Textbooks emphasizing visual elements in exposition can be enriched using crisp, concise, audio-taped commentaries to focus attention on essential points in each illustration. These text aids, packaged in the convenient form of cassettes (usually one per chapter), have a number of obvious advantages: (1) any teacher can prepare them; (2) they are immediately and cheaply transferred between institutions; (3) a cassette recorder is the only equipment required; (4) they are readily incorporated into any course, regardless of the teaching methodology--class size is not a limiting factor in their applicability; (5) the student receives a taped guide, complete with his or her own set of take-home visual materials, such as graphs, diagrams, tables, photos and electron micrographs; (6) the student is free to work at a time, place and pace of his or her choice. This freedom makes the modules eminently suited to extension or continuing education courses. (Author)