Synaesthesia is sometimes called an ‘extra ability’ that means some people mix colours and words or other sensory inputs. Now, it is becoming clear that it emerges in childhood to help us learn.
WHAT colour is the letter A? It is a question Nicholas Root often asks the volunteers he has recruited for his research. Most give him the same response. “They say the task is stupid and that letters don’t have a colour,” says Root.
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| Sharmelan Murugiah |
But they do for people with letter-colour synaesthesia, in which letters and words are associated with particular colours. That includes Jennifer Mankin, now a synaesthesia researcher herself, who recalls confusing her schoolmates in her teens by saying one of them had an orange name. “It became clear to me, in that moment, that my perception of the world was fundamentally different than most other people,” she says.
Scientists have known about synaesthesia for more than 200 years, but for much of that time it has been unclear why some people blend sensory information – why they associate words with flavours or sounds with textures, for example. These days, there is a consensus that some forms of synaesthesia, particularly letter-colour synaesthesia, are closely tied with learning. The revelation is pushing researchers like Mankin to go beyond asking why synaesthesia exists and explore what it reveals about how the brain functions.
This work has already shown how culture influences the way we learn and how our thinking is shaped in different ways depending on which language we speak and write. The latest discoveries may prove even more significant: we have seen tantalising signs that many people without synaesthesia unknowingly blend sensory information, which suggests that what we are learning about the trait might even tell us something more far-reaching about human consciousness.
The first convincing description of synaesthesia was published by Georg Tobias Ludwig Sachs in 1812. Sachs and his youngest sister had albinism – a perfect subject, he thought, for scientific investigation. But buried within his paper “A natural history of two albinos, the author and his sister”, there is a short section in which Sachs highlighted that the pigmentation he lacked in his physical body was more than present in his mind’s eye. He explained that “coloured ideas appeared” when he interacted with words, numbers and musical notes.
At the time, Sachs’s treatise was taken as little more than a scientific curiosity. But nearly 70 years later, Francis Galton – now infamous for his views on eugenics – began his own studies of synaesthesia. He speculated that the attribute was learned and that it could help those with it to more efficiently tackle cognitive tasks. From Galton’s writing, it is clear he was fascinated by synaesthesia. His peers were evidently less so: within a few years, interest had fizzled out and synaesthesia was largely ignored by science for most of the 20th century.
Linked to learning
“It wasn’t until the early 1990s when we see synaesthesia getting back into respectability,” says Marcus Watson at York University in Toronto, Canada. That was due in no small part to the work of neurologist and author Richard Cytowic, who wrote an influential book on the subject in 1989. “Now, we are at the point where there are about 50 to 100 papers published on synaesthesia each year,” says Watson.
This recent research has taught us, for one thing, that Galton’s views on synaesthesia were close to the mark. Letter-colour synaesthesia – which is often the focus of research because it is relatively easy to study – does indeed seem to be tied to learning, says Watson. This has been made particularly clear through remarkable research led by Julia Simner at the University of Sussex, UK, which has revealed how letter-colour synaesthesia develops over the course of several years during childhood.
The work involved repeatedly testing more than 2000 children who were being followed as part of a long-term study commissioned by the Scottish government. Significantly, this showed that a subset of these children began associating letters with colours at around 5 years of age – just when they were beginning their formal schooling.
Simner says doing so seems to help young children learn what they need to succeed in the first years of school: numbers, letters and other critical concepts. “Many cognitive scores in synaesthetes shift up by 2 or 3 per cent,” says Simner. “They aren’t all geniuses, but they have stronger abilities in the production and comprehension of vocabulary. They tend to test slightly higher in creativity, too.”
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| Sharmelan Murugiah |
This might be because associating letters with colours has benefits when recalling information, says Root, who is based at the University of Amsterdam in the Netherlands. There are, after all, multiple pathways to the same stored memory. “If I’m trying to remember the name of someone – let’s say her name is Brittney – I might remember her name is brown, and my B is brown, so I know her name must start with B,” he says.
Rare trait
All of which raises an obvious question: if synaesthesia is so useful for learning new information during childhood, why don’t all children make these connections? Simner’s research suggests that just 1 in 23 people consciously experience some sort of synaesthetic sensory overlap. Given the evidence that synaesthesia often runs in families, it seems likely that this rarity is at least partly down to genetics. The nature of that genetic component is probably complex. One possibility is that it may, in at least some cases, involve the neural pruning that occurs as we grow and learn during early childhood. This pruning eliminates certain neural connections in the brain that are underused, which is thought to improve efficiency. If some people with synaesthesia undergo slightly less pruning, they may be capable of more cross-talk between brain regions – such as those related to different senses. This may make it easier to forge the cross-sensory associations characteristic of synaesthesia.
Robert Wiley at the University of North Carolina Greensboro, who researches learning but not synaesthesia, thinks the idea is more than plausible. “So much of learning is based on association,” he says. “We know from neuroimaging studies of children before and after they learn to read and write that the acquisition of these skills dramatically changes the brain and what kind of connections are forming there.”
The research by Simner and her colleagues suggests that individuals make synaesthetic associations spontaneously. This explains why they can vary from person to person. For instance, while one individual with synaesthesia may learn that the letter H is orange, another may learn that it is blue.
But that isn’t quite the whole story. Despite this variation, we have known for a few decades that people with letter-colour synaesthesia often agree on the colour of a few letters. Some researchers now think this offers an insight into the workings of the human mind.
Take Mankin, who is based at the University of Sussex, UK. The letter J comes to her as a vibrant shade of pink. Root’s research suggests why. In many higher-income countries, cultural stereotypes tend to encourage young girls to view pink as their favourite colour. It is also common for young children learning the alphabet to recognise the first letter of their first name before most other letters and to use that letter as a way to distinguish their name from others. Root and his colleagues wondered whether this would prompt girls with synaesthesia to associate this letter with pink.
When they tested women with synaesthesia, they found evidence in support of this: English-speaking women with synaesthesia were 4.4 times more likely to perceive the first letter of their first name as pink than they were to perceive other letters as pink. This association, learned in early childhood, is so strong that it remains in place even in those who have long outgrown their pink phase and have a different favourite colour as adults.
“These associations may seem random, but they’re really not,” says Root. For instance, people with synaesthesia who learned the Latin alphabet at school are particularly likely to view its first letter, A, as red. Root thinks he knows why. “It’s one of the first things you learn, so it has this really salient colour,” he says. In the Korean alphabet, the first letter is (pronounced “g” or “k” depending on the context). Root’s work shows that, for people with synaesthesia who learn the Korean alphabet at school, it is this letter that is usually perceived as red. “We’ve now looked at about 20 [writing systems] and, in all of them, the first letter tends to be red,” he says.
“There is definitely a linguistic effect,” says Simner, whose research has also explored the links between synaesthesia and language. “We also see that letters that are similar shapes are more likely to be similar colours.”
Taking an international perspective also reveals how people with synaesthesia latch on to different linguistic properties, depending on the language or writing system they are learning. For example, in the past decade, we have discovered that people with synaesthesia who learned to read Japanese at school often associate similar colours with characters that make similar sounds. An example in English would be to associate the letters C and K with shades of the same colour. To be clear, though, people with synaesthesia who learned to read English at school don’t usually do this.
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| Sharmelan Murugiah |
This may reflect key differences between these writing systems: characters in Japanese tend to have a single pronunciation, whereas alphabetic letters in English may have several (such as the “o” in go, to and ow). As young children with synaesthesia learn to recognise the features of the writing system that will help them learn, they use their synaesthetic skills to make these features easier to memorise. “When you study thousands of synaesthetes, you start to see a bunch of interesting little rules that govern why they develop the associations they do,” says Simner.
All of this evidence that letter-colour synaesthesia plays a role in learning may leave people without it feeling left out. But we have known for 20 years that many people do, in fact, associate letters with colours when pressed to do so (see “Teaching synaesthesia”, below). Some of Root’s latest work suggests they do so in a way that is difficult to distinguish from people with synaesthesia.
In yet-to-be-published research, Root and his colleagues asked 51 English-speaking students in the US to associate letters with colours. None of the 51 thought of themselves as having synaesthesia – and none seemed to, based on tests. Nevertheless, for a subset of nine letters, the typical colour associations they gave matched those expected of someone with synaesthesia. For instance, they tended to associate A with red, B with blue, I with white and Z with black.
This isn’t a new finding. Researchers including Simner have made the same observation in the past. But some earlier studies suggested there were still important differences between people with and without synaesthesia. Specifically, we know that people with synaesthesia will consistently associate a given letter with a particular colour when tested multiple times. People without synaesthesia are far more inconsistent.
In their latest work, Root and his colleagues took a closer look at this consistency. They suspected that, although people without synaesthesia appear inconsistent in their letter-colour associations across the full alphabet, they might be consistent for the subset of nine letters. It turned out that they were: 31 per cent of the time, someone without synaesthesia would consistently associate these letters with the same colours.
Confidence is another important feature of letter-colour synaesthesia. When asked, someone with the trait will typically say they are certain that a particular letter is a particular colour. But, again, Root and his colleagues found that this certainty isn’t unique to people with synaesthesia: many of the students in their experiment also claimed to be confident about at least some of their letter-colour choices. In fact, 41 per cent of the students were both consistent and confident in the letter-colour association for at least one of the nine letters. Given that none of these students claimed to have synaesthesia, Root thinks this finding has implications for the way we define it.
“What makes a synaesthete special isn’t that they think A is red or that they associate similar sounds with similar colours,” he says. “What makes a synaesthete special is that they are consciously aware of it.” This suggests, he says, that we can think of someone with synaesthesia as an “easier-to-study version of every one of us”. It also hints that synaesthesia research may be about to offer us a new perspective on the difference between conscious and unconscious awareness.
Mankin says there is a range of synaesthetic experience waiting to be studied. She thinks the patterns that will be discovered will help us better understand the nuances of language, learning and consciousness. “It gives us such unique insights into all these processing networks the brain uses to help us speak or think,” she says. “And it’s not just the synaesthetes that have these rich and complex networks. It’s all of us.”
Teaching synaesthesia
Given the cognitive benefits that letter-colour synaesthesia can confer (see main story), researchers have long wondered if those without it can be taught to consciously associate letters with colours. While most early attempts largely failed in this endeavour, in 2014, researchers at the University of Sussex, UK, reported success.
A team led by Nicolas Rothen, now at UniDistance Suisse, recruited 33 university students to undergo 30 minutes of training five days a week for nine weeks. The training tasks were designed to reinforce 13 specific letter-colour pairings – and they worked. Afterwards, the students passed several tests designed to identify people with synaesthesia. “It shows us that visual perception is quite plastic,” says Rothen. “We can change how people perceive the world.”
The researchers even demonstrated, using electroencephalography and transcranial magnetic stimulation, that training led to changes in the cortex, suggesting a “rewiring” in the brain’s perceptual pathways. Participants also showed improved performance in colour-related memory tasks.
Anil Seth, a neuroscientist at the University of Sussex who also worked on the research, says they were initially unsure if the training would work. The fact that it did suggests there may be ways to leverage synaesthetic associations in people without synaesthesia to improve memory – which could be particularly useful for older adults who want to keep their memories from degrading over time.
“This challenges the idea that once you reach adulthood, it’s all downhill, cognitively speaking,” says Seth. “You can change someone’s perceptual experience and help them learn to see the world differently – and that could help us pick up new habits that can improve our cognition at any age.”
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