Book excerpt: Abstract: A reference text on cognition criteria and effects of communication media on the learning process advances an empirically-based theory relating basic symbolic modes of presentation to common thought processes and to learning. A number of propositions are offered concerning the particular kinds of mental processes required by and the specific mental skills enhanced by different symbol systems. A series of controlled experiments and field and cross-cultural studies to test these propositions are descibed and discussed, illustrating the kinds of learning and mental skill development that take place under various circumstances with different learner types. A general scheme of reciprocal interactions is advanced, between media symbol systems and the cognition, and mental activities of learners. The implications of these interactions for the design and use of instructional materials are explored. (wz).