A psychological model can show the technical writer how to present information for effective communication by explaining how readers perceive, understand, learn, and remember. The principles underlying the model are the reader's psychological set, the mind's pattern-forming tendencies, the span of short-term memory, and the mind's need for reinforcement. The psychological set explains the disposition of readers to think or act in a particular way, and interference occurs when a communication does not match the reader's mind set. The main reason people read technical literature is to know how to do something, so technical publications should be task oriented. Gestalt psychology suggests that the mind tends to seek meaningful patterns in perceiving, understanding, learning, and remembering. Therefore, the technical writer's objective should be to supply cues for forming helpful patterns and to avoid cues that may form misleading patterns. The fact that the capacity of short-term memory is 7 plus or minus 2 items has numerous implications for presenting information: sentence length, number of items to include on a chart, and the number of parts into which to divide a comprehensible whole. Information is simple when the number of items presented does not exceed the span of short-term memory. Reinforcement helps the reader review material, verify interpretation, and see information in alternative ways. Technical writers should organize information so it will be easy for the reader to review. (HOD)