Richardson, J. C. / 2003 / Examining Social Presence in Online Courses in Relation to Students' Perceived Learning and Satisfaction / Journal of Asynchronous Learning Networks 7(1):68~88 Shin, N. / 2003 / Transactional Presence as a Critical Predictor of Success in Distance Learning / Distance Education 24(1):69~86 So, H. J. / 2009 / When Groups Decide to Use Asynchronous Online Discussions: Collaborative Learning and Social Presence Under a Voluntary Participation Structure / Journal of Computer Assisted Learning 25:143~160 Steuer, J. / 1992 / Defining Virtual Reality: Dimensions Determining Telepresence / Journal of Communication 42(4):73~93 Stipek,D.J / 1993 / Motivation to learn: From Theory to Practice / Allyn and Bacon