I can certainly see imagery, but never to the level it becomes hallucinatory.

Instead, it feels more like a background process. The more I focus on a mental image the less I "see" the visual input to my retinas. I've attempted to figure out how many visual streams I can see at the same time and I struggle to imagine more than three. If I focus very intently on all of them it seems I don't see any of them in great detail.

Certainly if I block out my visual input or focus on some unchanging imagery it becomes far easier to make my mental imagery more intense and detailed, but they can also be disrupted quite easily again by some new visual stimuli or an errant thought.