If you ever hear someone casually state that triangles are pink and they like Wednesday because it tastes like chocolate-pudding, it does not necessarily mean they are on some psychedelic drug. Rather, you might have met a person with an amazing neurological condition called “Synesthesia”, where one sense perception immediately evokes another. The term is derived from Greek and literally means joint perception . To date, 60 types of synesthesia have been reported , but the true number is still a mystery to the scientific community. This is because not only can the five senses be coupled with any another, but each sense can be broken down into a variety of other perceptions. For instance, vision can be broken down into shapes or colours, touch into pain or texture. Therefore, establishing all the forms it can take is impossible . Further on, the information gained about this condition comes from the synesthetes themselves. Yet, most individuals who have synesthesia are not aware they perceive the world differently than the average person up until their adult life, if they ever do. If you’ve grown up perceiving flashes and brushes of colours when listening to music or feeling the same excruciating pain experienced by the patients in Dr. House in your own body, you will automatically assume this is true for everyone, rather than thinking you have Chromaesthesia or Mirror-touch synesthesia. For this reason, the prevalence of this supposedly uncommon condition is also debatable.
Grapheme-Colour synesthesia is one of the most common forms , where a person experiences numbers and letters (and by extension, words) endowed with specific shades in their “mind’s eye” . For some synesthete; 3 is green, L is orange and Baseball is white – for a fact, just as much as the sky is blue. Ordinal-linguistic personification is another form which usually co-occurs with Grapheme-Colour. In this case, ordered sequences such as numbers, weekdays, months and letters are embedded with personalities . The month of April might be a vivid, bubbly girl, while the letter F is a lazy middle-aged man. Although Grapheme-Colour synesthetes usually report different colour-digit combinations to each other, studies found some commonalities – such as A being very often red . You might be thinking that a person had a red A magnet when they were a kid, hence maintaining the association throughout their adult life, but that’s not how it works.
In truth, scientists are not really sure how it works. The proposed theories suggest that synesthetes’ brains are wired differently , that it all boils down to genetics or that it is acquired through social-learning . Our brains are very complex, so it could easily be a combination of all of these. What we do know is that although synesthesia can vary greatly, some few things are common along the spectrum:
- The mixed perception of senses is involuntary; it happens without thinking about it
- The condition is experienced, not imagined. So, if I asked the colour of a square, a synesthete will see, let’s say, yellow – without thinking about it and before the brain made the association
- The associations are always the same. Coldplay can’t taste like bacon one day and waffles the next
- Often, the second perception is more memorable than the primary one. So, if Keith is perceived with the colour purple, a synesthete will remember the purple first, which helps one remember that it’s Keith
- The perception may be really emotional. If the Jaws soundtrack at the cinema smells like gasoline, the synesthete may panic at the belief of an eventual fire 
This might suggest that synesthetes live very scary and confusing lives, however it is quite the opposite. Most report not imagining or even wishing to live without it . In certain cases, it can be impeding, like when perceptions have very intense sensations. For a particular barman with synesthesia, the name Derek, a loyal customer, tasted like earwax!  Still, this fascinating neurological condition has a number of pragmatic benefits. For instance, Grapheme-Colour synesthesia is a great mnemonic device as it allows for the person to recall information in different ways . If a student with synesthesia cannot remember the name of the first emperor that ruled Mesopotamia, the sense of green will help him remember it must start with an “S” and is therefore “Sargon”. A very inspiring synesthete is neurologist Dr. Joel Salinas, whose Mirror-Touch synesthesia has helped him become one of the most sought-after doctors in America due to the undeniable and incomparable empathy and understanding of his patients’ symptoms .
In the artistic world, post-impressionist artist Van Gogh, the abstract painter Kandinsky, the novelist/poet Vladimir Nabokov , the rock musician Tori Amos and contemporary singers Pharrell Williams and Lady Gaga  have all been reported to be synesthetes. Mind you – this does not mean that synesthesia endows individuals with talent. Rather, as research suggests, the wonderful experiences produced by the coupling of the senses may be a source of inspiration and the driving force towards self-expression .
Scientists have started showing a great deal of interest towards this condition and not only because of the fascinating perceptual realm. Cognitive researchers studying the wiring of a synesthete’s brain seek to understand how they code and process information in order to broaden our knowledge on perception, consciousness and cognitive functions such learning and memory .
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