with the name “kiki” and the latter with the name “bouba”.  It is very likely that our hominid ancestors made use of this ability in order to arrive at a shared vocabulary, a common point of understanding[5], [2].

      There are elements of synethesia in almost any creative endeavor. It is no wonder that so many artists were self-proclaimed synesthetes. The ability to create metaphors, tying together seemingly unrelated things has been responsible for some of the most beautiful poetry and prose created by human kind. It is this connection between senses, this cross-linkage that allows us to easily comprehend such abstract concepts as “the bitter wind” or such descriptions as “Juliet is the sun”[5].

      In conclusion, the extraordinary experience of synesthesia has opened the door to some of the most complicated and as yet uncharted functions of the brain. We all experience a certain amount of cross wiring, and it is this which defines us as human beings. Researchers have shown cases where color-blind synesthetes were actually able to perceive colors in numbers without ever having seen those colors before [2]. To me, this discovery is really the culmination of everything I have been learning about the brain. All on its own, the human mind can create something we have never experienced such as an abstract concept of color. It can produce a subtle and poetic language to tell stories about things we have never seen with our eyes. This one mass of cells can encompass our entire reality.
     
      References
[1] Nabokov, Vladimir. Speak Memory: an Autobiography Revisited. The Library of  America, New York, NY: 1996
[2] Hearing Colors, Tasting Shapes, Article published by Scientific American Inc. 2003: http://www.sciencecore.columbia.edu/demo/web/resources/readings/hearing.pdf
[3] Picture a World Where Senses Collide, Article published by Tampa Tribune, 2007 http://www.tbo.com/life/MGB0YDR79YE.html
[4] Synesthetic Colors Determined by Having Colored Refrigerator Magnets in Childhood, Cortex published online, 2006. http://www.synesthesia.info/Witthoft.pdf
[5] Wikepedia Article on Synethesia:  http://en.wikipedia.org/wiki/Synesthesia