This whole "just cross your eyes" thing has never worked for me, not once. I've seen these strange patterns printed on the backs of notebooks that supposedly make some sort of 3D effect when you "just cross your eyes". Later, when I saw similar images online, I was able to at least visualize these hidden shapes by opening the image in photoshop, duplicating the layer, setting the copy to "difference" and moving it left or right. The regular texture would eventually disappear and the shape would emerge. It's still a mystery to me what it feels like to view these the intended way though.