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A new method for assisting with the visualization of large multidimensional datasets is proposed. We classify datasets with more than one million elements as large. Multidimensional data elements are elements with two or more dimensions, each of which is at least binary. Multidimensional data visualization involves representation of multidimensional data elements in a low dimensional environment, such as a computer screen or printed media. Traditional visualization techniques are not well suited to solving this problem. Our data visualization techniques are based in large part on a field of cognitive psychology called preattentive processing. Preattentive processing is the study of visual features that are detected rapidly and with little effort by the human visual system. Examples include hue, orientation, form, intensity, and motion. We studied ways of extending and applying research results from preattentive processing to address our visualization requirements. We used our investigations to build visualization tools that allow a user to very rapidly and accurately perform exploratory analysis tasks. These tasks include searching for target elements, identifying boundaries between groups of common elements, and estimating the number of elements that have a specific visual feature. Our experimental results were positive, suggesting that dynamic sequences of frames can be used to explore large amounts of data in a relatively short period of time. Recent work in both scientific visualization and database systems has started to address the problems inherent in managing large scientific datasets. One promising technique is knowledge discovery, "the nontrivial extraction of implicit, previously unknown, and potentially useful information from data". We hypothesise that knowledge discovery can be used as a filter to reduce the amount of data sent to the visualization tool. Data elements that do not belong to a user-chosen group of interest can be discarded, the dimensionality of individual data elements can be compressed, and previously unknown trends and relationships can be discovered and explored. We illustrate how our techniques can be used by applying them to real-world data and tasks. This includes the visualization of simulated salmon migration results, computerized tomography medical slices, and environmental datasets that track ocean and atmospheric conditions.

Proceedings of Graphics Interface '93, Toronto, Ontario, Canada, 19-21 May 1993, 107-117

A new method for designing multivariate data visualization tools is presented. Multivariate data visualization involves representation of data elements with multiple dimensions in a low dimensional enviroment, such as a computer screen or printed media. Our tools are designed to allow users to perform simple tasks like estimation, target detection, and detection of data boundaries rapidly and accurately. These techniques could be used for large datasets where more traditional techniques do not work well or for time-sensitive applications that require rapid understanding and informative data displays. Our design technique is based on principles arising in an area of cognitive psychology called preattentive processing. Preattentive processing studies visual features that are “preattentively” detected by the human visual system. Viewers do not have to focus their attention on particular regions of an image to determine whether elements with certain features are present or absent. Examples of preattentive features include colour, orientation, intensity, size, shape, curvature, and line length. Because this ability is part of the low-level human visual system, detection is performed very rapidly, almost certainly using a large degree of parallelism. In this thesis we investigate the hypothesis that these features can be used to effectively represent multivariate data elements. Visualization tools that use this technique will allow users to perform rapid and accurate visual processing of their data displays. We chose to investigate two known preattentive features, colour and orientation. The particular question investigated is whether rapid and accurate estimation is possible using these preattentive features. Experiments that simulated displays using our preattentive visualization tool were run. The experiments used data similar to that which occurred in a set of salmon migration studies. This choice was made to investigate the likelihood of our techniques being relevant to real-world problems. Analysis of the results of the experiments showed that rapid and accurate estimation is possible with both colour and orientation. A second question, whether interaction occurs between the two features, was answered negatively. Additional information about exposure durations and feature and data interaction were also discovered.