brad duchaine showed me an mri scan of colleen's brain. is that a hole in her brain? duchaine: that's right. it's in the right temporal lobe. >> stahl: so back here. >> duchaine: that's right. >> stahl: and the location of that hole where the tumor had been was a clue-- if removing that area caused the loss of face recognition, could that be where all our brains process faces? it turns out that neuroscientists have been trying to figure out how it is that our brains recognize faces for decades. >> nancy kanwisher: face recognition is a very difficult problem, because all faces are basically the same. >> stahl: m.i.t. neuroscientist nancy kanwisher. >> kanwisher: there are these two roundish things here. there's this thing there. there's this thing there. they're all the same. and so discriminating one face from another is a very computationally difficult thing, because it's those subtle differences in the same basic structure that distinguish one thing from another. >> stahl: and it is exactly those subtle differences face blind people like jo livingston miss. >> livin