Neuroscience of Conscious Experiences (Qualia)

(July 6, 2022) Studies of split brain patients show that semantic information is not routinely transferred directly between brain halves as a sort of radio communication. Each brain half is like its own separate brain isolated from the other half unless it has neural connections. This narrows down the possibilities. Any sort of possible psychic  communication must be gated in some fashion.

The purpose of split brain surgeries is to isolate the seizure prone brain hemisphere from the healthy hemisphere so that the patient will not be completely disabled by a seizure. This is accomplished by cutting the corpus callosum (see figure), a bundle of fibers which connects the right and left cortical hemispheres.​

 Other connections remain between the two sides of the brain with many core personality connections still existing between the deeper subcortical centers. Other remaining connections include those in the cerebellum which allows for coordinated motor behavior like walking, and the anterior commissure which is a small connection that allows the eye inputs to cross over into the opposite hemisphere.​

A very rare patient in which both brain hemispheres had a language ability was studied by neurologist Victor Mark in 1996. This patient was rare because 90% of people have their language ability located in the left hemisphere meaning their right hemisphere can't talk or understand language. This dual language patient clearly shows the lack of inter-hemispheric communication by conscious experiences. She has a split cognitive perception even though she still retains an integrated emotional personality due to her intact sub-cortical centers:​

• On one occasion she mentioned she did not have feelings in her left hand. When I echoed the statement, she said she was not numb, and then the torrent of alternating “Yes” and “No” replies ensued, followed by a despairing, “I don’t know.” (Mark 1996)

Cristof Koch had this to say about a video he saw of this same patient:​

• "One half of the brain quite literally does not know what the other half does, which can lead to situations somewhere between tragedy and farce... When asked how many seizures she had recently experienced, her right hand held up two fingers. Her left hand then reached over and forced the fingers on her right hand down. After trying several times to tally her seizures, she paused and the simultaneously displayed three fingers with her right hand and one with her left. When Mark pointed out this discrepancy, the patient commented that her left hand frequently did things on its own. A fight ensued between the two hands that looked like some sort of slapstick routine. Only when the patient grew so frustrated that she burst into tears was one reminded of the sad nature of her situations. (Koch 2004, page 291)

References

(July 6, 2022) Our stream of consciousness is created out of a sequence of still images. This is clearly shown when the brain region responsible for creating this motion is damaged. This brain regions is localized to a small region in the middle of the temporal lobe on the side of the brain called the middle temporal area (MT). Most of its neurons are 10 times as sensitive to motion in one direction then the opposite (Koch 2004).

When this medial temporal area is destroyed in humans by a mini-stroke or hemorrhage the victim cannot perceive motion. The effect this had on patient called L.M. is described below:​

• She had difficulty, for example, in pouring tea or coffee into a cup because the fluid appeared to be frozen, like a glacier. In addition, she could not stop pouring at the right time since she was unable to perceived the movement in the cup (or pot) when the fluid rose. Furthermore, the patient also complained of difficulties in following a dialogue because she could not see the movements of the face and, especially, the mouth of the speaker. In a room where more than two other people were walking she felt insecure and unwell, and usually left the room immediately, because “people were suddenly here and or there but I have not seen them moving.”
• The patient experienced the same problem but to an even more marked extent in crowded streets or places, which she therefore avoided as much as possible. She could not cross the street because of her inability to judge the speed of a car, but could identify the car itself without difficulty. “When I’m looking at the car first, it seems far away. But then, when I want to cross the road, suddenly the car is near.” She gradually learned to “estimate” the distance of moving vehicles by means of the sound becoming louder. (Sacks 1998, page 77)

This example also makes clear the informational update strategy used by the brain. The brain only updates itself when either it detects an emotionally  significant (high valued) environmental change or a certain amount of time has elapsed.

This brain region is also responsible for the waterfall illusion which occurs after looking at a constant motion for over a minute. Most of this region's neurons are sensitive to motion in one direction (Koch 2004). After looking at a constant motion for over a minute, those neurons responding to the visual image movement direction become fatigued so that when a person looks at a blank surface neural noise produces the illusion of motion in the opposite direction because those neurons are no longer inhibited by their opposing counterparts.

This example also shows an important general brain principle which is that all perception centers are balanced between opposing pairs.

References

(July 6, 2022) Color is the archetypal sensory conscious experience in humans. The brain region responsible for generating the conscious experience of color is the 4th visual stage (V4) along the ventral pathway (Koch 2004, page 138). Recent imaging studies have confirmed that the color conscious experience is not produced at the earliest stage (V1) in the visual pathway (Watanabe and all, 2011). This first stage of vision is essentially an edge detector.​

Blindsight is a phenomenon in which the primary visual cortex region is damaged causing visual conscious sensations to disappear yet these same people are often able to unconsciously visually locate and avoid objects in their environment. This phenomena has been shown to use the evolutionarily earliest vertebrate visual pathway (noncortical) which started with fish and amphibians and which still exists in humans. The main center for this is on the back of the brain stem and it is called the superior colliculus (Yoshida and all 2012). This shows that the even the human brain can process information without consciousness experiences in a zombie like fashion. 

References

(July 6, 2022) Like the conscious experience of motion the conscious experience of space again demonstrates that most of our reality is created for us by our brains. Conscious experiences are just "hangers on" not required for behavior. People with damage to the “personal space” area of the cortex do not know such a space exists and because they don’t know it, they can’t interact with it.

Dr. Sacks describes a patient who had completely lost awareness of her left side, she could not turn left, move eyes to the left, or perceive anything in her left visual field. Yet she was able to know of her predicament intellectually and learned to turn right all the way around in order to find something she inferred that she was missing. She did this when she inferred that a part of her meal was still missing if she was still hungry:

• She finds this signally successful if she cannot find her coffee or dessert. If her portions seem too small, she will swivel to the right, keeping her eyes to the right, until the previously missed half comes into view; she will eat this or rather half of this, and feel less hungry than before. But of she is still hungry, or if she thinks on the matter and realizes she may have perceived only half the missing half she will make a second rotation till the remaining quarter comes into view. (Sacks 1998, page 77)

Space as a conscious experience is very interesting. We experience it and then assign other conscious experiences "out there." For example, a plant we see a few feet away has a certain color but that color is actually a conscious experience which is generated within our brains yet we assign it to the plant. The plant also generates conscious experiences of valuation (beauty, love, etc) but most people assign those as something internal to ourselves instead of "out there." Where we assign conscious experiences depends upon our brain wiring so once again the brain creates our reality.

References

Sacks, Oliver (1998) The Man who Mistook His Wife for a Hat and Other Clinical Tales, Touchstone, New York

(July 6, 2022) The conscious experience of body position defines our sense of self as someone different from others.  Damage in the space region of the brain can destroy people's ability to assign their own limbs to themselves. Once again Dr. Sacks provides a good example by describing a patient who thought one of his own legs was actually someone else’s severed leg that was inexplicably placed into his hospital bed. He threw it off the bed taking himself with it:

• ‘Look at it!’ he cried, with revulsion in his face. ‘Have you ever seen such a creepy, horrible thing? I thought a cadaver was just dead. But this is uncanny! And somehow -  its ghastly - it seems stuck to me!’ He seized it with both hands, with extraordinary violence, and tried to tear it off his body, and failing, punched it in an excess of rage.​
• ‘Easy!’ I said. ‘Be calm! Take it easy! I wouldn’t punch that leg like that.’​
• ‘And why not?’ he asked irritably, belligerently.​
• ‘Because it is your leg,’ I answered. ‘Don’t you know your own leg?’​
• He gazed at me with a look compounded of stupefaction, incredulity, terror, and amusement, not unmixed with a jocular sort of suspicion, ...​
• ‘I’ll tell you what it (the leg) looks like. It looks like nothing on earth. How can a thing like that belong to me? I don’t know where a thing like that belongs ...’ His voice trailed off. He looked terrified and shocked.
• ‘if this - this thing - is not your left leg then where is your own left leg?’​
• Once more he became pale - so pale that I thought he would faint. ‘I don’t know,’ he said. ‘I have no idea. It’s disappeared. Its gone. It’s nowhere to be found ...’ (Sacks 1998, page 55)

In very rare cases people go “blind” to body limb positions while retaining the sense of limb belonging. This happens when the dorsal (back side) spinal sensory neurons are damaged. Oliver Sacks describes one such patient:​

• She continues to feel, with the continuing loss of Proprioception, that her body is dead, not real, not-hers - she cannot appropriate it to herself. She can find no words for this state, and can only use analogies derived from other senses: ‘I feel my body is blind and deaf to itself … it has no sense of itself’ - these are her own words. (Sacks 1998, page 51)

This patient was able to move her body only by training her visual system to take over her body's internal position sensing. This took a year of physical therapy. If she closes her eyes or loses visual attention her body collapses.​

 The overlapping ability of vision to provide body position feedback (probably via the cerebellum) is the cause of various “out of body” illusions. The “rubber hand illusion” affects the conscious experience of one’s hand location. In this illusion people actually feel a touch on a fake rubber hand. To get this illusion, the test subject looks at a fake hand that is being stroked by a paintbrush in synchrony with stroking applied to the subject's own hand hidden in a nearby box. Synchronous stroking of the seen fake hand and one's own unseen (real) hand can induce the illusion that the fake hand “feels like it's my hand.” In this illusion the perceived location of the subject's hand drifts towards the fake hand. The illusory ownership and drift are much reduced when the stroking is asynchronous (Botvinick and Cohen 1998) (Tsakiris and Haggard 2005)

 Not only can body parts have their conscious location shifted but so can the whole body (Lenggenhager and all 2007). How this illusion works is to have the subject wear virtual reality goggles in which the subject is told is viewing their back but which in reality is someone else's back which has been shifted in position. Add to that various tactile and visual cues and the mind is fooled (Aspell and all 2009).​

The feelings of limb position tend to persist even when limbs have been amputated showing that the limb position perception is no longer being updated. Therefore it tends to persist. The U.S. Civil War surgeon Silas Weir Mitchell was one of the first to report phantom limb sensations from soldiers who had their limbs amputated due to injury (Mitchel, 1872):​

• Nearly every man who loses a limb carries around with him a constant or inconstant phantom or the missing member … faintly felt at times but ready to be called up to his perception by a blow, a touch, or a change of wind. (p 348)​
• I recently faradized (applied electric current) to a case of disarticulated shoulder without warning my patient of the possible result. For two years he had altogether ceased to feel the limb. As the current affect the brachial plexus of nerves he suddenly cried out, “Oh the hand, the hand!” and attempted to seize the missing member so real did it seem. The phantom I had conjured up swiftly disappeared ...(p 349)
• Impressions regarding the leg are much less vivid than those connected with the arm. The former limb when lost seems to lie straight, and there is usually some difficulty in determining whether or not it swings with the motion of the body in walking. In only one case did it appear to be bent at the knee.​
• In fourteen arm amputations at diverse points the arm seemed in two to hang at the side, and in seven to be bent, the hand lying in air a little way from the left breast or straight in front, and the hallucination as to position being insisted on even by those who declared themselves unconscious of the limbs continuity. The remaining five felt the hand to be in the air, somewhere in front of the chest, but had no conscious flexion at the elbow.... In many it seems to be at rest, extended, the fingers in a like posture; and these cases have .. the best powers of voluntary movements. Others carry with them a hand in a state of more or less violent flexion, and possess but slight control over it. Another class has the hand constantly in some painful position which it occupied before the operation, so that the last real sensation is so stamped upon the sensorium as to forbid its erasure by any future impression....​
• E.C., aged 32, lost his left arm five inches below the shoulder nine years ago. When shot the thumb turned into the palm, and it continued in this state of spasm, so when six hours later, the limb was removed, the nail of the palm had cut into the palm.... For nine years the absent thumb still remains cutting into the palm. The coming of a storm makes the spasm more severe and causes the fingers to close over it. The limb seems shortened six inches. (p 353) (Mitchel, 1872)

Dr. Sacks relays an observation from a man with an above-the-knee amputation:

• ‘There is this thing, this ghost foot, which sometimes hurts like hell - and the toes curl up, or go into spasm. This is worst at night, or with the prosthesis off, or when I’m not doing anything. I goes away, when I strap the prosthesis on and walk. I still feel the leg then, vividly, but it’s a good phantom, different - it animates the prosthesis, and allows me to walk. (Sacks 1998, page 69)

References

(July 6, 2022) In humans, the feelings of pleasure and fear are mostly generated in the evolutionary early subcortical (limbic) regions of the brain. The limbic system even exists in fish but there it is not involved in goal behavior circuitry but in reflexive "continue or flee" decisions.

Direct electrical stimulation of the amygdala in humans undergoing brain surgery most often produces the conscious sensation of fear. Damage localized to the amygdala in humans is very rare but one such patient was unable to recognize a fear based facial expression even though she could identify all the other major classes of facial expression. Low level stimulation of the amygdala added a fear bias to perception without the test humans being actually conscious of the fear producing stimuli (LeDoux 1998)​The reward or pleasure center of the brain is localized in a different subcortical region called the nucleus accumbens. This is the region responsible for the feelings of pleasure. Its direct activation by certain drugs such as cocaine often leads to addiction.

 Recent research using rodents has narrowed down the neuron classes within the nucleus accumbens responsible for addiction. Cocaine addiction results when one class of neurons (D1 neurons) become more active while another class (D2 neurons) become less active (Lobo and all 2010). One would therefore suspect the D1 class of neurons to be responsible for the conscious experience of pleasure in humans. When a person drinks alcohol, endorphins are released in the Nucleus Accumbens and in the orbitofrontal part of the prefrontal cortex. So both the pleasure center and the goal defining region are affected by alcohol (Mitchell and all 2012).

 When we hear an unpleasant sound the amygdala sends feedback to our auditory cortex changing our state of perception. Researchers found that the activity of the amygdala and the auditory cortex varied in direct relation to the level of unpleasantness (Kumar and all 2012). One should not assume that all neurons in the amygdala represent fear. Like the nucleus accumbens other neurons exist within it to provide a counterbalance to fear and anxiety production (Ciocchi and all 2010).​

These examples from the Amygdala and Nucleus Accumbens demonstrate the fundamental balance strategy used in the brain. Not only does a global balance exist between fear and pleasure but also in defining what produces the feelings of fear and pleasure.

References

(July 6, 2022) Mammals are constantly evaluating their route planning and reasoning on whether they should continue or stop. This meta evaluation is the recent neuroscience finding which invalidates the original foundation of dualism put forth by Zoroaster. According to Zoroaster conscious sensations like odors and other feelings are inherently good or bad. This meant the divine realm was divided into good and bad parts. These existence of separate brain sites for valuation shows this idea is false.

Like every other motivation in the brain, valuation of stimuli depends on the balance between two brain centers, the continuation center of the medial (middle) prefrontal cortex and the release center of the lateral (outer) prefrontal cortex which evaluates the importance of the distraction. The arbiter between the two is the orbital gyrus region below them.​

Damage to the lateral distraction center releases inhibition on the medial allowing behaviors to be overly tenacious. This produces the dorsolateral syndrome which is a pseudo-depression where the patient loses the ability to initiate new behaviors. Yet when behaviors can be induced after much effort they tend to persist without stopping. In severe cases the patient will lie passively in bed, neither eating nor drinking.

Patients with this syndrome are no longer bothered by pain even though they can describe the pain they feel just like normal people. Laughing gas does the same thing. This means valuation is a separate independent conscious sensation from the underlying feeling. Conscious experiences themselves are not inherently good or bad. Some just seem to have inherent valuations (like bad smells) due to evolution and context.​

Most of these patients will also have anosognosia in which they are unable to perceive their limitations because they cannot place a valuation on it. As a result they have no motivation to undergo rehabilitation exercises. Minor or slowly developing dorsolateral syndromes can be very hard to recognize in people because their friends assume that the person is becoming lazy or simply becoming disinterested in things due to age.​

A stroke patient with mostly dorsolateral syndrome but who also had damage to her middle (medial) part of her prefrontal cortex is described by Antonio Damasio.

The patients with dorsolateral syndrome still have conscious experiences but they are unable to form goals and reason to achieve those goals because the valuation signal has been stripped off the underlying feelings.

In contrast to the dorsolateral syndrome, damage to the medial tenacity center causes the orbitofrontal syndrome. This is a condition in which the patient lacks any sort of tenacity. The patient is emotionally dis-inhibited and impulsive. They are not able to defer immediate gratification and cannot see the consequences of their actions. They will say what is on their minds without regard to the social consequences (Goldberg 2001, page 144). The earliest celebrity example of this was Phineus Gage who had a railroad tamping iron go through the middle of his brain in 1848.​

A patient with orbitofrontal syndrome from a cancerous tumor was reported on by clinical neurologist Oliver Sacks. This patient, one Mrs. B, was a female research chemist. She seemed to realize she had lost her sense of valuation about social situations. Oliver Sacks says this:​

• When I saw her she seemed high-spirited, volatile - ‘a riot’ (the nurses called her) - full of quips and cracks, often clever and funny.
• ‘Yes, Father,’ she said to me on one occasion. ‘Yes, Sister,’ on another
• ‘Yes, Doctor,’ on a third
• She seemed to use the terms interchangeably. ‘What am I?’ I asked, stung, after a while.
• I see your face, your beard,’ she said, ‘I think of an Archimandrite Priest. I see your white uniform - I think of the Sisters. I see your stethoscope - I think of a doctor.
• ‘You don’t look at all of me? ’‘No, I don’t look at all of you. ’‘You realize the difference between a father, a sister, a doctor?’
• I know the difference, but it means nothing to me. Father, sister, doctor - what’s the big deal?’
• Thereafter, teasingly, she would say: ‘Yes father-sister. Yes, sister-doctor,’ and other combinations.
• Testing left-right discrimination was oddly difficult, because she said left or right indifferently (though there was not, in reaction, any confusion of the two, as when there is a lateralizing defect of perception or attention). When I drew her attention to this, she said: ‘left/right. Right/left. why the fuss? What’s the difference?’
• ‘Is there a difference?’ I asked.
• ‘Of course,’ she said, with a chemist’s precision. ‘You could call them enantiomorphs of each other. But they mean nothing to me. They’re no different for me. Hand … Doctors …. Sisters ...’ she added, seeing my puzzlement. ‘Don’t you understand? They mean nothing - nothing to me. Nothing means anything … at least to me.
• ‘And … this meaning nothing ...’ I hesitated, afraid to go on. ‘This meaninglessness … does this bother you? Does this mean anything to you?’
• ‘Nothing at all,’ she said promptly, with a bright smile, in the tone of one who makes a joke, wins an argument, wins at poker.’ (Sacks 1998, page 116)
• Dr. Sacks went on to concluded: ‘Mrs. B., though acute and intelligent, was somehow not present - ‘de-souled’ - as a person.​

Valuation is also dependent on perceptual context which suggests that it is easily changeable via emotional propagation. Heterosexual men find a perceived touch by a woman more enjoyable than that from a man. If men can be fooled by an experiment into thinking a woman is doing the touching then a man's touch is just as enjoyable. This perceptual valuation effect even shows up in their brain scans (Gazzola and all, 2012).​

Consciousness experiences comes in two varieties because of how goal paths are created in space. The space we experience is not a network like a road map but is continuous. Deep experiences provide valuation about the goal itself as in whether we want to get it or if we want to flee from it. These we call our deep feelings. Shallow experiences are constraints which help guild our path (whole body or hand) toward or away from a goal. These conscious experiences are involved in spatial perception, vision, body position, etc.​

Laughing gas affects the valuation of pain and other things and often induces light heartedness like that seen in patient Mrs. B above. My college roommate went to the dentist and experienced a light dose saying it "hurt like hell but I didn't care." The underlying conscious experience was there but not its valuation.

References

(July 6, 2022) An important but often overlooked conscious experience is that of “will,” which tells us that we moved our own arm instead of feeling that something else moved our arm. This is a form of internal feedback.

 One experiment makes this distinction clear. It was performed on brain surgery patients using electrodes placed directly on the motor cortex of the brain. At first the patients were told to press a button to change a slide in a slide projector. Later the patient’s own brain signals were detected by the electrodes and amplified so that they could change the slide without needing to press the button. When this happened the patients were quite disturbed because they felt they were not the cause of the change even though their motor cortex signals indicated their intent. (Walter, 1963).

 EEG signals from the brain actually define three stages of movement. At 350 milliseconds before an action brain waves indicate the thalamus has primed the action in what is termed a readiness potential. That is the pathways have been disinhibited. At 200 milliseconds before the action these brain waves change indicating that a goal action is underway. The feeling of "will" occurs at this 200 millisecond mark (Libet 1985).

 When this “will” feeling is not generated we naturally think we are not producing the movement. This is responsible for the seemingly mysterious effects of an Ouija board and other old spiritualist methods. In the Ouija game, people lightly place their hands on a pointer which then seems to move on its own to various letters on the board when everyone is asked a question. In time, a sequence of the letters spells out some answer.

In 1853 the great physicist Michael Faraday showed this Ouija movement effect was due to “quasi-involuntary action” when he investigated a similar séance activity called table moving. In this activity people sat around a sliding table, placed their hands on it, and asked the spirits questions. The table then seemed to move in response. At the time people thought spirits were actually moving the table.

Faraday reasoned that if spirits were moving the table then the table would pull their hands after itself. To test this he placed several layers of cardboard as hand place-mats for each person with each card attached to the other by a flexible, but non-rebounding (no springiness) rubber cement. He marked the cards relative to each other on their backsides so that after the séance he could tell if the hands lagged or led the table movement. The result was that the hands led the table showing that the people moved the table without generating the feeling of will (Faraday 1853)

The feeling of will is also lacking in schizophrenic patients who believe that the voices in their head are not made by them but come from somewhere else.

References

(July 6, 2022) That the generation of conscious experiences has a time component is proof that physical chemical processes lay behind its generation. This evidence is provided by the time lags seen during electrical stimulation studies of the brain.

Electrical stimulation of the somatic (touch) sensory cortex area in awake patients undergoing brain surgery produces a conscious experience described as "tingling" in various parts of the body. Yet this  conscious impression was only produced by a fairly long (more than 0.5 seconds) stimulation at a moderate 15 pulses per second (human neurons have a maximum firing rate of about 100 impulses per second). In contrast, an intense burst of stimulation less than 0.3 seconds long with twice the current at that same place produced no conscious experience even though it did produce a muscle twitch (Libet 1985 page 6).​

By the mid 1980's experiments testing visually triggered emotional reactions were also showing this conscious experience timing effect in what is now known as subliminal suggestion (LeDoux 1998, page 53). The key person in this research was Robert Zajonc who first demonstrated the phenomena known as the exposure effect in which otherwise emotionally neutral but familiar things are preferred over novel objects.

In one early subliminal suggestion experiment Zajonc presented pictures to people so fast that they had no conscious recollection of what they saw yet they still exhibited this exposure effect. Zajonc took his initial findings further by subliminally presenting an emotionally charged picture (a smiling or frowning face) just before presenting an emotionally neutral picture. The result was that his test subjects had a tendency to either like or dislike the neutral images according to what emotionally charged images appeared just prior to their appearance. These emotionally charged objects can be innate or previously learned associations (de Lange and all 2011). Previously learned associations which rewire the brain to produce new triggers for feelings are the subconscious.

These simple experiments show two things: 

1. Conscious experiences were generated separately and later than material-based neural sensory signals.

2. Sensory signals activity by themselves can prime the brain pathways to create short term expectations for conscious experiences. This priming is a short term memory and it also represents the short term subconscious.

More recent subliminal experiments use attention diversion (masking) to block conscious experiences. In this sort of research, the subliminal bias is called the “prime” because it primes the choice by setting up the neural pathways. The bias image is prevented from entering consciousness by the use of a perceptually antagonistic“mask” which shuts down the prime’s neural signal before it has time to become conscious. The masks are presented right after the primes and they are presented for a longer period of time. The test subject must also be paying attention to the task because subliminal suggestion does not happen in the absence of attention Naccache and all 2002).

References

(July 6, 2022) That conscious experiences were developed by evolution is shown by the existence of its genetic variations called synesthesia.

 Synesthesia is the production of conscious experiences which are not normal for a particular sensory channel (Cytowic and all 2009). Some people hear colors and some do see auras. This is commonly assumed to be due to some brain mis-wiring and that does seem to be the case for some people. But the more likely case is that they represent normal evolutionary genetic variation.

 Evolution determined which conscious experiences worked best for each task. The conscious color experience seems well suited for the visual sense as opposed to the conscious experiences associated with odors and sounds. Evolution would have selected the conscious experience (qualia) type based upon what worked best for that sense in a process of trial and error refinement. In any population of animals a variety of traits exist at any given time and such a variety of sensory-qualia associations should still exist for the more recently evolved cortical conscious experiences. ​

One example of synesthesia occurs when a person hears lights. This is how one person describes it:​

• Photonic hearing to me is the result of light. My eyes are another pair of “eardrums” to me. Every color emits a tone. Intensity, brightness, position - all influence the tonal quality of the emissions.
• For example, there is a radio tower miles in the distance. On the towers are series of lights, red or white (each color has its own note, tone, or key if you will). I hear the blinking of the lights and its intensity increases as I approach. Now add the reflectors along the side of the road. Every one of them I see emits its ping and the center striping of the road emits its own sound. Every car headlight has it tune. The tonal quality changes with respect to relative position, like a Doppler effect (Cytowic and all 2009, page 103)

Synesthesias come in a wide variety of types and are fairly common. The best study to date has synesthesia occurring in 1 out of every 23 people with the most common having colors triggered by days of the week followed by graphemes (letters, numbers) triggering colors. It has a genetic component and is found equally between men and women.

Many people with laboratory confirmed grapheme-color synesthesia also have other types of synesthesia. Some of the percentages are listed below (Cytowic and all 2009, page 25): 

• Weekdays - Color: 78%

• Month - Color: 72%

• Musical Sounds - Color 52%

• Personality - Color: 33.5% (Auras)

• General Sounds - Color: 31.5%

• Pain - Color: 23%

• Odor - Color: 22%

• Temperature - Color: 18%

• Touch - Color: 12%

• Sound - Touch: 12%

• Sound - Taste: 9%

• Sound - Smell: 6%

• Vision - Smell: 5%

Conscious experiences involving synesthesia come in a wide range of vividness ranging from thoughts (imaginings or verbal) to vivid memories to full strength like direct sensory perception.

 Not exactly synesthesia but very similar are the differing conscious valuations put on food and odors. Almost everyone has some food they do not like because it just tastes or smells bad. This is another example of genetic variation involving conscious experiences.

References