Prosopagnosia, also known as face blindness, is the inability to recognize faces. In severe cases, individuals with prosopagnosia may not recognize close family members, including parents and spouses, by their faces. For instance, someone with prosopagnosia might walk past their child in a crowd, only realizing their mistake upon noticing their child's distinctive backpack or favorite jacket. Prosopagnosia specifically impairs facial recognition, while the recognition of other objects or stimuli remains unaffected. As a result, individuals with prosopagnosia depend on non-facial cues, such as unique skin patterns, body shape and size, specific styles or colors of eyeglasses, and preferred clothing styles, to identify familiar people. For example, a person with prosopagnosia might recognize a coworker by their unusual haircut and the colorful frames of their glasses.

Prosopagnosia can be present from birth or acquired through brain injury, stroke, or neurological disease. Developmental prosopagnosia is characterized by inadequate connections and a reduced number of white matter fibers linking various brain regions responsible for facial recognition. This condition disrupts neural communication and hinders face processing from infancy through adulthood. For instance, a child born with prosopagnosia may struggle to recognize their classmates and teachers, relying instead on distinctive features like the teacher's loud voice or a classmate's distinctive freckles. Studies show that the fusiform gyrus in the temporal lobe is crucial for facial recognition, and damage to this area can cause prosopagnosia. For example, someone who suffers a stroke that damages the fusiform gyrus may suddenly find themselves unable to recognize even their own reflection in the mirror. Prosopagnosia demonstrates the limitations of brain plasticity, as facial recognition impairments persist throughout life despite repeated exposure to familiar faces.