Virtual reality
Around the same time, Douglas Engelbart used computer screens both as input and output devices. In 1968, Ivan Sutherland, with the help of many students including Bob Sproull, created what was widely considered to be the first head-mounted display (HMD) system for use in immersive simulation applications. It was primitive both in terms of user interface and realism, and the HMD to be worn by the user was so heavy that it had to be suspended from the ceiling. The graphics comprising the virtual environment were simple wire-frame model rooms. The formidable appearance of the device inspired its name, The Sword of Damocles.
Artificial Reality
Artificial reality is a book series by Myron W. Krueger about interactive immersive environments (or virtual realities), based on video recognition techniques, that put a user in full, unencumbered contact with the digital world. He started this work in the late 1960s and is considered to be a key figure in the early innovation of virtual reality. "Artificial Reality" was published in 1983 and updated in "Artificial Reality II" in 1991 (both published by Addison-Wesley).