Colin Ware

Evaluating stereo and motion cues for visualizing information nets in three dimensions

This article concerns the benefits of presenting abstract data in 3D. Two experiments show that motion cues combined with stereo viewing can substantially increase the size of the graph that can be preceived. The first experiment was designed to provide quantitiative measurements of how much more (or less) can be understood in 3D than in 2D. The 3D display used was configured so that the image on the monitor was coupled to the users actual eye positons (and it was updated in real-time as the user moved) as well as bring in stereo. Thus the effect was like a local “virtual reality” display located in the vicinity of the computer monitor. The results from this study show that head-coupled stereo viewing can increase the size of an abstract graph that can be understood by a factor of three; using stereo alone provided an increase by a factor of 1.6 and head coupling along produced an increase by a factor of 2.2. The second experiment examined a variety of motion cues provided by head-coupled perspective (as in virtual reality displays), head-guided motion and automatic rotation, respectively, both with and without stereo in each case. The results show that structured 3D motion and stereo viewing both help in understanding, but that the kind of motion is not particularly important; all improve performance, and all are more significant than stereo cues. These results provide strong reasons for using advanced 3D graphics for interacting with a large variety of information structures.

An evaluation of an eye tracker as a device for computer input2

Since humans direct their visual attention by means of eye movements, a device which monitors eye movements should be a natural “pick” device for selecting objects visually present on a monitor. The results from an experimental investigation of an eye tracker as a computer input device are presented. Three different methods were used to select the object looked at; these were a button press, prolonged fixation or “dwell” and an on screen select button. The results show that an eye tracker can be used as a fast selection device providing that the target size is not too small. If the targets are small speed declines and errors increase rapidly.

Fish tank virtual reality

The defining characteristics of what we call “Fish Tank Virtual Reality” are a stereo image of a three dimensional (3D) scene viewed on a monitor using a perspective projection coupled to the head position of the observer. We discuss some of the relative merits of this mode of viewing as compared to head mounted stereo displays. In addition, we report the experimental investigation of the following variables: 1) whether or not the perspective view is coupled to the actual viewpoint of the observer, 2) whether stereopsis is employed. Experiment 1 involved the subjective comparison of pairs of viewing conditions and the results suggest that head coupling may be more important than stereo in yielding a strong impression of three dimensionality. Experiment 2 involved subjects tracing a path from a leaf of a 3D tree to the correct root (there were two trees intermeshed). The error rates ranged from 22% in the pictorial display, to 1.3% in the head coupled stereo display. The error rates for stereo alone and head coupling alone were 14.7% and 3.2% respectively. We conclude that head coupling is probably more important than stereo in 3D visualization and that head coupling and stereo combined provide an important enhancement to monitor based computer graphics.

Cognitive measurements of graph aesthetics

A large class of diagrams can be informally characterized as node–link diagrams. Typically nodes represent entities, and links represent relationships between them. The discipline of graph drawing is concerned with methods for drawing abstract versions of such diagrams. At the foundation of the discipline are a set of graph aesthetics (rules for graph layout) that, it is assumed, will produce graphs that can be clearly understood. Examples of aesthetics include minimizing edge crossings and minimizing the sum of the lengths of the edges. However, with a few notable exceptions, these aesthetics are taken as axiomatic, and have not been empirically tested. We argue that human pattern perception can tell us much that is relevant to the study of graph aesthetics including providing a more detailed understanding of aesthetics and suggesting new ones. In particular, we find the importance of good continuity (ie keeping multi-edge paths as straight as possible) has been neglected. We introduce a methodology for evaluating the cognitive cost of graph aesthetics and we apply it to the task of finding the shortest paths in spring layout graphs. The results suggest that after the length of the path the two most important factors are continuity and edge crossings, and we provide cognitive cost estimates for these parameters. Another important factor is the number of branches emanating from nodes on the path.

Evaluating 3D task performance for fish tank virtual worlds

“Fish tank virtual reality” refers to the use of a standard graphics workstation to achieve real-time display of 3D scenes using stereopsis and dynamic head-coupled perspective. Fish tank VR has a number of advantages over head-mounted immersion VR which makes it more practical for many applications. After discussing the characteristics of fish tank VR, we describe a set of three experiments conducted to study the benefits of fish tank VR over a traditional workstation graphics display. These experiments tested user performance under two conditions: (a) whether or not stereoscopic display was used and (b) whether or not the perspective display was coupled dynamically to the positions of a user’s eyes. Subjects using a comparison protocol consistently preferred head coupling without stereo over stereo without head coupling. Error rates in a tree-tracing task similar to one used by Sollenberger and Milgram showed an order of magnitude improvement for head-coupled stereo over a static (nonhead-coupled) display, and the benefits gained by head coupling were more significant than those gained from stereo alone. The final experiment examined two factors that are often associated with human performance in virtual worlds: the lag (or latency) in receiving and processing tracker data arid the rate at which frames are updated. For the tree-tracing task, lag had a larger impact on performance than did frame update rate, with lag having a multiplicative effect on response time. We discuss the relevance of these results for the display of complex 3D data and highlight areas requiring further study,

Color sequences for univariate maps: theory, experiments and principles

Pseudocoloring for presenting univariate map information on a graphic display system is investigated. The kinds of information available in maps are divided into two classes: metric information denotes the quantity stored at each point on the surface, and form information denotes the shape or structure of the surface. Theoretical principles are proposed to predict which color sequences will be effective at conveying value and form information respectively. According to this theory, a scale that approximates the physical spectrum should be good at conveying value information, because of the reduced effects of simultaneous contrast. It should be poor at conveying form information, however, because the brain prefers form information to come through the lightness-processing channel. Conversely, a gray scale should be poor at conveying value information and good at conveying form information, according to the same theory. These predictions are tested in a series of psychophysical experiments that test five color sequences. The results show that simultaneous contrast can be a major source of error when reading maps, but only partially confirm the form hypothesis. Guidelines are given for designing color sequences to be effective in both conveying form and value information. An experimental color sequence is presented to illustrate these guidelines.<<ETX>>

Moticons: detection, distraction and task

In this paper, we describe an empirical investigation of the utility of several perceptual properties of motion in information-dense displays applied to notification. Notification relates to awareness and how dynamic information is communicated from the system to the user. Key to a notification technique is how easily the notification is detected and identified. Our initial studies show that icons with simple motions, termed moticons, are effective coding techniques for notification and in fact are often better detected and identified than colour and shape codes, especially in the periphery. A subsequent experiment compared the detection and distraction effects of different motion types in several task conditions. Our resutts reveal how different attributes of motion contribute to detection, identification and distraction and provide initial guidelines on how motion codes can be designed to support awareness in information-rich interfaces while minimizing unwanted side effects of distraction and irritation.

User Studies: Why, How, and When?

User studies offer a scientifically sound method to measure a visualizations performance. Reasons abound for pursuing user studies, particularly when evaluating the strengths and weaknesses of different visualization techniques. A good starting point in any study is the scientific or visual design question to be examined. This drives the process of experimental design. A poorly designed experiment will yield results of only limited value. Although a comprehensive discussion of experimental design is beyond the scope of the article, we offer suggestions and lessons learned. We also describe how we designed experiments to answer important questions from our own research.

Rotating virtual objects with real handles

Times for virtual object rotations reported in the literature are of the order of 10 seconds or more and this is far longer than it takes to manually orient a “real” object, such as a cup. This is a report of a series of experiments designed to investigate the reasons for this difference and to help design interfaces for object manipulation. The results suggest that two major factors are important. Having the hand physically in the same location as the virtual object being manipulated is one. The other is based on whether the object is being rotatted to a new, randomly determined orientation, or is always rotated to the same position. Making the object held in the hand have the same physical shape as the object being visually manipulated was not found to be a significant factor. The results are discussed in the context of interactive virtual environments.

Zooming versus multiple window interfaces: Cognitive costs of visual comparisons

In order to investigate large information spaces effectively, it is often necessary to employ navigation mechanisms that allow users to view information at different scales. Some tasks require frequent movements and scale changes to search for details and compare them. We present a model that makes predictions about user performance on such comparison tasks with different interface options. A critical factor embodied in this model is the limited capacity of visual working memory, allowing for the cost of visits via fixating eye movements to be compared to the cost of visits that require user interaction with the mouse. This model is tested with an experiment that compares a zooming user interface with a multi-window interface for a multiscale pattern matching task. The results closely matched predictions in task performance times; however error rates were much higher with zooming than with multiple windows. We hypothesized that subjects made more visits in the multi-window condition, and ran a second experiment using an eye tracker to record the pattern of fixations. This revealed that subjects made far more visits back and forth between pattern locations when able to use eye movements than they made with the zooming interface. The results suggest that only a single graphical object was held in visual working memory for comparisons mediated by eye movements, reducing errors by reducing the load on visual working memory. Finally we propose a design heuristic: extra windows are needed when visual comparisons must be made involving patterns of a greater complexity than can be held in visual working memory.