Form constants. The fascinating thing about them is the patterns being actual neural structures in the brain, made visible. Sort of like if you shine a bright light into the pupil sideways it can make the branching retinal veins visible, which they otherwise aren’t. So form constants are a view inside your brain, in a virtual-reality kind of way.
To put it concisely, I would say that a psychedelic trip makes you feel like a cat feels on a car trip.