Developing the mysterious condition in the 96% of people who do not have it may help to improve learning skills, aid recovery from brain injury and guard against mental decline in old age.
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| Illustration by Jamie Cullen |
Sitting in a small, computer-lined room trying to remember a succession of different-coloured words scrolling past on a screen doesn't sound like the cutting edge of scientific research. However, academics at the University of East London are using word tests to assess the impact synaesthesia can have on memory – and the potential it might have to ward off the decline in cognitive function that can affect the elderly.
Synaesthesia, the neurological condition that causes a blending of the senses – colours can be connected to letters and numbers, smells and tastes to music or touch to vision – has long been linked to creativity: famous synaesthetes include Sibelius and more recently Pharrell Williams and Lady Gaga.
But among the wider population it has remained a mysterious condition, although it is known to affect at least 4.4% of adults across its many forms.
For instance, a grapheme-colour synaesthete might "see" the days of the week, letters and numbers as particular colours; a lexical-gustatory synaesthete will experience a particular taste in their mouth when they hear a given word; and an odour-visual/spatial synaesthete will see shapes, movement and colours when they detect certain smells.
While scientists have known about synaesthesia for 200 years, only recently have researchers – across the fields of psychology, neuroscience and psycholinguistics – been able to focus their attentions on what effect the condition has on synaesthetes' broader cognitive function and, crucially, what synaesthesia may be able to do for the non-synaesthete population.
"There's definitely been a shift in the time I've been a synaesthesia researcher," says Dr Julia Simner, co-editor of The Oxford Handbook of Synesthesia, who runs the synaesthesia and sensory integration laboratory at the University of Edinburgh.
Her team has recently been awarded a €1.3m grant by the European Research Council to develop the first test to identify the condition in children.
And, in parallel, Simner and her team are working with researchers at the Max Planck Institute for Psycholinguistics in Nijmegen in the Netherlands on a study to try to identify the genes implicated in synaesthesia, which often runs in families.
"Before when I gave talks about synaesthesia, 96% of the audience would not believe it and the others – the synaesthetes – would think it was just obvious. Now it's shifted away from the burden of proof and we are free to explore the questions scientists really want to ask," Simner says, noting that advances in brain imaging had provided better evidence of the existence of synaesthesia.
"One of the streams of the latest research is to look at how synaesthesia affects development in a child. How much of your cognitive profile, what you're good at and what you're not good at, is affected by synaesthesia? We are looking for benefits and deficits as well as whether we can use multisensory effects to help learning in the average child," she says.
Dr Michael Banissy, senior lecturer in psychology at Goldsmiths, University of London, agrees that understanding how the condition develops in children will be a focus of future research and key to a broader comprehension of synaesthesia. "The focus previously has been on the synaesthetic experience alone but now there is interest in asking if more is going on beyond the synaesthesia."
Dr Nicolas Rothen, who is carrying out research into synaesthesia and memory at the University of Sussex, agrees attitudes towards synaesthesia have changed. "Ten to 15 years ago, researchers were mostly concerned with showing that synaesthesia was real and not just metaphorical thinking. Now it is basically accepted that synaesthetes perceive the world differently and we are asking how it relates to other cognitive functions," he says.
That may lead to interesting findings about cognitive function that can be applied to the general population. "People are different," says Rothen, "and we need to consider those individual differences. Synaesthesia is a neat way to study differences in perception and their relation to higher cognitive functions such as memory and language processing."
But while scientists are interested in the differences between the brains of synaesthetes and non-synaesthetes, research is also being carried out into how the two can be brought closer together.
"One thing we have found is that synaesthetes are not a different class of people – they simply have more explicit experiences," Simner says. "It's a more extreme manifestation of what all of us experience. Asking non-synaesthetes, 'What colour is A?' is a baffling question, but synaesthetes have a window into perception we all share; when pressed for an answer, we all pair more common letters with brighter colours or higher pitched notes with lighter colours."
Studies such as one carried out by Dr Clare Jonas at the University of East London aim to take that link between synaesthetes and non-synaesthetes one step further, by training non-synaesthetes to have the same associations that synaesthetes have – and then assessing the impact their newly acquired synaesthesia has on their memory and cognitive function.
That's where the word test comes in. After training a small group of young adults to associate certain letters with certain colours, the researchers use the test to find out if they remember words more easily if they are coloured to match their synaesthetic training.
So far, the results seem to suggest that they do. The researchers assessed participants' memory before and after the synaesthesia training, by getting them to look at a list of words in which there was an odd one out – either a word written in the colour they had been taught to associate with it or a word whose meaning did not fit in with the rest of the list.
"Using predictions based on what real synaesthetes do, there seemed to be a tendency towards the trained synaesthetes starting to behave like synaesthetes – having a better memory for things involved in their synaesthesia; if confirmed, that would be a good sign," Jonas says.
Synaesthetes tend to remember the stand-out word more easily if it is in the correct colour, while they perform worse on tests in which words stand out because of their meaning – a list containing the words colander, whisk, spatula and ballet, for example.
Researchers find that interesting in itself because going beyond the surface to the meaning of the word is normally the key to improving performance in these kinds of memory games.
Although the research is at an early stage, Jonas believes training synaesthesia could have implications for helping older people ward off the decline in cognitive function that accompanies the early stages of Alzheimer's or even for helping patients recover from brain injuries."One possibility," says Jonas, "is guarding against cognitive decline in older people – using synaesthesia in the creation of mnemonics to remember things such as shopping lists. As long as there is sufficient cognitive ability people could perhaps start doing the training in their 50s as a way of topping up their memory skills."
One obstacle for the moment is the dull and time-consuming memorising of letters and their matching colours that the training demands. But researchers in the Netherlands may have found a way round that, developing a browser plug-in that automatically colours certain letters as part of a wider study into whether synaesthesia could be learned.
Rothen, who has been carrying out studies involving training non-synaesthetes to behave like synaesthetes, also thinks synaesthesia research could have implications for the elderly, a potentially important breakthrough for an ageing population.
"People are only just beginning to study synaesthesia over the lifespan. There is a theory that it may be protective in the case of age-related cognitive decline. There is evidence that grapheme-colour synaesthesia in particular leads to enhanced memory functions and we wondered if non-synaesthetes could be trained to have the same associations as synaesthetes and if it would lead to the same enhancements."However, while the studies demonstrate that it is possible to train non-synaesthetes to make the automatic link experienced by synaesthetes – that C is yellow, for example – it is not yet clear whether the phenomenological experience, or the way synaesthetes will "see" either in their mind's eye or projected on to the page that C is yellow, can be induced.
"We know that synaesthesia comes with benefits and that certain aspects can be trained. What we don't know is which aspect of the synaesthesia leads to the advantage – the automatic association or the phenomenological experience," Rothen says.
But he adds: "We have some hints that synaesthesia leads to performance enhancements with regards to memory performance and visual mental imagery."
Banissy's particular area of focus is social neuroscience and he explains that research into mirror-touch synaesthesia, in which, for example, just seeing someone else's face being touched sparks the sensation in the synaesthete that their own face is being touched, could reveal interesting findings about what causes synaesthetic reactions, as well as possible ways to harness those for non-synaesthetes.
"Using brain imaging, we have shown that mirror-touch synaesthetes recruit similar parts of the brain as we all do when we observe others being touched," says Banissy. "However, mirror-touch synaesthetes hyper-activate this system to the extent that they literally experience what they see. In this regard, mirror-touch synaesthesia is interesting because it provides a unique window into how we represent other people's experience."
Banissy is interested in the way synaesthesia develops in the brain and in particular how so-called hyper-excitability in areas of the brain such as the somatosensory cortex could cause synaesthesia.
"In synaesthetes, the balance between excitability and inhibition is unusual. So the question is, can we generate synaesthesia in non-synaesthetes by manipulating that balance?"Scientists know that balance can be tipped by hypnosis or drugs: LSD, for example, produces a synaesthesia-like experience but more research is needed into other ways to change it.
"Using brain imaging, we can identify which areas are related to synaesthesia, but we can't tell what is causal. To do this, we need to modulate the relevant part of the brain and see what effect this has on generating synaesthetic experiences," Banissy says.
While the researchers are coming from different scientific backgrounds and investigating the condition from different angles, a common thread is exploring how synaesthetic techniques can be applied more broadly.
"Synaesthesia is obviously useful to synaesthetes in some ways," says Jonas. "It would be really nice if we could find a way to give the useful bits of synaesthesia to people who don't have it."
If you have colours for letters or numbers, and you are interested in taking part in the genetic test for synaesthesia, please email the Edinburgh synaesthesia lab at synaesthesia.research@ed.ac.uk
Uncommon sense: Types of synaesthesia
Grapheme-colour synaesthesia is one of the most common forms of synaesthesia. Grapheme-colour synaesthetes associate letters, numbers or words including days of the week or months with colours. On average, there are 2.2 grapheme-colour synaesthetes in each UK primary school, but many of them are not believed when they share their synaesthetic experiences.
Sequence-space synaesthesia is an umbrella term that describes the experience of perceiving ordinal sequences – letters, numbers, days, months – in a spatial arrangement. It sounds useful, but that internal spatial arrangement can hinder the synaesthete's mental arithmetic: numbers may be too closely packed to "see" properly.
Music-colour synaesthesia is a form of the condition in which different musical timbres or notes of the musical scale can spark colour perceptions. Higher pitched notes tend to be experienced as lighter colours.
Touch-colour synaesthesia is a form of synaesthesia in which tactile sensations against the skin trigger the perception of colours. The colour can be experienced as on the touched object or in the mind's eye.
Mirror-touch synaesthesia describes the variety of synaesthesia in which observing someone else being touched is felt as touch. A mirror-touch synaesthete will feel their own cheek being stroked if they see someone else's being stroked.
Lexical-gustatory synaesthesia entails experiencing specific tastes in response to certain words, which can be heard, read or thought. London might taste of strawberries to a lexical-gustatory synaesthete.
Sequence-personality synaesthesia describes the personification of everyday objects or sequences such as letters or numbers. In this form of synaesthesia, even speakers of languages that don't attribute genders to nouns may automatically think of certain words as masculine or feminine or even attribute personality traits to letters – B could be shy, for example.
