For some people, colour is much more than simple visual stimulation. As Chris Giles reports, a few have related their experiences to Monash researchers in one of Australia's first indepth studies of synaesthesia.
Imagine being unable to sit in your friend's lounge room because the dark red curtains set off a high-pitched sound that gives you a headache. Or squabbling with siblings over whether the word 'Tuesday' is blue or green and whether it smells like a bushfire or rotting fruit.
While to many this might sound too bizarre for words, there is a small percentage of the world's population for whom such sensations are a normal part of everyday life.
Monash University research indicates that about one in every 2000 Australian women and one in every 12,600 men experience the unusual state of synaesthesia -- a mixing of the senses which causes people to vividly see or associate colours with words, numbers or music or, less commonly, with smells or tastes.
A surprising number are creative, struggle with maths and directions, experience feelings of deja vu, coincidence or the paranormal, or share the sensation with other family members.
It's a phenomenon that has been written about for centuries, but only in recent years has there been a surge in research in Australia, the US and the UK.
A national newspaper article last year, mentioning an Australian-first study by Monash University's neuropsychology unit, generated more than 200 responses from across the nation. Of these, 15 Melbourne metropolitan synaesthetes who experience colours for letters and numbers -- including the state's only two male respondents -- have participated in a series of controlled visual computer tests at the Clayton campus.
"I'm lousy at maths because you can't divide or multiply colours!" (Letter to Monash Department of Psychology)
Headed by the university's Synaesthesia Research Group, including honours student Ms Anina Rich and supervisors Professor John Bradshaw and Dr Jason Mattingley, the study is designed to reveal more about synaesthetes' brain functioning and how the ability might interfere with, or enhance, decision-making processes.
Aside from confirming that synaesthesia is a fast, involuntary and automatic sensation, the study has found that the ways people experience it are as varied and baffling as the mysteries of the mind itself.
"Synaesthetes do not agree. They disagree vehemently about what the experience is for them, so perhaps something has happened at some point for them."
Ms Rich says respondents recall always having the ability, but many never considered it unusual. "There are two distinct groups: one who never knew they were unusual because perception is subjective -- I can never verify that what I see is the same as what you see," she says.
"The other group mentioned it to someone when they were young and were ridiculed, or had never met anyone who had the same sort of phenomena. They were relieved to learn of others like them."
While the cause is still controversial, Professor Bradshaw says one theory is that the process used by the brain to 'bind' information and categorise objects differs in synaesthetes.
"It may be that synaesthesia is an abnormal form of binding and that these people have retained more brain connections than most.
"In early childhood, we start off with a huge number of connections and we lose those that aren't useful or wanted. My suggestion is that with synaesthetes, certain brain connections that are present in everybody in childhood may be preserved beyond their use-by dates."
Most people would probably associate the month of January with hot weather or the start of the year, but for Ms Barbara Livett, it evokes a sense of "deep slatey-purple". To think of the word alone, without its meaning, it is a "pinky-jay colour".
The former secondary school teacher used to file her work in coloured folders, depending on which ones she associated with each subject -- pink for maths, green for physics and blue for chemistry. She has no need for gift tags, instead wrapping Christmas presents in coloured paper that best 'matches' the name of the recipient.
"Sounds are not as brightly coloured," Ms Livett says.
Describing her synaesthesia as a "vivid but pleasant sensation", Ms Livett says it even extends to sounds.
"Sounds are not as brightly coloured but tend to be more greys and browns and there is a little bit of texture associated with them, too. For example, a flute is a sort of cloudy, misty sound, but an upper register clarinet is a bit more metallic -- like welding sparks.
The South Blackburn woman, who is among 15 people involved in synaesthesia testing at Monash University, says she thought everyone 'saw' colours for letters, numbers and words until she read a magazine article several years ago.
"I had no idea that it was anything unusual or particularly interesting," she says. "It was a bit of a thrill to realise that people wanted to research it."
She is typical of many who responded to the call for study participants, although others expressed great relief about discovering that they were not "weird" after all.
A mature-age PhD neuroscience student, Ms Livett wonders whether her life-long love of colours and intrigue with patterns encouraged the unusual ability.
"From a very young age, I used to analyse patterns in the curtains and the relationship between them to see if there was some kind of algorithm how they were organised. I also liked sorting things, like lollies and toys, and arranging them in colour gradients."
- Chris Giles