WHAT IS CHROMAETESIA?

The synaesthetic experience depends exclusively on the left brain and is associated with a decreased blood supply to the neocortex. This results in enhanced limbic expression. Therefore, we can assume that the system responsible for synaesthesia is located or influenced by the limbic system more than the neocortex. Additional support for this is that there is an emotional aspect associated with a synesthetic experience. In fact, in order to fulfill the diagnostic criteria for synaesthesia an emotional response must be present. We are irrational creatures by design and that emotion, not reason, may play the decisive role both in how we think and act. Additionally, our brains are not passive receivers of energy flux, but dynamic explorers that actively seek out the stimuli that interest them and determine their own contexts for perception. Because there are more projections from the limbic system to the neocortex than the other way around, the limbic brain easily overwhelms thinking. It is the limbic brain that determines the salience of that information. Therefore, an emotional evaluation ultimately informs our behavior. Our inner knowledge behind the curtain is largely inaccessible to introspective language, which means that what we feel about something is more valid than what we think or say about that something. Reason is just the endless paperwork of the mind.

Cases of synaesthesia may be idiopathic (developmental), with the person having experienced synaesthesia as long as they can remember, or non-idiopathic, resulting from a known etiology or mechanism which is acquired and produced synaesthesia.

The most prevalent form of synesthesia is known as audition colorée(chromaetesia), the phenomenon of hearing of colors in music and vowels. Three psychological theories have been put forward for colored hearing synaesthesia. The doctrine of the unity of the senses or linkage theory, proposes that the perpetuation of a primitive perceptual experience in the limbic system is the root cause of color synaesthesia. As this system evolved, the perception was differentiated into two separate senses, hearing and vision. A similar theory, the crosstalk theory, holds that auditory and visual information pathways may cross in synaesthetes. These cross-modal neural connections may be numerically greater than usual or simply used in different ways. Some believe higher cognitive/cortical level processing (the limbic system is thought to be lower level) to be involved. According to this view, colored hearing synaesthesia is the result of a chain of mental associations, some of the intermediate links having dropped out of awareness. For instance, a person may see red every time they hear a trumpet because of the red uniforms of a brass band. Feedback connections aid us in imagery, memory, sensory attention and other cognitive functions, but
could they also result in synaesthesia? Auditory and visual information must meet somewhere in the brain or we could not process them in conjunction as they occur. These systems may contain feedback pathways normally but, in synaesthetes, they may be altered to include information from the other senses. Ramachandran's studies show that chromaetesia is the involuntary physical experience of a cross-modal association. Because the hearing center in the temporal lobes is close to the higher brain area that receives color signals from V4 sound-color synesthesia happens. He points out that the same effect could occur if the wiring-the number of connections between regions-was fine but the balance of chemicals traveling between regions was skewed. ( cross activation ) For instance, neighboring brain regions often inhibit one another’s activity, which serves to minimize cross talk. A chemical imbalance of some kind that reduces such inhibition – for example, by blocking the action of an inhibitory neurotransmitter or failing to produce an inhibitor-would also cause activity in one area to elicit activity in a neighbor. Such cross activation could, in theory, also occur between widely separated areas, which would account for some of the less common forms of snesthesia. Similarly, in some lower forms, the visual appearance of a letter might generate color, whereas in higher
forms it is the sound. Chromaetesia is perceived externally in peri-personal space, the limb axis space immediately surrounding the body, never at a distance as in the spatial teloreception of vision or audition where a synesthesia on hearing music, also see objects-falling gold balls, shooting lines, metallic waves like oscilloscope tracing – that float on a “screen” six inches from her nose. The experience is accompanied by a sense of certitude and conviction that what chromaetesies perceive is real or valid. This accompaniment brings to mind that transitory change in selfawareness that is known as ectasy.

Experiments show that hemispheric flows are low and inhomogenous to begin with, yet drop a further 18% on average in the left hemisphere during chromaetesia. Such a decrease is impossible to obtain in a normal person with, for example, a drug. Even during an activation trial with amyl nitrate, which subjectively intensifies the synesthetic experience, regional blood flows are decreased compared to baseline on people with synesthesia. Normally, any physical or mental task, or any activation procedure (e.g., drug administration, carbon dioxide or oxygen inhalation), increases blood flow by five to ten percent. Most of the time cortical metabolism drops so low during chromaetesia that would cause blindness, paralyziation, or other conventional sign of a lesion in non-chromaestetics. Such a depression of cortical metabolism during a distinct behavioral state disturbs traditionalists, who regard the more recently-evolved cortex as the seat of higher analysis and reason, while assigning the limbic system (the sub-cortical ring of tissue that encircles the brainstem and is much older in evolutionary terms) to handle the more "primitive" functions of emotion, memory, and attention. The hippocampus is also necessary for experiencing other altered
states of consciousness that are qualitatively similar to chromaetesia. For example, the perceptions during LSDinduced chorametesia, sensory deprivation, limbic epilepsy, release hallucinations, and the experiential responses during electrical stimulation of the brain possess a generic, elemental quality - just as they do in chrometesia ( Cytowic, 1989 ).

Research regarding musical pitch stimuli and the visual representations showed that when the pitch was regarded to be higher, the visual images were reported to be lighter in color, while pitches that were regarded as lower tended to produce visual images that were darker in color. This has been seen to occur in non-synesthetes in laboratory settings in the same frequency that synesthetic individuals report involuntary occurrences (Hubbard).

Experiments show that hemispheric flows are low and inhomogenous to begin with, yet drop a further 18% on average in the left hemisphere during chromaetesia. Such a decrease is impossible to obtain in a normal person with, for example, a drug. Even during an activation trial with amyl nitrate, which subjectively intensifies the synesthetic experience, regional blood flows are decreased compared to baseline on people with synesthesia. Normally, any physical or mental task, or any activation procedure (e.g., drug administration, carbon dioxide or oxygen inhalation), increases blood flow by five to ten percent. Most of the time cortical metabolism drops so low during chromaetesia that would cause blindness, paralyziation, or other conventional sign of a lesion in non-chromaestetics. Such a depression of cortical metabolism during a distinct behavioral state disturbs traditionalists, who regard the more recently-evolved cortex as the seat of higher analysis and reason, while assigning the limbic system (the sub-cortical ring of tissue that encircles the brainstem and is much older in evolutionary terms) to handle the more "primitive" functions of emotion, memory, and attention. The hippocampus is also necessary for experiencing other altered states of consciousness that are qualitatively similar to chromaetesia. For example, the perceptions during LSD-induced chorametesia, sensory deprivation, limbic epilepsy, release hallucinations, and the experiential responses during electrical stimulation of the brain possess a generic, elemental quality - just as they do in chrometesia ( Cytowic, 1989 ).

Research regarding musical pitch stimuli and the visual representations showed that when the pitch was regarded to be higher, the visual images were reported to be lighter in color, while pitches that were regarded as lower tended to produce visual images that were darker in color. This has been seen to occur in non-synesthetes in laboratory settings in the same frequency that synesthetic individuals report involuntary occurrences (Hubbard).

Based on these studies Cytowic has hypothesized that all human beings possess the ability to have synesthesia.  He believes that as children, all humans are synesthetic, that only as they mature into adulthood, the part of the brain that allows for cross-modalities to occur represses those abilities, making most adults forget they have synesthesia (Cytowic, 1989 as cited in Cytowic, 1995).

Another prevalent idea is that synesthetes are merely being metaphorical when they describe the note C flat as “red” just as you and I might speak of a “loud” shirt or “sharp” cheddar cheese. Our ordinary language is replete with such sense –related metaphors, and perhaps chromaeteses are just especially gifted in this regard.
Is this just a memory, or do you actually see the color as if it were right in front of you? When Ramachandran tried asking this question, he did not get very far. Some subjects did respond, “Oh, I see it perfectly clearly.” But a more frequent reaction was, “I kind of see it, kind of don’t” or “No it is not like a memory. I see the number as being clearly red but I also know it isn’t; it is black. So it must be a memory, I guess.”

Mechanistic explanations have been plentiful throughout synesthesia's history. The notion of crossed wires turns up repeatedly. As early as 1704, Sir Isaac Newton struggled to devise mathematical formulae to equate the vibration of sound waves to a corresponding wavelength of light. Goethe noted color correspondences in his 1810 work, Zur Farbenlehre. The nineteenth century saw an alchemical zeal in the search for universal correspondences and a presumed algorithm for translating one sense into another. This mechanistic approach was consistent with the then-common view of a clockwork universe based on Newton's uniform laws of motion.

Its phenomenology makes clear that chromaetesia is not an idea, but an experience. How does science approach this distinction between a first-person understanding of some experience and a third-person one that is supposedly objective? A lack of obvious agreement among chromaetesia compounds the apparent difficulty. In fact, this rather glaring problem - that two individuals with the same sensory pairings do not report identical, or even similar, chromaetesiatic responses - has sometimes been taken as "proof" that chromaetesia is not "real." Scriabin and Rimsky-Korsakov, for example, disagreed on the color of given notes and musical keys. The examples below represent some different photisms.

As can be seen above, "Chromaetetics never see complex dream-like scenes or have otherwise elaborate percepts. They perceive blobs, lines, spirals, lattices, and other geometric shapes." Dr Richard Cytowic notes that the generic and restricted nature of synesthetic percepts bear a considerable likeness to a series of forms first developed by Heinrich Kluver in the 1920's known as Kluvers "form constants". These generic shapes are common to chromaetesia, hallucinations and are frequently seen in primitive art. Variations in photism color, brightness, symmetry, and shapes have been recorded to vary as a result of variation in musical stimuli. Tempo for instance effects the shape of a photism; the faster the music, the sharper and more angular the photism. That pitch has a direct effect on the size of a photism has also been recorded. It has been observed universally that photism size increases as auditory pitch decreases. In this way high pitched sounds produce small photisms and low pitched sounds produce synesthetic percepts that are large in size. Loudness also has an effect on the size of the photism perceived by a chromaetesie. Lawrence E. Marks shares his understanding of Chromaetetic response to music :"Just as the important dimensions of the auditory stimulus that are responsible for musical synesthesiae can be quite complex, so too can be the synesthetic responses themselves." "Visual sensations aroused by music need not be limited or confined to simple spots of color. Often the entire visual field fills with colors that change over time with the music; some subjects report several colors simultaneously, each color reflecting a particular aspect of the music."

The study of chromesthetic phenomena often concerns itself with associations triggered by speech rather than music. This is perhaps due to the fact that speech is pathologically superior in its ability to evoke a synesthetic response. The component of speech that bears the greatest influence on the nature of the induced response is the sound of vowels. Both areas have tremendous significance in mapping out perceptual parallels between the modalities of hearing and vision. Firstly, when it comes to reports on musical synesthesia, we find that the important principles of visual-auditory association that manifest themselves in color music are basically the same principles that manifest themselves in colored vowels - that is, the relations of visual brightness and size to auditory pitch and loudness. Secondly, in an article published in 1968, Wayne Slawson showed that artificial two formant sounds are readily interpretable as vowels and as musical notes and that the vowel quality and musical timbre depend in similar ways on the structure of the sound (formant frequency and spectrum envelope).

HOW BRAIN PROCESSES VISUAL INFORMATION

An understanding of the neurobiological factors at work requires some familiarity with how the brain processes visual information. "Human sensory systems mediate four attributes of a stimulus that can be correlated quantitatively with a sensation: Modality, intensity, duration and location. "The attributes of intensity, duration and location apply to all five sensory modalities: vision, hearing, touch, taste and smell. Each of these sensory modalities has sub modalities, which in the case of vision include color whilst in hearing they include pitch. Our perception of light arrives to the brain via a series of Photo-receptive rods and cones in the eye. Audition on the other hand uses information gathered by mechano-receptive hair cells in the ear that measure vibrations in air pressure. The nature of the differences between the five modalities is suggested by the disparate nature of these sensory receptors. Whilst both photo-receptors and mechano-receptors measure intensity, location and duration, they both also measure a property of frequency.

After light reflected from a scene hits the cones (color receptors) in the eye, neural signals from the retina travel to area 17, in the occipital lope at the back of the brain. There the image is processed further within local clusters, or blobs, into such simple attributes as color, motion, form, and depth. Afterward, information about these separate features is sent forward and distributed to several far-flung regions in the temporal and parietal lobes. In the case of color, the information goes to area V4 in the fusiform gyrus of the temporal lobe. From there it travels to areas that lie farther up in the hierarchy of color centers, including a region near a patch of cortex called the TPO (for the juction of the temporal, parietal and occitipal lobes.) These higher areas may be concerned with more sophisticated aspects of color processing. For example, leaves look as green at dusk as they do at midday, even though the mix of wavelengths reflected from the leaves is very different.

WHY DOES IT HAPPEN?

Because the hearing center in the temporal lobes is close to the higher brain area that receives color signals from V4 colored-hearing synesthesia happens by cross wiring between V4 and the hearing area (both within the fusiform gyrus) or between higher color area (both in te TPO).

Chemical imbalance: The same effect could occur if the wiring-the number of connections between regions-was fine but the balance of chemicals traveling between regions was skewed. For instance, neighboring brain regions often inhibit one another’s activity, which serves to minimize cross talk. Cross activation could, in theory, also occur between widely separated areas, which would account for some of the less common forms of snesthesia. Similarly, in some lower forms, the visual appearance of a letter might generate color, whereas in higher forms it is the sound, or phoneme, summoned by that letter; phonemes are representad near the TPO. .

Generic component: Perhaps a mutation causes connections to emerge between brain areas that are usually segregated. Or maybe the mutation leads to defective pruning of preexisting connections between areas that are normally connected only sparsely. If the mutation were to be expressed (that is, to exert its effects) in some brain areas but not others, this patchiness might explain why some synesthetes conflate colors and numbers whereas others see colors when they hear phonemes or musical notes. People who have one type of synesthesia are more likely to have another, which adds weight to this idea.
Our insights into the neurological basis of synesthesia could help explain some of the creativity of painters, poets and novelists. According to one study, the condition is seven times as common in creative people as in the general population. One skill that many creative people share is a facility for using metaphor. Their brains are set up to make links between seemingly unrelated domains. Just as chromaetesia involves making arbitrary links between seemingly unrelated perceptual entities such as colors and sound, metaphor involves making links between seemingly unrelated conceptual realms.

In addition to clarify why artists might be prone to experiencing chromaetesia, is that this trait may have set the stage for the evolution of abstraction-an ability at which humans excel. The TPO (and the angular gyrus within it), which plays a part in the condition, is normally involved in cross modal synthesis. It is the brain region where information from touch, hearing and vision is thought to flow together to enable the construction of high-level perceptions.