People who experience unusual sensory combinations might provide new insights into how our minds work.

Vladimir Nabokov had it. So did Oliver Messiaen and Richard P Feynman. What could a Russian author, a French composer and an American physicist have in common, apart from a celebrated flair for their chosen vocations? All three experienced the psychological condition known as synaesthesia, where a person experiences unusual sensory combinations.

Feynman and Nabokov perceived certain letters and numbers as distinct colours. For the physicist, this meant that algebra took on a kaleidoscopic effect: the letter ‘j’ became tan, while ‘n’ took on a violet hue, and ‘x’ appeared dark brown. Nabokov’s alphabet was similarly colourful, but it’s possible that his condition took the associations a step further and certain words would evoke visual images such as a fork lying in the sun. For Messiaen, the colour associations were linked to sound. Music prompted vivid colour perceptions, which he was sometimes considerate enough to mark down on his scores for the advice of other musicians. 

These letter-colour and sound-colour forms are just some of the many sensory combinations that have been attributed to synaesthesia. Some synaesthetes have reported sound-taste combinations where, for example, hearing the word ‘prison’ could conjure up the taste of greasy bacon. Others have described a visual-taste effect where shapes have flavours: a strawberry circle or an almond square.

Dr Kristen Pammer from the School of Psychology at ANU has a “golden-brown coloured voice”. This was the estimation of a colour-sound synaesthete who graciously agreed to be part of her enquiry into synaesthesia. Pammer, a psychologist with a passion for unlocking the workings of the brain, believes that one of the best ways to find out how something functions is to look at those instances where it malfunctions. She is drawn to synaesthesia in part because it’s a case of a malfunction resulting from something other than deficiency.

“One of the interesting things about synaesthesia is that it’s the presence of something, rather than the absence of it,” Pammer says. “Most of our understanding of the brain is about people losing something – an inability to read, an inability to do something. Synaesthesia is an excess or an addition of something, which can be very informative.”

By finding out more about the synaesthetic experience, Pammer hopes to learn more about how the brain functions for the majority of people.

Looking back, looking forward

In his essay Concerning Human Understanding, composed around the late 17th century, John Locke wrote of a blind man who perceived the colour scarlet as the sound of a trumpet. Some scholars suggest this was a reference to Professor Nicholas Saunderson, a contemporary of Locke’s who enjoyed a distinguished career in Mathematics at Cambridge after losing his vision as a young man. It’s unclear if Locke was writing literally or metaphorically here, and it’s debated as to whether or not this was one of the earliest references to synaesthesia in modern scientific literature. Other such potential hints and veiled references abound up until the 19th century, when synaesthesia became a topic for the fledgling field of psychology. It was even afforded its own international conferences in the early 20th century, but fell out favour as a field of study in the middle of that century in part due to the rise of behaviourism, which focussed on externalities. But as increasing numbers of scientists have returned to cognition
and consciousness studies, synaesthesia has grown to become one of the hot topics in the field of psychology.

“People did start to look at it because it’s not just an interesting phenomenon, but something that can inform our understanding of attentional processes, brain behaviour, sensory processing and so forth,” Pammer says.

As the field of research blossomed, so too did the difficulties of estimating how many people are effected by synaesthesia. Pammer has heard figures ranging from one in 20,000 up to one in 1,000, and even a suggestion that as many as one person in every 200 may have the condition. But what is clear is that as public awareness about synaesthesia grows, so to do the number of people who are realising that the way they perceive the world may be quite different from the norm.

“The reasons for the low number of reported incidences are because it is not something that people would think was abnormal,” Pammer conjectures. “The classic statement we hear is, ‘I didn’t realise I was synaesthetic’.”

“It would be like somebody saying to you that you seeing red is not what everybody else sees. But how can everybody not see red? Once somebody challenges your own sensory experiences, it really becomes unsettling.

“Our sensory experiences form the absolute core of who we are. They inform everything we can feel, taste, smell, hear and see. To realise that we don’t share the same sensory experiences challenges people.”

Many shapes and forms

As the cases of Nabokov, Feynman and Messiaen demonstrate, synaesthesia can encompass a wide variety of sensory combinations. Grapheme-colour synaesthesia, the involuntary association of colours to letters and/or numbers, is one of the most commonly reported forms. Sound-colour, as experienced by our French composer, is also relatively common. To deal with this diversity, scientists have developed a range of categories that divide the synaesthetic experience based on various combinations.

But Pammer says these boundaries can be problematic. “The more I read, the more I believe those groupings aren’t informative. When you look at sound-colour synaesthetes, such broad categories start to become murky.”

In some sound-colour cases, the evoked or perceived sense is dependent on semantic context. Some synaesthetes experience particular colours on hearing certain words – ‘blossom’ is pink, while ‘submarine’ is blue. For others, like Messiaen, it’s the tone and pitch that trigger the secondary sense. Thus Pammer argues that the sound-colour category requires further differentiation to accommodate examples like the colour-word and tone-colour split.

“Somebody responds that high C is a particular colour, while someone else responds that the word ‘wink’ is a particular colour. These are two completely different things as far as I’m concerned, even though they’re classed as sound-colour synaesthesia. One has a contextual component to it and the other doesn’t. The broad categories can be somewhat misleading.”

Pammer also suggests that the existence of contextually triggered synaesthesia suggests that there is something more than sensory duplication taking place.

“Where it’s been argued by some people that synaesthesia is a purely sensory phenomenon, I would argue on the basis of that evidence alone that it can’t be, because the individual has to know what the symbol is before it has a colour component.”

The diversity of experiences caught under the synaesthesia umbrella extend to how the condition manifests itself, too. For some grapheme-colour synaesthetes, the letters and numbers literally appear to be a certain colour. For others, a colour sensation is consistently triggered inside the head. 

Window to the brain

In order to see how the brain functions during a synaesthetic experience, Pammer needed to be able peer through the hair, scalp and skull to see exactly what the brain was doing. Enter magnetoencephalography, or MEG, which is a clever technology that creates real-time imaging of electrical activity inside the brain.

“One of my subjects is a tone-colour synaesthete. I’m interested in what his brain is doing when he hears a sound and ‘sees’ a colour. Preliminary evidence suggests that when he hears a tone, the colour parts of his brain light up where normal brains don’t. I’ve been looking at the timing involved. Does he need attention for the synaesthesia to occur, which would suggest it’s a cortical higher level process, or is it something that happens spontaneously in the absence of attention?

“One of the defining symptoms of synaesthesia is that it’s spontaneous – the synaesthete doesn’t have to think about it – but that’s a slightly different thing from what I mean. If there is no attention directed to the stimulus, is colour still experienced as far as the brain is concerned?

“This research should tell us if it’s a process caused by stimulus – a bottom-up process – or if it’s a top-down process influenced by context and cognitive processing.

Pammer is also interested in the ‘binding problem’, or how our brains combine sensory input to arrive at understanding of the world.

“In order for you to look in one spot and identify something, you’ve got to be able to identify variables like shape, colour, and movement – all those components are processed in completely different parts of the brain. We combine all that information within 200 milliseconds. We don’t know how the brain is doing it.

“One argument is that different parts of the brain are firing at different frequencies. The cells in one part of the brain are firing at a particular frequency band, 10HZ for example, while another part of the brain is firing at 10HZ. Can we assume that they’re communicating? I’m interested to see if the synaesthetic experience is different in its frequency dynamics to the normal experience.”

As Pammer’s case indicates, science possesses far more questions than answers about synaesthesia at present. It’s still not clear what causes the condition, if it is something hereditary or acquired, or even if it can be consistently simulated. But as well as increasing our understanding of brain function, Pammer hopes that her research could yield clinical benefits in the longer term, helping to ‘switch on’ parts of the brain that may be damaged or dormant. If this is the case, a rare condition that scrambles sensory combinations could ultimately enrich the lives of more than just synaesthetes.

• Dr Kristen Pammer is always keen to hear from people who’ve had synaesthetic experiences. 
Email: Kristen.pammer@anu.edu.edu

• Research for this article included a number of entries from Wikipedia (www.wikipedia.com).
 

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ANU Reporter 
Summer 2007