A few things to add here:
1) the link http://viscog.beckman.uiuc.edu/djs_lab/demos.html
shows some of the films, and has a link to some of the experiments on a DVD at http://www.viscog.com
(down right now)
2) Humans are supposedly adapted to detect motion, probably as a result of us evolving from both predator and prey. I'd suspect we 'notice' motion (i.e. our processing machine gives it a stronger weight) more than say colors. I also personally think that we may process images that we see as the collection of objects they represent, rather than as 'pictures', which means we can again assign higher weights to objects that are more important to us in the analysis. Even position might be noticed more - Phil Goldstein makes some assertions to this related to equivoque, and if you search the web you may find a bizarre, humorous, and possibly even accurate joke about how men select urinals when presented with a number of them on the wall to choose from.
3) Just because a spectator doesn't comment on something doesn't mean they didn't see it. And just because one spectator doesn't see it doesn't mean the other didn't. Dick Zimmerman showed an item in his lecture once involving the production of a stack of coins from apparently completely empty hands (he showed a spectator his hands), then produced the coins for an audience).