A Sorting

Sadly it is now late in the evening, and the dream i wish to describe happened early in the morning; however, i shall attempt to express it as i remember it in any event:

I was in a classroom of some sort, i believe i was attending college somewhere. There were some younger, as well as older students with me. The teacher (the emotive / reactionary title, she was not thought of as "professor") conducted an exercise involving assigned classroom reading. Unbeknownst to us, it was also to provide an experiment and illustration of some sort, involving certain psychological types. The subject of the reading was implied to be quite interesting, though i don't know specifically what it was at this point. However, after reading for a little while I suddenly became aware that half, if not more than half of the other students had gotten up and left. I looked up and around me, and there were only seven of us left, including an older, gray-haired gentleman, and several younger students of uncertain age and varying gender. The teacher, with a smirk, started to explain something about how certain personality, or psychological types tend to become so absorbed in what they're doing that they tend to unconsciously ignore what's going on around them. Without having to say so, it became clear what had happened. While we were reading, the teacher had apparently announced that the class was dismissed, particularly for those who were paying attention and/or heard her say so.