the role of the artist

I'm a little bit confused about McLuhan's idea of the role of the artist. He seems to be saying that the artist must make people aware of the profound cultural changes brought about shifts in the types of media we use. The artist does so (I'm led to believe) by drawing attention to the media as important: it's not what's on television that matters, but the television itself.

That idea of art seems necessarily hypermediate, as opposed to immediate. Any artist working in the pre-modern age, when the mandate (according to Bolter and Grusin) was to make the medium almost invisible, so as to fully immerse the viewer, does not seem to meet the above criteria set about by McLuhan. That seems wrong to me, but I can't figure out what or whom I'm misunderstanding. Any ideas?