Answer: Faces

Among the many neurological conditions that can affect humans, prosopagnosia is one of the more peculiar. Suffers of prosopagnosia are, in layman’s terms, “face blind”. Their brain does not process or distinguish differences between the faces of the people they interact with or see in media.

The disorder is incredibly difficult to diagnose because those suffering from it have usually had the disorder from birth and are largely unaware that other people have the ability to distinguish other humans based on facial characteristics. Famous neuroscientist Oliver Sacks, for example, studied prosopagnosia for years before discovering that he himself was afflicted by it.

Those suffering from prosopagnosia usually develop secondary methods of recognizing people in their environment such as a person’s clothing style, gait, accessories (such as glasses), body shape, or voice. There is no known effective treatment for the disorder.