McLuhan sees comic books as being similar in production values and perceived worth by the cultural elite as nothing short of the pre-Gutenberg block-printed Biblia Pauperum--"Bibles of the Poor," something I've never heard of. "These cheap and popular prints, despised by the learned, were not preserved any more than are the comic books of today." That's right, you naysayers: comic books stand in the tradition of not only the stations of the cross but a missional version of the Bible itself. I'd like to get my hands on one of them.
As despised as the Biblia Pauperum and other such visually oriented media may have been by the literati, "the woodcut, and even the photograph, were . . . eagerly welcomed in a literate world." Beyond their remedial function as onramps to conversations for those who were less educated than the elite--a picture, remember, paints a thousand words, which means a thousand words fewer to read or, more significantly, recognize--pictorial sources of information stressed the participation of the "reader."
The old prints and woodcuts, like the modern comic strip and comic book, provide very little data about any particular moment in time, or aspect in space, of an object. The viewer, or reader, is compelled to participate in completing and interpreting the few hints provided by the bounding lines. (McLuhan, Understanding Media, p. 160)
McCloud picks up on this idea from McLuhan as he deconstructs the comic medium. McLoud gives insight into how one "reads" the space between frames (the "gutter," if I recall correctly) in a comic strip or comic book: in these gutters scenes change, time passes, conversations are processed, or drama is intensified by means of the gutter's "pregnant pause." No matter how empty that gutter space appears on the page, it's endowed with quite a bit of assumed meaning. It's the responsibility of the reader to decipher that meaning.
So visual media offer nonverbal communication in ways that pure print media simply can't. McLuhan thus compares comic books not to pulp fiction or other literature but rather to other more participatory media:
Not unlike the character of the woodcut and the cartoon is the TV image, with its very low degree of data about objects, and the resulting high degree of participation by the viewer in order to complete what is only hinted at in the mosaic mesh of dots. Since the advent of TV, the comic book has gone into a decline. (McLuhan, Understanding Media, p. 161)
Good point there. "From Life to General Motors," McLuhan goes on to say, "and from the classroom to the Executive Suite, a refocusing of aims and images to permit ever more audience involvement and participation has been inevitable" (p. 166). Hence comics extended into TV and film and action figures and costumes and conventions. Participation is the coin of the new realm, and the degree to which products and services--from books to churches to families--fail to facilitate active participation of their audience, is the degree to which they render themselves irrelevant.