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What is synesthesia?

Synaesthesia is a condition whereby a stimulus involves one or more senses other than those normally involved in processing it: one can 'hear a colour' or 'see a sound' (hence the rhetorical figure of poetry). Let's find out more about what synesthetic people experience.

Causes of synesthesia

The synesthesia causes are still unclear, particuarly those that are mainly identified are genetic, at least those that develop in the first years of life, or refer to brain problems or alcohol use. 

What is known, however, is that synesthesia can be caused by the intake of certain drugs (e.g. antidepressants) or the abuse of narcotic substances (especially hallucinogenic drugs, such as LSD, mescaline and, in some cases, marijuana), as well as brain injuries (e.g. in the case of a stroke). In essence, all causes that lead to perceptual interference. Increased communication between the brain regions responsible for processing information from the sense organs creates a fertile ground for synesthetic manifestations.

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How many types of synesthesia are there?

The types of synesthesia are different and depend on the sense that is affected. However, it can be said that they all depend on the alteration of sensory perceptions, for example: words have a colour, sounds have a smell and numbers have a taste.

Sound-to-color synesthesia

Sound-color synesthesia, or chromesthesia, associates sounds with colours: a melody, the barking of a dog, the opening of a door can trigger visual experiences. 

Those affected report seeing their synesthetic experiences in outer space, while others claim to have them directly in their mind, but often the latter have difficulty describing the inner spatial location, and say they have it 'in front of their eyes'. 

For some, synesthesia is elicited only by spoken words, for others by any acoustic stimulus, single sounds or actual melodies. There are also differences in the visual stimulus elicited: some perceive colours (true chromesthesia), others geometric shapes.

Grapheme-color synesthesia

Grapheme-colour synesthesia associates graphemes (i.e. individual letters of the alphabet and numbers) with a specific colour. In some cases, even whole words can have their own colour: this form appears especially in the early school years, when the child first comes into contact with certain shapes.

Colours vary according to shape, arrangement in space, transparency, intensity and shade. The association between grapheme and colour also differs from person to person: for example, if the letter A is red, for another it might be blue. One study showed that it is not the shape of the letter that causes the colour, but its meaning: patients saw words and a series of numbers in which some letters and some digits were indicated with the same symbol (letter S for the number 5, or Z for 2). Synaesthetic patients perceived the same symbol in different colours depending on whether they recognised it as a 5 or an S.

Lexical-gustatory synesthesia

In lexical-gustatory synesthesia, specific word are associated with a particular taste, this results in remarkably intense taste perceptions as well. For some people the taste often lingers for a long period of time upon hearing a particular word, while for others it disappears almost immediately. Studies have shown that those who experience this condition have a much stronger connection between the part of the brain that deals with taste and the part of the brain that deals with hearing than those who do not have such perceptions.

Symptoms of synesthesia

Synesthesia has different symptoms, which vary depending on the type of synesthesia one suffers from. They can be: 

  • visual: the association of a sound or noise with a certain colour (Sound-color synesthesia); or when a grapheme corresponds to a certain colour (grapheme-colour synesthesia); or when music is perceived as colours in the air (musical-colour synesthesia) or when the person perceives abstract concepts as shapes projected into the surrounding space (conceptual synesthesia);
  • tactile: the perception of tactile sensations in oneself upon seeing a person being touched (tactile-specular synesthesia);
  • gustatory: the association of specific taste with a specific word (lexical-gustatory synesthesia).

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How common is synesthesia ?

Synesthesia affects a fairly small segment of the population (between 0.05% and 4%) but many artists, poets and writers have experienced it. 

Kandinsky claimed that the colours became 'a chorus' on the canvas and hoped that others could also hear his paintings. Baudelaire, on the other hand, composed the 'vowel sonnet' under the effect of sensory distortions, probably induced by narcotics. 

Synaesthesia is also felt by scientists, such as the physicist Richard Feynman, father of nanotechnology and Nobel Prize winner for Physics in 1965, who said he could see equations with coloured figures; and by musicians, such as Stevie Wonder, who have shared their experiences with sound-color synesthesia, wherein they associate certain sounds with specific colors.

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How is synesthesia diagnosed?

There is no official test for synesthesia, just as there is no effective method for diagnosing it. This is because, although it is often referred to as a 'neurological condition', it is listed neither in the diagnostic manual of mental disorders nor in the classification of diseases and related health problems. Normally, synesthesia does not interfere with daily activities and is even perceived as pleasant by those who experience it.

However, there are guidelines that indicate what needs to be done to identify people who actually suffer from it. They consist in finding out whether: 

  • they experience perceptions voluntarily: synesthetic people do not consciously evoke the reaction;
  • they have the same perception every time;
  • they remember the perception better than the sensation that triggers it: a synesthetic who correlates the colour violet with the name Maria, often remembers that a woman's name is violet, without associating the word Maria with the same person;
  • have pleasant emotional sensations linked to these perceptions: these are normally either creativity-stimulating or neutral sensations, rarely negative feelings or experiences;
  • they project sensations outside the mind (they see colours floating in the air while listening to certain sounds): in essence, the image is projected into the space around them;
  • have a generic perception: i.e. colours, lines or shapes in response to a certain smell, but not something very complex (a room with people, furniture and pictures on the walls).

How is synesthesia treated?

At the moment, there are no treatments or cures for synesthesia. This is primarily because many individuals do not experience negative effects, making treatment unnecessary and rarely sought after. In general, the approach that has shown the best results at the moment is hypnosis. However, there are different degrees and forms of synesthesia, so it is best to assess the actual effectiveness and necessity of the treatment on a case-by-case basis.

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