Imagine that a Stephen Hawking-like person is an artist.
He has no significant sensory impairments. He can see, hear and smell perfectly well. He also possesses great cognitive function. His sole disability is a complete lack of motor function.
Assuming Hawking's easily recognisable computer would be replaced by some form of limited telepathic communication, and he otherwise is unaided by others, or tools made by others, then what could this person's artworks be?
I've considered this question for a few weeks now and am unable to come up with a single example of what this person could produce as art. My best attempt was a gathering of sorts where the person's body apparently does nothing, like 4'33" or The Artist Is Present, but even in those cases there remain unanswered questions. How could he write the invitations so that an audience is present, for example? Or how could he get to the stage and arrange the piano? Position the chairs in the exhibition room? They are but small physical interventions, but they are what makes the difference between those works and someone simply sitting silently in a room.
This thought experiment thus is a way to arrive at the conclusion that manipulation of objects is a strictly necessary condition for art. And it conversely shows that concepts and visual stimulation are mere contingencies. They are often present, but never needed.