Prosopagnosia

Prosopagnosia, or face-blindness, is a neurological condition that renders a person incapable of recognizing faces. It is unrelated to the person's ability to see faces. Someone with perfect vision can suffer from prosopagnosia.
In the normal brain there is a center that is dedicated to face recognition. Prosopagnosia arises when that special center becomes damaged or is otherwise unable to perform its function.
In this page I try to give an understanding for how prosopagnosia can arise, and in the rest of this site I try to explain what it can be like to live with prosopagnosia.


Let me say it up front: I am not a neuropsychologist!
This page is a face-blind layman's attempt at explaining prosopagnosia. If you think that I have misunderstood something, or there is something I should add, please write to me at cb@prosopagnosia.com and let me know.



Processing of an image

To understand how prosopagnosia arise, one has to understand something about how the brain works with an image.

When the eye first sees an image, it only gathers color and brightness information from an immense number of directions. Then the nerves start to try to bring some order into that information.

The nerves in the eyes do 'simple' tasks, like finding lines, or motion. The brain does the more difficult tasks, like trying to identify what it is we are looking at.


Many brain centers
In the brain the image is processed in parallel in many different brain centers. In the picture the brain centers are symbolized by ellipses.


When we look at something, we see the fields of light and dark and color that make up the image. This is the kind of information you can capture on a painting or in a camera. This is also the kind of basic information that we generally think of as 'seeing'.

The brain also tries to process the image in many other ways. For example in the General Pattern Recognition center. Here it compares the object it is looking at with things it has seen before. This center tries both to see both if the object fits any known category, and if it has seen this particular object before. This is how we would recognize for example a stone, building, tree or bridge.

If the object that we are looking at is a face, then a number of specialized centers are triggered by the image.
This one is a center that is specialized in trying to identify the individual we are looking at. It looks in the 'archive' of known faces, and tries to find a match. If it finds a match, then it will use the found identity to look up all other facts about this person (such as name, when we last met, name of his pet, etc.). If it fails to find a match it will assign this face a new 'identity-code' and store it in the archive.
This center works with identity and is therefore designed to ignore changes caused by aging, cosmetics, glasses, clothing, etc.

There are also a number of other brain centers that are used specifically for faces:

Without thinking about it we can estimate someone's approximate age, just by looking at his or her face.

We can also immediately see someone's gender, usually with absolute certainty.

We can see the mood or facial expression in a face.

We can see very well where someone has turned his or her attention. Usually we can tell within one or a few degrees where someone is looking, especially whether they are looking at us or not. We can also estimate how attentative they are.

After we reach a certain age, we start to have an opinion on how attractive other people are.


There is more information that we also get from the face, for example race, lip-reading etc. Since this site is about prosopagnosia, I will not go any further into these other things here.


Inborn Brain Centers
The abilities listed above are not cultural. They can be practiced, but we are born with these basic abilities. The brain is hardwired to perform these tasks. A baby can identify its parents, and see their moods, and demand attention, and recognize its favourite toy. These are not things someone has to teach the baby, they are inborn.

Failing Face Processors
Since all these different types of information are processed in different parts of the brain, it is possible to have a malfunction that affects only one of them. Prosopagnosia occurs when the face-processing center for identity fails. This is indicated in the picture by

Hard to Realize
Most people think that if you can see something like a face, then you must also automatically know what you are seeing. The problem with this approach to prosopagnosia is that you do see the face. You see it as an image using the center . You can also see it using any of the other intact centers. This means that you can see the person's gender, age etc. But you just can not see who it is. These symptoms are very confusing for someone who has them, and they are probably the reason why many face-blind people go through all their life not knowing that their problems are caused by prosopagnosia.


Failing of the brain centers
A failure in each of these brain centers will cause a typical neurological condition. Some of these conditions are more or less common in combination with prosopagnosia.

These are examples of conditions caused by failure in the different centers:

A failure to see the image, while still being able to get information from what one is looking at, is called blindsight.

A failure in the general pattern recognition center should render the person unable to recognize objects he or she sees. You can find out more about that handicap at this agnosias mailing list.

A failure to see the identity in faces is called prosopagnosia, and prosopagnosia is what this site is all about. Note that prosopagnosia only affects the ability to see the identity. Just like blind people we know perfectly well who someone is after we have identified them.
Personally I have prosopagnosia. I don't think I have any of the other conditions.

A failure in this center should render the person unable to see the age of other people. So far I have heard of two such cases.

A failure in this center should render the person unable to see the gender of other people.
I have tried hard to find the scientific name of this condition. If you know it, please e-mail it to me at cb@prosopagnosia.com.

A failure in this center renders the person unable to see the facial expression in a face. This is a condition that sometimes runs together with face-blindness, as in the case of Bill Choisser.

A failure in this center renders the person unable to see where someone has turned his or her attention. In other words, they would be unable to tell what someone was looking at. I have heard of at least two cases where a person had both this condition and prosopagnosia.