As was with many of the earlier parts of this series, we will start by describing a mental condition or disease. The reason is that mental illnesses give us a great insight into how the brain functions. When neurologists analyze mental illnesses they understand what parts of the brain are involved in different cognitive functions and how specialized different parts of the brain can be.
Today our topic of discussion is face recognition. Face recognition is very different from recognizing other objects. This fact is illustrated by the mental disorder named Prosopagnosia. The word Prosopagnosia comes to us from two Greek words: prosopon( face) and agnosia( not knowing). A person suffering from this disease is able to recognize objects and his intellectual abilities are normal however such a person has difficulty in recognizing faces. So from this we condition we understand that face recognition is a very specialized task and different from recognizing other objects around us.
Recognizing faces and understanding the emotional content of faces is extremely important for social behavior. A child as young as two days old looks at faces carefully and tries to mimic the expressions on others. However at that age he/she is not able to judge the emotional messages that are encoded in these expressions. By the age of 5-7 months a child is able to distinguish between expressions of fear, happiness and anger when he sees the faces of people around him/her.
Scientists have a way of finding out which part of the brain is used for which function. It is called fMRI or functional Magnetic Resonance Imaging . This method detects changes in blood flow to different areas of the brain to find out which area is responsible for what function. When a set of subjects were shown faces and cars scientists found that a certain area of the brain known as fusiform showed much higher levels of activity when the subjects viewed faces than when they viewed cars. This area is now known as fusiform brain area and we know that it specializes in recognition of faces. Recognition of other objects ( not faces) happens using a different mechanism and is not specialized.
So the fusiform brain area is very active when we see faces but not active when we see cars or say birds. But a group of scientists did another extremely interesting experiment. They took a group of people who were expert bird-watchers. When these people were shown different birds their fusiform brain areas showed a very high level of activity- similar to normal people viewing faces. So the theory is that when we see something that we are extremely interested in, or experts in, the fusiform brain area is triggered. So another way of looking at it is that we are all experts at and extremely interested in face recognition.
Now let’s discuss Prosopagnosia. If the fusiform face area is damaged the person loses the specialized ability to recognize faces. But he is able to recognize other objects like the rest of us. So a person with this condition recognizes faces the way we recognize other inanimate objects around us and therefore the person is not able to do it very well. Children with Prosopagnosia are extremely shy because they are not able to recognize people easily. So they tend to make friends with children with easily distinguishable features( like distinct colour of eyes or a scar on face etc).
In face perception, race can also play a role. If a person does not have contact with people from other races, he tends to think that all of them look alike. This is called the cross-race effect. In experiments scientists found that when a person was shown images of people from other races, the motivation to differentiate based on facial expression decreased subconsciously thus decreasing the ability of a proper facial recognition. In an experiment a set of store counter clerks were asked to recognize people who came to their shops to purchase goods. They tended to do very well at recognizing people from their own race but people from other races all seemed to “look alike”. However if a person from one race is constantly in contact with people from other races, the ability to do a proper facial recognition increases. In a very interesting study, scientists found that the cross-race effect decreases after subjects consume alcohol. So maybe alcohol is the best way to ensure global peace and brotherhood
Face recognition also has a conscious and unconscious component. People with Prosopagnosia were shown pictures of people within their families and also pictures of completely unfamiliar people. As expected the subjects could not recognize any of them however when the conductivity of their skin was measured, there was a great difference between the readings when seeing “known” people and unknown people. So even though there was no conscious recognition of the faces, there was a subconscious emotional response on seeing the people “known” to them. In a “Mysteries of the Brain” series VERITAS posted in 2005 we had discussed a condition known as Capgras Syndrome(http://unvarnished-veritas.posterous.com/mysteries-of-the-brain-part-13-capgras-syndro). A person suffering from Capgras syndrome can recognize people but feels no emotional response to them. So for example when a person suffering from Capgras syndrome meets his mother, he recognizes her but feels no emotions. In fact he may think that she is some other woman who looks exactly like his mother. So this inversion of emotions and recognition indicates that Capgras syndrome is the inverse( or reverse) of Prosopagnosia.
Another very interesting effect related to face recognition is known as the Thatcher effect or illusion. Imagine that you are shown two pictures of a face: one picture is upright and the inverted. Now an identical change is made in the two pictures. You would immediately be able to find the difference in the upright image but recognizing the change in the inverted image would be much more difficult. So when we process an upright face we use the efficient face recognition system but when we see the image of an inverted face, we try to recognize it like any other object which does not employ the efficient face recognition system( fusiform area). A person with Prosopagnosia does not show the Thatcher effect because for him both the upright and inverted faces are “normal” images that are recognized/perceived in a similar way without using the fusiform area. This effect is known as Thatcher effect because it was first demonstrated using the image of Margaret Thatcher. For some very amazing ( and shocking ) images of Thatcher effect see : http://en.wikipedia.org/wiki/Thatcher_effect and http://www.bbc.co.uk/bang/article_thatcher.shtml
So we see how complex and interesting our brain is. We humans needed a way to process faces efficiently to perceive even the minutest emotional signals in the faces of people around us and to be able to recognize the people that we know really fast, and evolution gave us a dedicated face processing unit. Fantastic isn’t it?
How can we end a VERITAS devoted to faces without some face poetry which is of course inspired by beautiful faces 🙂
Give me a look, give me a face,
That makes simplicity a grace;
Robes loosely flowing, hair as free,–
Such sweet neglect more taketh me
Than all the adulteries of art:
They strike mine eyes, but not my heart.
— Ben Jonson
Go wondrous creature, mount where science guides
go measure earth, weigh air, state the tides,
instruct the planets in what orbs to run
correct old time, regulate the sun