It is very easy to believe that our visual system works by giving us reliable information from the outside environment and that the brain is simply a receptacle for these images that tell us about what is going on in the world. However, the truth is that our nervous system plays a very active role in processing this information to make it coherent and meaningful.

The prosopagnosia is a phenomenon that serves to remind us of this fact.

What is prosopagnosia?

It is, in short, a failure of our nervous system whose consequence is that, whoever experiences it, is not able to recognize human faces . This means that despite having perfect eyes and being able to collect all the visual information related to a person’s face, they are not able to detect the patterns that make that face unique. In short: we see the face but we don’t recognize it .

Prosopagnosia is a type of visual agnosia , since there are several kinds of neurological disorders in which what is seen is not recognized normally by the brain. It is also one of the best known types of agnosia thanks to, among others, the neurologist Oliver Sacks, who recently passed away, as he spoke about his experience with visual agnosia patients in one of his most famous books: The Man Who Mistaken His Wife for a Hat .

How do people with prosopagnosia perceive faces?

People with prosopagnosia perceive faces as a blurry image, and are able to notice the existence of the typical organs of a face (eyes, nose, etc.) but not their exact location within the whole. However, there are cases in which they can recognize some characteristics of the face of a few people, or be better able to perceive in an approximate way the faces of certain groups (people of a certain sex, or with Asian features, etc.).

Prosopagnosia does not make it impossible to recognize someone , since people with this neurological disorder can identify others by their walk, their clothes, their hair…

What are the causes of prosopagnosia?

Prosopagnosia can be due to lesions in specific areas of the brain, but it can also be a condition that one is born with. The part of the brain that is thought to function abnormally in people with this disorder is the fusiform gyrus , an area of the cerebral cortex located in the temporal lobe near the temples. Thanks to the fusiform gyrus we are extremely sensitive to all the subtleties that a human face can contain, and also thanks to it we have an unprecedented propensity to see faces in all sorts of things, including inanimate objects (these “illusions” are called pareidolias).

When the fusiform gyrus or the neural networks that connect this area with other parts of the brain function abnormally, this can translate into an inability to detect the visual patterns needed to “see” a face as a whole .

The brain has mechanisms to overcome this condition

However, in a sense the brain does get visual information about faces, so other areas of the nervous system can process this information subconsciously. This explains why people with prosopagnosia show emotional activation when they see the faces of people close to them (their mother, their friends, etc.), even though they may not consciously recognize them. This occurs because, despite the fact that the fusiform gyrus does not work well, some of the visual information is processed in parallel by the limbic system, which is responsible for causing emotional responses to arise.