I know this is possible because I've done it in my dreams once. It was right when I was falling asleep, and I opened my eyes for some reason to look at the physical world, right as I was falling asleep. The visual physical realm and my imagined visual realm were completely merged. I believe it's kind of like a way to hallucinate naturally, as my thoughts/impressions were the basis for what I saw.

Also, as I believe these to be related, I'm trying to figure out how to change a 2d image into 3d. This also happened to me during a dream once. I was just staring at this 2d picture on my laptop, and suddenly my depth perception played tricks on me, morphing it into 3d. I believe it has something to do with diverging your eyes, like those old magic eye books, but I just can't seem to figure it out! My mom also told me once that when she gets bad headaches, everything around her turns 3d, like she'll be trying to read her book and then suddenly the words just pop out at her.

I'll try staring at a single point in a picture for a long time, and eventually lose peripheral vision to where some parts of the picture disappear before my eyes. Take this for example. Extend your hand and stare right off the point to where your fingers are pointing, and then change your focus from the tip of your finger to the background. You will notice a double image appear depending on which one you're not focusing on. I believe it has something to do with this visual phenomenon. I tried focusing on images using this technique, and I can begin to see them turn 3d, but my eyes quickly snap back to normal! I can't seem to get them to stay in that perfectly diverged state.

Once, during a deep open eyed meditation, the objects I was staring at on my bed completely morphed into something that they're not. I was able to imprint my own impression onto them, with only their previous shape and form staying intact. I can't seem to do it again though, and it took a lot of concentration!

Does anyone know anything about this/how to do it?