[Nzen]

To communicate to others my experience with imagination versus hallucination in discussions like this, I've used the device of seeing differently from either eye at the same time.

If I put my hand a couple inches away from my face, in front of one eye only, I can still 'see' aspects of that hand with the uncovered eye.

Analogously, when I imagine a 'red star', it is visible in a different medium / realm (like my covered eye) than the rest of the things I see around me (with my uncovered eye). I can 'insist on' or 'overlay' the imagined image, like the red star situated in a particular spot on my desk, but I do not feel that they 'become the same visual stream', ever, such that I would think that the star could be physically present in the room.