Synesthesia

The alphabet in the individual perception of a synesthet: in addition to its color, every letter also has a very specific position in space.

The Synästhesie (from ancient Greek συναισθάνομαι synaisthánomai , German , compassion ' or, at the same time perceive') denotes primarily the coupling of two or more physically separate modalities of perception. It comes about through the interweaving of sensory modalities . This concerns the connection of color and temperature (for example the connection “warm green”), sound , music and space . In a narrower sense, synesthesia is the perception of sensory stimuli by co-excited processing centers of a sensory organ in the brain when another organ is stimulated. People who experience perceptions linked in this way are called synaesthetes or synaesthetes.

Synesthesia occurs in families. In one study, 43% of the synaesthetes surveyed stated that there was at least one other synaesthet among the first-degree relatives.

Synesthesia are individually different perceptions. By themselves they are not symptoms of disorders; However, they can occur due to illness (for example after blindness) or drug-induced (for example through hallucinogens ).

In rhetoric, the term stands for the mixing of sensory levels .

Physiological norm variant

An example of emotional synesthesia: discomfort shows up as a white drop

Synesthesia, which is experienced under normal conditions and typically develops in childhood, is a normal variant of perception. In synaesthetes, a sensory stimulus from one sensory modality triggers an additional “perception” in at least one other sensory modality or submodality of a sense. This means that, for example, tones “stroke” the skin, taste sensations take on different “shapes” or movements are accompanied by a “sound”. More than 60 variants of synesthesia are known. A sensory stimulus does not always have to be present. Many synaesthetes perceive numbers in color and for some the mental visualization of the number is enough to trigger the coloring.

“Synesthesia is a luxury; a variety of evolution that allows consciousness to generate more information by linking the senses and coupling it with feelings. Scientific studies with imaging methods have shown that synesthetes have a more complex networked brain. "

- Markus Zedler 2019

The term synesthesia encompasses some other phenomena that do not represent a strict link between the five main senses , with a new definition of synesthesia being discussed. Emotions are involved in feeling synesthesia. It has been found that emotions can evoke synaesthetic colors and that some individuals personify numbers and other abstract stimuli. In individuals, tactile materials cause certain emotions. Another phenomenon is the feeling of being touched on one's own body, which is triggered by observing another person being touched. The mental visualization of subtitles that accompany spoken or thought words was also related to synaesthesia. In addition to the five main senses, motor skills in connection with hearing, for example, can also trigger synaesthesia. This phenomenon would manifest itself in that the person associates a certain posture with a sound. Thus, with six sensory modalities (hearing, seeing, tasting, feeling, smelling, motor skills) thirty possible two-way combinations of modalities result.

The triggering stimulus of synesthesia is called an inducer in the English-language literature . The synaesthetic additional sensation is called concurrent . The concurrent can be in or out of thought, and in the latter case the source of the perception is clear. For example, some synaesthetes can not only hear noises, but also “see” shapes and colors. In addition to the usual properties, the sound has these additional properties. The image that is created in this way, however, is only superimposed on what is perceived by very few synaesthetes, but becomes visible to an “inner eye”. But even if the synaesthetic additional perception is superimposed on the triggering stimulus, the synesthesia is to be regarded as additional. The triggering stimulus is not replaced by the concurrent, but continues to be perceived, so that both the triggering stimulus and the concurrent are experienced.

Synesthesia can be clearly distinguished from hallucinations : if a synaesthetes, for example, a certain tone sounds like a bright orange ball, then it is clear to him that in reality there is no orange ball that he could see with his eyes. Likewise, a synesthete who projects synaesthetic colors onto printed letters sees what color the letters are written in and knows that the synaesthetic shades of color are produced by the brain. When a synesthet automatically imagines a number in a certain color, this can be compared to some extent with other visual thoughts.

A distinction is usually made between sensory and cognitive synesthesia. In sensory synesthesia, stimulation of one sense leads to involuntary and simultaneous synaesthetic sensations in other sensory systems. For example, the sound of a musical instrument can lead to color perception. In cognitive synesthesia, groups of things (for example numbers or letters) are assigned sensory assignments, such as smell and taste. For example, letters are perceived as colors: the letter A = pink, the letter B = blue or the letter C = green.

It has been suggested to abandon the distinction between sensory and cognitive synesthesia in favor of the idea of ideesthesia . This term describes the conception that synaesthetic experience always has a cognitive, i.e. semantic, and a sensory aspect. The trigger of the synaesthetic sensation is therefore a concept (for example the meaning of the number "5") and the synaesthetic perception itself is a sensory attribute (in the result, for example, "blue").

Categorization

Color synesthesia in letters and numbers

In general, a distinction is made between three forms of synesthesia:

1. Genuine synesthesia: All types of synesthesia in which an external perception involuntarily triggers a synaesthetic perception. The characteristic of this innate (genuine) synesthesia consists in the immutability of the respective synaesthetic impression (a trumpet sound, for example, is always accompanied by a blue, round impression).
2. Emotional synesthesia : is a sub-form of genuine synesthesia. Here feelings trigger perceptions in some synaesthetes, e.g. B. Color vision. Emotional synaesthetes form z. B. on the second inner "screen" does not show the semantic content from another sensory channel, but rather the accompanying emotional states of feeling. Sensory synaesthetic perceptions are subject to a certain variance, because just like the emotions involved, they cannot be reproduced in exactly the same way. This can also be observed in some genuine synaesthetic perceptions. So z. For example, when hearing colors, the basic character of the perception of music remains the same (e.g. the basic color nuance or the tactile nature of the instrument sound), but a sound from different sources (noisy portable radio versus hi-fi system) may produce correspondingly different perceptions.
3. Metaphorical synesthesia: is an associative phenomenon that has not yet been well researched scientifically, which can occur in any person in which emotional states are associated with associated imagined perceptions.

Color synesthesia with digits - everyone sees different colors

Example of an associated grapheme-color synesthesia that is interwoven with a sequence-space synesthesia: Numbers have colors in thoughts and take up spatial positions

Example of a projected grapheme-color synesthesia: As described in the Gestalt theory , the brain makes an auto-completion of what it sees and thus gives it properties that are not directly derived from the visual information. The white color of the figures makes a smoother, more even and lighter impression than the three-dimensional, slightly irregular-looking white color of the background. In addition, the impression of an edge is created between the perceived object and the background. At the same time, however, we are aware that the white color is the same everywhere. In a similar way, for example, the black printing ink of the number “5” in grapheme-color synesthesia can have a bright orange-deep black effect, although it is clearly seen as “black”.

There are different forms of synaesthesia (Grossenbacher 1997) due to the possibilities of the different combinations of sensory impressions as triggers ("inducers") and subsequent synaesthetic perceptions as so-called "concurrents". The most common are synesthesia triggered by linguistic codes (letters, numbers and words). Most of the concurrents are of a visual nature (patterns, colors). Depending on whether one pays attention to the triggering stimulus (inducer) or the subsequent triggered synaesthetic experience (concurrent), various categorizations of synaesthesias can be made ( Flournoy , 1893). Ramachandran and Hubbard also suggested in 2001 that the various forms of synesthesia should be divided into "deeper" and "higher" forms - depending on whether the inducers are at a lower level, with tones or lights, or at a higher level of processing, as with Letters, numbers and sequences work synaesthetically. With regard to the Concurrents, it can be stated that the visual impressions range from an impressive photo-like projection to an overwhelming mental image. In 2004, Dixon described these two extremes as projectors and associators (Projector, Associator) .

In researching the characteristics of synesthesia, the American neurologist Richard Cytowic identified six characteristics, which are reproduced here in a revised version:

1. Synesthesia happens involuntarily, but needs a trigger.
2. Synesthesias are clearly distinguishable: different things evoke different synesthetic perceptions (for example, A and R are both red, but with different hues).
3. Synesthesia are based on simple and abstract forms: A synaesthetic sensation is often triggered by abstract forms (for example geometric figures).
4. Synesthesia can be remembered: Synaesthetes can easily remember synaesthetic perceptions.
5. Synesthesia run in one direction: Synesthesia is comparable to a one-way street; A synesthetes can see colors while listening to music, but the reverse does not work. This point is debatable. Some synaesthetes who see numbers, shapes or letters in color may unconsciously convert a color or a range of colors into numbers, shapes or letters.
6. Synesthesia are noetic : synaesthetes describe the feeling of their talent as “natural” (4 = naturally green); the sensation has always been there.

frequency

While earlier estimates assumed lower numbers, a more recent study shows that four percent of people could have synesthesia. Research at an art school showed that 23 percent of the students were synaesthetes. There are differing data on the distribution of the frequency between women and men, ranging from 1: 1 to 7: 1.

Many synaesthetes are not aware of the peculiarity of their perception and only recognize their synaesthesia when they are made aware of it. Therefore there is a corresponding number of unreported cases. Synesthesia is a popular research topic internationally, as one hopes to gain knowledge about the functioning of human perception. Media attention has increased in recent years.

For some sufferers, synesthesia includes a sense of social togetherness. In the past, synaesthetes dared to tell others about their particular perception less often because they were viewed as perceptual disorders . This has changed in the 21st century. Synesthesia is no longer viewed as a disorder in science, especially since most synaesthetes experience it as pleasant. In addition, more and more articles about synesthesia appear in the media, so that the public is now better informed than before.

causes

A mixture of genetic reasons, chance and experience is believed to be the cause of the congenital synesthesia. However, the aspect of congenital synesthesia is controversial in science. Since synesthesia only occurs when the person has experienced and learned the respective sensory stimuli that trigger synesthesia (for example, intervals , hearing sounds), scientists are currently assuming that synesthesia will develop after birth. The role of experience is particularly evident when learned contents such as the alphabet, months or days of the week trigger synesthesia.

Acquired synesthesia

In addition to the often congenital synesthesia, there is also the very rare acquired synesthesia, which arises after impairment of a sense (e.g. blindness) or brain damage. An example of this is Jason Padgett, who acquired savant skills through brain damage and since then suddenly visualized mathematics as fractal images, or Derek Amato, who developed an island talent through a severe concussion and constantly perceives tones as squares, which he plays on the piano in compositions realized even though he had never played the piano before his accident.

trigger

Nonverbal visual

In Motion Hearing Synesthesia , movements or flashing lights are accompanied by a synaesthetic sound. The acoustic concurrents are typically simple non-verbal tones such as beeps, humming tones or knocking noises.

Color-taste synesthesia has been described as another form of synesthesia induced by a non-verbal visual trigger. Other possible synesthesias with a non-verbal visual trigger are, for example, movement-color synesthesia, movement-smell / taste synesthesia or synesthesia, in which seeing a color triggers a synaesthetic sound.

Non-verbal acoustic

The tone-color synesthesia is one of the most well-known forms of synesthesia. Different aspects of the sounds or noises heard (pitch, timbre , volume, intervals) can determine the visualization. A heard pitch can also influence the coloring of synaesthetes without perfect hearing : In the study by Ward, Huckstep and Tsakanikos from 2006, the synaesthetic coloring of a person with relative hearing is depicted. For piano tones of different pitches, this person perceived a color gradient from dark red to yellow (with dark red for the lower tones, red for tones of medium height and yellow for the higher tones).

Tones can also have a certain shape or trigger textures (in addition to tone-color synesthesia or as independent synesthesia). Smells, tastes or a sense of touch were, for example, described as non-visual concurrents. One synesthesiologist reported that through her tone-touch synesthesia, she felt the sounds of different instruments in different parts of the body as tactile sensations. In another synaesthetist, intervals of tones triggered taste sensations (e.g. sweet, bitter).

Synesthesia, especially in the musical field, is described in more detail in the section “Synesthesia and Music”. Synaesthesias also occur in the musical field, which are not triggered by the tones heard, but by other aspects in the field of music, for example tone designations .

Taste or smell

During a private occasion in 1980, a synesthete remarked to neurologist Richard Cytowic that the taste of his food didn't have enough dots, but sadly instead was almost spherical. This taste-shape synesthesia aroused Richard Cytowic's interest in synesthesia and thus gave an enormous boost to scientific research into synesthesia.

Other concurrents that some synaesthetes are triggered by taste or smell are, for example, colors, sounds or touch sensations.

Body sensations

Somatosensory sensations such as touch, pain or temperature sensations trigger a color, sound, taste sensation or other concurrent in some people. These forms of synesthesia have not yet been well researched. A single case study by Simner and Ludwig from 2012 deals with touch-color synesthesia.

People or emotions

The visual observation of a person or a person's emotional expression, heard emotions, one's own emotions, or the affective component of concepts can trigger synesthesia. In 2012, Ramachandran's research group described a synaesthet who “saw” synaesthetic colors as color phenomena projected around the person concerned. In the case of another synesthet who projected synaesthetic colors around people, some words (especially names) also triggered colors, with the coloring of the words depending heavily on the affective component.

Sensory imitation of observed touches

One to two percent of people “feel” when they observe another person being touched, they automatically “feel” this touch on their own body. This simulated touch is located on the corresponding part of the body, i.e. on one's own arm if another person is touched on the arm, or on one's own leg if another person is touched on the leg.

This phenomenon is referred to as “Mirror-Touch Synesthesia” or “Mirrored Sensory Experience” (as a sub-category of socially contagious phenomena) in the English-language specialist literature.

Language, writing or concepts

The specialty of language is that on the one hand it encompasses the acoustic and (with the writing) also the visual modality and on the other hand it is linked to semantic concepts. When speaking, motor skills and somatosensors ( tactile sensations , proprioception ) are also involved.

Language can trigger synesthesia at the level of individual letters or numbers ( graphemes ), individual spoken sounds ( phonemes ) or at the level of whole words. In addition, a form of synesthesia was discovered, in which different swimming styles trigger synaesthetic colors.

Depending on which sensory modality the triggering linguistic or conceptual stimulus belongs to, different localizations of synaesthetic competitors are possible. In the case of linguistically triggered synaesthetic colors, there are these possible localizations:

• a customized color projected onto the written grapheme, which is completely merged with the grapheme (“projector”)
• a colored veil in the area of ​​the written word or grapheme (“projector”)
• a colored copy of the grapheme overlaying the written grapheme (“projector”)
• a color visualized in the imagination, whereby the color has a certain place in three-dimensional space, for example near the person speaking or at a fixed position relative to one's own body (“associator” or “mental screen projector”)
• a color visualized in the imagination without the spatial position of the color (“associator”)
• a mere knowledge of what color a grapheme has, without mental visualization of the color (“know-associator”)
• a color fused with a spoken phoneme

With regard to grapheme-color synesthesia, the question was discussed whether the sensory properties of graphemes (e.g. curves, lines) or the classification in a linguistic category (e.g. “number 5”) triggers the synaesthetic concurrent. It has been found that in the case of ambiguous graphemes, the coloring depends on the context in which the grapheme is presented. In addition, a capital letter is typically the same color as the corresponding lower case letter, despite a different appearance. In the case of a great many synaesthetes, the linguistic categorization, not the sensory perception, seems to trigger the synesthesia. Since synaesthetes differ greatly from one another, there are still synaesthetes in whom sensory properties could trigger synaesthesia. In addition, sensory properties of the graphemes sometimes also have a (subtle) influence on the coloring in synesthesia, which is triggered by the linguistic categorization of the graphemes.

Sequence-space synesthesia

Time-space synesthesia on weekdays. Description of the artist: “ … this is a very rough sketch of how I view the days of the week via my spatial-sequence synesthesia. It's a circle, where Saturday and Sunday are farther away and Wednesday is closest to me. It's really hard to depict this properly. [...] this is not necessarily how the actual words look to me, just the DAYS. [...] the days are also colored based on how they are colored to me (via my grapheme-color synesthesia). "(German:" This is a very rough sketch of how I see the days of the week with my room-sequence synesthesia. It's a circle in which Saturday and Sunday are further away from me, and Wednesday is on me It's really hard to get that right. […] The days are colored the way they are colored for me (by grapheme-color synesthesia). That's not necessarily what the actual words look like to me, just the days.")

A very common form of linguistically or conceptually triggered synesthesia is sequence-space synesthesia (“Sequence-Space Synesthesia”). According to an estimate from 2013, it occurs in 9% - 14% of people. The triggering sequences are often units of time such as days of the week or months, the alphabet or numbers. Synesthesia forms of this type for other sequenced units such as shoe sizes, temperatures, historical epochs, TV channels are rarer. The objects within such a sequence get (in the imagination) different positions in three-dimensional space. The various objects are arranged relative to one another. For example, the days of a week can be arranged on an ellipse , which in turn can be interwoven in a representation for a year. The arrangements differ greatly from one individual to the next, but remain stable within a person. It is remarkable that it is possible for these synaesthetes to vary the perspective, the section and the size of the image within these mental visualizations.

The subtype of this synesthesia, which only refers to time units as triggering sequences, is called time-space synesthesia. The subspecies in which numbers trigger spatial perception is also known in the English-speaking world as “Number Form”.

The brain areas that are activated primarily when processing well-ordered sequences and the brain areas that are activated when imagining things are both close to each other in the temporal lobe (Eagleman 2009; Peissig). This allows both areas of the brain to activate each other and trigger synaesthetic perceptions.

Word-color synesthesia, grapheme-color synesthesia

Example of an automatically visualized subtitle when hearing the word “Strawberries” combined with a grapheme-color synesthesia. Below is the achromatic component of the subtitle extracted.

In word-color synesthesia, entire words or concepts, often days of the week or months, trigger the synaesthetic color.

In grapheme-color synesthesia, graphemes such as letters or numbers trigger the synaesthetic colors. This is a form of synesthesia that is one of the best-studied synaesthesias to date. Their occurrence in the population is estimated at around one percent. With this form of synesthesia, great interindividual differences were found with regard to the experience of the colored competition (Associator, Projector). In some synaesthetes, grapheme-color synesthesia is linked to sequence-space synesthesia. This is expressed in a spatial representation of colored numbers or colored letters of the alphabet.

About seven percent of the population visualize subtitles that automatically accompany the words heard or thought (“ticker tape experience”). This phenomenon occurs more frequently than grapheme-color synesthesia or word-color synesthesia. In combination with a grapheme-color synesthesia, each individual grapheme of the subtitles can be colored accordingly.

In a group of synaesthetes, it is not the graphemes but the spoken phonemes that trigger the synaesthetic colors.

Linguistic-induced synesthesia with other concurrents

In addition to colors or spatial positions, linguistic stimuli trigger completely different types of competition in some synaesthetes. With the Savant Daniel Tammet , numbers not only trigger colors, but also other competition such as shapes and movements. The very rare lexical-gustatory synesthesia (“Lexical-Gustatory Synesthesia”) became particularly well known. In her, the language or writing triggers taste sensations. Personifications were also described as concurrent: In “Ordinal Linguistic Personification”, elements are personified within sequences. Elements such as certain time units or numbers are given personal characteristics (e.g. age, gender) or character characteristics (e.g. nice or bitchy).

Synesthesia and music

The keys and colors are arranged according to the circle of fifths

As a special form of synesthesia there is the music-color synesthesia: This is the generation of color impressions through tones or sound impressions through shapes or colors. This form of synesthesia is based on note names, pitches, keys, timbres and chordal structures. If you change a tone, the synaesthetically perceived color or color combination also changes.

In auditory-visual synesthesia, there are so-called rules of correspondence: When volume, tone or tempo changes, shapes, sizes of objects and brightnesses vary.

Emotional experience of music is reinforced by the visual reaction. The synesthesia is additional, but in no way disturbs the musical feeling.

Pitch perfect

Keyboard with tone-color assignment according to Alexander Nikolajewitsch Skrjabin

When absolute auditory sensation of a certain, correct pitch is independent of an audible tone. The absolute listener can imagine and perceive the corresponding pitch for any note or a specific piano key without having to hear, play or sing. The simultaneous perception of pitch and tone designation or of pitch and piano key can also go hand in hand with the perception of colors, so that even three perceptions occur simultaneously: piano key, pitch and color or tone designation, pitch and color. The composer Michael Torke said that he couldn't imagine his piano key-color synesthesia being possible without perfect pitch. The French composer Olivier Messiaen and the Austrian composer György Ligeti were such synaesthetes.

On the other hand, the composer Alexander Nikolaevich Scriabin had no perfect pitch and still had piano key-color synesthesia. The link between pitches and colors is also reflected in the color piano , which was invented by Louis-Bertrand Castel in 1725 .

Kandinsky's color-sound analogies

The synesthesia of the sensory modalities of hearing and color-seeing may also have occurred with the artist Wassily Kandinsky ; However, it is not clear whether he was a synesthet himself or was only interested in the subject. There are numerous quotes from the painter that could indicate synaesthetic perception or interests:

“The color is the key. The eye is awesome. The soul is the piano with many strings. "(Kandinsky 1911)

Differentiation from cross-modal correspondence

Bouba / Kiki-Effect: Which shape would you call "Bouba" and which one "Kiki"?

Cross-modal correspondence is understood to mean assignments of aspects of one modality to aspects of another modality, for example the assignment of pitches to spatial heights or to brightnesses. The cross-modal correspondence is not counted as synaesthesia, but is present in the vast majority of people. Further terms for cross-modal correspondences (but not for synesthesia) are “Synesthetic Associations” or “Synesthetic Correspondences”. Marks, a pioneer of modern synesthesia research, and Martino also used the term “weak synesthesia” to denote the cross-modal correspondence.

The scientific evidence for the existence of cross-modal correspondences is broadly based: Spence and Deroy cited a whole series of experiments in 2013 in which cross-modal assignments were found. Some experiments showed cross-modal assignments of pitch to spatial height, brightness, size or angularity of shapes. But cross-modal correspondences were also found for other sensory modalities.

A well-known, not accidental assignment of language to shapes is the bouba / kiki effect : almost all people assign the spoken word “bouba” to a shape with rounded curves and the word “kiki” to a shape with acute angles rather than the other way around.

How synesthesia can be differentiated from the cross-modal correspondences depends on whether the triggering stimulus can be described by means of an axis with two poles (low tone - high tone) or whether the triggering stimulus consists of many categories, as in can consist of 26 different letters. With regard to the competition, too, it depends on whether it can be described with one axis consisting of two poles (dark - light) or with several axes (for example as a color wheel ). If both the trigger and the concurrent can each be described with bipolar axes, there are basically only two options for pairing them with each other (low tone = dark and high tone = light). In another study, subjects had to assign a tone to a taste. It emerged that a sweet or sour taste was assigned a higher tone and a bitter or umami taste a low tone. With regard to pitch and brightness, it was found that both synaesthetes and non-synaesthetes choose the option “low tone = dark” and “high tone = light” from the two basic assignment options. Synesthesia can be distinguished from such cross-modal correspondence by the fact that synesthesia is associated with a conscious experience of the competition (for example, visualized in thought), while in the context of cross-modal correspondence a triggering stimulus does not trigger a consciously experienced concurrent.

In the case of grapheme-color synesthesia, however, this principle no longer applies without restriction. In this synesthesia, the trigger consists of a number of categories (for example, a few different letters). The colors are also not an axis with two poles, but are often represented with a color wheel. This means that there are not just two, but many possible combinations for assigning colors to graphemes. It was found among synaesthetes and also among non-synaesthetes that different people often agreed more than randomly in the choice of color for a few specific graphemes, but overall the different people did not agree well with one another across all graphemes. There are obviously too many different ways of assigning colors to graphemes. In a study, therefore, people could also be identified as grapheme-color synaesthetes who did not report that they “see” the colors, but instead spoke of only “knowing” which colors the graphemes have. Over time, these synaesthetes showed good consistency of grapheme color and were referred to as “know-associators” by Ward, Li, Salih and Sagiv in 2007.

Time-Space Synesthesia, Mental Benefits, and Its Relationship to Savant Syndrome

Time-space synesthesia is a sub-category of sequence-space synesthesia. Time units are spatially arranged in the performance. Simner et al. found in their study that synaesthetes with this talent performed significantly better than normal test persons in memory tests and tests for visual memory and manipulation of figures, images and silhouettes.

People with unusual abilities are very rare and in many cases these forces go hand in hand with similarly large deficits in other areas. Probably the most prominent example of an excellent talent that is accompanied by severe deficits was the island talented Kim Peek , whose life story served as the template for the 1988 film Rain Man by director Barry Levinson . Due to brain malformations, including the absence of the corpus callosum , Kim Peek not only developed an autistic disorder, but was also able to absorb information very quickly and reproduce it with almost no errors ( hyperlexia ) (Hughes 2010). He could read a page of a book in 8 seconds with one eye. Its replay accuracy in memory tests that were carried out immediately afterwards was 98%. Normal subjects read a page in 48 seconds and achieve an average reproduction accuracy of 45% (Hughes 2010). Due to his deficits in other areas, Kim Peek was neither able to find meaningful employment, nor to dress, let alone lead an independent life (Wisconsin Medical Society 2010).

According to Simner, synaesthetes of the visual-sequential type have massive memory advantages for episodic and autobiographical memory compared to normal subjects. For both groups (synaesthetes and non-synaesthetes) the dates of events that had taken place during their lives were asked. Their knowledge of film and music events was also tested. An error distance was calculated from the difference between the actual year and the year given by the test person for the event. Synaesthetes had a shorter error distance than other subjects in all areas.

In addition to having advantages in remembering events, synaesthetes are also better at performing visual tasks. Synaesthetes performed better than normal test persons, for example in experiments to remember spatial arrangements (3D test practice). Synaesthetes also had considerable advantages over tests for recognizing 3D objects using two-dimensional images, for tasks to manipulate 3D figures using two-dimensional images (“Mental Rotation Test”) and for tasks relating to visual short-term memory (“Patterns Test”) Non-synaesthetes (Simner 2009). It is noteworthy that visual-spatial synaesthetes have no other deficits, although they can achieve above-average performance in areas related to their abilities.

They are compared with the savants who have island talents but suffer from autism or Asperger's syndrome . Corresponding to earlier research data on savant syndrome, the mental advantages of synaesthetes cannot be traced back to a general intelligence factor. In her above-mentioned study of synaesthetes and non-synaesthetes using the “National Adult Reading Test”, which correlates with the Wechsler intelligence test to be 0.6 and is an intelligence test for premorbid intelligence, Simner found no differences between synesthetes and non-synaesthetes be able to demonstrate their general intelligence. With regard to performance in visual tasks, Simner found that the advantages of synaesthetes over non-synaesthetes are not directly based on advantages in visual-spatial abilities, but can only be explained by the presence of synesthesia. Through the mental representation of the inner calendar, the synaesthetes of the visual-spatial type have the possibility of easier access to memory information, which gives them considerable advantages over normal subjects with regard to episodic and autobiographical memory.

There is empirical evidence that also supports the claim that savants have similarly accessible internal representations. In her study, Simner also tried to establish a connection between savant syndrome and the spatial-sequential type of synesthesia. Their argumentation was based on the case of A. J., who would also have a visual-spatial calendar, but could not defend itself against the flood of memories ( hyperthymetic syndrome ), which was reminiscent of Savant's syndrome. In contrast to the synaesthetes that Simner had examined in her study, A. J. could not fully control what she remembers. Even the smallest trigger could create a cascade of interrelated memories. The constant recall of memories meant that A. J. dealt intensively with her past and her memories, which is tantamount to an obsession such as can be found in an island talent. In contrast to the Savant Syndrome, A.J. did not develop any domain-specific knowledge and did not show any seriously impairing deficits in other areas.

Simner concluded that the presence of synesthesia related to obsession, such as that found in autistic people, increases the likelihood of hyperthymetic syndrome. From the similarities that the A.J. case showed with regard to both synesthesia and savant syndrome, one can further ask the question to what extent synesthesia, autism and savant syndrome are related. The comparison between an island talent and creative thinking, as explained by the networking of different brain regions, is also of interest (Simner 2010, Chakravatry 2010, Murray 2010, Hughes 2010).

Murray attributed the abilities of the visual-spatial synaesthetes to the ability of reification . Reification means the ability to transfer abstract concepts into concrete representations. In relation to Simner's study, this would mean that normal test persons would have queried their memory when interrogating the events until the information had occurred to them, while the synaesthetes would have used their visual-spatial calendar for help. In extreme cases of synesthesia, the synaesthetes could inspect their internal calendar and read the information directly.

Simner's study showed that the synaesthetes examined had, in addition to memory advantages, advantages in visual-spatial tasks. This indicates that synaesthetes of this type can transfer their skills to new tasks. According to Simner, they can better visualize objects from memory and therefore have considerable advantages in creating mental images.

Synesthesia and Creativity

Chakravatry (2010) describes creativity as a complex neuropsychological phenomenon that is primarily about understanding and expressing new connections. According to Graham Wallas of 1926, this creative process goes through four stages: preparation, incubation, illumination and verification.

Preparation is the development of skills or the knowledge base that enable creative performance in a field. Einstein and Newton, for example, spent years studying to prepare for their discoveries. Other cultural achievements are only possible after a thorough preparation phase.

The next phase would be the incubation phase, which is also part of a kind of preparation. According to Chakravarty (2010), this phase belongs to a prepared mind. According to Hélie et al. (2010) a kind of implicit processing of the recorded information is involved in incubation. Incubation is described by Chakravatry (2010) as a phenomenon that seems to exist between implicit and explicit processing and implicit and explicit knowledge.

Then the phase of illumination is run through, which can be understood as a kind of Eureka experience. It is the moment when the time of preparation and incubation manifests itself in an idea or a discovery.

In 1926, Graham Wallace mentions the final stage as the critical examination of a hypothesis, an idea or a discovery as it is common and necessary in scientific discourse.

Due to their talent and knowledge in a specific field, some savants are able to produce enormous creative achievements (Chakravatry 2010). It is not general intelligence that enables the islanders to do so, but a specific intelligence in a domain. The knowledge that they have accumulated over the years can be viewed as a kind of well-founded preparation. Synaesthetes of the visual-spatial type have the opportunity to escape conventional ways of thinking through reification. You can imagine and manipulate objects and thereby find other ways of finding a solution, especially when it comes to visual tasks. As an example of such synaesthetic thinking, Chakravarty (2010) names Richard Feynman , a Nobel Prize winner and physicist who first imagines his concepts visually and only then translates them into mathematical formulas.

By being able to connect senses that are otherwise disconnected, synaesthetes can find new approaches to specific areas. This could be an advantage in the incubation and illumination phase, because the freedom of thought, advantages in perception (Hughes 2010) and the possibility to apply new unconventional ways of thinking or the transfer of synaesthetic skills to related tasks and problems (Simner 2006) , can have a positive effect on the production of ideas and the creative process as a whole. There are various examples from the field of literature and music which suggest that synaesthetes are capable of particularly creative achievements due to their special talent. Chakravarty himself names 2010 none other than Kandinsky , Baudelaire and Rembrandt .

According to Chakravarty (2010), many artists with synesthesia would often use their skills to communicate sensory impressions in another channel. In addition, the networking of different senses and different brain areas would contribute to divergent thinking and thus to creativity. Neurologically, this would manifest itself in the fact that there would be hyperconnectivity between otherwise unconnected or less connected areas of the brain. In synaesthetes of the visual-spatial type, the angular gyrus is particularly hyper- or hypostimulated. This is interesting considering its central location as a junction. The co-activation of different areas of the brain would help solve a fixation and increase the production of ideas. Synaesthetes, who regularly experience co-activation of different areas of the brain in everyday life, also seem to be able to use these abilities in a creative way and also do better than normal subjects in tests on divergent thinking and creativity.

Savants also seem to have a higher degree of networking between local regions (Hughes 2010). At the same time, global networks seem to be less present and central control seems to be largely inhibited, which is shown by an autistic disorder (Hughes 2010). Treffert called this "ending the tyranny of the left brain". Injury to the left frontal lobe would allow the right hemisphere to develop savant skills. These facts support the thesis that synesthesia comes about through co-activation and unusual networking of brain areas. They also suggest a relationship between Savant Syndrome and synesthesia.

Synesthesia and the Qualia Problem

It is unclear whether two different people looking at the same object have the same conscious experience. What the first person experiences as a "blue square", a second person could experience what the first person would describe as a "square-shaped vanilla scent". It is also conceivable that the second person experiences a sensation as the “blue color” that is not known to the first person at all. The subjectively experienced contents of consciousness are called qualia . This includes the consciously experienced sensory perceptions such as colors, tones and smells, but also other consciousness contents such as emotions. The mystery of what these qualia really are is known as the “qualia problem”.

Representationalist approaches to describing the qualia problem assume that the conscious perceptions are not the external reality itself, but represent the external world. Objective representationalism assumes that one and the same physical property is represented by all people with the same sensory perception. An image of the world is constructed that depicts the world roughly as it actually is (provided that this property can be processed with the sense organs). When different people see the same light with their eyes, they all have the same conscious experience. It is not that one person experiences as “red” what someone would call “blue” if he knew the other person's experience. Subjective representationalism, on the other hand, considers it possible that different people represent the same physical stimulus with different sensations.

The representationalist approaches have been associated with a subset of synesthesia in which the concurrent is felt to be outside of thought and an inherent property of the triggering stimulus. It is controversial whether these synaesthesias require an adaptation of representationalism. If such synesthesia show that the same physical property is experienced by different people with different sensations, the possibility would be falsified that one and the same physical property is perceived by all people with the same sensation. The possibility of an objective representationalism would be refuted in this case and the representationalism would have to be adapted accordingly.

Adaptation of representationalism to synesthesia

Cytowic and Eagleman quote the synesthet DS, who describes that for them the acoustically triggered forms do not differ from hearing. For them, acoustically triggered, colored forms are what sounds are . Another synesthet who feels sounds as shapes assumed that everyone feels the same way. When people said that they didn't feel sounds as shapes, she was so surprised "as if they said they didn't know how to walk, run, or breathe". Such examples have consequences for representationalism. According to Rosenberg, such synaesthetes indicate that different people use slightly different sensory perceptions in order to represent the same information from the external world.

Can synesthesia be described with a structural approach?

Sollberger adapts representationalism to this view and describes a structural approach. As a basis for this approach, he also uses those synesthesias in which the concurrent is experienced outside of thought and as an inherent property of the triggering stimulus.

According to Sollberger's suggestion, a sensation like a color does not have to be linked to a specific physical property. The sensation of a color can relate to physical light, or to differences in air pressure on the eardrum or to other senses. (In order for a tone-color synaesthetic to be able to say with certainty that the acoustically triggered sensory perception is a color, the color must of course not only represent differences in air pressure with certain frequencies, but must also occur in visual perception and there electromagnetic ones Represent frequencies. Only in this way can he determine through verbal communication with other people that this sensory perception is referred to as a color.)

The differences in air pressure on the eardrum could also be perceived as spectrograms . According to Sollberger, however, the sensations do not somehow map the information about the external world, but rather target structures that are biologically relevant. With the acoustic information, therefore, not all information is mapped equally as a confusing spectrogram. Instead, the focus is on a structure of the acoustic information that is usually assigned to the experience of a pitch, and on structures that are typically assigned to the experience of the timbre. Which sensation a person uses to represent structures of the external world is irrelevant as long as the structures of the external world are represented in such a way that the person can find his way around in the external world. The sensation “brightness”, for example, is an axis with two poles and is therefore suitable for depicting structures of the outer world that can be described by two poles, as can be the case with visual brightness or acoustic pitches. An acoustically triggered color or shape can therefore just as well be a real acoustic perception as a pitch or a timbre, if the assignment to the corresponding acoustic structures of the external world is clear. It is believed that the synaesthetic sensations (as well as the non-synaesthetic sensations) are used to interpret information about external reality and to emphasize relevant aspects.

The evidence suggests that this might be possible. The synaesthetic sensations are assigned to the corresponding physical properties. Synesthesia goes hand in hand with a functioning orientation in the external world. If, for example, tone-color synaesthetes experience an acoustically triggered color, then it is clear to them that this color experience relates to certain acoustic frequencies. A visualized sound is not mistaken for a visible object in the air. Synaesthetes do not confuse the sources of the perceptions.

No adjustment of representationalism necessary

Two different ways of interpreting synesthesia in such a way that representationalism need not be adjusted were discussed. According to these views, the objective representationalism can be maintained, according to which one and the same physical property is experienced by all persons with the same sensation.

Further noted physical information?

This hypothesis also applies to those synesthesias in which the synaesthetic sensation is perceived as being outside of the thoughts. According to this view, these synesthesias may not demonstrate that different people associate different sensations with the same property of the external world. It is also conceivable that synaesthetic sensations represent additional information from the external world. The synaesthetic sensations could relate to information about the external world that is ignored by persons without these synaesthetic sensations. Accordingly, the synaesthetic sensations would show true properties of the external world that other people do not notice. In the case of synesthesia, in which each pitch has a specific color, this argument has been called into question. By experiencing the color, no further physical acoustic information seems to be represented than by the experience of the pitch.

Synesthesia as “wrong” perception?

Alter and Lycan describe another way of interpreting synesthesia. With this possibility, synesthesia does not exclude that one and the same physical information is represented by all persons with the same sensory perception. In their view, objective representationalism can be maintained. Age as well as Lycan also refer to those synesthesias in which the concurrent is experienced more like a real perception than a thought. Your hypothesis says, applied to the example of tone-color synesthesia, that an acoustically triggered color could also represent a light property. The synaesthetic color is related to tones, but would possibly stand for physical light, that is, represent physical light. This can be compared with the perception of an optical afterimage that occurs, for example, when one has looked at a color for too long and then looks at a white surface. The afterimage is felt as if it represented a physically present light. But it is recognized that this is a wrong representation of light: the light is not really there. The acoustically triggered shapes and colors could also represent physical light properties in a similar way and thus be perceived as if they were visible to the eyes. The synaesthetes would know (as with an afterimage) that this light is not actually there. Accordingly, there is a possibility that these synaesthetes represent the acoustic information just like other people only through pitches and timbres, while the synaesthetic color (incorrectly) represents physical light. Since this possibility exists, the synesthesia do not jeopardize the theory that one and the same physical information is represented by all persons with the same sensory perception.

Sollberger contradicts this. It, too, refers exclusively to those synaesthetes who experience their synaesthetic sensation as being outside of thought, as an inherent property of the triggering stimulus. According to his objection, with these synaesthetes, for example, an acoustically triggered color is not a perception that represents physical light like an afterimage and would be misleading if the synaesthetes did not question it. These synaesthetes do not see any pseudo-hallucinatory light spots that would have to be mentally corrected so that an orientation in the external world is possible. The synaesthetic sensation is perceived by these synaesthetes from the outset as part of the triggering stimulus. This can be compared to a mental color that is perceived from the start as a thought and not as an afterimage seen with the eyes. A color seen is also automatically perceived as seen with the eyes and not as a color in thought. Comparable to this, these synaesthetes perceive an acoustic color from the outset as a representation of physical acoustic information and not as a thought or as a representation of physical light. Statements by synaesthetes, like that of synesthet D.S., who said that the shapes of sounds are part of what hearing is , can be taken literally in Sollberger's view. Transferred to the projected grapheme-color synesthesia, this means that the synaesthetic color is not perceived incorrectly as a representation of the font color, but as a representation of the trigger, i.e. the recognition of the grapheme. According to Rosenberg's view, these synaesthetes see, on the one hand, the color, which represents the font color, and, on the other, the synaesthetic color, which represents the recognition of the grapheme.

Auvray and Deroy also contradict Alter and Lycan's hypothesis that synaesthetes would perceive the triggering physical stimulus with the same sensory perception as any other person (while the synaesthetic concurrent would incorrectly represent a non-existent physical property). You use a very similar argumentation as Sollberger. They emphasize that synaesthetes who perceive the concurrent as outside of thought typically experience it as merged with the triggering stimulus. Applied to an example of a possible tone-form synesthesia, this statement means that on the one hand a sound is experienced and on the other hand a shape is not seen with the eyes that would float in the air like an afterimage. Instead, the sound and its shape are experienced merged into a single perception. The sound itself is shaped. The shape does not represent light like an afterimage, but acoustic properties. According to Auvray and Deroy, synaesthesias of this kind therefore indicate that the same physical stimulus may be perceived by different people with different sensations. In their opinion, representationalism might have to be adapted to this.

History of synesthesia research

The oldest, generally accepted, description of synesthesia comes from the doctor Georg Tobias Ludwig Sachs . A synesthete himself, he described the symptoms in his 1812 dissertation. In 1866 the term synesthesia was first used by the neurophysiologist Alfred Vulpian . He tried to create a word that describes the transfer of stimuli to nerves that are not specific for the transmission of the stimuli. To this day, however, the term has also established itself for specific productive processes in artistic and literary representation. It is made up of the ancient Greek words syn (composed) and aisthesis (sensation). To date, many scientists have tried to find new, different names for the phenomenon. The most common is the French term audition colorée (abbreviation a. C.), Which can be translated as "hearing in color" and refers to a very common form of synesthesia.

It can be said that actual research on synesthesia did not begin until the 20th century, and it became more systematic over time, but on the condition that interest in the subject was inconsistent. Many different disciplines attempted explanatory models, which ultimately led to the realization that synesthesia ignores the boundaries of scientific disciplines. This knowledge was only implemented in Germany from 1925, from then on one could speak of "synaesthesia research". In particular Georg Anschütz and his assistant Friedrich Mahling as well as Albert Wellek published on this topic, further below.

The two Swiss physicians Eugen Bleuler and Lehmann are paving the way for the definition of terms and the foundations of the synesthesia research just described . In 1881 they published a study on synesthesia with 77 test subjects. In order to find an approach and a common language with a view to solving the problem, they created the following categories related to the nature of synesthesia:

• Sound photisms
• Light photisms
• Taste photisms
• Olfactory photisms
• Imagination of colors and shapes for pain, warmth and tactile sensitivity
• Color conception for shapes

The scientist Théodore Flournoy published Des phénomènes de synopsie in 1893 , a standard work of the time. Inspired by the work of Bleuler and Lehmann, he added further points to distinguish synesthesia. In addition to the nature of the synopsies according to Bleuler and Lehmann, he also wanted to consider the original sensory causes (“idea”) and the intensity of the synopsies. Furthermore, he divided the phenomena of the synopsy into

• Photisms
• Schemes a) Symbols b) Diagrams
• Personifications

Flournoy was also a member of a commission of the Congrès international de Psychologie physiologique (1890), whose task it was to deal with audition colorée phenomena and also posed questions of principle relating to synesthesia, whether it was innate or acquired, psychological or physiological and be an idea or an actual sensation. In this context, Flournoy influenced various scientists, Richard Henning, for example, suspected in 1896, on the one hand, “physiological chromatic synopsies” (that is, compulsory and uninvolved synopsies) and “psychologically chromatic synopsies” (that is, judiciously created, but close and inseparable connections).

It became clear that the synaesthetic problem, which was agreed in the course of the second half of the 19th century, required the formation of analogies and thus a merging and cooperation of the disciplines in search of the “higher formula”, “hidden synthesis” (Goethe ). But for the time being, the representatives of individual sciences did their research alone. The approaches of the various sciences are listed in Friedrich Mahling's essay The problem of audition colorée from 1926.

Neurophysiological findings

Major technical advances in the 1980s and 1990s allowed researchers to study the human brain more closely. Using neurophysiological examination methods such as functional magnetic resonance imaging (fMRI) or the EEG , the scientists were able to understand what is happening in the brain and identify which part of the brain is active when. Neuroscientists such as Richard Cytowic now suspect that every person from birth has nerve connections between the sensory system that processes the triggering stimulus and the one in which an additional sensory impression is created. The ability for synesthesia is therefore innate and cannot be learned.

When examining the brains of newborns, Cytowic found that these nerve connections begin to wither or disappear completely after about three months. The facts that synesthesia occurs more in children than in adults and that synaesthetes start their synesthesia in their childhood ("since I can think"), confirm the scientist's findings. He also suspects that some people have certain genes that help maintain these connections and thus maintain synesthesia.

Psychologists were able to show that synaesthetes were able to perform better in a memory test compared to a norm sample.

The inheritance of synesthesia suggests that genes have an influence on the development of this phenomenon. However, this cannot be the only factor, as identical twins were studied who had various types of synesthesia. The presumption that synaesthesia is inherited in an X-linked manner has so far not been scientifically confirmed or rejected.

The following finding serves as “proof” that synesthesia is not a product of heightened imagination or mnemonic techniques: The V4 / V8 region in the brain is the visual region that is used to process colors. There is a V4 / V8 region in each half of the brain. With word-color synaesthetics, the left V4 / V8 area only jumps to words, but not to colors. Language also shows lateralization: for most people, the most important language centers are more in the left than the right hemisphere. In the case of the word-color synaesthetes examined, the authors suspected a link between speech areas in the left hemisphere and the left V4 / V8 region.

In poetry

In rhetoric , the term stands for the mixing of sensory levels. This way of conveying feelings was particularly popular with romantics . Many theories of poetry even go so far that they do not assume a mixing of what was previously separated, but fundamentally deny that sensory areas can be clearly separated from one another. In the poetry this circumstance only comes to the fore particularly clearly, as in these verses by Brentano :

Listen, the flute is complaining again,
And the cool fountains rustle,
golden tones blow down -
silence, silence, let's listen!

Holdes pleadings, mild desires,
As it speaks sweetly to the heart!
Through the night that embrace
me, the light of tones looks at me.

What is seen (“golden”), what is heard (“the tones down”), what is felt (“hurt”) are mixed here. Sometimes what you see and what you hear comes in the same line: "Golden sounds blow down", "Look at me the light of sounds". It is true that such sentences cannot be resolved analytically, and an object of our experience cannot be assigned to every word; however, the text is not meaningless or incomprehensible.

In modern poetry, Georg Trakl's poetry is a good example of the use of synaesthetic elements. A more recent example of synesthesia in literature is the novel Tabu by Ferdinand von Schirach , the chapter of which is divided according to color. The protagonist of the novel, the photo artist Sebastian von Eschburg, is a synaesthetic, which is reflected in his photographs.

Philosophical Aspects

It is true that there is no concrete picture when reading the verse, but despite everything it gives something to understand. What it says is unambiguous , although no object in the world of our experience corresponds to it. This happens because the sensual and the content cannot be separated in such poetry: there is no “statement” in the poem that is independent of its linguistic form. The poet does not first have an “idea” that he then promises, but the condensation takes place in the language itself .

The synaesthetic character of poetry is therefore closely linked to everyday language, which - unlike scientific analytical terms - always depicts the world of our experience in all its diversity, without fundamentally separating between different physical sensory regions. Such a sharp separation is only brought about by the scientific understanding of the world, in that it makes the concepts of space and time their highest standards, under which everything is from now on located. According to Martin Heidegger , however, such a space-time separation is a metaphysical-philosophical assumption, a dogma that shows the world in a distorted light. The primacy of space and time only proves its legitimacy through the practical success of the sciences, i.e. the mastery of nature, but that it represents the only true access to the world as a metaphysical view, it cannot prove from itself. Heidegger's claims to overcome the metaphysical consideration, however, go far beyond the scientific concept of synaesthesia, since this assumes a fundamental separation of the sensory areas despite possible intermingling.

If one looks at synesthesia in the context of the occidental history of human perception theories, it becomes clear that the sensory areas were only separated from one another through the separation of bodily sensation and mental cognition. In the ancient doctrines of perception, the relationship between the senses was still thought of as symbiotic, and in early Christianity there are numerous synaesthetic descriptions that praise the perception of God. It was not until the 15th century that the physical and sensual perception of the world began to move into the background in favor of an increasingly intellectual knowledge of the world. The associated desensualization process was associated with a dissociation of the senses and their specialization. They were gradually upgraded techn (olog) ically in the further course. These developments led to synaesthesia as a physical form of perception being forgotten. The term synesthesia, which can only be proven in the lexicons of the 19th century, is therefore used either as a poetic or language-magic technique that was praised as bold or despised as pathological. In medical lexicons of the same time, however, synesthesia is defined as a mix-up of physiological processes. It was not until the 20th century, which reacted to desensitization in the course of a somatic turn, that synesthesia began to be scientifically rediscovered as a cognitive phenomenon or as a genetic relic.

literature

• G. Beeli, M. Esslen M., Lutz Jäncke : When colored sounds taste sweet: An extraordinary type of gustatory synesthesia . In: Nature , 434, 38, 2005.
• Valeri Brainin : Employment of Multicultural and Interdisciplinary Ideas in Ear Training ("Microchromatic" Pitch. "Colored" Pitch). (PDF; 370 kB) . In: Proceedings: International Society for Music Education , 28th World Conference, Bologna 2008, ISBN 978-0-9804560-2-8 , p. 53-58.
• David Brang, VS Ramachandran : Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words? In: PLoS Biol 9, 11, 2011: e1001205. Full text: doi: 10.1371 / journal.pbio.1001205 . Associated conversation with V. S. Ramachandran
• David Brang, Eun Seon Ahn: Double-blind study of visual imagery in grapheme-color synesthesia. In: Cortex 117, 2019: 89-95. Abstract.
• Patricia Duffy: Every blue letter smells of cinnamon - How synesthetes experience the world . Goldmann 2003, ISBN 3-442-15242-9 .
• Is my blue your blue Neurophilosophical considerations on synesthesia . Audio CD. Concept and direction: Klaus Sander, Anja Theismann. Narrator: Hinderk M. Emrich, Manuela Lube, Matthias Waldeck. supposé 2008, ISBN 978-3-932513-83-1 .
• Hinderk M. Emrich, Udo Schneider, Markus Zedler: What color is Monday? Synesthesia: Life with linked senses. Hirzel, Stuttgart 2002, ISBN 3-7776-1114-X .
• John Harrison: When sounds have colors. Springer-Verlag, Heidelberg 2007, ISBN 978-3-8274-1864-7 .
• Michael Haverkamp: Synaesthetic design - creative product development for all the senses. Carl Hanser Verlag, Munich 2009, ISBN 978-3-446-41272-9 .
• Eva Kimminich: Synesthesia and disembodiment of perception. Remarks on a historical development in Europe from the 17th to the 20th century. In: Zeitschrift für Semiotik 2002, pp. 71–109.
• Omer Linkovski, Naama Katzin, Moti Salti: Mirror neurons and mirror-touch synesthesia. In: Neuroscientist 23, 2, 2017: 103-108. doi: 10.1177 / 1073858416652079 . PDF.
• Lawrence E. Marks: The Unity of the Senses. Interrelations among the modalities. Academic Press, New York 1978.
• Anna K. Rowedder: For you. Synesthesia - A journey into the world of perception. Synaisthesis , Luxembourg 2009, ISBN 978-99959-622-1-0 .
• Natalia Sidler, Jörg Jewanski: Color - Light - Music: Synesthesia and colored light music . Peter Lang, Bern 2006, ISBN 3-03910-636-8 .
• J. Simner, N. Mayo, M. Spiller: A foundation for savantism? Visuo-spatial synaesthetes present with cognitive benefits . In: Cortex 45, 2009, pp. 1246-1260.
• Julia Simner, Edward M. Hubbard (Eds.): The Oxford Handbook of Synesthesia , Oxford University Press, Oxford 2013, ISBN 978-0-19-960332-9 .
• Jasmin Sinha (Ed.): Synesthesia of feelings. Synaisthesis, Luxembourg 2009, ISBN 978-99959-622-6-5 .
• J. Ward, J. Simner: Is synaesthesia an x-linked dominant trait with lethality in males? Perception 34, 2009, pp. 611-623.

Web links

Commons : Synesthesia  - collection of images, videos and audio files

Wiktionary: Synesthesia  - explanations of meanings, word origins, synonyms, translations

General

• cba.fro.at: radio talk on synesthesia
• syn-aesthesie.de: Description of forms and types of synesthesia
• Gehirn-und-geist.de: Symphony in red
• Deutschlandfunk , Das Feature , March 23, 2012, Heike Tauch: I see what you only hear - about synaesthetic perceptions . In: dradio.de (March 24, 2012)
• The world of synaesthetes - When Mozart tastes like marzipan (MP3; 18.1 MB) Podcast for the radioWissen program on December 12, 2013

research

• psychologie.uzh.ch: Synesthesia research at the University of Zurich - Chair of Neuropsychology
• synaesthesie.unibe.ch: Synesthesia research at the Psychological Institute of the University of Bern
• ch-forschung.ch: Synesthesia research at the neuropsychological institute of the University Hospital Zurich

Testing

• psycho.uni-duesseldorf.de: Test for synaesthetes
• psycho.uni-duesseldorf.de: Association test for non-synaesthetes

Associations

• synaesthesie.org: German Synaesthesia Society e. V.

Descriptions

• michaelhaverkamp.de: Texts & images on the topics of synesthesia, auditory perception and multi-sensual design
• soundphotographer.de Report about a synaesthetic
• monis-synaesthesie.de: The phenomenon of synesthesia - representations of the sensory impressions of a synaesthetist.
• youtube.com: Synesthesia - visually impressive implementation of the topic

Individual evidence

1. ↑ Susanne Will: Do you taste it? (A conversation with the psychiatrist Markus Zedler.) In: Die Zeit No. 22, 23 May 2019, p. 37
2. ↑ ^{a b c d e f} K. J. Barnet: Familial patterns and the origins of individual differences in synaesthesia . In: Cognition . 106, No. 2, 2008, pp. 871-893.
3. ↑ ^{a b} J. Ward: Synaesthesia . In: Annual Review of Psychology . 64, 2013, pp. 49-75. doi : 10.1146 / annurev-psych-113011-143840 . PMID 22747246 .
4. ^ C Sinke, JH Halpern, M Zedler, J Neufeld, HM Emrich, T Passie: Genuine and drug-induced synesthesia: a comparison . In: Conscious Cogn . 21, No. 3, September 2012, pp. 1419-34. doi : 10.1016 / j.concog.2012.03.009 . PMID 22521474 .
5. ↑ C Hyung Keun Park, Seul A Kim, Joon Sung Shin, Daewook Kim, Yong Min Ahn: Synesthesia occurring after the use of Japanese kiken drugs: A case report. In: Psychiatria Danubina 30, 2, 2018: 223–226. PDF.
6. ↑ Noam Sagiv, Lynn C. Robertson: Synesthesia: perspectives from cognitive neuroscience . Oxford University Press , Oxford 2005, ISBN 978-0-19-516623-1 , pp. 3 and 31, OCLC 53020292 .
7. ↑ Richard E Cytowic, David M Eagleman: Wednesday is Indigo Blue: Discovering the Brain of Synesthesia (with an afterword by Dmitri Nabokov) . MIT Press , Cambridge 2009, ISBN 0-262-01279-0 , p. 45.
8. ↑ ^{a b} E. Richard Cytowic: The Man Who Tasted Shapes . MIT Press , Cambridge, Massachusetts 2003, ISBN 0-262-53255-7 , OCLC 53186027 .
9. ↑ ^{a b} M Saenz, C Koch: The sound of change: visually induced auditory synesthesia . In: Current Biology . 18, No. 15, August 2008, pp. R650-R651. doi : 10.1016 / j.cub.2008.06.014 . PMID 18682202 .
10. ↑ ^{a b c} J Simner: Defining synaesthesia . In: British Journal of Psychology . 103, No. 6, 2012, pp. 1-15. doi : 10.1348 / 000712610X528305 . PMID 22229768 .
11. ↑ ^{a b} VS Ramachandran, EM Hubbard: Synaesthesia: A window into perception, thought and language . In: Journal of Consciousness Studies . 8, No. 12, 2001, pp. 3-34.
12. ↑ Susanne Will: Do you taste it? (A conversation with the psychiatrist Markus Zedler.) In: Die Zeit No. 22, 23 May 2019, p. 37.
13. ^ HM Emrich, J Neufeld, C Sinke: Synaesthesia, a neurological phenomenon . ( Memento of the original from September 24, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: See this sound , website by Dieter Daniels. Retrieved February 7, 2014. 
14. ^ ^{A b} Ward J .: Emotionally mediated synaesthesia. . In: Cognitive neuropsychology . 21, No. 7, 2004, pp. 761-772. doi : 10.1080 / 02643290342000393 .
15. ↑ ^{a b} VS Ramachandran, L Miller, MS Livingstone, D Brang: Colored halos around faces and emotion-evoked colors: a new form of synesthesia. . In: Neurocase . 18, No. 4, 2012, pp. 352-358. doi : 10.1080 / 13554794.2011.608366 .
16. ↑ ^{a b} Simner J, Holenstein E: Ordinal linguistic personification as a variant of synesthesia . In: Journal of Cognitive Neuroscience . 19, No. 4, April 2007, pp. 694-703. doi : 10.1162 / jocn.2007.19.4.694 . PMID 17381259 .
17. ↑ Ramachandran VS & Brang D .: Tactile-emotion synesthesia . In: Neurocase . 14, No. 5, 2008, pp. 390-399. doi : 10.1080 / 13554790802363746 . PMID 18821168 .
18. ↑ ^{a b} M.J. Banissy: Prevalence, Characteristics, and a Neurocognitive Model of Mirror Touch Synesthesia . In: Experimental Brain Research . 192, No. 2, 2009, pp. 261-272.
19. ↑ ^{a b c} CA Chun, JM Hupé: Mirror-touch and ticker tape experiences in synesthesia. . In: Frontiers in Psychology . November 2013. doi : 10.3389 / fpsyg.2013.00776 .
20. ↑ Johannes Barkowsky: Hearing colors - How to recognize synesthetes among your students . In: Music & Education . tape 6 , 1999, p. 33-37 .
21. ↑ Simner, J .: The rules of synesthesia. In: J. Simner, EM Hubbard (Eds.): The Oxford Handbook of Synesthesia. Oxford University Press, Oxford 2013, p. 150.
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50. ↑ See Oliver Sacks in: Musicophilia , Chapter 14 The Key of Clear Green: Synesthesia and Music
51. ↑ Cordula Bachmann: Les Offrandes oubliées - Olivier Messiaen ( Memento of the original from November 10, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) Abaco Orchestra (2014), accessed on November 10, 2014 
52. ↑ Eva Blaskewitz: The phenomenon of synesthesia and the music , radio Germany (November 10, 2014), accessed on 11 November 2014
53. ↑ See The Synesthet Scriabin
54. ↑ Bad title - Media Wiki. (No longer available online.) In: www.uni-weimar.de. Archived from the original on July 5, 2016 ; Retrieved July 5, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
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