How minds play tricks with words and colours
New Scientist, 21 August 2004
a condition in which people make weird sensory associations, may rely
more on the plasticity of the brain than on any genetic predisposition.
This might mean that all of us are capable of having a synaesthetic
People with synaesthesia often say that letters,
words and numbers have innate colours. Even when tested years later,
their associations remain consistent. But no one really knows why or
how these odd associations form.
In 1996, Simon Baron-Cohen and
his team at the University of Cambridge estimated that about 1 in every
2000 people had the condition and that it was likely to be a genetic
trait encoded on the X chromosome (Perception, vol 25, p 1073). But now
a study of blind and blindfolded people by Megan Steven and colleagues
at the University of Oxford suggests that while genes almost certainly
play a role, it may be a minor one.
Steven and her team
recruited six "late-blind" subjects, all of whom were synaesthetes
before losing their sight. For three of them, their synaesthesia
changed after they became blind. One man, JF, for instance, had always
thought of days and months as having colours. Instruments in an
orchestra and even his pay scale at work were also colour-coded in his
mind. After learning Braille, he began experiencing colours when he
touched the raised Braille characters denoting letters, numbers or
musical notes - or even when he simply thought about touching them.
of Braille, instruments and remuneration are all learned, Steven points
out, so people such as JF must be adapting their pre-existing
synaesthesia to incorporate them. But that still leaves a big question:
can all brains adapt to make these unusual associations, with the
ability only being unmasked in a select few people? Or are the
associations themselves rare?
Evidence from a blindfolding
experiment hints that the associations might be universal. For
instance, DB, who was not known to be synaesthetic, was blindfolded for
five consecutive days, and saw very vividly a frightening face whenever
he listened to a specific passage of Mozart's Requiem. It only happened
while he was deprived of vision. Though this mental association was not
genuine synaesthesia, it did have many of the hallmarks of the
condition, the researchers claim. It could be reproduced, was
consistent and was triggered by something specific.
suggests that even non-synaesthetes may have the neural machinery for
generating a synaesthetic experience and that changes to the brain
might expose them, they say in a forthcoming issue of Perception. "It
can't be entirely genetic," Steven says. She speculates that in
non-synaesthetes, the input of visual signals may be inhibiting tactile
and auditory inputs to the "visual" areas. "When there's no more visual
stimulation, maybe other connections become more important," she says.
agrees that genes and environments are likely to interact in shaping
synaesthesia. But he questions whether atypical cases like these can
teach us much about more common varieties. His main work is in autism
and he points out that up to 40 per cent of congenitally blind children
show autistic behaviours in early childhood, such as persistent
rocking. But blind kids tend to grow out of such rocking behaviour,
while those with true autism don't. "We should be wary of assuming
phenomena that resemble synaesthesia - such as coloured hallucinations
in a subject blindfolded for five days - involve the same brain
mechanisms that give rise to 'naturally occurring' synaesthesia."