Synaesthesia Synaesthesia is the neurological mixing of the senses.

In this article

What is it? What is synaethesia?

Symptoms Causes and risk factors

Somebody affected by synaethesia may 'experience' colours when they hear or read words, while others 'see' sounds or 'hear' colours.

There are many different types and they can involve all senses - vision, hearing, touch, taste and smell. The most common form is colour-letter synaesthesia.

Most synaesthetes couldn't imagine life without these extra sensations and see it as a gift.

For some synaesthetes, certain concepts that come in sequences - such as days of the week, months of the year, decades, letters, numbers, and so on - are experienced in a particular spatial orientation.

For example, some see the months of the year in a running track shape, with, say, August and September taking up most of the right-hand side and the rest of the months squashed on the left. Or they might see the numbers one to ten from left to right, then ten to 20 going upwards, and 20 to 30 over their right shoulder, and so on. People who experience a visual week or year are often able to use this information to recall times and dates extremely well.

While there’s a relatively clear idea of the factors that govern synaesthesia in adults, there's a lack of information and scientific evidence about the origins and development of the condition.

Synaesthesia appears to be caused by cross-talk between areas of the brain that wouldn't normally communicate. It joins sensations together that are normally experienced separately. For example, in most people, there's no functional connection between the area of the brain that processes letters and the areas that deal with the awareness of colour.

A study conducted by the University of Edinburgh found that about four per cent of the population have some type of synaesthesia - that's more than 2 million people in the UK. Most people are entirely happy about it and many don't even realise other people don't share their sensations.

Synaesthesia appears to run in families, which suggests a genetic link. But what's passed on seems to be a general predisposition, rather than a particular type. A mother who sees coloured letters might have a son who tastes words, for example.

There may be slightly more women synaesthetes than men, and it's difficult to find cases of a father passing synaesthesia to his son. Both suggest the trait could be passed down on the X chromosome, in a dominant fashion. An actual synaesthesia gene has yet to be identified.

Anecdotal reports appear to suggest the condition has advantages and disadvantages.

The advantages include:

• Literacy skills, such as being good at spelling
• Ability to learn mathematical concepts
• Time-management skills
• Better memory recall

Children need to learn how to use their synaesthesia to gain an advantage. The problem is the people who would usually teach them, their parents and teachers, may not be familiar with the condition.

Disadvantages may arise not from the child's cognitive abilities, but society's lack of understanding of the nature of the phenomenon.

Synaesthesia can be a distraction - it can make it difficult to concentrate. The colour of sounds can be a little overwhelming, and any slight sound a huge distraction.

A steadily growing group of synaesthetes academics - cognitive psychologists, neuroscientists, cognitive neuropsychologists and neurologists - are trying to understand this phenomenon.

This article was last medically reviewed by Dr Gill Jenkins in August 2009.