What is synaesthesia?
Ever seen colours when you listen to music, thought of letters as having personalities, or felt a touch on someone else as though it were on your own body?
Exciting news: you have synaesthesia!
Or you’ve taken a psychoactive drug, which is also exciting but in a very different way.
Synaesthesia is a harmless but unusual perceptual phenomenon in which senses and thoughts get tangled together in a way that they don’t for most people.
I have synaesthesia! For me, anything that goes in a sequence, like numbers, the alphabet, even playing cards, all have positions in space around me when I think about them, almost like I know where my hands are when I think about them. Sometimes music makes me see patterns, and a few tastes and smells have textures or shapes.
Synaesthesia is one of my favourite topics in the world. I like it so much that I did my PhD on it, then spent seven years researching it before I quit academia. Now comes the fun part: attempting to condense ten years of knowledge into a blog so that you can learn about it too!
Defining synaesthesia
Synaesthesia usually involves two elements:
An inducer, which is the thing that triggers the synaesthesia – like thinking about a number.
A concurrent, which is the unusual perception or thought – like feeling it ‘belongs’ in a particular location in space.
When talking about synaesthesia, it’s common that the name will take the form [inducer]-[concurrent], so when I think of sequences as having positions in space, that’s called sequence-space synaesthesia. Another example is lexical-gustatory synaesthesia, where reading a word causes you to experience a taste.
Mm, tasty words.
There are a few exceptions to this inducer-concurrent rule, like when certain sounds cause strong negative emotions – this is called misophonia and may be a type of synaesthesia (you can read more about it in my blog on misophonia here).
Though there are lots of different synaesthesias, they have several things in common. Synaesthesia is, as far as we know:
Idiosyncratic: everyone’s concurrents are different. Not all synaesthetes have all kinds of synaesthesia, and even people who have the same kind of synaesthesia have different experiences. While A might be bright red for one synaesthete, it could be dark red for another, or blue for a third. Sometimes you get synaesthetes whose associations are based on something like childhood fridge magnets, but that’s not very common.
Arbitrary: there’s no particular reason for the concurrents to be what they are, though we can see some patterns, like similarly-shaped letters tend to be similar colours.
Highly specific: If A is red, it’s not just any red, it’s one exact shade of red.
Automatic: you can’t avoid experiencing it.
Consistent over time: if A is red, it’s always red. (I actually don’t think synaesthesia needs to be consistent over time in order to be synaesthesia, and nor do some other synaesthesia researchers, but it is easier to set up experiments for consistent synaesthetes than inconsistent ones, so we know a lot more about them.)
Lifelong: most synaesthetes say that they’ve had synaesthesia for as long as they can remember, though it seems likely that it’s a lot less consistent in childhood than in adulthood, and that for at least some synaesthetes it fades as you age.
How many synaesthetes are there?
Good question! We’re not really sure, because a lot of the time people don’t realise that they have synaesthesia. I didn’t until I was 20 and happened to catch a documentary about it – up until then I assumed that was how everyone thought about the world! However, we can make some approximations. Somewhere around 1 in 10 people have sequence-space synaesthesia, which is one of the most common types, while only around 1 or 2 in 50 have letter-colour or number-colour synaesthesia. Some types of synaesthesia are so rare that we don’t have an estimate of how many people have them.
My favourite rare type is auditory-tactile synaesthesia, where sounds cause you to feel touch.
Why are there synaesthetes?
We don’t know!
Some researchers believe that we are all born synaesthetes. This could be because, at first, we can’t tell the difference between different kinds of perception like sound and touch and we have to learn to do this, or it could be that babies are literally synaesthetes. Unfortunately, we cannot ask babies what they are experiencing – but we can show them things that we think go together, like a rising pitch and a rising ball, and see if they spend longer looking at ‘matching’ pairs than ‘mismatching’ pairs. And they do! …but it isn’t really synaesthesia. They are doing a kind of matching across the senses called a crossmodal correspondence, which just about everyone does.
OK, let’s have a look at genetics. There’s clearly some role for genes, since synaesthesia tends to run in families. However, family members often don’t have the same type of synaesthesia. For example, my dad and I both have synaesthesia, but while mine is sequence-space (and a few other things), his is a kind called ticker-tape, where he sees words scrolling across his vision as he’s speaking. Yes, like subtitles. There are even cases of identical twins where one has synaesthesia and the other doesn’t, which rules out a totally genetic explanation.
It seems that some people are likely to develop synaesthesia, based on their genes, but since they don’t inevitably become synaesthetes, there must be some role for experience too. One possibility is that people who have a genetic predisposition to developing synaesthesia only do so under certain circumstances – for example, if the first language they learn is one like English, where there isn’t a consistent link between the sound of a word and the way it’s written.
Consider ‘ough’: that’s enough dough; have a thought for the coughing ploughman who must take it through the loughs.
The most recent explanation I’ve found is that the genetic predisposition to develop synaesthesia is not particularly about synaesthesia. Instead, people who have the genes for synaesthesia have brains which develop in multiple different ways from other people (we’ll cover these in the next section), and those differences cause some people to develop synaesthesia as well. If this is the case, then as far as evolution is concerned, having synaesthesia isn’t the important thing so much as the benefits that come along with it…
What are synaesthetes like?
Synaesthetes are different from other people in ways beyond their synaesthesia. However, a lot of the studies on ‘what synaesthetes are like’ look at people who have letter-colour and number-colour synaesthesia as they’re fairly common and easy to test for, so be cautious as they may not be true for all synaesthetes.
First off, synaesthetes seem to be more creative than other people in some ways.
Jaune Rouge Bleu by Wassily Kandinsky (public domain). Kandinsky may have been a synaesthete - he said some things that suggested he perceived colours as having sounds.
Second, synaesthetes tend to have better memories than other people. Most of the time this is subtle, like having more vivid recollections of childhood memories. There are occasions when synaesthetes have extraordinary memories, though: Daniel Tammet has memorised pi to over 22,000 digits, making use of his number-space, number-colour and number-texture synaesthesia.
Daniel Tammet is also autistic, which brings us to the third thing: synaesthesia seems to be linked with autism. Austistic people are more likely to have synaesthesia than non-autistic people, and if you are an autistic person or a synaesthete, you are likely to have increased sensory sensitivity compared to others.
This isn’t a complete list of the ways in which synaesthetes are different from non-synaesthetes, but all of the ones I’ve covered are useful in evolutionary terms: creativity can help us with problem-solving, heightened sensory perception can help us with things like recognising colours and textures, and I’m sure you can think of a thousand useful things that a good memory can do for you. Maybe synaesthesia is just a by-product of these other things.
Can I become a synaesthete?
At this point, you might be curious about what it’s like to have synaesthesia. Unfortunately, it doesn’t seem likely that you can become a synaesthete if you’re not already one, though some people develop synaesthesia after going blind.
Nonetheless, there are a few things you can try which can give you an impression of what synaesthesia is like.
As I mentioned at the start, synaesthesia sounds an awful lot like tripping on psychoactive drugs, so… you could take some. If you’re going to, please do so in a safe environment and check your local drug laws.
If drugs aren’t for you, then perhaps you can find someone to hypnotise you and suggest that you have synaesthesia! Unfortunately, not everyone is susceptible to hypnosis, and even if you are there’s no guarantee that you’ll experience anything like synaesthesia as people respond to post-hypnotic suggestions in very different ways.
Or maybe you could try training yourself to have synaesthesia. Extensive training will probably help you experience something like synaesthesia, but is pretty boring, consisting of lots and lots and lots of repeats of the specific pairings that you want to develop (lots of red Ss and green Es, for example) and then lots of tests of how well you remember the associations.
If none of these appeal, then the best recommendation I have is a browser plugin that will change letters to whatever colours you want. The plugin was inspired by research on training people to have letter-colour synaesthesia by getting them to read lots of text with certain letters in certain colours, and though it won’t be exactly like synaesthesia, it’s still pretty fun.