1. Ausubel, D. P. (1968). Educational Psychology. A Cognitive View. New York: Holt, Rinehart & Winston.
2. Bååth, J. A. (1980). Postal Two-way Communication in Correspondence Education. Malmö: Liber Hermods.
3. Bloom, B. S. (1976). Human Characteristics and School learning. New York: McGraw-Hill.
4. Brody, P. J. (1982). ?Affecting instructional textbooks through pictures?, in Jonassen, D. H. (ed.) The Technology of Text: Principles for Structuring, Designing and Displaying Text. Englewood Cliffs, New Jersey: Educational Technology Publications.
5. Caroll, J.B. (1963). ?A model of school learning?, Teachers College Record, 63, 723?733