Once the introduction and directions have been made explicit, the learning activity can commence. During learning activities, the instructor should observe the learners constantly to determine if they understand what is happening and if the timing, pace, level of complexity, and content are appropriate. When learners are passive, as at lectures and exhibits, instructors must be aware of learner receptivity to the presentation. Waning interest usually indicates that a change of pace, content, or level of learner involvement is needed.