This paper describes a radial basis memory system that is used to model the performance of human participants in a task
of learning to traverse mazes in a virtual environment. The memory model is a multiple-trace system, in which each
event is stored as a separate memory trace. In the modeling of the maze traversal task, the events that are stored as
memories are the perceptions and decisions taken at the intersections of the maze. As the virtual agent traverses the
maze, it makes decisions based upon all of its memories, but those that match best to the current perceptual situation, and
which were successful in the past, have the greatest influence. As the agent carries out repeated attempts to traverse the
same maze, memories of successful decisions accumulate, and performance gradually improves. The system uses only
three free parameters, which most importantly includes adjustments to the standard deviation of the underlying Gaussian
used as the radial basis function. It is demonstrated that adjustments of these parameters can easily result in exact
modeling of the average human performance in the same task, and that variation of the parameters matches the variation
in human performance. We conclude that human memory interaction that does not involve conscious memorization, as
in learning navigation routes, may be much more primitive and simply explained than has been previously thought.
As virtual environments may be used in training and evaluation for critical real navigation tasks, it is important to
investigate the factors influencing navigational performance in virtual environments. We have carried out controlled
experiments involving two visual factors known to induce or sustain vection, the illusory perception of self-motion. The
first experiment had subjects navigate mazes with either a narrow or wide field of view. We measured the percentage of
wrong turns, the total time taken for each attempt, and we examined subjects' drawings of the mazes. We found that a
wide field of view can have a substantial effect on navigational abilities, even when the wide field of view does not offer
any additional clues to the task, and really only provides a larger view of blank walls on the sides. The second
experiment evaluated the effect of perspective accuracy in the scene by comparing the use of displays that were corrected
for changing head position against those that were not corrected. The perspective corrections available through headtracking
did not appear have any influence on navigational abilities. Another component of our study suggests that
during navigation in a virtual environment, memory for directions may not be as effective as it could be with
supplemental symbolic representations.
KEYWORDS: Virtual reality, Computer simulations, Electronic imaging, Human-machine interfaces, Human vision and color perception, Buildings, Head-mounted displays, Head
In this research we are concerned with computer interfaces with which subjects navigate through maze simulations which are essentially buildings, with corridors and intersections, such as frequently encountered in computer games and simulations. We wish to determine if virtual reality interfaces introduce a performance enhancement that might be expected for display configurations which mimic natural perceptual experiences. We have experimented primarily with two display conditions for presentation of and navigation through the mazes. Subjects either view the maze on a desktop computer monitor, turning and moving within the maze with the mouse in a way that is similar to the configurations used in most first-person role playing computer games, or they viewed the maze from a standing position with a head-mounted display, being free to direct the view of the maze through body and head movements, and using the depression of a mouse button to effect movement in the direction that they were facing. Head-tracking was required for this latter condition. As expected there are striking individual differences in subjects’ abilities to learn to traverse the mazes. Across a variety of maze configuration parameters which significantly do influence performance, the results indicate that the virtual reality enhancements have no effect subjects' ability to learn the mazes, either as route knowledge or as cognitive maps.
We have conducted experiments in which subjects are asked to make judgments about the shape of graphically rendered, rotating convex objects. As compared with monoscopic display, stereographic display enhances the subjective clarity of object shape. There are two obvious candidates for the source of this enhancement. One possibility is that the occluding contour is seen as a rotating 3D outline, providing greater object stability, and therefore better cues to the overall shape. Another possibility is that patches of the shaded surface may be perceived in depth, providing a clearer perception of the local surface curvature, and therefore a better sense of the overall shape. In this paper we present an empirical examination of the effects of including stereopsis in the task of shape understanding, and we isolate and compare these two possible explanations.
Future computer interfaces will likely use 3D displays with stereographic viewing to take advantage of the increased information inherent in 3D. The appropriate roles of devices to manipulate 3D displays, including the mouse, joystick and head tracking remain unresolved. Our research centers on the use of head tracking for the control of perspective. For monoscopic viewing, we previously found that viewers can control displays effectively with head movements. They learn rapidly to use head movements, though scene adjustments amplify or even reverse natural perspective changes, and this ability persist over time. With stereo viewing, if head movements do ont produce the expected change in perspective, the viewer may be confused, reducing the effectiveness of head tracking. We tested these conjectures in the experiment reported here, establishing the extent to which the flexibility found under monoscopic viewing extends to stereo. As in previous experiments, the viewer makes head movements to see a target sphere through a ring positioned in virtual space between the viewer and the target. We used a variety of ring sizes and position to measure the speed and directness of movement under four conditions that varied the scene location in depth, plus the extent and direction of perspective change. These combinations permit us to evaluate the effects of direction and extent of scene adjustment on viewers' ability to use head movements to alter virtual viewpoint. While we found no difference for reversed adjustments under monoscopic viewing, these conditions appear more difficult in stereo viewing. Furthermore, viewers perform better when perspective changes are amplified.
KEYWORDS: Genetics, Neural networks, Neurons, Network architectures, Optical character recognition, Computer programming, Genetic algorithms, Databases, Signal processing, Control systems
Determining exactly which neural network architecture, with which parameters, will provide the best solution to a classification task is often based upon the intuitions and experience of the implementers of neural network solutions. The research presented in this paper is centered on the development of automated methods for the selection of appropriate networks, as applied to character recognition. The Network Generating Attribute Grammar Encoding system is a compact and general method for the specification of commonly accepted network architectures that can be easily expanded to include novel architectures, or that can be easily restricted to a small subset of some known architecture. Within this system, the context-free component of the attribute grammar specifies a class of basic architectures by using the non-terminals to represent network, layers and component structures. The inherited and synthesized attributes indicate the connections necessary to develop a functioning network from any parse tree that is generated from the grammar. The attribute grammar encoding is particularly conducive to the use of genetic algorithms as a strategy for searching the space of possible networks. The resultant parse trees are used as the genetic code, permitting a variety of different genetic manipulations. We apply this approach in the generation of backpropagation networks for recognition of characters from a set consisting of 20,000 examples of 26 letters.
Effective computer graphic applications should accurately convey 3D shape. Previously, we investigated the contributions of shading and contour, specular highlights, and light source direction to 3D shape perception. Our experiments use displays of convex solid objects based on the superquadric parameterization, permitting continuous variation in their cross-sectional shapes. Our present work concerns the impact of surface markings. Rotating wireframe or uniformly shaded objects may produce perceptually distorting shapes. We investigate the idea that such distortions interfere with shape judgements, and that surface markings may either enhance perceptual accuracy by encouraging stability, or impair it by interfering with global shading patterns. Our displays include rotating objects with no surface markings, stripes, latitudinal or longitudinal stripes, each with two different scene illuminations. Observers view pairs of objects, a target shape and a second object whose shape they adjust, using mouse clicks, to match that of the target. Our principal result is that these surface patterns do not enhance performance, even though the chosen stripe intensities minimize interference with global shading, and the stripe patterns may actually encode surface curvature. We are now investigating alternatives for applying surface patterns to modelled objects, including hardware supported texture mapping. Our long term goal remains the identification of a comprehensive set of conditions for optimizing shape understanding of graphic objects.
Identifying appropriate roles for the components of advanced interfaces is a significant research challenge. We expect head movements to assume their natural role in controlling viewpoint, and we are investigating the use of head tracking to provide perspective control. We apply this to a task of adjusting the viewpoint to detect a target at the bottom of a virtual cylinder. The cylinder varies in diameter, height and orientation. We record viewpoint trajectories and elapsed times. Observers participate in one of two conditions: in the Head-as-Head condition, viewpoint changes correspond to observing a real scene; in the Head-as-Hand condition, rotational directions are reversed, simulating manipulation of an object. To evaluate initial learning and consolidation effects there are two sessions of massed trials, two day apart. The results show a rapid learning effect, and solid retention over the two day interval. Performance levels are similar for the two opposite mappings, indicating flexibility in the use of head- controlled viewpoint. We continue to apply the paradigm to other questions about head-controlled viewpoint manipulation, such as establishing a boundary between small movements producing natural parallax changes, versus extended movements involving large scale viewpoint changes.
Accurately conveying three-dimensional shape is a requirement for many computer graphic applications. The general belief that we call the photorealism assumption asserts that understanding of depicted object shapes improves with increasing realism of the display. We contend that parameters determining a graphic rendering vary widely in importance for accurately portraying shape. By identifying the relative contributions of rendering parameters, we provide a framework for developing cost-effective display systems. Our current work concerns the role of light direction in conveying the three-dimensional shape of depicted objects. In our experiments, we present sequences of displays that each show an elongated superquadric object. An observer attempts to reproduce the shape of the cross section orthogonal to the elongated axis by adjusting a sample contour. The object rotates continuously so that observers solve the task from an overall understanding of the shape, rather than from static two-dimensional features. We vary the shapes of the superquadric objects, as well as the illumination directions. Our results indicate that the accuracy of observer's estimates is surprisingly robust to these variations.
During normal viewing of an object, a human observer will typically make small movements in the position of the head resulting in small parallax-related image changes. The significance of these changes is apparent when viewing a static stereographic display. Since the observer expects modifications in viewing direction that accompany side to side head movements, the lack of such changes in viewing stereographic displays creates the striking illusion that the static display is rotating in a compensatory direction. Using head tracking, we generate the appropriate pairs of images on a stereographic display device in order to maintain a stable virtual stereo object for the viewer. Unnatural, but learnable mappings from input devices such as a mouse or a joystick are typically used to bring about changes in the viewing direction and viewing distance in graphic displays. As an alternative to these techniques, we have extended the use of the monitored head position, resulting in a display system that permits control of graphic objects with subtle head movements. The device permits a zone of small head movements for which there is no rotation or scaling of the virtual object, but only parallax-related images changes as projected to each eye. A slightly exaggerated head movement initiates rotation and/or scaling of the scene that terminates when the head returns to a central viewing position. We are carrying out experiments to test the performance of human subjects in tasks that require head movements to control the rotation of graphic objects. A preliminary study that only examines rotation around a single axis suggests that it may be a very effective and natural technique.
Graphic displays for virtual environments and telerobotics require effective communication of the details of 3-D object shape. This paper presents empirical evidence on the relation between human perception and several properties of graphic shape depiction. A series of experiments examined a 3-D shape discrimination task requiring judgments of superquadric volume primitives varying in shape within different rendering and display conditions. The displays were dynamic, with constant rotational motion. Over the series of experiments, the contributions of diffuse and specular shading, occluding contour, aspect ratio, and covarying size were evaluated. The results revealed a consistent sensitivity to differences in superquadric shape parameters, that was surprisingly robust over rendering variations. One major finding was that the presence of specular highlights did not enhance shape discrimination performance beyond that observed for purely diffuse reflectance. The results suggest strategies for optimizing interface properties where 3-D shape is a primary component of the display. They also support the use of superquadric primitives in situations where humans interact with shape display systems.
A central issue in teleoperation is the provision of appropriate perceptual information for the remote human operator. We have developed an experimental teleoperation system which provides the capability of displaying graphic simulation images that accurately depict actual robot operation. Our experimentation compares the use of monocular operator-controlled- viewpoint displays to conditions in which the operation of the robot is viewed directly. The robot gripper was moved through a balanced set of trajectories relative to an object in the workspace, and subjects were required to make a forced-choice judgement as to whether or not the gripper would collide with the object. Significantly more errors were encountered in the live-monocular and fixed-simulation conditions than were found in either the live-stereo or the controlled-simulation conditions, while there were no significant performance differences between these two more effective display conditions. An analysis indicates that the angle formed between viewing direction and the line of motion of the robot gripper is a strong determiner of the number of errors that are made.
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