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Synesthesia: Blending Senses

leigh urbschat's picture

Each of us has encountered a “loud” shirt or “warm” colors, however, for most individuals these terms are metaphors and not actual physical experiences. Those living with the neurological condition synesthesia, in fact, do encounter this blending of senses on a regular basis. Senses like hearing and vision, or touch and taste become combined in the synesthete’s brain rather than remaining separate as in the majority of the population. The study of synesthesia dates as far back as 1880 with the work of Francis Galton in the journal Nature. However, due to the stigma that synesthesia is the product of the imagination, memories from childhood, or drug experiences, little interest was expressed in the subject until recently.1 The condition is very subjective in nature, causing most of the data obtained to be qualitative rather than quantitative. This fact makes it difficult to have any conclusive physical evidence about synesthesia. Scientists do not have a clear answer as to what causes synesthesia or even as to what is occurring within the brain of a synesthete. Although many theories have been purposed, the many complexities of this fascinating condition are likely to keep researchers puzzled for years to come.

One of the most recent explanations for the phenomenon of synesthesia is that it is due to cross wiring, or additional connections within the brain. When individuals process light, the reflected light from an object or scene hits the color receptors in the eye, which triggers neural signals from the retina to be sent to the occipital lobe. There, the image is processed for details. Information on color is sent to fusiform gyrus of the temporal lobe, where it is then sent further along in the brain for even more detailed processing.1 Information involving numbers is also processed in many areas of the brain, including the fusiform gyrus, where the shapes of each number are processed.1 Due to the close proximity at which both colors and numbers are processed, it has been suspected that the cross wiring, or presence of addition connections occur within these closely related areas. Further evidence comes from the fact that the auditory processing center in the brain, located in the temporal lobe, is close to the area of the brain that receives color as well, which would support an explanation for sound-color synesthesia.1

A fascinating hypothesis that could lead to an explanation for the occurrence of this cross wiring comes from the Neonatal Synesthesia hypothesis. The hypothesis states that all babies, until an age of around four months old, are unable to differentiate between senses.2 If this were true, those who experience synesthesia as an adult may have never lost those additional connections within the sensory areas of the brain. Testing signs of synesthesia in such young children is seen as unethical as it entails the use of radiation, which is why research on the Neonatal Synesthesia hypothesis has not been extensive.2 The hypothesis, however, does raise a very important question: if we are all born synesthetes, what must occur within the brain to allow one individual to experience synesthesia into adulthood and another to loose the ability?

It makes one wonder whether we are missing out on a condition of higher-knowledge that has yet to be harnessed into allowing individuals to reach their highest potential. Scientists have found synesthesia to be a dominant genetic condition that is passed along the x-chromosome. Does this mean that there are positive attributes of the disorder that are keeping the gene that carries it within populations (and fairly prevalent, an estimated 1:25,000 persons3)?

One of the reasons that synesthesia is so difficult to comprehend is that it is such a subjective condition. The blending of senses that each synesthete experiences is very different and when they share their experiences they find little to no agreement.4 In Richard Cytowic’s book, Synesthesia: A Union of Senses, he introduces the idea that a non-synesthete’s expectation that all synesthete’s experience their condition in the same way is derived from the fact non-synesthetes agree in “our mutual illusions.”4 With this phrase he is saying that we all agree on such perceptions as a banana being yellow or an apple being red. He mentions, however, that depending on the time of day, a color should look different. Due to the spectrum of daylight, an object will seem bluer in the morning and redder at night.4 We, however, do not perceive the banana or apple as looking any different despite the change in light. In all non-synesthetes’ minds a banana will always be yellow; there is a constant perception as to what the banana looks like. Synesthetes, on the other hand, will not all see the number five as being green, or see the color blue when a C is played on the piano. A synesthete’s experiences are individual within the population of other synesthetes, but are indeed constant within their own mind. Cytowic notes, in fact, that synesthetes who were tested with color number association almost always gave the same colors when tested years later.4

We must now consider what creates this sense of constancy within the brain. Is it the repetition of seeing an object like a banana so many times that engrains the color yellow associated with it into our mind? Or is there a part of our brain that ignores these changing shades in order to simplify how we view the world. In class discussion, students brought up the fact that each one of their experiences with a friend is much different from how another one of them experiences that same friend and how that friend experiences herself. An individual’s experience with another individual who is able to express ideas and interact, however, is very different from an individual’s experience with an inanimate object. Is there any way for us to relay the information needed to know whether our experience with the banana is different from another person’s? Even within the synesthete there is constancy within the brain. Just as we imagine the banana to be yellow at all the times, the synesthete sees the five as green without fail. In considering this aspect, there may be more similarities than expected between the sensory preceptors within the brains of synesthetes and non-synesthetes.

Despite the lack of conclusive evidence as to what actually differentiates the synesthete’s brain from that of the non-synesthete, the study of synesthesia raises some interesting questions regarding our sensory preceptors and the notion of illusion. Synesthesia may be, in fact, a more complete way in which to view the world or a way in which to release one’s highest potential. When scientists are able to understand the physical aspects of synesthesia, they will simultaneously be able to understand more about the human brain than ever before.


  1., Scientific American article on Synesthesia
  2., “Is There a Normal Phase of Synaesthesia in Development?” article written by Simon Baron-Cohen on Neonatal Synesthesia Hypothesis.
  3., “Synesthesia: Phenomenology And Neuropsychology, A Review of Current Knowledge” article written by Richard E. Cytowic, M.D.
  4. Cytowic, Richard E., M.D. Synesthesia: A Union of the Senses. Cambridge: The MIT Press, 2002. pgs. 61-70


Serendip Visitor's picture

I have synesthesia.

I have synesthesia.

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