W.J. was a 51 years old man who became a shepherd after suffering several strokes. He had a peculiar ability: he could recognize and distinguish each one of his sheep; however, he could not recognise any of his family members, and most generally, he could not distinguish human faces.
Dr. P. was a music teacher. He couldn’t recognise his student by their faces, unless they spoke to him. Not only he failed to see faces, but he saw faces where there were none to see; for example he often mistook fire hydrants for children.
Can you imagine to wake up one morning and not be able to recognise the people around you, even those who are closely related to you? Yeah, it seems like the plot of a movie, however this is what people with prosopagnosia experience every day. Glenn Alperin, blogger for Psychology today uses a metaphor in his personal website (http://home.earthlink.net/~blankface/prosopagnosia.shtml) to describe this condition that afflicts him: “Imagine that every person has a camera inside their head. Every time they meet somebody for the first time, they take a picture with their camera, develop the picture, and file it away for future use. …For me, I take a picture with my camera, but I never store it away.”
Prosopagnosia, also known as face blindness, it’s the inability to recognize faces. Originally it was thought that this disorder was due to damage of certain brain areas as a consequence, for example, of a stroke. Now it is known that, although true in most cases, this is not always the case, and about 2% of the population suffer from congenital prosopagnosia.
The brain regions involved in this condition are the parts of the occipital and temporal lobes involved in perception and memory, and specifically a region of the temporal lobe called fusiform gyrus.
The importance of this region for facial recognition has led to it being commonly known as the fusiform face area (FFA). There is a fusiform gyrus in both sides of the brain, but the one in the right hemisphere is what is usually associated with face processing.
There is evidence suggesting that fusiform gyrus damage tends to bring about difficulties in face perception and recognition, whilst damage to other areas of the temporal lobes is associated with difficulties accessing memories of faces. It has therefore been suggested that there are two subtypes of prosopagnosia, one affecting the way we perceive faces (apperceptive prosopagnosia), and the other affecting our memory for faces (associative prosopagnosia).
Congenital prosopagnosia, instead, manifest itself from early childhood, and is not associated to any specific brain damage. People with congenital prosopagnosia seem to fail to develop the visual mechanisms necessary for successful face recognition. There have been reports of families in which multiple members have the condition, suggesting a genetic link in some cases; this hypothesis has been also confirmed by studies of identical and non-identical twins.
So what goes wrong in the perception of faces by people with prosopagnosia? Do they perceive them normally? The answer to this question is yes, they don’t see faces in a distorted manner. However, they find it very difficult to use the visual information to recognise familiar faces.
Moreover, the process they use to analyse faces is different from the one used by other people. Research suggests that faces are processed in a unique way, differently to other types of objects. People with normal face recognition abilities appear to process faces ‘holistically’. This means that the face is processed as a whole, taking account of the relationship between features rather than focusing on the features themselves. Rather than processing faces as a whole, individuals with prosopagnosia seem to adopt a feature-by-feature strategy, in which faces are processed in a piecemeal manner and each feature is looked at in turn. Not only does this make face recognition a longer and more difficult process, but it also ignores the spatial relations between features – information that is critical for successful recognition.
Do you want to test your ability to recognise faces? Take this simple test: http://www.cbsnews.com/videos/do-you-have-trouble-recognizing-faces-take-a-test/
If you are interested to read about stories of patients suffering of prosopagnosia and other neuropsychological disorders, read this book: Oliver Sacks “The man who mistook his wife for a hat”.