The word prosopagnosia, which combines the Greek words "prosopon," or face, with "agnos," or lack of knowledge, dates back to when researchers first identified the "condition" in people with brain damage to a specific area of the brain called the fusiform face area, or FFA, about 30 years ago. Scientists believe the FFA is thought to play a key role in our ability to identify a face.

Prosopagnosics, they found, had severe difficulties recognizing familiar faces — even, sometimes, their own.

But you don't have to have experienced brain damage to have prosopagnosia.

More recently, researchers have diagnosed the condition in perfectly healthy people who appear to be born with it. The deficit, called "developmental prosopagnosia," doesn't appear to negatively affect other intellectual efforts in these people. Oliver Sacks, the renowned neurologist and prolific writer, for example, was a prosopagnosic.