Virtual Reality Scientific and Technological Challenges (1995) / Chapter Skim
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2 The Visual Channel
2 The Visual Channel
Pages 111-133
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From page 111... ...
An effective visual interface provides an appropriate match of the parameters of stimulation to the characteristics of the sense organ. The production of visual stimuli in such a system depends in part on technological capabilities for monitoring movements of the observer (to generate both movement-contingent and noncontingent sensory information)
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From page 112... ...
. Indeed, perturbations of normal visual stimulation may be disturbing but not necessarily destructive of perception in either real or synthetic environments.
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From page 113... ...
eye movements are not perceived as blurred because visual sensitivity to the target is reduced during the period beginning about 50 ms before the saccade is initiated to 50 ms after the new fixation point is reached (Latour, 1962~. Slower target motions in the range of 5 to 40 deg of visual angle per second resulting in pursuit eye movements are much less subject to suppression effects, thus presenting a challenge for the display designer.
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From page 114... ...
These connectivity patterns yield two important insights to the functioning of the visual system that have relevance for the display designer. The primary flow of information through the lateral geniculate nucleus is from the retina to the visual cortex.
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From page 115... ...
As mentioned above, 20 percent of fibers from the optic tracts converge on the superior colliculus. This midbrain structure has close links to lower autonomic centers responsible for emotion, arousal, and motor coordination.
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From page 116... ...
Channel capacity sets a fundamental limit on all attributes of the displayed imagery, including spatial resolution, temporal update rates and lags, contrast, luminance, and color resolution. Distortion of optical factors can arise in connection with (among other things)
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From page 117... ...
It must also be lightweight and easily adjustable for a wide variety of human users. In the case of stereoscopic displays, great care must be taken to ensure adequate alignment of the images provided to the two eyes and minimization of the inherent conflict between ocular convergence and accommodation (e.g., see Miyashita and Uchida, 1990~.
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From page 118... ...
Beyond approximately 1 m, these monocular depth cues predominate in creating the percept of depth, whereas in the near field (arm's length) , the combined use of motion cues with stereopsis becomes crucial for eliciting three-dimensional perception that is convincing.
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From page 119... ...
Sensory Adaptaton to Visual Distortion Many simple alterations involving the visual channel are effortlessly adapted to. For example, most users have little difficulty learning to position a cursor on a vertical computer screen through the use of a mouse constrained to a horizontal tabletop.
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From page 120... ...
. At present, the majority of visual displays for synthetic environments are physically coupled to the head of the operator by mounting display
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From page 121... ...
In addition, servo-controlled or multiple static display surfaces must be used to provide a completely encompassing visual environment. Another approach to increasing viewing volume is to use head position and orientation sensors of the same type and form used on head-mounted displays.
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From page 122... ...
Hybrid panel display systems exist that use smaller display surfaces servo-controlled or manually steered to the user's head position and orientation (Oyama et al., 1993; MacDowall et al., 1990~. These systems remove the inertial burden of head-mounted displays yet allow the use of more readily available, nonminiature, high-resolution color panel display devices to generate the imagery.
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From page 123... ...
An advantage of SE applications is the ability to control the illuminatio environment, making many problems in LC display technology, such as angular field of view, less critical. Some indication of the possible resolution available with LC techniques on silicon is the application of liquid crystals to diagnosis of failing integrated circuit parts, in which lines of under 3 ,u are routinely imaged (Picart et al., 1989~.
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From page 124... ...
are required and no inertial burden is added to the human user. Depending on the size of their viewing zone or viewing volume, autostereoscopic displays can be seen by multiple viewers.
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From page 125... ...
Since autostereoscopic displays entail either restricted viewing volumes or large, resolution-limited display surfaces, however, they may not be appropriate for SE applications requiring a completely encompassing viewing volume (McKenna and Zeltzer, 1992~. Lenticular Displays A lenticular sheet is an array of cylindrical lenses that can be used to generate an autostereoscopic three-dimensional image by directing different two-dimensional images into viewing subzones.
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From page 126... ...
As the mirror vibrates, its focal length changes, and a reflected monitor is imaged, over time, in a truncated-pyramid viewing volume. The mirror continuously changes its magnification, so that imagery scanned over time (as a CRT operates)
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From page 127... ...
Holographic Displays Computer-generated holograms fall under two main categories, computer-generated stereograms and computer-generated diffraction patterns Computer-generated stereograms are recorded optically, from a set of two-dimensional views of a three-dimensional scene. The final hologram projects each two-dimensional image into a viewing zone, and stereo views can be seen with horizontal parallax (Benson, 1982~.
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From page 128... ...
Integrated Systems In the United States, following the pioneering work of Ivan Sutherland and his students in the late 1960s, research and development of display systems for synthetic environments have been carried out at MIT's Media Lab, the Ames and Langley Research Centers of the National Aeronautics and Space Administration (NASA) , Wright-Patterson Air Force Base, the Naval Ocean Systems Center, the University of North Carolina, LEEP Optics, the University of Washington, the Japanese government's Mechanical Engineering Laboratory at Tsukuba, CAE Electronics, VPL Research, Virtual Research, Technology Innovation Group, Kaiser Electronics Electro-Optics Division, Hughes Electro-Optical & Data Systems Group, Stereographics Corporation, and Fake Space Labs, to name a few of the more prominent research and development centers in academia, government, and private industry.
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From page 129... ...
These systems are often commercial variants of military systems and are introducing color CRT-based and advanced solid-state-based display devices to the commercial marketplace. Virtual Research, upon discontinuing its successful Flight Helmet, introduced a lightweight helmet-mounted display using miniature monochrome CRTs with color wheels known as the EYEGEN3.
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From page 130... ...
x 960 (V) interlaced resolution using color filtering techniques.
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From page 131... ...
weight and inertial burdens imposed by most HMDs affect the incidence of symptomatic motion sickness, the ability of users to make proper judgments concerning orientation, and their longterm habitability; and (3) due to size, performance, and cost constraints, fixation/focus compensation is utilized in most HMDs and conflicting visual depth cues are provided to the user.
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From page 132... ...
It seems prudent for both CRTbased and solid-state device-based approaches for display devices to be pursued. A particular area for emphasis should be the development of miniature, high-resolution CRT and solid-state display surfaces, since commercial pressures tend toward larger versions of these devices and HMDs require smaller versions.
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From page 133... ...
How do we design a comfortable HMD that integrates visual, auditory, and position tracking capabilities? These are but a few of the many research issues that impact the practical design of any visual display system for synthetic environments.
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