Gaining and then maintaining learners' attention is prerequisite to effective instruction. That's because people process, encode, and remember only what they attend to, and our attention span is strictly limited. The classic demonstration of the filtering effect of attention is the “dichotic listening task” (Anderson, 2010, p. 65). Participants were asked to listen to two different lectures simultaneously (one in each ear) but were instructed to attend to only one. Although they heard both lectures, they were able to recall information only from the one they actively attended to.