Synaesthesia: About

Synesthesia is a perceptual condition in which the stimulation of one sense triggers an automatic, involuntary experience in another sense. This can occur between any combination of senses or cognitive pathways such as seeing sounds, tasting words, or feeling a sensation on the skin when certain scents are smelt. It is a sensory phenomenon that is unrelated to memory so anyone could teach themselves to start associating particular colours with certain numbers. But this wouldn't be a similar brain response to a synesthete's. Someone with grapheme-colour synesthesia would have a more difficult time picking out the black 2's from the black 5's in the image on the right. however, if you have colours associated with numbers then you will see the triangles almost instantly.

fig. 1

• 4% of the population has some form of the condition
• a lot of popular musicians have the condition 
• artists with synesthesia may have an advantage, Claude Monet is known as the master of impressionism 
• scientists do not know the exact cause of synesthesia, other than that people have a cross-wiring in their brains between areas that process different sensations
• 40% of synesthetes have a close relative who also has the neurological condition
• synesthete Daniel Tammet set a record for memorising 22,514 of pi in five hours (2006)
• people taking LSD experience some of the same effects as synesthetes, so if a synesthete was to take LSD at a concert then their senses would start to go into overload - colours exploding, draining, overwhelmed
• scientists still do not understand how humans bind all of their perceptions into one complete package e.g. holding a baseball and knowing the colours, shape, and texture of the ball. Studying synesthesia may help scientists to gain some new insights into the phenomenon
• most synesthetes are surprised to find out they have synesthesia because it is a neurological condition and they do not understand that other people don't see the world as they do

Personification

This type is known as ordinal-linguistic personification or OLP. The individual will associate ordered sequences with various personalities. Ordered sequences may include numbers, letters, months etc. For example, someone may look at the letter ‘A’ and think in his mind that ‘A’ is a rude letter.

Lexical-gustatory synaesthesia

This one of the rarer synaesthesia types and those who experience this kind of synesthesia evoke different kinds of tastes when they hear certain words or phonemes. Research has shown that associations between the words and what a synesthete is able to taste are constrained by tastes he or she has experienced early in life.

Synesthesia can occur between any two senses or perceptual modes, so there are a large number of combinations that could be made but there are some that are known to be more common. 

Grapheme-to-colour synesthesia (most common)

Associating/seeing individual letters or numbers with a specific colour. Usually, two people do not associate the same colours, apart from the letter A which has commonly been reported to be red.

Sound-to-colour synesthesia

Sound triggers the visualisation of coloured, generic shapes. For certain people, the stimuli are limited, and only a few types of sounds will trigger a perception. Usually, the perceived colours appear in generic shapes such as squares, circles and triangle.

Number-form synesthesia

A number form is a mental map that consists of numbers. When a person with number-form synesthesia thinks about numbers, a number map is involuntarily visualised. Number forms are a product of 'cross-activation' between regions in the parietal lobe - a part of the brain that is involved in numerical and spatial cognition.