Hair today, gone tomorrow

Scientists have come up with a bona fide excuse for failing to notice your partner’s new hairdo. “Hair blindness” affects some people in the same way that others have trouble recognising faces.

Brad Duchaine, a cognitive neuroscientist who works extensively with people affected by face blindness, or prosopagnosia, noticed that his subjects use hair to recognise people.

His research, published in New Scientist, investigated whether the brain processes hairstyles distinctly from other facial features.

People who have no trouble identifying faces often struggle to recognise upside down faces, although they recognise other objects equally well, whether inverted or not. This “inversion effect” indicates that humans process faces differently to other objects.

Duchaine’s experiment involved cropping everything but hair from a set of faces and asking volunteers to memorise the hairstyles. The volunteers were then asked to pick out familiar hairstyles among hair they have never seen.

Their performance dropped by 15–18 per cent on inverted hairstyles, while the difference with faces can be as high as 25 per cent. This suggests that the brain pays close attention to hair, but does not necessarily see hair as a facial feature, as it does eyes and noses.

Until recently prosopagnosia was thought to be rare and solely associated with brain injury or neurological illness. But some evidence suggests a there is also a highly variable form of congenital prosopagnosia which could affect around 2 per cent of the population.

It has been suggested that up to 10 per cent of the population are affected by mild face blindness.