>> hodes: not only. >> jo livingston: the memory is never created. >> stahl: the face doesn't get putdoesn't get filed. >> stahl: so they have to rely on other strategies to identify people-- hair, body shape, the way people walk, their voice, even style of dress. but jacob told us that it can all fall apart when someone changes their hair, like a colleague named sylvia who he couldn't find one day until she started putting her hair into her usual ponytail. >> hodes: and she, like, put it into the ponytail, and once it was in place, that was sylvia. it clicked. then, she took her hair back out of that ponytail. >> stahl: right then and there? >> hodes: yep. she just put it in and then took it out and... >> stahl: so she went from sylvia, not sylvia, sylvia, not sylvia? >> hodes: she disappeared. >> stahl: come on. >> hodes: yeah. >> stahl: to him, it was as though her face had changed into someone else's before his eyes. >> hodes: so now, i'm confronted with this situation that... that got weird. because i knew this person was sylvia, but it didn't feel like sylvia. >> stahl: faces me