Synesthesia - SpeedyLook encyclopedia

Diagnostic criteria

The neurologist Richard Cytowic identifies the following criteria in order to diagnose synesthesia:

synesthesia is involuntary and automatic;
the synesthetic images appear spatially, which means that they often have a position defined in space;
synesthetic perceptions are consistent and generic;
synesthesia is memorable;
synesthetic perceptions have an emotional load.

Kevin daN adds two other criteria:

synesthesia is not linguistic, and to some extent unutterable;
synesthesia concerns people having a brain not presenting any sign of disease.

Synesthesia indicates also a poetic or artistic process which makes it possible to highlight an image by calling upon other sensory methods. One often quotes like example this well-known passage of the poem Correspondances of Charles Baudelaire:

It is fresh perfumes like flesh of children,

Doux like oboes, greens like meadows,

- And others corrupted, rich and triumphing, ''

The first scientific description would have been made by some Georg Sachs , Bavarian doctor, in 1812. It became very with the mode in the romantic movement fine 19th beginning 20th, then was discredited and fell a little into the lapse of memory. It was " redécouverte" in the Years 1980, and popularized by the tendencies " Old New " anti-rationalists before becoming again a scientific object " sérieux" since a few years.

Synesthetic experiments

The synesthètes often report that they did not even know which them synesthesia was unusual until they carry out that the majority of people did not try out the same feelings as them. Others synesthètes acknowledge to have kept their secret synesthesia all their life, of fear of being misunderstood or turned into ridiculous. The automatic and unutterable nature of synesthesia shows well that this association of direction seems completely ordinary for the synesthète. The fact that synesthesia is involuntary and consistent watch that this one is a real experiment.

Reminding an experiment of her childhood, Patricia Lynne Duffy wrote: “One day, I say to my father, " I have just returned account to me that to write the letter " R" , all that I have to make is to draw a " P" , and then a line on the basis of its boucle." And I was so much surprised to note that I could transform a yellow letter into orange letter, just by adding a line. ”

In spite of the general information which allows the definition of the phenomenon of synesthesia, one should not however forget that the individual experiments vary in many ways. This irregularity was noticed with the whole beginning of research on synesthesia (Flournoy 1893), but was reconsidered by the modern researchers only recently. Whereas some synesthètes graphèmes → colors declare that their colors seem " projetées" outside, the majority declare that their colors are perceived " in their tête" . Some synesthètes declare that their vowels are more coloured, whereas for others they are the consonants (Day 2005). Descriptions below can give an idea of to what can resemble a synesthetic experiment, but cannot capture all the richness of it.

Some calculators wonders which see the answers appearing to them are probably reached of synesthesia.

Categories of synesthesias

Synesthesia can appear between any direction or perceptive mode. Because of large variety of the types of synesthesias, the researchers adopted a convention indicating the type of synesthesia by using the following notation X → is the additional experiment there, in which X is the release of the synesthetic experiment, and there. For example, to perceive the letters and numbers (collectively called graphèmes) colors a synesthesia graphèmes → colors would indicate. In the same way, when synesthètes see colors and movements by listening to music, it is about a synesthesia sounds → colors, movements.

Whereas almost all the combinations of direction are theoretically possible, certain types of synesthesia are more widespread than others.

Bimodal synesthesia

Bimodal synesthesia relates to the crossing between two sensory methods. This crossing is generally one-way: a color which starts a sound perception for example (but not the reverse). Although all associations were not inevitably observed, several authors suggest that all are possible. The proprioceptive direction is also likely to intervene (this direction relates to the temperature, the positioning of the body in space, the pressure, etc…)

Multimode synesthesia

Rarer than bimodal synesthesia, it relates to the crossing of at least three sensory modes, in a bidirectional way.

Cognitive synesthesia

This category of synesthesia is generally regarded as concerning the cognitive higher functions: it is about the association of a sensory mode to a mental representation in general: for example a color associated with a letter.

Types of synesthesias

Synesthesia graphèmes → colors

In one of the most widespread types of synesthesia, individual letters of the alphabet, as well as the numbers are " teintés" of a certain color. Whereas two synesthètes will not bring back the same colors for all the letters and numbers, of the studies show that certain tendencies are repeated. (for example, the letter has is often red at the anglophone synesthètes) (Day 2005; Simner and Al 2005).

A synesthète graphèmes → colors testifies: “I often associate the letters and the numbers with colors. Each figure and each letter are associated with a color in my head. Sometimes, when the letters are written on a piece of paper, they will briefly appear color if I am not concentrated above. For example, " S" is red, " H" is orange, " C" is yellow, " J" is yellow-green, " G" is green; " E" is blue, " X" is mauve, " I" is yellow pale, " 2" is brown, " 1" is white. If I write SHCJGEX, or ABCPDEF, these letters will form a rainbow whereas I read them. ”

Synesthesia graphèmes → colors appears stronger in the use of a language whose orthography is phonetic (Spanish Breton, , German, etc) rather than in others where sonorities of a letter vary according to its context (English) or if the combinations of letters modify sonority (French, ex " ho" and " eau").

Synesthesia music → colors

The synesthètes music → colors perceive colors in answer to sounds. Like the synesthétes graphème → colors, the synesthètes seldom bring back the same colors for tons given. (For a synesthéte, A sharp can be red; for another synesthète, it will be green) Cependant, the synesthétes are constant: tested months later, a synesthète will bring back the same experiments that it had previously paid. The changes of colors imply several criteria: the color, the luminosity (the quantity of black in a color, red with black can appear maroon), saturation (the intensity of the color, for example it pink pale is less saturated than it pink fushia), and the color can be affected to differing degrees (Campen/Froger 2002). Moreover, the synesthètes music → colors, unlike the synesthètes graphèmes → colors, often report that the colors change, or move in their field of view.

Numerical synesthesia

The " synesthesia numérique" is a mental chart of the numbers, which appears automatically and involuntarily when the synesthète in question thinks of numbers or temporal units. Thus, the numbers can be aligned according to an axis going up, and the months of the year can form a half-circle. This was documented and named for the first time by Sir Francis Galton. Research which followed identified it like a type of synesthesia. In particular, it was suggested that these " charts numériques" are the result of a cross activition (cross-country race activation) between the areas of the parietal Lobe which are implied in numerical and space cognition. In addition to their interest for numerical synesthesia as a synesthesia, the researchers in numerical cognition started to explore this type of synesthesia for the outlines which it can unconsciously give on the neurological mechanisms of numerical/space associations present of each one of us.

Lexical synesthesia → gustatory

In a not very widespread type of synesthesia, lexical synesthesia → gustatory, the individual words as well as the phonemes of the spoken language evokes feelings of tastes in the mouth.

“With each time I hear, read, or thinks of words/syllables, I perceive a feeling of taste immediate and involuntary on my language. These very specific associations of taste never change and remained the same ones further I remember it. ”

Jamie Ward and Julia Simner studied in detail this type of synesthesia, and realized that synesthetic associations are conditioned by the food of the subject at the time of its childhood (Ward & Simner 2003; Ward, Simner & Auyeung 2005). For example, James Wannerton does not have synesthetic perceptions implying of the coffee or the curry, whereas it takes some regularly at the adulthood. On the other hand, it tastes marks of cereals and candies which are not sold any more at present, but that it ate rather regularly in its childhood.

The direction of the word plays sometimes a part in the taste which is allotted to him: thus, the word " bleu" for James Wannerton a taste " has; of encre". The pronunciation of the word plays in the same way a great part in the attribution of its taste: in certain cases, the tasted word will in common have phonemes with the name of tasted food. (For example, /I/, /n/ and /s/ start a chopped meat taste. (" mince")). However, other tastes have less obvious origins (For example, starts a taste of sorbet (sherbet)). In order to show that the phonemes, rather than the graphèmes, are the crucial releases of the taste synesthetic, Ward and Simner showed that, for James Wannerton, the taste of the egg ( egg ) is associated with the /k/ phoneme, that he is written with a " c" (to accept, to accept ), K (York), ck ( chuck ), or X (fax).

Personification

Ordinal/linguistic personification (POL., or personification to make shorter) is a type of synesthesia in which sequences, like the numbers, the days of the week, the months and letters are associated with personalities. Although this type of synesthesia was documented in 1890, it interested the modern researchers only recently.

" T is generally geignard, not very charitable. U is a thing without heart. 4 is honest, but… 3 , not, I cannot trust him. 9 is dark, a gentleman, large and grâcieux, but politicking under its aspects suaves."

" I is distressed a little sometimes, even if it is rather enjoué; J is a man, joker at first sight, but with a strong personality; K is a woman, quiet and responsible… "

For certain people, in addition to the sequences of numbers or letters, the objects are sometimes soaked with personality, which is sometimes compared with a form of Animisme. This type of synesthesia is more difficult to distinguish from nonsynesthetic associations. However, recent research started to show that this type of synesthesia cohabits with other types of synesthesia, is consistent and automatic, and thus answers the criteria synesthetic.

History of research on synesthesia

Although synesthesia was mentioned before, this phenomenon collected for the first time the interest of the scientific community in the Années 1880 thanks to Francis Galton. According to these initial observations, research on synesthesia exploded, with researchers coming from England, Germany, France and the United States of America, all investigant this phenomenon. However, because them difficulties encountered to prove and measure completely internal and subjective experiments, as well as rise of the behaviorism in Psychology, which banished any mention of internal experiments, the interest carried to synesthesia blunted in the Années 1930. In the Years 1980, whereas the cognitive revolution had started to return the study of the sizeable Conscience again, the scientists started to re-examine this attractive phenomenon. Led to the the United States by Larry Marks and Richard Cytowic, and in England by Simon Baron-Cohen and Jeffrey Gray, research on synesthesia started to explore reality, consistency and frequency of the synesthetic experiments. At the end of the Years 1990, the researchers were interested in synesthesia graphèmes => colors, one of the most spread types of synesthesia, and more easily étudiable. In 2006, the newspaper Cortex published an special issue on synesthesia, composed of 26 articles. Synesthesia was the object of many scientific books, as well as novels and short films reporting of the characters synesthètes.

Prevalence and genetic cause of synesthesia

The estimates of Prévalence vary enormously (of 1 person out of 20 to 1 out of 20000). However, these studies suffered all owing to the fact that they took into account only the testimony of the people declaring synesthètes. I.e. the only people included in these studies were those which brought back their experiment to the researcher. Simner and Al led the first studies carried out on a random sample of the population, newcomer to a prevalence of 1 person out of 23. The current data suggest that synesthesias graphème → color and day of the week → color are most widespread.

Almost all the studies on the subject suggested that synesthesia has an origin Génétique, because certain families count much more case of synesthesia than of others. The first references to this factor go back to 1880 (Francis Galton). Since, other studies supported this conclusion. However, it is probable that certain studies, which brought back a higher number of synesthètes for the women than the men, (to 6 women for 1 man), suffered owing to the fact that the women tend more to declare synesthètes than the men. More recent studies, using random samples, find a ratio of 1 per 1. There were twin cases of vraix in which only one twin was synesthète, and it was noted that synesthesia can jump of the generations in a family. Moreover, Simner and Al note that it is common that the synesthètes of the same family present various types of synesthesia, which suggests that the Gène or the genes implied in the development of synesthesia does not involve specific types of synesthesia. On the contrary, of the développementaux factors such as the expression of a gene and the environment must as play a part in the determination of the type of synesthesia as a synesthète will develop.

Demonstration of the authenticity of synesthesia

To prove that somebody is really synesthète is easy. The simplest tests imply tests of constancy over long periods. The synesthètes obtain usually a better result on such tests that the non-synesthètes (either with names of colors, coloured gommettes or even a selector of colors proposing 16,7 million choice of colors). The synesthètes can obtain a rate of constancy as high as 90 percent after one one year period, whereas nonsynesthètes obtains a score of 30/40 percent after only one month, even when they are prevented that they would be retestés (for example, Baron-Cohen and Al 1996).

More specialized tests include modified versions of the Effet Stroop. According to the paradigm of standard Stroop, it is more difficult to name the color of ink of the word " rouge" when that this one is printed in blue ink that when it is printed in red ink. In the same way, if one presents to a synesthète graphèmes → colors figure 4 printed in blue ink whereas the synesthète perceives it red, this one is slower to identify the color of ink. This is not with the fact that the synesthète cannot see blue ink, but rather because the same kind of conflict responsible for the Stroop effect occurs between the color of ink and the automatically associated color of the graphème. Alternatives of the Stroop effect can be conceived; for example, one asks a synesthète music → colors to name the color of a red spot whereas it is listening to a sound producing a feeling of blue (Ward, Tsakanikos & Bray 2006) or when one asks for a synesthète note music → taste to identify a bitter taste whereas it is listening to a note causing a sweetened taste (Beeli, Esslen & Jäncke 2005).

Lastly, of the studies carried out on synesthètes graphèmes → colors showed that the synesthetic colors can improve of the performances on certain visual tasks, or at least for some synesthètes. Inspired by tests on the Daltonism, Ramachandran and Hubbard (2001) diagrams representing of tens of figures 5 presented between which are encrusted with figures 2 with synesthètes and non-synesthètes. These figures 2 can form one of these 4 forms: square, rhombus, rectangle or triangle. The synesthetic colors help the synesthètes to find the " appear cachée" : for a synesthète which sees the 2 reds and the 5 greens, the red of the 2 will be detached from the green of the 5. Other studies explored these effects with more attention, and showed that: 1. the results vary between synesthètes Smilek & Merikle 2004; Hubbard and al.2005a" , 2. whereas synesthesia is present early in the perceptive treatment, it does not intervene before Attention (for example, Edquist and Al 2006; Sagiv, Heer & Robertson 2006a).

These studies result in differentiating strong or true synesthesias , of weak synesthesias which are normal associations that one can make, in particular, by associating the red with the heat or blue cold. Phenomena synesthesic can also occur at the time of state of tiredness or about somnolence, one speaks sometimes about synesthesia of drowsiness. It is probable that number among we lived such associations of direction, for example, a door which opera hat or a noise intense, and dry, can cause an impression of luminous flash if one is in phase of light sleep. The synesthesic hallucinations perceived under the influence of psychotropic substances can represent an average form of synesthesia.

Consequently, it is advisable to make a distinction between physical reality, perceptive reality, and simulation: the synesthètes do not simulate, that is proven by the above mentioned tests as it would be impossible to succeed as well by simulating associations of perceptions. The physical characteristics of the stimulis are independent of perceived stimulations (for example, a written letter in black and sight in blue do not have the wavelength corresponding to blue).

Possible neurological base of synesthesia

The theories considering a neurological base with synesthesia have as a root the observation that certain areas of the brain are specialized for certain functions. Based on this concepts of " areas spécialisées" , some scientists suggested that " connections" between various areas specialized in various functions can result into different types of synesthesia. For example, like the areas implied in the identification of the letters and figures are adjacent with the area implied in the treatment of the colors (V4), the additional experiment to see colors by looking at graphèmes can be due to this " cross-country race activation " of V4. Normally, balance between the excitation and inhibition are maintained. However, if these exchanges are not inhibited correctly, then the signals coming from later training courses of multisensoriels treatment could influence secondary training courses of treatment, such kinds that notes of music would more activate visual cortical surfaces at the synesthètes music → colors that at nonthe synesthètes. In this case, that could explain why certain users of psychedelic drugs such as LSD or the Mescaline report synesthetic experiments when they are under the influence of drug.
Studies Mtoe put at the day of the important differences between the brains of synesthètes and nonsynesthètes. Recent studies using IRM showed that the V4 surface is more active at the synesthètes word → color and graphème → color. However, these studies miss data to confirm one of the two advanced theories (déshinibées ways of exchange/defect in the elimination of the neurons.)

Associated cognitive features
One knows very little in connection with the cognitive features associated with synesthesia nor even if it of A. Of the studies suggested there that the synesthètes are unusually sensitive to the external stimuli. Other studies suggested that the synesthètes have a memory higher than the average. Ramachandran and Hubbard (2001) support that this effect can be the neurological origin of the symbolic system of the sound, according to which the pronunciation of a word is sometimes associated with its direction. (For example, the word " petit" is pronounced with the mouth hardly between open, whereas one needs to open the very large mouth to pronounce the words " grand" or " large".) Thus, the researchers on synesthesia hope that, thanks to these unusual conscious experiments, the study of synesthesia will bring to a better comprehension of the conscience and in particular on the bonds between the brain and the conscience, or in connection with the mechanisms of the brain which make it possible to be conscious. In particular, some scientists suggested that synesthesia is in connection with the philosophical phenomenon of the qualia
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