The educational use of television, film, and related media has increased significantly in recent years, but our fundamental understanding of how media communicate information and which instructional purposes they best serve has grown very little. In this book, the author advances an empirically based theory relating media's most basic mode of presentation -- their symbol systems -- to common thought processes and to learning. Drawing on research in semiotics, cognition and cognitive development, psycholinguistics, and mass communication, the author offers a number of propositions concerning the particular kinds of mental processes required by, and the specific mental skills enhanced by, different symbol systems. He then describes a series of controlled experiments and field and cross-cultural studies designed to test these propositions. Based primarily on the symbol system elements of television and film, these studies illustrate under what circumstances and with what types of learners certain kinds of learning and mental skill development occur. These findings are incorporated into a general scheme of reciprocal interactions among symbol systems, learners' cognitions, and their mental activities; and the implications of these relationships for the design and use of instructional materials are explored.