In Mental Paint (the second version thereof), Ned Block wishes to attack representationalism by appeal to phosphene experiences (the little lights that appear before your eyes if you gently press on them while they are closed).
Lycan (1987) says: “…given any visual experience, it seems to me, there is some technological means of producing a veridical qualitative equivalent–e.g. a psychedelic movie shown to the subject in a small theater.“ (p. 90) But there is no guarantee that phosphene experiences produced by pressure or electromagnetic stimulation could be produced by light. (Note: I don’t say there is a guarantee that phosphene-experiences could not be produced by light, but only that there is no guarantee that they could; I have no idea whether they could or not.) I do wonder if Lycan’s unwarranted assumption plays a role in leading philosophers to suppose that the phenomenal characters of phosphene-experiences, after image-experiences and the like are exhausted by their representational content.
I think Lycan is taking on more of an argumentative burden than he needs to here, and therefore that Block’s objection misses the mark. I doubt that it is a necessary condition of an experience being represenational that it potentially be veridical. After all, a representational painting need not be potentially veridical. I suspect the constraint is closer to that the experiences be locally potentially veridical–that is that the individual constituents of the experience be potentially veridical, not that the entire field of vision could be veridical.