How Do We Motivate Students to Read Materials in Our Online Course?

This recent comment by Stef raises an important issue for class management of the online course, motivating students to actually read or view course materials we provide them. In the traditional onsite course, we can gauge whether or not students have read materials through interaction more easily than in the online course, and can set aside class time for it if necessary and actually observe whether or not students are doing it. In the onsite course, if it became apparent to me most students had not read assigned material, I have been known to stop class and do a read-aloud of a short reading, or a passage of a longer reading, and use that as the basis for discussion. It isn't always possible to track student views of much online content, so how do we know students are reading or viewing materials?

Perhaps more importantly, how do we motivate students to read or view materials?