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W. W. Johnson

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Publications by W. W. Johnson (bibliography)

1988

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Bennett, C. T., Johnson, W. W., Braunstein, M. L., Flach, J. M. and Wolpert, L. (1988): Perspective Displays: The Control of Motion in 3-D Virtual Space. In: Proceedings of the Human Factors Society 32nd Annual Meeting 1988. pp. 1359-1360.

“Perspective displays have been used to better understand how people perceive self translation and rotation. Much of the early work in this are was conducted with cinematic displays and a passive observer. More recently, making use of lower cost, high speed graphics oriented computers, investigators have studied the interactive regulation of perspective scenes. The study of the active control of optical flow has both challenged some early hypotheses, and provided some insight into the impact that methodology has on the perception of perspective displays. The use of perspective displays has also expanded with the opportunity for people to work in 3-D virtual environments. Examples of such environments include work stations in the space shuttle, or indeed any hostile environment where the operator is remote from the viewing plane of a sensor. Such teleoperation has placed a burden on designers of such work stations to understand both the mathematical principles that underlay perspective, as well as the perceptual sensitivity to optical variables. The panel members will discuss the recent developments in the study of optical flow as it relates to the perception of computer generated virtual worlds, and the analytical and methodological techniques involved in the study of perspective displays. But, emphasis will be placed on optical flow and the perception/control of motion while observing perspective displays. The empirical and computational study of optical flow has led to a more complete understanding of the visual information used to control self motion. The term optical flow refers to the relative motion of surface texture elements during angular and/or translational transformation of an observer. Although the mathematical transformation of an entire image is computationally intense, the actual calculation of the movement of texture elements is not difficult. It is based on only three variables: slant angle, slant range, and velocity. Slant angle incorporates both azimuth and elevation of a surface point from the observer. Slant range is the actual line of sight distance between the observer and the texture element. Velocity, of course, incorporates both the speed and the direction of translation or rotation of the observer. It is important to remember that the term optical flow makes reference to the geometric relationship of surface points to an observer, and how that relationship changes as the observer moves. In using the term optical flow, it is not assumed that the observer can or does make appropriate use of the optical information. Optical flow merely makes reference to the physical stimuli. The term visual flow refers to those elements in the optical flow that are supra-threshold. Perspective displays are typically based on the graphical representation of a surface. At a minimum, these displays incorporate the density and compression gradients that describe the plane. Density is defined as the frequency of surface elements within a given viewing angle. Compression refers to the apparent decrease in distance between surface elements as distance from the observer increases. If we are to describe and quantify how a human operator uses a perspective display, we must be careful how we operationally define the very basic concepts discussed above. How such concepts have been quantified will serve as the central theme of the discussions.”

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