I was making some autostereograms, and my friend was getting frustrated because he couldn't see the 3D images in them. We spent a while trying to get his eyes to unfocus so he could merge the different points together and focus to form the image. When we finally got his eyes to do that, he noted that he didn't see a 3D image. I pulled up some stereo pairs(two images taken from slightly different angles which, when merged together, give the illusion of depth). He told me he always hated those because he couldn't see the difference between the 3D image and the originals. He says that if he closes one eye, it looks the same as having both eyes open(no depth). He says the only reason he knows how far away I am from him is because he knows how big I am. Both of his eyes work individually, and when he looks through both eyes at once, he only sees one image, but is it possible that his brain doesn't interpret the images together to perceive depth? Feel free to answer as deeply as possible.