Without it there cannot be education, since it is the process of intellectually interacting with content that results in changes in the learner's understanding, the learner's perspective, or the cognitive structures of the learner's mind. The oldest form of distance teaching that aimed to facilitate interaction with content was the didactic text. In medieval times nearly all texts were aimed at instructing, not merely informing, and certainly not at entertaining. In the nineteenth century the use of print for teaching was advanced by the invention of home study guides that accompanied a text, providing explanations of it and directions for its study. In more recent times learners have interacted with content broadcast on radio and television programs, and with electronic recordings on audiotape, videotape, and computer software.
Interactive videodisc is the most advanced form of didactic interaction invented so far.
Some learning programs are solely content-interactive in nature. No other professional teaching expertise is provided, and learning is largely self-directed. In this interaction, distance instructors attempt to achieve aims held in common with all other educators. These may be presentations of information, demonstrations of skill, or modelling of certain attitudes and values. Next instructors try to organize students' application of what is being learned, either the practice of skills that have been demonstrated, or manipulation of information and ideas that have been presented.