Since I got interested enough in Neanderthal man to start reading about him, and because this leads to questions about whether or not modern man could have bred with Neanderthal, I have found myself getting into the habit of constantly checking out the slope of the foreheads of every person I now see. This has become a habit: I do it automatically, and don't make any effort. I realized today that I'm hardly paying attention to any other aspect of people's faces anymore: I'm just keeping an eye on everyone, waiting fo them to offer that profile view so I can gage the slope of their forhead. This is a pretty extreme example of an odd mental filter. Throughout my life I've gone through a long succession of less bizarre ones. Another one I can recall is going around paying particular and exclusive attention to color. This has happened a few times, sometimes in conjunction with being heavily involved in artwork, and sometimes because of reading about how the eyes and brain create and percieve color. I wonder if anyone else has any examples they recall of especially strange mental filters, like noticing the slope of peoples' forheads all the time?