Autism used to be like pregnancy -- you either had the condition or you didn't. But updates to medical science eventually recognized that autism is in truth a spectrum, from those completely ignorant of the fact that other human beings have internal lives and communicate these by social cues, through the various shades of Asberger's, to simple difficulties understanding the meanings of social interactions. Now the same continuum is proposed by researchers at Harvard for prosopagnosia.
This matters to me because I'm pretty sure I'm somewhere on that continuum. In its purest form, prosopagnosia is a complete inability to recognize faces, no matter how often you see them -- including one's spouse and children. I'm not as bad as all that. But I do have much trouble remembering faces, and frequently people think I'm (pick one) (a) snubbing them,(b) dim-witted, or (c) self-centered, because I can't remember who they are until I get an external cue.
Voices help. But, as Harvard researchers recently declared, we semi-prosopagnosiacs use other clues, too, in our frantic search for a name to go with that person confidently claiming acquaintanceship. I try to memorize hair color and style, glasses type, dress. Then the person will dye her hair, get contacts, and become a devotee of Zac Posen, and I'm lost again.
I have the same trouble with movies (another common symptom). I confuse actors unless they look very different from each other, rendering plots hard to follow. Nor do I recognize actors from previous movies. I didn't recognize Sigourney Weaver in GALAXY QUEST until the credits rolled. She went blond.
It's an embarrassing problem. However, it could be worse -- I could have been a politician. Writers have a certain leeway in being weird. Or we can just stay in our studies and write. I always know who my fictional characters are.