Prosopagnosia, the inability to recognize human faces
It is very easy to believe that our visual system works by giving us reliable information about the external environment and that the brain is simply a receptacle for these images that tell us about what is happening in the world. However, the truth is that our nervous system plays a very active role in processing this information so that it is coherent and makes sense.
The prosopagnosia It is a phenomenon that serves to remind us of this fact.
What is prosopagnosia?
It is, in short, about a failure of our nervous system whose consequence is that, whoever experiences it, is not able to recognize human faces . That means that despite having the eyes perfectly and being able to collect all the visual information relative to a person's face, it is not able to detect the patterns that turn that face into something unique. Definitely: we see the face but we do not recognize it .
Prosopagnosia is a type of visual agnosia , since there are several classes of neurological disorders in which what is seen is not recognized in a normal way by the brain. It is also one of the best known types of agnosia thanks to, among others, the neurologist Oliver Sacks, recently deceased, as he spoke about his experience with patients with visual agnosias in one of his most famous books: The man who confused his wife with a hat.
How do people perceive faces with prosopagnosia?
People with prosopagnosia perceive the faces as an image similar to something fuzzy, and are able to notice the existence of the typical organs of a face (eyes, nose, etc.) but not their exact location within the set. However, there are cases in which they can recognize some characteristics of the face of a few people, or be better to perceive in an approximate way the faces of certain groups (people of a certain sex, or with Asian features, etc.). ).
The prosopagnosia does not make it impossible to recognize someone , since people with this neurological disorder can identify the rest by their way of walking, their clothes, their hair ...
What are the causes of prosopagnosia?
Prosopagnosia may be due to injuries in specific areas of the brain, but it may also be a condition with which it is born. It is believed that the part of the brain that functions abnormally in people with this disorder is that of fusiform gyrus, an area of the cerebral cortex located in the temporal lobe, near the temples. Thanks to the fusiform turn 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 kinds of things, including inanimate objects (these "illusions" are called pareidolias) .
When the fusiform gyrus or neural networks that connect this area with other parts of the brain work abnormally, this can translate into inability to detect the visual patterns necessary to "see" a face as a whole .
The brain has mechanisms to overcome this condition
However, in a certain sense the brain does get visual information about the 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 if they do not consciously recognize them. This happens because, although the fusiform gyrus does not work well, part of the visual information is processed in parallel by the limbic system, in charge of making emotional responses to be born.