Close your eyes. Picture your closest friend. Maybe you see her blue eyes, long nose, brown hair. Perhaps even her smile.

If you saw her walking down the street it would match your imagined vision. But what if you saw nothing at all?

James Cooke, 66, of Islip, N.Y., can’t recognize other people. When he meets someone on the street, he offers a generic “hello” because he can’t be sure if he’s ever met that person before. “I see eyes, nose, cheekbones, but no face,” he said. “I’ve even passed by my son and daughter without recognizing them.”

He is not the only one. Those with prosopagnosia, also known as face blindness, can see perfectly well, but their brains are unable to piece together the information needed to understand that a collection of features represents an individual’s face. The condition is a neurological mystery, but new research has shed light on this strange malady.