When your eyes scan a page of text do you see certain letters in colour? Can you taste colours or sounds? asks Dick Ahlstrom. If so, you might have an unusual condition in which sensory signals get mixed up to deliver a unique view of the world.
The term used to describe this is synaesthesia, and a multidisciplinary team of Irish researchers has begun a new study to determine how many people here have it. It runs in families and women are three times more likely to have it than men, according to Dr Kevin Mitchell of Trinity College Dublin who is heading the project.
As many as one in 2,000 people exhibit synaesthesia to varying degrees, says Mitchell, a lecturer in Trinity's Smurfit Institute of Genetics. "We want to see how common this is in the Irish population and see what the genetics of it is," he says.
Partners in the research include Dr Fiona Newell, a cognitive scientist in Trinity's department of psychology, Dr Aiden Corvin, of the department of genetics and Ciara Finucane, also of the department of psychology. Mitchell himself is a specialist in developmental neurobiology or neurogenetics. "We are interested in the genes that specify how the brain should wire up," he says.
The brain is a staggeringly complex organ and researchers are only beginning to understand how the brain's various circuits are connected. "The basic thing we are trying to understand here is how different parts of the brain link to different functions," says Mitchell. "During development those areas have to be all wired up correctly."
The normal wiring pattern goes somewhat awry for those with synaesthesia, he says. "It can best be described as a mixing of the senses." There might be an audible stimulation but the person hears as well as "sees" the sound.
"Most commonly the person experiences the perception of colour in response to a non-visual stimulus," he explains. Many synaesthetes also have extra colour perception when looking at plain black text.
"They will see particular letters of the alphabet or numbers in a particular colour. That colour will be particular to that individual," he says. "The number five might always be red, the number two might always be yellow. The question is how is this happening. It relates to how we integrate perceptual information from the various senses."
Sensory inputs from the eyes should only reach visual centres in the brain, but extra connections seem to exist that link say to hearing or colour or taste. "We think there is some cross-wiring happening. We are not sure why this happens."
Generally it is harmless, but if severe it can be very disturbing, with say a touch producing a cascade of sensory responses including smells, sounds and colours. "In some rarer cases it can be highly distracting," says Mitchell.
While there is some data suggesting synaesthetes have more difficulty with maths, it can assist learning. "Things are naturally colour-coded for them," he says. "It also seems to be more common among artists and composers," with Franz Liszt, Rimsky-Korsakov and Wassily Kandinsky all thought to be synaesthetes.
Although potentially quite common, few are aware of it. "One of the reasons some people haven't heard of it is if you report as a child you tasted colours or smelt sounds you would be corrected by parents or made fun of by other children," says Mitchell.
"We want to look at whether people have multiple forms of synaesthesia, and also whether a particular kind of synaesthesia runs in a family or if the family members have different forms."
It is three times as common in women, suggesting it might have something to do with the X chromosome. "Or maybe there is something different in the way the male and female brain is wired that makes women more susceptible to it," says Mitchell.
"We would like people to contact us and fill in a questionnaire that will give us some details of the kind of experiences they have had." People may then be asked if they would be willing to undertake simple visual tests in order to measure how strongly they experience synaesthesia.
The ultimate goal over time would be to do a genetic study of the genes associated with synaesthesia, given the permission of those involved, says Mitchell. Understanding how the brain sometimes miswires itself could lead to a better understanding of how more typical brain connections occur.