Can the face-blind distinguish attractive and unattractive faces?
The human visual system is one of the more complex set of structures in the brain. Different neurons each represent tiny parts of the visual world that add together to make a full image, like pixels in a digital photograph. There are separate regions for discerning an object’s colour or motion, or whether it’s part of a larger object or part of the background. Deeper parts of the system respond to more complex properties, and there are even regions that respond specifically to faces.
Much of our understanding of brain function comes from studying the behaviour and abilities of people who have suffered brain injury. If a particular part of the brain is damaged, and a person can no longer perform a specific task, we can be pretty confident that the damaged region is implicated in that task.
One such condition is prosopagnosia, also known as face blindness. It’s caused by damage to the fusiform gyrus, which is at the back of the brain, just inside where the neck meets the skull. People who have this condition find it difficult to recognise faces, but have no difficulty recognising other objects. While unaffected people recognise faces very quickly, people with prosopagnosia have to rely on other features, like the sound of a voice or body shape. And this means that people with prosopagnosia can help us to understand more about how the visual system works.
For example, it’s been suggested by some researchers that when we see faces, we process socially relevant information separately from information used to recognise a person. Socially relevant information would include a person’s attractiveness, which arguably has little to do with how recognisable they are. On the other hand, we might use information on how distinctive a face is, how far it is from the average face, to help us recognise who it belongs to. After all, caricatures, images that exaggerate the way in which a person’s face differs from most other people, are often more easy to recognise than unaltered photographs.
To test whether these two properties — the social and the distinctive — really are processed separately, Claus-Christian Carbon of the University of Bamberg in Germany recruited 14 people with congenital face blindness. He also recruited two control groups of unaffected individuals, to compare with the face blind participants. All participants were shown photographs of 22 female faces, and asked to rate the faces for how attractive they were, and also for how easily each face would stand out from a crowd.
Carbon found that attractiveness ratings didn’t differ between the groups. Face blind and unaffected participants found the faces similarly attractive. However, the participants with prosopagnosia found the faces much less distinctive than the unaffected participants. People with face blindness didn’t think any of the faces really stood out.
This finding confirms that we do indeed process social information separately from information used in recognition, and that this divergence occurs early on during perception.
Carbon, C. C., Gruter, T., Gruter, M., Weber, J. E., & Lueschow, A. (2010). Dissociation of facial attractiveness and distinctiveness processing in congenital prosopagnosia. Visual Cognition, 18(5), 641–654. Read summary