Understanding Visualization through Spatial Ability Differences Maria C. Velez* Deborah Silver* Marilyn Tremaine* Center for Advanced Information Processing Rutgers, the State University of New Jersey ABSTRACT Little is known about the cognitive abilities which influence the comprehension of scientific and information visualizations and what properties of the visualization affect comprehension. Our goal in this paper is to understand what makes visualizations difficult. We address this goal by examining the spatial ability differences in a diverse population selected for spatial ability variance. For example, how is spatial ability related to visualization comprehension? What makes a particular visualization difficult or time intensive for specific groups of subjects? In this paper, we present the results of an experiment designed to answer these questions. Fifty-six subjects were tested on a basic visualization task and given standard paper tests of spatial abilities. An equal number of males and females were recruited in this study in order to increase spatial ability variance. Our results show that high spatial ability is correlated with accuracy on our three-dimensional visualization test, but not with time. High spatial ability subjects also had less difficulty with object complexity and the hidden properties of an object. CR Categories: H.1.2 [Models and Principles]: User/Machine Systems—Human factors H.5.2 [Information Interfaces and Pre- sentation (e.g., HCI)]: User Interfaces—Evaluation/methodology; J.4 [Computer Applications]: Social and Behavioral Sciences— Psychology Additional Keywords: Gender differences, orthogonal projections, spatial ability, standardized testing 1 INTRODUCTION Three-dimensional (3D) representations are common in virtual reality (VR) applications, scientific visualizations, information visualizations, and other computer-human interfaces. Some examples include VR environments used in rehabilitation, orthogonal projections used in 3D design and manufacturing, VR applied to computer-aided instruction, 3D surface renderings of MRI data, 3D representations of financial data, 3D representations of WWW document collections, and interactive virtual worlds that support the exploration of bibliographic retrieval. Experiments in some of these areas suggest that visualization comprehension may vary widely depending on the user’s skills and visualization characteristics. Given the prevalence of 3D imaging devices in all medical specialties (CT, MRI, and fMRI) and the use of these technologies by many fields (e.g., physical therapy, psychology, airport luggage screening), as well as the introduction of 3D representations into general user applications (e.g., WWW information search and retrieval), it is important to understand what factors lead to proper comprehension of 3D visualizations. For example, the picture shown in Figure 1 utilizes a common visualization technique for the estimation of tumor size, shape and location. Low spatial ability skills can negatively impact performance in this or any task that involves the understanding of visualizations containing such implicit spatial arrangements. Research has shown that individuals have highly variant spatial abilities. For example, spatial ability has been found to be one of the most consistent cognitive gender differences [19]. In the field of visualization, the prevailing approach to evaluating scientific and information visualizations is to isolate a particular task or set of tasks that are specific to that visualization or user interface. Such an approach is more like a hill-climbing technique which finds a local solution that may not uncover larger and more serious problems. Furthermore, the number of subjects tested is generally small and/or the selection of subjects based on spatial skills are not accounted for. Paying attention to both of these issues can uncover effects that may have been missed in other studies. This study has chosen to concentrate on fundamental visualization tasks instead of specific applications. To do that, we have designed a basic visualization test that asks the experiment participants to form a mental picture of a 3D object based on its 2D projections. We relate this test to standard spatial ability tests and try to understand what makes a particular visualization difficult for different levels of spatial ability. In this paper we first review work directly related to this area. This is followed by a presentation of the experiment we conducted. We also give an overview of the participants’ demographics in order to confirm that we have successfully recruited a diverse subject population that will provide us with a wide range of spatial skills. Then, we proceed to describe the experimental method. This description includes subject treatment and measurements taken in this study. We conclude this paper with an analysis and summary of the results, illustrating how the methods proposed can be used in a large variety of studies that investigate visualization difficulties. 2 RELATED WORK 2.1 Issues in Visualization Understanding Researchers are constantly looking for new and better ways to visualize complex data. This search has led to a variety of 2D and 3D methods of visualization. Classic 2D visualizations include Figure 1. Example of a visualization task [13] which tests the user’s ability to estimate volume based on 2D visualizations of 3D objects. _____________________________ * mariacv, silver, mtrmaine@caip.rutgers.edu