It has long been suspected that, in perceiving things in the outside world, people may have different qualia, which are qualia that have different phenomenal characteristics even if they are qualia of the same thing, occurring in their minds. For example, when people look at the same color C, the color quale of red may appear in some, while the color quale of blue, green, or other colors may appear in others [Figure 9.1]. It is also possible that some extraordinary colors that are not in the color spectrum that general people perceive may occur in some people. Yet, they will all call what they see in their minds the same, “color C”, even if the phenomenal characteristics of the colors in their minds are different. Even more bizarre possibilities are that other types of qualia, such as auditory qualia, olfactory qualia, or qualia of unusual percepts that do not occur in general people, may occur instead of the color quale in some people! And all of them will still call it “color C”! Notably, at least at present, there is no way to prove definitely that qualia (of the same thing) that occur in people have the same or different phenomenal characteristics. However, theoretically, are these possibilities real – can qualia of the same thing be such randomly different in people?
Figure 9.1 Different color qualia among people
The answer, according to Theorem VIa and Theorem VIb, which state that identical/ similar neural processes have identical/similar mental processes and identical/similar qualia, is “no”. But is there evidence that they really cannot be different and that both theorems are correct?
Hypothetically, there can be several types of different qualia, and each type is basically different from the others. So, they have to be examined type by type to see whether which one of them can really occur. They can be classified into three major types as follows.
9.1. Objectively different qualia
9.2. Randomly different qualia
- 9.2.1. Completely randomly different qualia
- 9.2.2. Partially randomly different qualia
9.3. Restrictedly different qualia
- 9.3.1. Inverted qualia
- 9.3.2. Shifted qualia
- 9.3.3. Identical-structure qualia
9.1. Objectively different qualia
First, it must be noted that different qualia of the same thing among people are possible objectively because many physical, anatomical, and physiological factors are involved in the process of perceiving anything and because these factors – which have effects on perception neural processes and their signaling patterns, which will inevitably affect perception mental processes and qualia – are different among people. For example, in the case of perceiving a color, the involved physical factors in the outside world (such as the light that shines on the color, the light’s angle of incidence and of reflection, and the intervening medium between the color and the observer’s eyes) and the anatomy and the physiology of the whole visual perception pathway (from the corneas of the eyes to the neural circuits for visual perception) are slightly different among people. So, the resulting perception neural processes and their signaling patterns, together with their mental processes and qualia, will be slightly different, and it is very likely that people will consciously experience (mentally see) the same color differently, but only subtly if their brains are normal and if other factors are very similar. Different qualia that result from objective differences in physical, anatomical, and physiologic factors are called objectively different qualia in this theory. The differences of objectively different qualia of the same thing among people are usually subtle because the differences in the resulting neural processes and signaling patterns among them are only slight, as noted. Drastic differences of objectively different qualia of the same thing under similar perceiving conditions in normal people are not possible and do not occur.
Synesthesia is a condition in which a stimulus in one sensory modality automatically and consistently triggers a concurrent percept in another modality [1-18], or in another form of the same modality. For example, people with color-music synesthesia will have color perception occurring when they hear musical sounds and people with grapheme-color synesthesia will have perception of colors occurring when viewing letters or numbers. Many scientists believe that synesthesia occurs because there are unusual neural connections between perception neural circuits of different modalities such that, when a perception neural circuit of one modality (such as auditory) is stimulated to function by some stimulus, another perception neural circuit of different modality (such as visual) will function simultaneously (such as in people with color-music synesthesia). In other types of synesthesia, the unusual neural mechanisms activate perception neural circuits of different types but of the same modality, such as between visual perception of form and visual perception of color in people with grapheme-color synesthesia . Other possible underlying mechanisms for synesthesia generations are disinhibited feedback, hyper-connectivity/hyperbinding, or enhanced white matter connectivity . However, the evidence from some studies have shown that synesthetic experience (e.g., synthetic perception of colors) is not equivalent to true perception (e.g., perception that occurs in seeing colors)  and that the cause of synesthesia may be something else, such as a special kind of childhood memory that is recalled when there is some sensory perception  or distributed processing of synesthetic associations . However, despite the uncertainty of what the exact mechanisms that generate synesthesia are, it can be concluded in general that they are physical mechanisms involving neural connections and/or functions.
Qualia that occur in people with synesthesia are thus different from qualia in general people experiencing the same thing because there is more than one type of qualia occurring simultaneously. Because these different qualia occur due to some physical mechanisms, they are objectively different qualia.
Objectively different qualia are not the evidence that Theorem VIa (identical neural processes have identical mental processes and identical qualia) is wrong because the conditions that create objectively different qualia are not identical. Theorem VIa is valid only in identical conditions.
9.2. Randomly different qualia
Excluding objectively different qualia, is it possible that identical subjects perceiving the same thing in the outside world under the same condition have different qualia occurring in their minds? And, if we examine this question down to the level of neural processes, is it possible that identical neural processes (in the same person or different persons) perceiving the same thing in the outside world under the same condition have different qualia occurring in their processes? If the answer is “yes”, it means that qualia of the same thing can be different in identical subjects and identical neural processes not because of objective physical factors but because of the nature of the qualia to be arbitrarily or randomly different in identical subjects and identical neural processes. This type of different qualia may be called “subjectively different qualia” in contrast to “objectively different qualia” because they are not determined by objective factors. However, as there are no subjective factors that determine how qualia will be in each subject or neural process, the term “subjectively different qualia” may not be appropriate. Because the principal feature of this kind of different qualia is that they can be randomly different in identical subjects and identical neural processes without any rules, they should be more aptly called randomly different qualia (RDQ), and this is the term that will be used in this theory. RDQ can be classified into 2 groups, depending on whether they are completely random or are partially random.
9.2.1. Completely randomly different qualia (CRDQ) are qualia that appear randomly different in all neural processes, no matter whether the neural processes are identical or not and no matter whether the neural processes are in one individual or in separate individuals. For example, the color quale C may appear sometimes as the red quale, sometimes as the blue quale, and sometime as another quale no matter whether it occurs among identical or non-identical neural processes in one individual or in separate individuals. They are thus complete in their randomness.
9.2.2. Partially randomly different qualia (PRDQ) are qualia that do not appear randomly different in identical neural processes in one individual but appear randomly different in all other neural processes, including identical neural processes in separate individuals. For example, the color quale C always appears as the red quale among identical neural processes in one individual but always appears as the blue quale among identical neural processes in another individual and always as some other color qualia in other individuals. They are thus only partial in their randomness because they require separate individuals to manifest the differences in their manifestations.
Now, the question is whether RDQ do occur in the real world. To answer this question, we shall examine the two types of RDQ one by one as follows.
9.2.1. Completely randomly different qualia (CRDQ)
For CRDQ – qualia that appear randomly different in all neural processes, no matter whether the neural processes are identical or not and no matter whether the neural processes are in one individual or in separate individuals – there is evidence that they do not occur in the real world. Consider this example:
A visual image that occurs in one’s mind is not an all-or-none phenomenon, i.e., it is not that the image must occur as the whole image or not occur at all. Instead, the whole visual image is composed of millions of independent tiny visual images, joined seamlessly together by the visual perception neural processes. Each tiny visual image is the result of a tiny perception neural process of that point in the visual field. If there is damage to some of these tiny neural processes, the damage will affect only them and will be reflected in the corresponding points of the visual field, leaving the non-affected part intact. For example, a lesion of a portion of an occipital cortex can result in a scotoma (defect) in the corresponding portion of the visual field, leaving the rest of the visual field undisturbed. Also, as there are separate perception neural processes for each specific characteristic (color, shape, dimension, movement, etc.) , various types of defects can occur separately and independently of each other. For example, a unilateral occipito-temporal infarction can result in a contralateral hemi- or quandrantic achromatopsia (cerebral color blindness in a half or a quarter of the opposite visual field) [22-25] while other components (shape, dimension, movement, etc.) of the vision are still intact. Thus, the whole visual image in the mind is composed of millions of independent, tiny visual images, each composed of several independent types of visual characteristics.
Now, suppose one is looking at a screen of homogeneous color “C” (Figure 9.2).
All the tiny neural processes for color perception must be creating the same signals – the color “C” signal – separately, and the quale for each tiny neural process must be occurring separately. If CRDQ are possible, each quale of the millions of tiny neural processes that generate the whole image should manifest itself differently as red, blue, green, or other colors randomly, and the whole visual image should not be a homogeneous color but a mixture of myriad different color bits (as in Figure 9.3). But in reality, this does not happen. A screen of pure red color (Figure 9.4) is always perceived as a pure red screen (as in Figure 9.4), not a screen of numerous different colors (as in Figure 9.5).
Similarly, a pair of same-color discs (red and red, Figure 9.6) are always perceived as a pair of same-color discs (red and red, as in Figure 9.6), not a pair of different-color discs (such as red and blue, as in Figure 9.7), which can occur if CRDQ are possible.
Even a pair of same-color discs that are separated in different visual fields (Figure 9.8) are always perceived as a pair of same-color discs (such as red and red, Figure 9.8), not a pair of different-color discs (such as red and blue, Figure 9.9), which can occur if CRDQ are possible.
So, it means that, for the same color in the outside world, the same color qualia occur in all those millions of tiny neural processes and that CRDQ do not occur. Also, it never happens that color qualia occur at some points in the visual field, but auditory, olfactory, or other kinds of qualia occur at other points in the visual field. This means that the signals from all the tiny neural processes for color perception are generating only visual qualia, not randomly different kinds of qualia.
Similarly, with the same consideration, there is no evidence that CRDQ ever occur in other sensory perceptions either. For example, when someone hears two identical musical instruments playing the same musical note “M” (M stands for a certain musical note), the quale of each sound has the chance to manifest itself differently if CRDQ are possible: one may appear as the piano sound of note C while the other may appear as the violin sound of note G. This is, of course, absurd and never happens – he/she always hears the two sounds as the same musical note of the same musical instrument, such as the flute sound of note A if it is the flutes playing the note A. The same scenario is similar for other sensory perceptions, such as the feeling of the same touches on both arms, the pain from the needle stabbing with similar strength on both legs, and the taste of the same sugar on both sides of the tongue – the qualia of the same things on both sides are always the same, not randomly different.
Thus, evidently, there is no randomness in the manifestation of qualia in any individual. This “no randomness in manifestation” of qualia has been consistently true for a long time in billions of humans nowadays and in the past – no normal person has ever reported having a mixture of different qualia occurring when perceiving a homogenous stimulus or identical stimuli. Thus, even though CRDQ have had virtually infinite chances to manifest themselves, they have never ever done so. Therefore, in reality, it can be concluded that completely randomly different qualia (CRDQ) do not occur. Also, it is noteworthy that the non-occurrence of CRDQ is evidence that qualia are neural-process dependent phenomena, because if qualia were neural-process independent phenomena, CRDQ would occur – they would appear randomly different independently of neural processes, and all the strange phenomena in the above examples would occur.
9.2.2. Partially randomly different qualia (PRDQ)
However, is it possible that randomly different qualia do not occur in an individual because all the separate qualia occur in one single person, with one consciousness to experience the qualia, but that they will occur (manifest themselves differently) among individuals, with different consciousness to experience the qualia? If so, it means that, even though all the neural processes in any single individual are not the same one and are at different anatomical positions and even though the neural processes on the right and on the left hemisphere are widely separated, these dissimilarities are not enough for qualia to manifest themselves differently and that it requires separate individuals for qualia to do so. If this is the case, then such qualia are not “completely randomly different qualia” but are “partially randomly different qualia” (PRDQ) because they do not appear completely randomly different; only in some circumstances – among separate individuals – will they appear so.
Now, is there evidence that PRDQ do occur or do not occur? The answer is that there is evidence that PRDQ do not occur either. Let’s consider an example is a case of visual qualia: if PRDQ is possible, then a certain color may have a red color quale occurring in some people while having a blue, green, yellow, or some other color quale occurring in other people (that is, my red is your blue as some people suspect). To see whether PRDQ can really happen, consider a pair of red disc and blue disc in Figure 9.10 below. Everyone with normal color vision will agree that the two colors are markedly contrasting in their hue. However, if PRDQ are possible, the red disc can appear as a yellow disc and the blue disc as a green disc in some people by chance, and the pair will be of yellow and green color discs as in Figure 9.11a. In those people in whom the qualia appear as yellow and green will say that the two colors are not markedly contrasting in their hue, in disagreement with people who see them as red and blue. The disagreement will be even more obvious if the pair of red and blue discs is perceived as a pair of yellow and light-yellow discs as in Figure 9.11b, which can occur in some people if PRDQ are possible. But such disagreement never occurs in billions of people with normal color vision. This is evidence that even PRDQ do not occur.
Another visual evidence is a color wheel. Everyone with normal color vision will agree that the hue of a color in the color wheel like the one in Figure 9.12 gradually changes from one disc to another successive disc. However, if PRDQ occur, the color quale of each disc in the wheel will manifest itself haphazardly and result in a color wheel that the hues of successive discs do not gradually change, like the color wheel in Figure 9.13, in some people. But this never happens in billions of people with normal color vision. They always agree that the hues of the colors in the color wheel like the one in Figure 9.12 gradually change from one successive disc to another. So, PRDQ do not occur in this case either.
The evidence in auditory perception is that if PRDQ occur, the sound qualia of musical notes must be randomly different among people. For example, some may perceive the sound quale of a certain musical note “M” as the note C, some as the note F, and some as the note A#, and for the next sound that is one semitone higher, or note “M#”, some people must randomly perceive it as the note C#, some as the note Cb, and some as the note G, by chance. A musical scale must sound different among people if PRDQ occur. Also, a train of musical notes that have sound qualia as C-D-E-C-E-C-E in some people may have sound qualia as F-E-G-F-G-F-G in some people and as something else in others; a train of musical notes will appear as music for some people, but as an erratic train of sounds in others. But these strange phenomena never happen. People agree on the orderly sounds of a musical scale, the sound that is music, and the sound that is chaotic. This is similarly true for other sensory perceptions. For example, the sensory perception of a series of smoothly-increasing vibration stimuli or a series of smoothly-increasing sweetness stimuli will always be that the stimuli are smoothly increasing in strength, in all individuals. It will not be that in some individuals the perception is of haphazardly-changing-strength stimuli – which can occur in some individuals if PRDQ are possible.
Thus, evidently, there is no randomness in the manifestation of qualia among people. This “no randomness in manifestation” of qualia has been consistently true for a long time in billions of people nowadays and in the past. Thus, even though PRDQ have had virtually infinite chances to manifest themselves, they have never ever done so. It can, therefore, be concluded that PRDQ do not occur among people in the real world.
9.3. Restrictedly different qualia
Still, is it possible that qualia can manifest themselves differently among people in some restricted forms that people cannot recognize as different qualia? This kind of different qualia may be called restrictedly different qualia because they do not and cannot appear randomly different – there are some rules that restrict how they appear different among people so that people cannot tell that they are experiencing different qualia. There are several possible kinds of restrictedly different qualia. Let’s examine some forms of restrictedly different qualia to see which kind can occur among people without people knowing that they are experiencing different qualia.
9.3.1. Inverted qualia
Inverted qualia are qualia that have a certain characteristic inverted. For visual qualia, there are a few kinds of inverted qualia. One of them is the inverted light spectrum qualia in Figure 9.14.
Figure 9.14 Inverted light spectrum with respect to the wavelength
Generally, when people with normal color vision see a spectrum of light like the one in panel A, they will agree that there are definite changes in color hue around wavelengths of 410, 470, 490, 570, 590, and 610 nm. If the qualia of light spectrum are inverted with respect to the wavelength in some people, the light spectrum will be like the one in panel B. Evidently, people with inverted qualia would not agree with the previous observation – for them, definite changes in color hue occur around wavelengths of 510, 530, 550, 630, 650, and 710 nm. But people with normal color vision never disagree around what wavelengths a light spectrum changes color hues. So, there is no evidence that inverted color qualia of this kind occur in people.
Another way to invert the color spectrum is to invert each color to its complementary color (color inversion). This will result in an inverted spectrum that looks like the one in panel B, Figure 9.15.
Figure 9.15 Inverted color spectrum by color inversion
The inverted spectra in this way still have problems of different changes of hue along the spectra. For example, from wavelength 580 to 640 nm, the upper spectrum (A) changes from yellow to red, the definitely different hues, but the lower spectrum (B) changes from dark blue to light blue, the slightly different hues. Also, between wavelength 510 and 590 nm, the upper spectrum (A) appears as green and yellow, the fairly close hues, but the lower spectrum appears as magenta and dark blue, the quite different hues. Therefore, if this kind of inverted spectrum really occurs among people, people will be able to tell that they are experiencing different color spectra. But this does not happen. So, there is no evidence that inverted color qualia of this kind really occur in people, either.
For auditory qualia, inverted chromatic scales in equal temperament, such as scale 1 and scale 2 below, will have different effects when chords are constructed from the equivalent notes. (The primed C, or C’, is one octave higher than the unprimed C.)
Scale 1: C C# D D# E F F# G G# A A# B C’
The chord constructed from the 1st, 5th, and 8th notes (C-E-G) will sound like C Major.
Scale 2: C’ B A# A G# G F# F E D# D C# C
The chord constructed from the 1st, 5th, and 8th notes (C’-G#-F) will sound like F Minor, which is different from C Major of the above chord.
So, the same chords constructed from the inverted scales will sound different, and people, especially musicians, will not agree on what the mood of each chords is, which is not the case. Thus, it can be concluded that such inverted auditory qualia do not happen.
9.3.2. Shifted qualia
Figure 9.16 Shifted light spectrum along the wavelength
Shifted qualia are qualia that has its spectrum shifted. The situation in shifted qualia of a light spectrum is like that in inverted qualia. If the spectrum of light is shifted, such as shifted to the reader’s left side as in panel B (Figure 9.16), although we cannot say definitely about the new color qualia that occur in the vacated portion, it is evident that people with shifted qualia will not agree with people with non-shifted qualia about at what wavelengths the light definitely changes color hues in the remaining portion. But this kind of disagreement never happens. So, like inverted-spectrum qualia, there is no evidence that shifted light-spectrum qualia occur among people.
For shifted sound-pitch qualia, if the spectrum of sound-pitch qualia shifts up or down among people, it will be impossible to prove behaviorally whether shifted sound-pitch qualia occur or not. This is because shifted sound-pitch qualia have the characteristics of the following qualia type – the identical-structure qualia – which enable them to occur among people without people knowing that they are experiencing different qualia.
9.3.3. Identical-structure qualia
It is possible that there are other kinds of inverted or shifted qualia that may occur among people and that people may not be able to recognize as different qualia (please see more discussion in ref 26). However, one kind of different qualia that can theoretically occur in people without people being able to tell that they are experiencing different qualia is identical-structure qualia. Identical-structure qualia come in sets. Each set is composed of qualia that have phenomenal characteristics that are different from their counterparts in other sets. But all sets have identical qualia structures**, that is, they have the same number and types of their phenomenal characteristics and have the same spectral characteristics. One example of identical-structure qualia is the shifted sound qualia discussed in the previous section. Shifted sound qualia in each set has sound pitches that are shifted relative to their counterparts in other sets. But they have the same number and types of their phenomenal characteristics: pitch, loudness, timbre, envelope, and duration. And they have identical spectral characteristics, that is the internal relationships of sound qualia in each set are identical to those in other sets, such as the identical repeated similar sound every octave (in different pitches) and the identical relation of notes in every particular chord. So, all sets of shifted sound qualia behave identically, and people will not be able to tell the differences between them.
(** See more details about qualia structure in PQ2.6. Chapter 4.)
For another example, consider the color spectra of two sets of identical-structure qualia in Figure 9.17. The lower panel has qualia that have different phenomenal characteristics from their counterparts in the upper panel and that occur in only some people (so we cannot know what the lower panel’s qualia are like and cannot demonstrate them here in the picture). But the qualia in both panels have the same number and types of their phenomenal characteristics: color, brightness, shape, dimension, acuity, and velocity. And the spectral characteristics or all the internal relationships among qualia in each spectrum of both panels are the same.
Figure 9.17 Two color spectra of identical-structure qualia
For example, the way the colors change their hues along the spectrum, the apparent brightness at all wavelengths along the spectrum, and the perceived hue differences between colors of different wavelengths (such as between the color at 440 nm vs. the one at 700 nm [which is blue vs. red in the upper panel] and between the color at 540 nm vs. the one at 590 nm [which is green vs. yellow in the upper panel]) are the same in both panels. Thus, if such identical-structure visual qualia occur among people, people will not be able to tell that they are experiencing different visual qualia.
Therefore, identical-structure qualia can occur among people, and, behaviorally, people will not be able to tell that they are experiencing different qualia. However, it is important to note that identical-structure qualia are restrictedly different qualia – they cannot occur haphazardly but must occur in some restricted ways, with some rules governing their manifestations. The governing rules for identical-structure qualia must be that
- The qualia must have different phenomenal characteristics among people.
- The qualia must have the same number and types of their phenomenal characteristics.
- The qualia must have the same spectral characteristics.
In humans, the spectral characteristics of qualia may be very complex and peculiar, such as those of the light spectrum, which changes color hues and brightness in an idiosyncratic way. Therefore, if identical-structure qualia do occur, the physical problem about them is “What is the mechanism that keeps them occurring restrictedly according to these complex rules?”. And the philosophical question about them is “Why should qualia manifest themselves differently in only certain restricted ways, why not in a totally random way, or why not not-differently at all?”.
From all the evidence at present, it can be concluded that, in reality,
– objectively different qualia can occur,
– completely randomly different qualia do not occur,
– partially randomly different qualia do not occur, and
– restrictedly different qualia in some forms, such as identical-structure qualia, may occur, and, behaviorally, people will not be able to tell that they are experiencing different qualia.
However, theoretically, these issues can be investigated by examining the signaling patterns of those different qualia, and according to Theorem VIa and Theorem VIb, it will be found that the signaling patterns of qualia of the same things under the same conditions are identical or similar and that, because those signaling patterns are themselves qualia, those qualia are identical or similar and that different qualia that are not objectively different qualia do not occur.
Predictions about different qualia are the same as predictions for Theorem VIa and Theorem VIb. They will be reiterated here as follows:
- Craniopagus twins who share a certain perception neural process and can access the shared neural process of the other twin will find that the quale (of some object) that occurs in his/her neural process is similar to the quale (of the same object) that occurs in the other’s neural process provided that their neural processes for that perception are similar.
- If, in the future, there is a way to connect neural processes of different persons together so that one person’s consciousness neural process can access and read the signaling pattern of a perception neural process (such as a visual perception neural process) of another person who is experiencing the same thing (such as looking at the same color), the first person will find that the quale that occurs in the second person’s perception neural process is similar to the quale that occurs in his/her perception neural process.
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