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An important area of application for VR systems has always been training for real-life activities. The appeal of simulations is that they can provide training equal or nearly equal to practice with real systems, but at reduced cost and with greater safety. This is particularly the case for military training, and the first significant application of commercial simulators was pilot training during World War II. Flight simulators rely on visual and motion feedback to augment the sensation of flying while seated in a closed mechanical system on the ground. The Link Company, founded by former piano maker Edwin Link, began to construct the first prototype Link Trainers during the late 1920s, eventually settling on the “blue box” design acquired by the Army Air Corps in 1934. The first systems used motion feedback to increase familiarity with flight controls. Pilots trained by sitting in a simulated cockpit, which could be moved hydraulically in response to their actions (see ). Later versions added a “cyclorama” scene painted on a wall outside the simulator to provide limited visual feedback. Not until the Celestial Navigation Trainer, commissioned by the British government in World War II, were projected film strips used in Link Trainers—still, these systems could only project what had been filmed along a correct flight or landing path, not generate new imagery based on a trainee’s actions. By the 1960s, flight trainers were using film and closed-circuit television to enhance the visual experience of flying. The images could be distorted to generate flight paths that diverted slightly from what had been filmed; sometimes multiple cameras were used to provide different perspectives, or movable cameras were mounted over scale models to depict airports for simulated landings.
Inspired by the controls in the Link flight trainer, Sutherland suggested that such displays include multiple sensory outputs, force-feedback joysticks, muscle sensors, and eye trackers; a user would be fully immersed in the displayed environment and fly through “concepts which never before had any visual representation.” In 1968 he moved to the University of Utah, where he and his colleague David Evans founded Evans & Sutherland Computer Corporation. The new company initially focused on the development of graphics applications, such as scene generators for flight simulator systems. These systems could render scenes at roughly 20 frames per second in the early 1970s, about the minimum frame rate for effective flight training. General Electric Company constructed the first flight simulators with built-in, real-time computer image generation, first for the Apollo program in the 1960s, then for the U.S. Navy in 1972. By the mid-1970s, these systems were capable of generating simple 3-D models with a few hundred polygon faces; they utilized raster graphics (collections of dots) and could model solid objects with textures to enhance the sense of realism (see computer graphics). By the late 1970s, military flight simulators were also incorporating head-mounted displays, such as McDonnell Douglas Corporation’s VITAL helmet, primarily because they required much less space than a projected display. A sophisticated head tracker in the HMD followed a pilot’s eye movements to match computer-generated images (CGI) with his view and handling of the flight controls.
Advances in flight simulators, human-computer interfaces, and augmented reality systems pointed to the possibility of immersive, real-time control systems, not only for research or training but also for improved performance. Since the 1960s, electrical engineer Thomas Furness had been working on visual displays and instrumentation in cockpits for the U.S. Air Force. By the late 1970s, he had begun development of virtual interfaces for flight control, and in 1982 he demonstrated the Visually Coupled Airborne Systems Simulator—better known as the Darth Vader helmet, for the armoured archvillain of the popular movie Star Wars. From 1986 to 1989, Furness directed the air force’s Super Cockpit program. The essential idea of this project was that the capacity of human pilots to handle spatial information depended on these data being “portrayed in a way that takes advantage of the human’s natural perceptual mechanisms.” Applying the HMD to this goal, Furness designed a system that projected information such as computer-generated 3-D maps, forward-looking infrared and radar imagery, and avionics data into an immersive, 3-D virtual space that the pilot could view and hear in real time. The helmet’s tracking system, voice-actuated controls, and sensors enabled the pilot to control the aircraft with gestures, utterances, and eye movements, translating immersion in a data-filled virtual space into control modalities. The more natural perceptual interface also reduced the complexity and number of controls in the cockpit. The Super Cockpit thus realized Licklider’s vision of man-machine symbiosis by creating a virtual environment in which pilots flew through data. Beginning in 1987, British Aerospace (now part of BAE Systems) also used the HMD as the basis for a similar training simulator, known as the Virtual Cockpit, that incorporated head, hand, and eye tracking, as well as speech recognition.
Sutherland and Furness brought the notion of simulator technology from real-world imagery to virtual worlds that represented abstract models and data. In these systems, visual verisimilitude was less important than immersion and feedback that engaged all the senses in a meaningful way. This approach had important implications for medical and scientific research. Project GROPE, started in 1967 at the University of North Carolina by Frederick Brooks, was particularly noteworthy for the advancements it made possible in the study of molecular biology. Brooks sought to enhance perception and comprehension of the interaction of a drug molecule with its receptor site on a protein by creating a window into the virtual world of molecular docking forces. He combined wire-frame imagery to represent molecules and physical forces with “haptic” (tactile) feedback mediated through special hand-grip devices to arrange the virtual molecules into a minimum binding energy configuration. Scientists using this system felt their way around the represented forces like flight trainees learning the instruments in a Link cockpit, “grasping” the physical situations depicted in the virtual world and hypothesizing new drugs based on their manipulations. During the 1990s, Brooks’s laboratory extended the use of virtual reality to radiology and ultrasound imaging.
Virtual reality was extended to surgery through the technology of telepresence, the use of robotic devices controlled remotely through mediated sensory feedback to perform a task. The foundation for virtual surgery was the expansion during the 1970s and ’80s of microsurgery and other less invasive forms of surgery. By the late 1980s, microcameras attached to endoscopic devices relayed images that could be shared among a group of surgeons looking at one or more monitors, often in diverse locations. In the early 1990s, a DARPA initiative funded research to develop telepresence workstations for surgical procedures. This was Sutherland’s “window into a virtual world,” with the added dimension of a level of sensory feedback that could match a surgeon’s fine motor control and hand-eye coordination. The first telesurgery equipment was developed at SRI International in 1993; the first robotic surgery was performed in 1998 at the Broussais Hospital in Paris.