This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
2003 First Paper
Synesthesia is defined as the sensation produced at a point other than or remote from the point of stimulation, as of a color from hearing a certain sound. (From the Greek, syn=together+aesthesis=to perceive).
In common language synesthesia is an involuntary blending of the senses by some people, which allows them to see colors when looking at numbers, for instance.
This is a topic that was introduced over a century ago, but has not been taken serious until recently with the development of tests capable of testing whether or not the condition was real. Previously, scientists thought that this was a figment of the imagination, drug abuse, or in its most concrete form one of memory. As if seeing a number paired with a color, say in early childhood was the reason that a person paired them later on in life. There was also the theory that these people were very creative and when they said that they could taste a shape, it was only an unconventional metaphor.
However, thanks to in depth pursuit of this topic by scientists, especially Ramachandran and Hubbard the validity of such statements has been proven. One test they developed to test the ability of people to pair colors with the site of ordinary numbers involved printing up sheets with similar numbers, like 2 and 5. Many people claimed to see a certain color when presented with the number 2 and a different color when shown 5.
The 2's and 5's were arranged in such a way that one number formed a distinct shape in the midst of the jumble of the other number. A non-synesthetic would be incapable of distinguishing any pattern due to the close resemblance of the numbers. But, in 90% of the cases where people claimed to see colors they were easily able to discern the shape because it registered stood out for them as a completely different color.
One wonders what takes place in the brain to cause such phenomenal differences in perception. The cause is unknown for certain, like many things in the realm of science it has not been researched nearly enough, but there are some indications.
The merging of certain senses points to a crossing of signals in the brain. Although the theory is an old one, it has come to the forefront of the scientific researcher's minds, with increased focus on the topic. Perception of the five senses has a lot to do with the brain's lobes. The color receptors send their signals to the occipital lobe that controls sight, sound goes through the temporal and touch through the parietal. Although these lobes are distinct, they are located very closely together, and there is even a (TPO) juncture above the lobes where signals from different lobes meet. Therefore, it would not be a leap of faith to assume that signals for color can get mixed up within the TPO where numerical computation functions. This mix up would be considered "higher" synesthesia, as opposed to "lower" synesthesia that takes place in the occipital lobe where both color and the visual appearance of numbers reside together. 
Much of the initial observations made by scientists were that cross-wiring was a physical action that took place in the brain, but upon deeper probing have decided that cross wiring could be a chemical action too. Some chemicals inhibit others and therefore cause a chain reaction where a region in the vicinity of an inhibiting region would also be affected. This could happen between distant brain regions as well, but nothing has been proven yet. If distant regions could affect one another, it might be a reason for the intermingling of senses and perceptions that are physically distant from one another in the brain.
What does all this technical stuff mean for someone like me and you? Well, I think that this subject will have a ripple effect on other currently undiscovered topics that concern the brain. The author of one of my articles said that there could be a link to creativity and the mixing of senses, as well as find out if seemingly random perceptual commonalities in people with synesthesia actually have a logical connection. I became fascinated by the effect this topic could have on the arts. I am English major and a poet.
What if one day the exact relationship between the senses and their mingling were discovered. Could I produce poetry that was edible, could a person taste a rainbow like they say on all those Skittles' commercials? Would a greater understanding of other people be fostered if we could somehow touch their pain?
The last one was a big jump from the current evidence that is out there, but we can't think of science on a yearly scale, a right now immediate scale, but rather in terms of decades or centuries. In the thirties who would have thought that dishes could wash themselves?
Back to the Synesthesis, I found a fascinating poem by Arthur Rimbaud; where he discusses the taste of purple and the smell of black as reflected by blood and flies respectively. And he wrote in the 17th century. But, the most interesting discovery I made was from a Hebrew Medical Faculty man by the name of Zvi Rosenstein. He traced Synesthesia back 3313 years to the moment when the Hebrews received the Torah on Mount Sinai. In the old testament of the Bible (Exodus, 20, 18) it says that when the Ten Commandments were given all of the people saw sounds and heard images.
How is that for every thing in science being traced back to one?
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