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What is Synesthesia?

Are you part of the ranks of people with their senses intertwined? Can you smell sounds, hear colours, or taste words?

What is Synesthesia?

Synesthesia is a phenomenon where a person may experience one sensation as an involuntary result of another. For example, someone may view the number 12 as a shade of green, or experience a sweet taste in their mouth after playing a note of music. The American Psychology Association suggests it affects one in 2,000 people.

The Synesthesia can either be experienced in the real world (i.e. the person feels that they can actually see the colours in front of them, or hear a sound from a particular direction), or in the mind’s eye (i.e. the person imagines the experience, similar to how a memory might suddenly playback in your mind).

The Synesthesia debate

Some researchers do not believe it is a neurological condition, as brain scans don’t look any different in those with Synesthesia and those without.

Some feel it comes about because of childhood memories. People may have drawn an association between, for example, a letter and a colour because as a child they had seen that number written on an alphabet block in that colour. However, other researchers strongly feel that the experiences occur because of a crossed connection in the brain.

A common test to see if Synesthesia exists is to ask someone who sees colours when reading numbers or letters the exact shade of colour they experience. After at least a year, the same person is asked to identify the colour they see for the same text. Someone with Synesthesia will be able to identify the exact same colour, despite how long has passed since they first identified it.

What causes Synesthesia?

The cause of Synesthesia is not yet known, as research into the condition is relatively recent.

  • Synesthesia is reported to often run in families, although different people can experience it in different forms. This doesn’t automatically mean it is a genetic condition, as parents are likely to raise their children in a similar way to how they were raised themselves. This means if they have Synesthesia, they may inadvertently be teaching their children to experience the world how they do.
  • Men and women are equally as likely to have the condition.
  • Usually, Synesthesia is present from childhood.

Types of Synesthesia


One of the most common types of Synesthesia is known as grapheme-colour. This is where a person experiences colours at the same time as seeing a number or letter. No two people with Synesthesia experience it in the same way. Therefore, people do not all have to see a letter in a certain colour to be classes as having it. However, often people with this form of Synesthesia will perceive the letter A to be red, the letter B to be blue, and the letter C to be yellow.


This is another form of Synesthesia, where a sound is associated with a colour. The sound of a word, music, or a voice causes people who have this type of Synesthesia to visualise colours around them, or see them in their mind’s eye.


Mirror-touch Synesthesia is a newly discovered, rare form of Synesthesia. It is where someone experiences the emotions or sensations felt by another person. The severity of this condition can vary. For example, someone may feel severe pain in their arm after seeing someone else suffer an injury to their arm. Others may feel a slight tingling sensation.  

Do I Have Synesthesia?

If you suddenly experience Synesthesia as an adult, visit your doctor to make sure you have not suffered a brain condition or injury. Synesthesia is almost always present from early childhood, therefore experiencing it suddenly in adulthood may be a sign of another problem.

Richard E. Cytowic and David Eagleman say that certain eye conditions may cause symptoms of Synesthesia, in their book Wednesday is Indigo Blue: Discovering the Brain of Synesthesia. Injury to the eye, cataracts, macular degeneration, and glaucoma are just a few examples of eye conditions that distort the vision. Sudden symptoms of Synesthesia may be an underlying eye condition, and you should talk to an optician immediately.