Instructional systems design (ISD) is the integration of general systems theory, instructional theory, and communications theory. Edgar Dale, a leader in the fields of reading and journalism and a pioneer in the humanistic/communications tradition of the field of instructional technology, related the concrete to abstract continuum to media decisions in his textbook, "Audio-Visual Methods in Teaching." Dale believed that learning becomes more meaningful when abstract learning and concrete experience are related. Dale advanced the field theoretically through the Cone of Experience, a way to classify media experiences in relation to the concrete and abstract psychological dimensions of learning. The Cone of Experience was historically important in its attempt to connect psychological/instructional theory and communications media. While the direct to vicarious and purely symbolic experience continuum is still valid, the cone is dated in its description of media. The cone was introduced in a different time period when there were fewer theories and those that existed were used more uniformly. Today, there is no widely accepted theory which follows in the tradition of the Cone of Experience, and the result is a gap in instructional design theory. New directions in theory worth pursuing in order to close the gap include: more specialized models; new ways to test models; models which combine design, development, and evaluation; and message design theory which relates types of learning and other variables. (Contains 20 references.) (SWC)