Synaesthesia is well studied in adults and is thought to be a result of unusual connections created during brain development, but it has been hardly studied in children – until now.
A new study published online in Brain searched for letter-colour synaesthetes in 6-8 year old children and found not only are they relatively common, but that the condition changes as the children grow.
Synaesthesia is where the senses are crossed, so perceiving something in one sense triggers a perception in one of the other senses. The type targeted by this study was letter-colour synaesthesia where people perceive colours when they see certain letters.
Synaesthesia is known to be partly inherited and there is brain imaging evidence that people with the letter-colour type have greater number of white matter connections between brain areas known to be involved in word and colour perception.
A popular theory is that synaesthesia results from an unusual form of brain development where certain connections in the brain are not ‘cut’ or ‘pruned’ during the early months of life.
However, letter-colour synaesthesia requires that the person can read and understand letters, which usually doesn’t happen until much latter, so it is likely that there is something going on throughout the critical learning period when children begin to learn to read.
This new study, led by psychologist Julia Simner, tested over six hundred six to seven year-old children with a computerised test that showed them letters and numbers and asked them to select a colour which best fitted the character on screen.
After 10 seconds, the test was repeated. One of the hallmarks of people with letter-colour synaesthesia is that their associations remain constant, so this helped pick out who was the most consistent.
Children who did better than average on this were tested again with a surprise test at 12 months, and those who were more consistent at 12 months than the average child at 10 seconds were classified as having synaesthesia.
Using this, admittedly strict, criteria 1.3% of children had letter-colour synaesthesia and the total number of children with any form of synaesthesia is likely to be greater owing to the fact that the researchers only tested one for one type.
The study also allowed the researchers to see how synaesthesia had developed over the year. Interestingly, the synaesthetic children showed an average of 10.5 stable letter-colour associations aged 6-7 years, but 16.9 aged 7-8, suggesting that the condition is developing and growing over time.
Although not able to confirm it statistically, the study hinted that some people may actually lose synaesthesia over time.
The researchers note that in anecdotal reports adults have described synaesthesia in childhood that died out, while the reverse pattern – synaesthesia spontaneously appearing in adulthood that didn’t exist in childhood, is not reported. A further hint is that in the study, the number of children who had synaesthesia at ages six and seven outnumbered those who had it at ages seven and eight by 2.5 to 1.