Help?!?! said:
Not really possible IME. You can sort of toy with the visual disturbances if you change your focus, which is kind of hard to explain really.
This has essentially been my experience, though over the years I've had experiences with volitional influence over specific features or themas that I've found intriguing. Dissociative visuals appear more amenable to control than 5HT psychedelics. For example, I've experienced a dissociative vision of two whirlwinds of smoke "dancing" in a vast dimly spotlit ballroom where I seemingly had free reign over their movement across the floor, though could not morph them into other objects, suggesting volitional extension into the domain of "psycho-object dynamics" but not object content. Similarly, I've been able to change color hues of such objects at will by thinking "violet, violet, violet" or the like, and seem to be able to dissolve a scene and invite a new one, though I fall short of being able to direct what exactly will populate the novel vista.
I theorize that this degree of control, and the differences in its applicability between dissociatives and 5HT psychedelics, is partially attributable to the types of sub-conscious intelligence modules that are being employed in their production. That is, dissociative visuals may be more amenable to cognition because they're engaging the wetware of dream or hypnogogic hallucination production, whereas 5HT psychedelic OEVs are more the province of fully automatic early perceptual processes taking place between the successive layers of the primary visual cortex. Controlling perception of these later types of visuals is more a matter of attending selectively to simple and particular features of their output like speed or rotation, or by priming via conditioning to particular asthetic themes (i.e. looking at flowers for hours may result in a florid composition to ones visuals, burning anime into ones brain may come to be reflected in boldly expressive anthropmorphic CEVs, etc.). It's actually more accurate to say you're exercising control over your interpretation of the perception than control of the perception itself.
I hypothesize that it is possible to cultivate one's ability to control psychedelic perceptions (and perhaps other sub-conscious visualization tendencies) by exercising discipline over visual projections against a white noise field. The best way I know of to do this practically is to tune an old television to a snow channel and just stare into the chaos. You will eventually see ribbons or rings or platonic solids emerge from the noise as your brain naturally attempts to apply pattern recognition processes to the essentially random information before you. I've not spent as much time doing this as I originally hoped I would, but have found in the short time I've devoted to the effort that I can evoke changes of perceptual object shape, direction of rotation, direction of on-screen trajectory, or make other simple yet intriguing changes willfully. It's fascinating and sort of surreal because I know I'm consciously manipulating a dynamic production of my subconsciousness in real-time, stone sober, and that the fairly elaborate characteristics of what I'm seeing right there in front of me is definitely not what others would be seeing were they doing the same. I speculate that this sort of technologically-assisted "meditation" might have unique benefits relative to other forms of meditation that focus on practicing visualization but lack its degree of visually explicit biofeedback.
