Oliver Sacks became famous with the publication of his 1985 book, The Man Who Mistook His Wife for a Hat. The title story was about a patient of his who had severe global agnosia; while his eyes functioned perfectly well his brain could not integrate what he saw, rendering him unable to recognize anything he looked at. He mistook fireplugs for children, and, looking around for his hat when leaving Sacks' office, he reached out and grabbed his wife's head. In a more recent book, The Mind's Eye, Sacks devotes a chapter to a less severe agnosia, the inability to recognize faces. This is called prosopagnosia. People with this condition cannot recognize peoples faces. They can literally talk to someone for an hour, but if that person leaves the room and comes back in wearing different clothes, they won't recognize them. They can walk past a parent or sibling on the street and have no idea who they are. Now, what is a bit startling to me is that Sacks reveals that this problem, which frequently runs in families and therefore is probably genetic (except when caused by stroke or other brain insults), is very much more widespread than even many neurologists and neuroscientists realize. The majority of people born with it do not report it to any doctor and it's just not tested for, like colorblindness or hearing problems. But, it's estimated by some researchers to affect 2% of the population. That's 6 million people in the US alone. That being the case, there must be PF'ers who suffer from it, who don't realize it's an inherited genetic condition, and who have just considered themselves really poor at remembering faces. Here's a site: http://www.faceblind.org/ They have a famous face recognition test: http://www.faceblind.org/facetests/index.php (They ask for your age for the test and I think that's because they give you an age appropriate selection of famous faces to recognize. If you're 18 I think you'll get a whole different selection of faces to identify than I did, being 57. The test is not definitive at all, but if you really suck at it it could be a red flag. I did pretty well with 97%.) I am not aware I have ever met anyone with this problem, but, as with many conditions, people who have it develop elaborate compensatory mechanisms that can hide it. Still, 2% of the population seems very like a very high figure for it to be so unknown. I was additionally blown away when Sacks dropped the quiet bombshell of revealing that he, himself, has suffered from it his whole life. He describes his problem in detail and the compensatory mechanisms he's created. I would like to ask him why he never mentioned it in The Man Who Mistook His Wife For A Hat, It certainly seems to explain why that patient was so salient to him, but it seems a bit disingenuous of him to allow the reader to marvel at the patient's condition while not mentioning he, himself, was halfway toward the same condition.