I think persisting effects from psychedelic use are the result of increased awareness of phenomena that are already present in the visual system.
I remember my ability as a small child to project visions on the wall of my bedroom. Also I would get the phenomenon that Ann Shulgin described throughout my childhood and into my teens, albeit with steadily decreasing frequency. This re-occurred unexpectedly - continuing to happen every couple of weeks or so for maybe a year - a couple of years ago but I can't quite remember why. It's rather enjoyable. Probably I now could induce it if I really wanted to.
Strangest was when I once awoke in a pitch dark room to find everything aglow like an old green computer monitor. All the objects in the room were clearly apparent. To this day I have no idea how that happened or what it was about. Possibly I was recovering from a fever or other sickness.
βThere is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
β Jacques Bergier, quoting Fulcanelli