Imagine if every time you heard a particular sound you automatically saw a block of a particular colour. Or every time you heard a particular musical instrument you got a particular taste in your mouth. This is the experience of synaesthesia, where letter A’s are bright red and trombones are bitter.

Synaesthesia is a condition where an experience through one sense – perhaps hearing- is involuntary experienced through another sense as well – perhaps taste. In this way trombones aren’t just heard by those affected, but experienced as a bitter taste as well, or reported as producing blocks of purple colour.

It’s unclear how many people have synaesthesia, and estimates range from one in every 2,000 people to eighty seven in every 2,000. One of the complications in estimating the number is that it can often go unreported. This isn’t from shame or embarrassment, as most synaesthetes enjoy the combinations and connections between their different senses. In fact the under-reporting is for a very different reason – synaesthesia is so natural and coherent that synaesthetes assume that most people experience things in the same way.

Whilst people’s individual experiences of synaesthesia, and the connections it makes, are consistent for them they aren’t consistent across synaesthetes as whole. The composers Liszt and Rimsky-Korsakov argued about the colours of musical keys, with Rimsky-Korsakov experiencing B major for instance as “ a gloomy dark blue with a steel shine”. This particular form, where sounds invoke colours, is called chromesthesia and is the second most common form of synaesthesia.

The most common form is grapheme-color, where letters, numbers, or words will be seen as tinted or shaded in particular colours. Whilst some associations are more common, such as the letter ‘A’ being red, as with chromesthesia the letter:colour pairings are largely unique to each person. This is an area where people can find the condition an advantage. They have described being able to remember spellings, or solve maths problems, partly through paying attention to how congruent the colour combinations were.

Another feature of synaesthesia is that peoples’ perception of the space around them is often different. Many talk in terms of “going to” or “looking at” a space around them where they attend to the accompanying sense. As well as this some also experience numbers or dates and times as being consistently placed around them in three dimensional space. Numbers for instance may be experienced as on a vertical scale which when referred to consistently occupies the same space in front of them.

Whilst attempts to train non-synaesthetes to learn the ability have ended in failure induced synaesthesia is pointing towards advances in pain management. A number of clinical procedures and treatments need the patient to be conscious but helped to manage their pain. Currently this is often through virtual reality, where the aim is to shift the attention away from the sensation and any anxiety. By simulating a synaesthetic experience the virtual reality can become more immersive and engaging than exploring a virtual landscape or playing a game. The result is better pain control, and less reliance on pharmacological pain relief, with its attendant issues.

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