Imagine waking up one morning and discovering that you had a sixth sense that had been dormant, but had suddenly activated. Imagine realising you’d been hearing in black and white all your life, and now suddenly you can hear in colour. Or imagine you can see emotions, taste colours, feel numbers…imagine any two of your senses have been combined into something greater than the sum of their parts and you now experience the world in a whole new way.

What I’m describing really does exist. It’s known as synaesthesia, which loosely means “union of the senses”. It’s something I’ve had all my life, but it wasn’t until I was around 19 that I realised it wasn’t ‘normal’ and not everyone has it¹. Synaesthesia is sometimes called a neurological condition, however it isn’t listed in the DSM-IV as it doesn’t interfere with daily functioning and in general has no adverse side effects. In fact, many synaesthetes don’t even know they have this condition until they discover that the majority of others don’t, and this is exactly what happened to me.

(As you’ll have no doubt guessed, this week’s post is a little lighter on physics than normal, but read on to see why I think my synaesthesia has been a huge help to my ability to do maths…!)

I have two types of synaesthesia: colour-grapheme synaesthesia (perceiving written words as having colours) and chromesthesia (the association of sounds with colours). To me, listening to music is a bit like being inside one of those Windows Media Player visualisations from the early 2000s, except it’s in 3D and all around me. Sounds have shapes, textures, and depth. Pure sine waves are just a single colour that varies with their frequency, but as more harmonics are added of different frequencies (colours) and at different volumes, the colour and texture starts to emerge. I have a sneaking suspicion that this is why I’ve always been drawn to the sound of a distorted electric guitar: distortion is just the amplification of higher (usually inaudible) harmonics, and different types of distortion lead to very different colours and shapes. I can’t quite imagine being without this – it would be as if the world became black and white, or two-dimensional.

The other form, colour-grapheme synaesthesia, is one of the most common types of the condition, where written words are percieved as having colour. The best way I can explain this is if I said ‘Imagine this text was red’. You know it isn’t red, but you can visualise it, right? Colour-grapheme synaesthesia is just like that, but having it going on all the time, unconsciously. For those who write code for a living, imagine if the syntax colouring of your favourite editing software was applied to everything you read, and you won’t be far off from understanding synaesthesia …!

The colours are not entirely random though, at least not the way I see them. For me, every letter has a different colour, but every word takes the colour of the first letter unless there are ‘stronger’ colours somewhere else in the word. For example, the word ‘green’ is actually orange, as ‘g’ is orange, but the word ‘yellow’ is a pale yellow because although ‘y’ is white, ‘l’ is bright yellow and so they shine through. ‘A’ is blue. ‘2’ is red, but ‘two’ is dark blue. Some cast shadows, others are shiny, but every single letter is unique in a way that’s hard to put into words or explain to anyone else.

This association follows through into mathematics. I’m a theoretical physicist, but instead of seeing my work as a sea of black equations on a white page, instead I see everything in colour. Integral signs are yellow, the ubiquitous variable ‘x’ is brown, even Greek letters all have colours of their own.

Some report that synaesthesia makes it hard to do mathematics – for example, if ‘1’ is blue and ‘2’ is yellow, but adding them and finding that ‘3’ is orange when it really should be green, this can cause some cognitive dissonance – but I’ve only ever found it useful. For example, if an equation changes colour from one line to the next, it sometimes means I’ve made a mistake, and this helps me spot simple errors in copying text from one line to another. I also find that it helps me to make sense of what would otherwise be a sea of similar-looking symbols on page, as even similar looking symbols can have very different colours associated with them – long and complex equations aren’t as nearly as intimidating in colour as they are in monochrome!

I’m far from the only physicist to have it. Though I’m not sure he ever used the term ‘synaesthesia’, Nobel prize-winning physicist Richard Feynman also spoke of something very similar: “When I see equations, I see the letters in colors…light-tan j’s, slightly violet-bluish n’s, and dark brown x’s flying around. And I wonder what the hell it must look like to the students.”

Although Feynman and I see the colours differently, it sounds very much like the same thing I experience when I look at mathematical formulae. Personally, I find it very helpful for organising and manipulating equations in my mind – it would be very interesting to hear from other physicsts and mathematicians who see numbers this way, and whether others also find it helpful to their work!

Where does it come from?

It’s not all sunshine and rainbows, however. Some weak evidence exists that synaesthetes are more prone to migraines and other forms of cortical hyperexcitability, although there is not a lot of research on the topic. After all, as the saying goes, correlation does not imply causation. Some people even experience synaesthesia only during severe migraines, and not during their regular waking hours. This suggests that there may be a neurological basis for synaesthesia, and indeed there is some evidence that synaesthesia may be caused by ‘hyperconnectivity’ within the brain.

The idea, if I undestand correctly, is that connections between brain regions which should have been pruned as part of normal brain development have somehow stuck around long after they should have disappeared. So in other words, it’s less a case of synaesthete brains doing something incredible, and more that they’ve just failed to be normal in a way that leads to some particularly interesting consequences².

Interestingly, there is also some evidence that synaesthesia is far more common in people diagnosed with autism than in the overall population, and there is anecdotal evidence that people with autism can experience signifiant discomfort from the effects of synaesthesia. The evidence stops short of being a causal relationship or a direct link, but it is nonetheless an interesting observation.

Synaesthesia in Art

While I don’t know of many other examples of people with synaesthesia who are professional physicists or mathematicians – although I’d love to hear from you if you’re out there! – it seems like lots of synaesthetes end up being artists or engage in other creative professions, perhaps drawn to the profession by the idea of communicating the unusual, maybe even unique way that they see the world. Wassily Kandinsky, one of my favourite abstract artists, was a synaesthete, something I didn’t discover until many years after hanging a few prints of his work on the walls of my flat.

A few years ago, I stumbled onto some paintings of music done by synaesthete Melissa McCracken and these are truly the best illustration of chromesthesia that I’ve ever seen, beautiful abstract works of art that capture the experience of seeing and feeling sound. In a 2019 WBUR article, her description of chromesthesia is one that matches mine almost exactly: “The best way that I can describe it is that it kind of sits where my memories sit, but kind of floating in space a little bit. It doesn’t inhibit my sight in any way. But it’s almost like a filter, kind of above my eyeline a little bit."

While different synaesthetes experience the world in different ways, and not all of Melissa’s paintings match the way I see music, her painting of Jimi Hendrix’s ‘Little Wing' captures what I see in this song almost perfectly. In fact, I’m incredibly envious of Melissa’s ability to communicate and share her synaesthesia through her paintings and give others a glimpse of what it’s like to live in an extrasensory world populated by a lucky few.

Conclusion

So, while synaesthesia may sound weird and hard to explain, for the majority of people who have it, it can be a wonderful and unusual way to see the world. I hope this post has given you some insight into what it’s like to have synaesthesia, or possibly even awakened you to the possibility that you’ve had it all along and never knew until now! If you’re a synaesthete, newly discovered or otherwise, you’re part of a very small fraction of people who get to see the world in a different way from everyone else. As Ramachandran & Hubbard put it in their 2001 article:

"Far from being a mere curiosity, synaesthesia may provide a window into perception, thought and language."

(Ramachandran & Hubbard, Journal of Consciousness Studies, 8, No. 12, 2001, pp. 3–34)

Do you have synaesthesia too, or know anyone who does? What colour do you see words, and are they different from mine? Drop me a message on Twitter and let me know!

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1. Frankly I’m still half-convinced that everyone else in the world does have it but just doesn’t realise - see the ‘bouba/kiki’ effect! ↩︎

2. I can only dream that ‘failed to be normal but in an interesting way’ will be my epitaph. ↩︎