Your brain gets two different inputs from your eyes and tries to create a composite that blends them together. Normally this works fine because each of your eyes are looking at the same thing just from a slightly different angle. When you get two different images however then your brain still does that thing but now it's freaky.
It actually works with one eye closed, AND it also works if you only look at one of the two sets of images. For example, try covering up the left side of the GIF with one hand, so that only the right side (plus the cross-hair in the center) is visible, and it still works. Reading the abstract, the principle at work is not the brain combining the images on the left and right, but rather the brain making relative comparisons between subsequent images on both sides, and using those to construct your mental image of each face. Because the faces are all aligned at the eyes, it is easy for the brain to pick out relative differences between one face and the next, and as you flip quickly through them, the differences become increasingly exaggerated. This is thanks in part to the fairly sophisticated facial recognition "software" that we all have, and the fact that our brains take a lot more liberties in constructing the mental image of everything we see than most people realize.
Strictly speaking not animated gifs, but since there are so many fans of optical illusions here, perhaps this page might be of interest.
Although I haven't yet seen the Avengers, I kinda thought the action would look a bit better than that...
If you apprecionated women like we bros do, you would totally understand as well as work somewhere that it wouldn't matter. With reference to the Neil Patrick Harris gif above, it's weird how he seems to have almost perfectly inverted the Bob Saget-Danny Tanner principle of super nice guy played by blue comedian. Except in this case due to the requirements of tv instead of blue comedy you get generic misogyny hinging on his delivery.
I was viewing the posting of the Barney gif as "Oh, that Barney - he's a funny cartoon misogynist," and I didn't really think anything more about it, let alone ascribe nefarious or clueless motives to the poster. Did I give too much benefit of the doubt?
That's pretty much how the character's played on the show. Isolated as a gif on a forum, however, it comes across a bit differently.
Yeah that was my problem with it. Anyone who knows Barney will Get It, everyone else will see it as LOL bitches, amirite?
I was just thinking out loud with respect to how I come across him these days, which is mostly through out of context gifs and stills like these that are pretty generically shitty. I didn't really think much about it either, until salwon brought it up.