Using his mother-in-law as his test subject, the 20+ year industry veteran used the very first puzzle (which was later transformed into a tutorial) of Sam & Max: Season 1 to witness how someone completely foreign to video games would respond to interactive design he took part in - a design most gamers would probably argue is about as accessible as it gets. The results are equal parts interesting, humorous and educational.
It turned out she was playing the scene more like a find-the-hidden-object-in-the-picture game, although I had also seen her try some drawers and other non-yellow objects that might be used as containers. Further questioning revealed that it simply had not occurred to her that there might be more to the game than what was on the screen. She wasn't thinking of it as a world; she was thinking of it as a picture.
Fans of intelligent game design ruminations or just plain good writing, both being fortes of Grossman, would do well to read the whole piece.
Source: Gamasutra
Anyways, excellent article. Max's teeth-picking and the 1 minute interlude between cutscene and gameplay were both very insightful observations, especially the latter. I'll need to mull this over.