Can you hear colors and numbers

What is synesthesia?

You will get to the scientific version with references → here.
An explanation of terms and the most important features

Synesthesia describes a variant of cognition based on a neural brain structure in which different areas of the brain are connected to one another in a special way. This enables certain perceptual phenomena and thought processes that are not possible or of a different nature in a “neuro-typical” brain.

Synesthesia is not a disease, it is a physiological variant of human consciousness that can bring synaesthetes predominantly advantages and, in certain, but rarer situations, also disadvantages (see below).

About 4% of the population have at least one form of synesthesia. Due to the accumulation in families, an (inconsistent) heredity is assumed.

The word synesthesia is derived from the ancient Greek words syn (= together) and aisthesis (= feeling). Synesthesia translates as the co-excitation of a primarily not involved brain area. Typical synaesthetic perceptions are based on additional neural connections between two or more brain areas that process sensory stimuli (seeing, hearing, smelling, tasting, proprioception, feeling - tactile and haptic perception). In synaesthetically gifted brains, there are also connections to other neuronal structures and areas that are responsible for feelings / emotions, memory, intelligence and other cognitive phenomena. The brains of synesthetes show more gray matter (nerve cells) in different areas and an increased density of white matter (nerve connections) in other areas. The research on this is extremely fascinating and far from over.

Typical examples of synaesthetic perception are colored hearing, i.e. the visualization of tones in color and / or shape in front of the inner eye or the consistent assignment of colors to certain characters (numbers or letters), grapheme-color synesthesia. Furthermore, words can taste like something or a smell can cause color perception, etc. All connections between the senses are conceivable and in some cases have already been described (see synaesthesia list by Sean Day). Synesthetic perceptions, however, are not only linked to a stimulus from a peripheral sensory organ. Thoughts and ideas can also trigger synaesthetic sensations. Sequence-space synesthesia, for example, goes hand in hand with the visualization of time units or combinations of numbers and is therefore independent of an external stimulus.

Characteristics of synesthesia are (according to J. Ward):
  • A stimulus (inducer, triggering stimulus) is followed by a synaesthetic perception (concurrent).
  • Synesthetic perceptions are involuntary and are not subject to voluntary control, but can be (briefly) faded out through conscious control of attention.
  • Synesthetic sensations are similar to normal perceptions, the triggering stimulus can be information from the outside world, but also a concept (a thought, e.g. thinking of a letter or an idea).

Synesthetes are normal people who can be found in all social classes and all conceivable professions, but who have a potential that enables them to have their special neural structure. The talent for synesthesia is either present or not, but the extent to which this potential is used or can be used varies from person to person.

Described characteristics of synesthetes are:
  • increased creativity
  • increased memory
  • better imagination / picture thinking
  • better perception of detail
  • increased sensitivity to sensory perception
  • increased emotional empathy

Increased neural activity, increased imagination, in combination with increased sensitivity can also explain the disadvantages that synesthetes report; this can lead to overstimulation in a noisy or hectic environment and, under certain circumstances, to a certain fear reaction to unforeseen or uncontrollable environmental influences.

In addition to the above-described neural brain structures for processing sensory stimuli, memory, conceptual thinking and imagination, the limbic system is also included in the synaesthetic neural loops. This fact explains that synesthetes describe their synesthesia as very pleasant and actually indispensable in the majority of cases, but that there can also be increased reactions to unpleasant, fearful stimuli.

Research on synesthesia is still young, although it has grown exponentially in recent years, so that we will certainly be able to report much more on this fascinating phenomenon in a few years.

The most common forms of synesthesia include:
  • Grapheme-color synesthesia: Letters and / or numbers are inextricably linked with a color impression
  • Colored hearing: Noises and / or music are perceived in color and / or shapes at the same time
  • Sequence-space synesthesia: Time units such as days of the week, months, the year or even digits have a certain spatial arrangement or position in front of the inner eye
  • Ordinal Linguistic Personification (OLP): Graphemes are assigned not only with color and shape, but also with a gender, character traits and possibly emotions.
  • Emotional synesthesia: Emotional states are perceived in color and / or as a form.
  • Person-color synesthesia: Personalities are each assigned a characteristic color. It is also possible to assign digits.
  • Ticker tape synesthesia: Perception of spoken, heard, imagined words as "news ticker" or by appearing the words for fractions of a second in front of the inner eye.
  • Lexical-gustatory synesthesia: Words have a certain taste and / or texture that you can feel on the tongue.
  • Other forms of synesthesia: Often times too Flavors, Smells, or Body sensations, such as. pain accompanied by a synaesthetic visual sensation.

The American anthropologist, linguist and synesthet Sean A. Day lists over 80 different forms of synesthesia on his website This list is growing continuously.


Ideasthesia is a form of synesthesia, or rather a term that describes certain perceptual phenomena in synesthetes even more accurately.

The term “synesthesia”, ie feeling together, was chosen historically to describe that when one sense is stimulated, another is stimulated in parallel. When hearing sounds, for example, there is also an impression of color and / or shape, i.e. a visual phenomenon (sound-color synesthesia / colored hearing). Or when reading and / or listening to words, word-taste synesthetes have a gustatory experience in the mouth (lexical-gustatory synesthesia). These interconnected sensory experiences can be aptly described as synesthesia. This is the basis of the theory of linked brain areas (cross activation theory), which is based on brain areas of the individual sensory organs that have been interconnected via stable nerve and synapse connections since birth.

Then, however, in people gifted for synesthesia, there are very often phenomena that cannot be adequately explained by simply connecting the brain areas for sensory perception. Many synesthetes have the perception that certain letters or numbers (graphemes) are colored (grapheme-color synesthesia). Some also see numbers, time units (week, month, year, decades, centuries, etc.) and other abstract terms (e.g. future, past) visually arranged spatially in front of the inner eye (sequence-space synesthesia). Spoken, heard and thought words are displayed visually in front of the inner eye and can be read (ticker tape synaesthesia). Thoughts and imaginations can be visualized as geometric shapes and colors. These perceptions almost always occur with some synesthetes, with others sometimes and with others only rarely or even once (“one shot”). They allow the synaesthetes who perceive them to concretise abstract concepts and to better understand and classify them through visualization and assignment with shape, color, texture or even character traits. For example, the idea of ​​a number, a weekday, a train of thought or a solution strategy is abstract and not easy to represent or explain.

These synaesthetic brain functions are better explained by current synaesthesia research, which assumes that synaesthetically inclined people are able to attach meaning (semantics) to abstract concepts and to concretise the abstract through the involvement of consciousness, learning and memory formation. The processing therefore runs through higher cognitive abilities and not on the basis of the pure interconnection of sensory organs (conceptual level theory). The term “ideasthesia” is more suitable for this, ie the feeling of an idea or the perception of a concept. The term “conceptual aesthetics / conceptesy” is also in use, but it has not become generally accepted.

Thus a grapheme that is perceived as A is given a color; if it is recognized as H with vertical bars approximated above, but not (or vice versa). A stimulus seen must first be given a certain meaning before it is syn- / idesthetic with other properties.

Most synaesthesias can be understood as idesthesias, but the research results are still inconsistent (as of 2020). It remains to be seen whether, with better and more recent findings, the term ideasthesia will prevail and replace synesthesia.

Even the vast majority of people are able to assign meaning to sensory experiences, i.e. to grasp them semantically (Kiki-Bouba effect). In the case of synesthetes, this is more pronounced and is perceived more consciously. Research into synesthesia / ideasthesia allows deeper insights into human consciousness in general, which can benefit all people.

See also: Ideasthesia in Wikipedia

Synesthesia is not a disease, hallucination, or imagination.

Synesthesia as a neurobiological phenomenon is a normal physiological variant of human thinking. Synaesthetic phenomena can be clearly demonstrated using modern imaging methods in medical technology, but also in psychological tests. They are consistently detectable and mostly constant throughout life. Phenomena reminiscent of this after illness or under the influence of drugs are of a temporary nature and should not be confused with healthy, innate so-called genuine (genuine) synesthesia.

Synesthetes show far more similarities in cognition with other people than differences. Synesthetes are therefore “normal” people with an additional talent for processing sensory stimuli as well as perception and thinking. The synesthetic perceptions are perceived by the respective synesthetes as completely normal, many are amazed when they learn that not everyone thinks and feels the same way.

Synaesthetic perceptions often serve unconsciously as a reminder and orientation in everyday life. Synesthesia can, for example, be of help in assessing situations or physical sensitivities (e.g. classifying pain through visual perception). Spelling is made easier with ticker-tape synesthesia. Combinations of numbers can be memorized more easily through grapheme-color synesthesia. Most synesthetes perceive the additional ability as enriching, indispensable and an essential part of their own identity.

Scientific research into synesthesia

The research of the neurologist and neuropsychologist Richard E. Cytowic on the subject of synesthesia, which led to the book "The Man Who Tasted Shapes" in 1980 and to two publications in the journal Brain & Cognition in 1982, was the main reason for the resurgence of the synesthesia topic ( and its scientific research) around 1980.

While in the 1990s a frequency of 1: 2000 - 1: 1000 in the total population was assumed, the more recent studies with objective measurement criteria indicate a significantly higher percentage of at least 4%. This fact and the increasingly better research possibilities are likely to be responsible for the fact that the interest in scientific research on synesthesia is growing noticeably internationally and is currently experiencing a real boom. The interest in synaesthesia is also based on the hope that knowledge about cognitive processes in all people, as specifically, for example, in memory research. Linked to the new knowledge is the prospect of being able to help sick people.

Synesthesia research is active worldwide, especially in England, the USA and Australia. Much research is being carried out on synesthesia in Germany and Switzerland too. Research locations in Germany are currently: Hannover Medical School, University of Regensburg, Research Center Jülich.

The DSG cooperates with well-known research locations as well as with other national and international synaesthesia societies.

You can find more about the current scientific status and sources → here.

Well-known synesthetes

As already mentioned, synesthetes are often capable of special achievements in terms of memory, intelligence and creativity. Many artistically gifted people are synesthetes, among artists it is far more than the average 4%. However, not everyone who calls himself a synesthet has the real, innate form (genuine); Sometimes you have to ask more precisely because synaesthesia is considered modern and worth striving for, especially among artists!

Famous synaesthetes were e.g. the physics Nobel Prize winner Richard Feynman and probably also the inventor Nikola Tesla; also the composers Franz Liszt, Jean Sibelius, Olivier Messiaen, Nikolai Rimsky-Korsakov, Leonard Bernstein, György Ligeti and the author Vladimir Nabokov. The painter Wassily Kandinsky used his gift to paint particularly “musical” pictures. It is also very likely that Vincent van Gogh was a synesthete.

Well-known synaesthetes * as far as we know today are e.g. musicians such as Lady Gaga, Lorde, Mary J. Blige, Tori Amos, Billy Joel, Pharell Williams, Kanye West and Chris Martin, the singer of the British band "Coldplay". The same goes for the French pianist Hélène Grimaud, the Californian painter and set designer David Hockney and the comic artist Michel Gagné (“Ratatouille”).
This well-known scene from the film "Ratatouille" shows the form of synesthesia, in which a taste sensation triggers a visual sympathy:

See also: → Synesthesia Lexicon → Synesthesia Links
External: → Wikipedia entry on synesthesia