Shapes, colours, forms: it's harmless

Patients who report tastes as shapes or music as colour are not mentally ill, a US expert says, but part of the minority of the population with synaesthesia. At least 1% of the population has the harmless neurological condition, where "stimulation of one sense triggers anomalous perceptual experiences", wrote Assistant Professor David Eagleman in the BMJ (online). "Synaesthesia is a fusion of different sensory perceptions: the feel of sandpaper might evoke an F sharp, a symphony might be experienced in blues and golds, or the concept of February might be experienced above the right shoulder," he wrote. The condition was thought to occur when normally separated areas of the brain became connected, said Professor Eagleman, of the department of neuroscience, Baylor College, Texas. "Whether this cross-talk results from increased physical connectivity between areas or a slight imbalance of inhibition and excitation, is unknown," he wrote. "Interestingly, synaesthesia clusters in families, and the patterns of inheritance suggest the possibility of a single dominant gene." There are many different varieties of the condition, and experiencing letters and numbers as colours or textures is one of the most prevalent. "Another very common form is spatial-sequence synaesthesia, in which a person perceives sequences … as having a spatial three- dimensional form," Professor Eagleman wrote. "For example, someone with this form of the condition may say that Monday is to the front of them to the right, next to that is Tuesday, and so on." He urged doctors not to mistake this phenomenon for "a peculiar type of cognitive fragmentation"....