I think it is a good thread to resurrect, and the contributions are pretty good, it gets me thinking.
48 years ago on some of my first acid trips I found that the open-eye effect was like looking through photographic slides.
My parents had lots of slides from their trip to mexico which was magic to me anyway, but I would look at these little plastic squares with colored film pictures by holding them up to the light, and sometimes I would look through more than one slide to see the glory of one warm beautiful scene blended with another.
This was epiphanic to me.
looking through layers at clear celluloid images was very much like what I was seeing.
with acid it was usually beautiful but occasionally terrifying.
then during the come down, I would see writing on the ceiling intermixed with cartoony hieroglyphics in which Goofy was a very dominant character along with duck billed persons.
cannibis was always very rich, almost particulate rather than layered, or layered in smaller frames with a much more intense body feeling.
shrooms were very much like acid but the blending of layers was more smooth, just as gorgeous and dark but the combination of images - more melted.
salvia also produced a layered visual field, but seems to keep the layers very solid, so the mix is chaotic, and a sense of dimensional disruption ensues to accommodate the non-blendable layers of things that are happening - easy to feel like you are in a strange machine - very often the salvia mind produces multiples of the same thing to fill the odd multi-dimensional expanse.
Maybe DMT (I did not yet try it) is like that, though I think it's similarity to mushroom smooths the edges and blends the layers and dimensions to a more pleasant finish than salvia's more raw multi-dimensional layering.
in all of them there is definitely persistence and impingement of visual and mental frames upon subsequent ones, and a wonderful willingness to appreciate the abundance of life.