Biology 103
2003 First Paper
On Serendip

"The sound of colors is so definite that it would be hard to find anyone who would express bright yellow with bass notes, or dark lake with the treble," wrote Wassily Kandinsky in Concerning the Spiritual in Art (1). As the reaction to his book proved, he was largely underestimating the public's propensity to deride any assertion made with assurance, especially one so seemingly subjective. When Kandinsky followed this comparatively general statement with detailed profiles for each basic color - light red, for instance, was "warm," gave one "a feeling of strength, vigor, determination, triumph," and corresponded to the "sound of trumpets, strong, harsh, and ringing" - some of his more outspoken readers suggested that the artist was more fit for an insane asylum than for a painter's career. While today we cannot deny Kandinsky's artistic merits, an interesting question remains. Were the details of his descriptions mere metaphors resulting from the vividness of his imagination? Or was there a physical experience behind such an extravagant way of seeing the world?

It turns out that you don't have to be an artist to have an experience of reality akin to that of Kandinsky. Psychologist Carol Crane, for instance, always sees the letter c in tawny crimson (2), blue accompanies the sounds of the piano for professor of English Sean Day (2), and when journalist Allison Bartlett thinks of a year, she has a distinct vision of a horseshoe with different months distributed over it (3). All of them (including Kandinsky) have a neurological condition called synesthesia - a peculiar mingling of the normally separate senses. For synesthetes, the stimulation of one modality causes a perception in one or more different modalities, so that colors evoke sounds, tastes conjure up shapes, etc.

The name synesthesia is composed of two Greek root words, syn meaning "together," and aisthesis meaning "to perceive" (2). This "together-perception" is relatively rare: some researchers say that approximately 1 in 20,000 is affected (3), others suggest that as many as 1 in 200 may experience a basic form of this condition (4). As one can easily see, there is not much agreement among the scientists, and this is the case not only among the researchers, but also among the synesthetes themselves. The variations of synesthesia are virtually endless and difficult to categorize - though some attempts have been made (4) - because although synesthetic perceptions of one person are consistent over time, it is almost impossible to find two people with identical experience. In other words, if the letter a has always been dark blue for one synesthete, it has always been mustard yellow for another, light green for the third, and so forth.

There are only a few facts about synesthesia on which the researchers have come to an agreement. Synesthesia is genetic and is linked to the x-chromosome (5). It is more common in women than in men, with the ratio ranging from 2:1 to 8:1 (2). And, most importantly, two recent experiments evince that the elusive phenomenon is real. In 1993 Simon Baron Cohen, an experimental psychologist at the University of Cambridge, and his research group conducted a study that proved that synesthetic perceptions are consistent over time. They provided a group of synesthetes and a group of non-synesthetes with a list of numbers, words, and phrases and asked them to record the color each evoked. A week later they repeated the test without warning with the control group, whose responses were only 37 percent consistent with their initial answers. The same follow-up test was given to the synesthetes a year later - 92 percent of them gave an answer identical to one they gave previously (2). Baron-Cohen's later research shows that synesthesia can be measured using positron-emission tomography and functional magnetic resonance imaging. Thus, in synesthetes with colored hearing, areas of the brain connected with visual image processing as well as the areas responsible for sound processing become activated in response to sound stimuli, while in non-synesthetes the visual processing centers do not (6).

At this point one may ask a serious question: why should we care? While synesthesia is a fascinating and unique phenomenon, its very rarity should preclude it from being a general concern. Moreover, it is a condition that is "abnormal" only because it is rare. Tests have shown that synesthetes are mentally stable (7), they are physically and socially active, their secondary sensory experiences do not (except in some extreme cases, when the synesthetic colors, sounds, etc. are particularly unpleasant) interfere with their daily life (3). Thus, synesthesia is not an "abnormality" that requires medical treatment; on the contrary, most synesthetes enjoy having a multi-variable experience of reality and would never want to lose it. It seems that scientists should have ceased being interested in this phenomenon, having satisfied their curiosity as to its objective existence and having raised the awareness of it both in medical circles and in society, so as to affirm that synesthetes are not mentally or psychologically deficient. However, this is not the case. Groups of dedicated scientists in the world's major research institutes and universities are still studying synesthesia and have no intention of ceasing their efforts any time soon. Why? To answer this we have to ask another question: why is it that the synesthetes' experience of the world is so different from the non-synesthetes'.

The researchers have not found a single unifying explanation for this difference. However, major theories advanced by them suggest that, far from being an unusual and therefore mostly irrelevant phenomenon, synesthesia may actually provide a path to solving some of the most fascinating mysteries of how the human brain works. One of the researchers suggesting this possibility is Richard Cytowic, whose studies mark the modern revival of interest in synesthesia. Cytowic postulates that the synesthetic neural processes occur not in the neocortex (an area of the brain associated with "higher-level" thinking) but in the limbic system (regarded as more primitive in evolutionary terms and responsible for emotional, rather than logical, processes). Based on his experiments with synesthetes using the radioactive xenon method, which showed a great decrease in the subjects' cortical function during synesthesia, he proposed that neuroscience had greatly underestimated the importance of emotion in human thinking process. While conventional models of the brain describe neocortex (and rational thinking) as influencing the limbic system (and emotional or associative reasoning), synesthetic processes show that the two are interdependent. Moreover, as Cytowic suggests, the limbic system, in fact, plays the more important role in the process due to the fact that there are more projections from the limbic system into the neocortex than otherwise. (7)

Some may argue that synesthetes cannot act as convincing examples for such a generalization, since apparently their perception of the world is entirely different from that of the non-synesthetes'. Cytowic, however, advises that we should cease thinking of neural processes in terms of terminal events (for instance, of human perception of a color as the final stage of a linear neurological process, whose origin is in the cortex), but instead focus on the intermediate stages of neural transformations. What may then be inferred is that synesthesia is "a premature display of a normal cognitive process" (7). That is, perception is by its very nature holistic, and we are all, in fact, synesthetes, although only few people can "sample" not only the final isolated product (i.e. taste, color, smell), but also the work-in-progress, as it were. (7)

Although another synesthesia researcher, Simon Baron-Cohen, proposes that the brains of synesthetes and non-synesthetes are physically different (and in that disagrees with Cytowic), his explanation of the neurological basis for the condition suggests that this difference is not inherent, but acquired. According to Baron-Cohen's theory, synesthetic experiences are the result of an overabundance of neural connections in the brain. While in the normal human brain there exist separate unconnected modules responsible for different sensory perceptions, in the synesthete's brain there are connections between these centers, causing the unusual mingling of several modes of perception (6). Nevertheless, this theory does not imply that there are two distinct "kinds" of people - those with synesthetical connections and those without - but, rather, that all human infants are born synesthetic. In the majority of humans the connections between different modules are "trimmed" as they grow older, but in some they remain intact as the result of genetic predisposition (8). Therefore, synesthesia may still be helpful in gaining a better understanding of human neurological makeup.

Peter Grossenbacher, a psychologist at Naropa University, Colorado, offers yet another explanation for synesthesia. Unlike Baron-Cohen, he believes that the human brain does not have to have a physically different structure to be able to arrive at synesthetic perceptions. Grossenbacher advances a concept of uninhibited "feed-backward" neurological connections in synesthetes' brains. In the human brain there are "feed-forward" connections, which carry information from lower-level single-sense areas of the brain to the high-level processors, and "feed-backward" connections, which transport the processed information from these multi-sensory processors back to the single-sense areas of the brain (9). Normally, the processed information returns only to an appropriate single-sense area, thus allowing one to focus on a single sensory perception. However, in the brains of the synesthetes the neural pathways of the "feed-backward" connections may become disinhibited, allowing the information to return to more than one area and thus effecting a simultaneous perception in several sensory modalities (3). While in the synesthete's brain this disinhibition happens naturally, in the non-synesthete's brain certain hallucinogenic drugs (like LSD or mescaline) can induce a similar process (2). From this it could be inferred that most activity in the human brain depends not so much on its physical structure as on the exchanges of neurons between its different areas.

Vilayanur Ramachandran and Edward Hubbard of the University of California at San Diego support Grossenbacher's theory to some extent. Their research findings suggest that a process they term "cross-activation" occurs in the synesthetes' brains. Due to an imbalance of chemicals travelling between various areas of the brain, the normally inhibited "cross-talk" (the exchange of information between two separate modules) becomes disinhibited, so that one area produces an effect on the other. This theory accounts for the fact that certain forms of synesthesia (like sound-and-color connections) are more common, while others (like taste-and-shape) are less common. With the more common forms, the areas of the brain responsible for processing the different sensory perceptions are closer to each other, thus facilitating cross-activation, while the opposite is true for the less common forms (10). However, unlike Grossenbacher, Ramachandran and Hubbard do not consider this process of "cross-activation" an abnormality. Rather, they see it as a basis for something common to all humans, namely, for our propensity for metaphor, which is based on our ability to extract a common denominator from seemingly distinct sensory properties. According to them, this "extraction" can only occur if there is a time when all information, as it were, flows together in the brain, that is, when different sensory modes are engaged in cross talk. Since this predisposition for metaphor, and thus creativity, is essential to a human, synesthesia cannot be considered simply an obscure abnormality, but a more vivid manifestation of the process common to all of us (10).

Paradoxically, what these studies suggest is that we are all "closet synesthetes." While synesthesia par excellence is relatively rare, it would not be unfounded to suppose that cross-modal references occur in everyone's brain, although it is difficult to pinpoint them in non-synesthetes due to their diminished state (11). What implications then does synesthesia have for our perception of reality and what does its existence suggest about the nature of reality in general?

The synesthetes claim that not only objects, but also abstract concepts have a multitude of sensory qualities: color, sound, shape, smell, etc. Could it be that the nature of reality in general is multi-variable, that all phenomena objectively possess several qualities, some of which are more pronounced and others less? Some of Ramachandran's and Hubbard's research indirectly supports this assertion. They presented their subjects with two drawings (one blob with soft curved outlines and another with jagged sharp-edged outlines) and two nonsensical words (bouba and kiki). 99 percent of the subjects associated the curved blob with bouba and the sharp-edged with kiki (10). From this it may be inferred that there is some connection between the visual curviness/jaggedness and the auditory softness/sharpness, and, thus, that there are inherent connections between sensory modalities that we normally separate (for example, between visual and auditory modalities).

If the nature of reality is indeed multi-variable, it follows that humans normally suppress some of the qualities of perceived objects during the processing of the neural signals in the brain. Synesthetes, on the contrary, do not suppress most modalities due to a genetic predisposition. However, it is interesting that some synesthetes report that they can diminish their synesthesia by focusing on something other than the object or concept that evokes their secondary perceptions. Thus, Sean Day, who normally sees colors when he hears music, claims that if he closes his eyes or consciously concentrates on something other than the sound, the colors go away (4). Would it be possible for a non-synesthete to do something diametrically opposite, that is, to develop a conscious perception of the "abnormal" sensory variables of a given object? In this respect, it is interesting that some blind people report perceiving color and light via tactile experiences (11), while color-blind synesthetes report seeing vivid synesthetic colors (10).

Holistic nature of sensory perception (albeit unconscious) is important because it allows for a more complete understanding of the world, but also because it presupposes the existence of a certain common basis of reference that makes communication and understanding between humans easier. Synesthesia suggests that every person's conscious perception of reality is different from everyone else's (and that is also probably true - to a lesser extent - for non-synesthetes). On the other hand, some researchers have found common tendencies even in the seemingly endless variety of synesthetic perceptions (4), which may in turn suggest that our experience of reality is not as subjective as other researchers (among them Grossenbacher) would have us believe. But even if the results (the perceived colors, smells, tastes) of the neurological processing of sensory input are different (if each of us suppresses and, therefore, experiences different modalities), in the earlier stages of the process, when cross-activation takes place, our experience of the world is still much the same in its multi-variability. This is true even if one assumes that objects do not in reality posses multi-variability, but, rather, that different areas of the brain are randomly and subjectively cross-activated (that is, if the color blue really does not have a sound associated with it, but, rather, the signal "blue" randomly cross-activates the parts of the brain responsible for visual and sound perception). There is still some basis for a common experience.

Another important assumption that can be made based on synesthesia research is that emotions have a profound effect on our perception of reality. Synesthetes often report that their secondary perceptions become more vivid if they are emotionally involved in the experience. One of the more famous synesthetes - the Russian composer Scriabin, for whom music evoked colors - claimed that normally he had a "faint feeling" of color, which grew stronger and ended in a visual image of color as his emotional involvement in the music escalated. He also noted that not all music could produce synesthetic experiences in him. Some composers, like Beethoven, were too "intellectual" for that, while more "emotional" modern composers, like Tchaikovsky, inevitably evoked vivid colors. (12)

If we accept the notion that we are all "closet synesthetes," then future research on synesthesia and emotion may lead to a greater understanding of the neurological basis for our liking and disliking certain smells, tastes, colors, etc. It may also add to our comprehension of why purely intellectual pursuits have emotional value for humans, leading some to quasi-ecstatic states, while remaining a boring chore for others. The link between synesthetic experiences and emotions may also uncover the neurological basis for the psychological effects of colors (for example, the calming effect of blue) and music.

As one can see, the areas of research for which synesthesia is important are numerous and crucial for neurobiology and philosophy of science. Therefore, the continual scientific study of this condition is not based on mere curiosity, but on a desire to unlock some mysteries of the human brain. When the theories that the scientists arrive at become popularized, perhaps, people will recognize that even the "simple" and "natural" processes like seeing a color or hearing a sound are more complex than they think. Moreover, even such seemingly bizarre statements like that of Kandinsky would be attributed not to artistic whims and not even to a subjective and rare neurological condition, but, rather, to a neurological process of perception common to everybody. After all, how many of us would really associate bright yellow with bass notes and dark blue with C sharp? It turns out that not only we may really hear yellow, but that it may be as natural to a human as slandering every groundbreaking scientific theory or suspecting every observation that transcends the boundaries of "normal" experience (which, in turn, may, as synesthesia research shows, be self-imposed and subjective).

References

1)Kandinsky, Wassily. Concerning the Spiritual in Art. New York: George Wittenborn, Inc., 1947.

2)"Do You See What They See?" on "Discover" magazine home page, by Brad Lemley

3)"An Ear for Color" on "Washington Post" home page, by Allison Bartlett

4)"Professor Making Sense Out of Senses" on Journal-News.com, by David Brown

5)"I Can Taste My Words" on "BBC News" page, by Jane Elliott

6)"Everyday Fantasia: The World of Synesthesia" in "Monitor on Psychology" on American Psychological Association home page, by Siri Carpenter

7)"Synesthesia: Phenomenology and Neuropsychology" on "Psyche" page, by Richard Cytowic

8)"Is There a Normal Phase of Synaesthesia in Development?" on "Psyche" page, by Simon Baron-Cohen

9)"Cortical Feedback Improves Discrimination Between Figure and Background by V1, V2 and V3 Neurons" on "Nature" journal home page, by Hupe et. al.

10)"Hearing Colors, Tasting Shapes" on Scientific American.com, by Vilayanur Ramachandran and Edward Hubbard

11)"Synesthesia - A Real Phenomenon? Or Real Phenomena?" on "Psyche" page, by Luciano da F. Costa

12)"Synesthesia and Artistic Experimentation" on "Psyche" page, by Cretien van Campen


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