Camilla Forsell

An heuristic set for evaluation in information visualization

Evaluation is a key research challenge within the international Information Visualization (InfoVis) community, and Heuristic Evaluation is one recognized method. Various sets of heuristics have been proposed but there remains no consensus as to which heuristics are most useful for addressing aspects specific to the complex interactive visual displays used in modern InfoVis systems. This paper presents a first effort to empirically determine a new set of such general heuristics tailored for Heuristic Evaluation of common and important usability problems in InfoVis techniques. Participants in the study rated how well a total of 63 heuristics from 6 earlier published heuristic sets could explain a collection of 74 usability problems derived from earlier InfoVis evaluations. The results were used to synthesize 10 heuristics that, as a set, provided the highest explanatory coverage. The paper also stresses the challenges for future research to validate and further improve upon this set.

Multi-Touch Table System for Medical Visualization: Application to Orthopedic Surgery Planning

Medical imaging plays a central role in a vast range of healthcare practices. The usefulness of 3D visualizations has been demonstrated for many types of treatment planning. Nevertheless, full access to 3D renderings outside of the radiology department is still scarce even for many image-centric specialties. Our work stems from the hypothesis that this under-utilization is partly due to existing visualization systems not taking the prerequisites of this application domain fully into account. We have developed a medical visualization table intended to better fit the clinical reality. The overall design goals were two-fold: similarity to a real physical situation and a very low learning threshold. This paper describes the development of the visualization table with focus on key design decisions. The developed features include two novel interaction components for touch tables. A user study including five orthopedic surgeons demonstrates that the system is appropriate and useful for this application domain.

Interaction Support for Visual Comparison Inspired by Natural Behavior

Visual comparison is an intrinsic part of interactive data exploration and analysis. The literature provides a large body of existing solutions that help users accomplish comparison tasks. These solutions are mostly of visual nature and custom-made for specific data. We ask the question if a more general support is possible by focusing on the interaction aspect of comparison tasks. As an answer to this question, we propose a novel interaction concept that is inspired by real-world behavior of people comparing information printed on paper. In line with real-world interaction, our approach supports users (1) in interactively specifying pieces of graphical information to be compared, (2) in flexibly arranging these pieces on the screen, and (3) in performing the actual comparison of side-by-side and overlapping arrangements of the graphical information. Complementary visual cues and add-ons further assist users in carrying out comparison tasks. Our concept and the integrated interaction techniques are generally applicable and can be coupled with different visualization techniques. We implemented an interactive prototype and conducted a qualitative user study to assess the concepts usefulness in the context of three different visualization techniques. The obtained feedback indicates that our interaction techniques mimic the natural behavior quite well, can be learned quickly, and are easy to apply to visual comparison tasks.

2D and 3D representations for feature recognition in time geographical diary data

Time geographical representations are becoming a common approach to analysing spatio-temporal data. Such representations appear intuitive in the process of identifying patterns and features as paths of populations form tracks through the 3D space, which can be seen converging and diverging over time. In this article, we compare 2D and 3D representations within a time geographical visual analysis tool for activity diary data. We identify a representative task and evaluate task performance between the two representations. The results show that the 3D representation has benefits over the 2D representation for feature identification but also indicate that these benefits can be lost if the 3D representation is not carefully constructed to help the user to see them.

Concurrent volume visualization of real-time fMRI

We present a novel approach to interactive and concurrent volume visualization of functional Magnetic Resonance Imaging (fMRI). While the patient is in the scanner, data is extracted in real-time using state-of-the-art signal processing techniques. The fMRI signal is treated as light emission when rendering a patient-specific high resolution reference MRI volume, obtained at the beginning of the experiment. As a result, the brain glows and emits light from active regions. The low resolution fMRI signal is thus effectively fused with the reference brain with the current transfer function settings yielding an effective focus and context visualization. The delay from a change in the fMRI signal to the visualization is approximately 2 seconds. The advantage of our method over standard 2D slice based methods is shown in a user study. We demonstrate our technique through experiments providing interactive visualization to the fMRI operator and also to the test subject in the scanner through a head mounted display.

An Introduction and Guide to Evaluation of Visualization Techniques Through User Studies

The objective of this chapter is to increase awareness of what constitutes a sound scientific approach to evaluation through user studies in visualization, and to provide basic knowledge of current research practice relating to usability and evaluation. The content covers the most fundamental and relevant issues to consider during the different phases of an evaluation: planning, design, execution, analysis of results and reporting. It outlines how to proceed to achieve high quality results and points out common mistakes during the different phases and how these could be avoided. The chapter can be used as a guide when planning to conduct an evaluation study. The reader will also learn to better judge the relevance and quality of a publication presenting an evaluation when reviewing such work, since the same guidelines apply.

A Guide to Scientific Evaluation in Information Visualization

This paper addresses some fundamental and practical issues that should be considered when pursuing evaluation studies in Information Visualization. The main focus is on quantitative experimental research but the general information applies to all kinds of studies. The purpose is to increase awareness of what constitutes a sound scientific approach to evaluation and to point out common pitfalls and mistakes during the phases of such study. These phases cover how to plan, design, conduct and analyse the outcome of an evaluation and finally how to report in a way that enhances readability, provides details relevant to the outcome and that allows replication. The paper could be used as a guide when conducting evaluation and it could also be helpful when reviewing publications since the same rules apply.

The impact of feedback design in haptic volume visualization

Enhancing volume visualization with additional cues from our sense of touch has shown the potential to increase both speed and accuracy in the data exploration. Research in the area display a wide array of modes of interaction and many of these have been evaluated to demonstrate their capabilities. There are, however, few studies performed that compare different approaches for their strengths and weaknesses and there is a lack of guidelines on how the haptic feedback should be designed to allow for best performance. This paper describes a study on the influence of the basic principle chosen for data representation on the ability to identify faint structures in the data. Three metaphors are compaired, two types of shape metaphors and one force metaphor. Based on statistical analysis on evaluation data, interviews and observations a set of guidelines on the design of haptic visualization is described.

Analysis of the JND of stiffness in three modes of comparison

Understanding and explaining perception of touch is a non-trivial task. Even seemingly trivial differences in exploration may potentially have a significant impact on perception and levels of discrimination. In this study, we explore different aspects of contact related to stiffness perception and their effects on the just noticeable difference (JND) of stiffness are surveyed. An experiment has been performed on non-deformable, compliant objects in a virtual environment with three different types of contact: Discontinuous pressure, continuous pressure and continuous lateral motion. The result shows a significantly better discrimination performance in the case of continuous pressure (a special case of nonlinearity), which can be explained by the concept of haptic memory. Moreover, it is found that the perception is worse for the changes that occur along the lateral axis than the normal axis.

Voyage Analysis Applied to Geovisual Analytics

This paper demonstrates the synergy of common InfoVis and GeoVis interaction techniques and the logistic application domain demonstrated in the customized visualize performance data (VISPER) application. In VISPER multi-dimensional, multi-source, time-varying and geospatial digital information from voyage analysis is represented to facilitate decision-making. Using common InfoVis components for multivariate data together with logistics visualization in a new synergy aids the users in their work examining ship and route performance. An evaluation of the usability was performed to gather insights for future development. The results from the evaluation show that the overall impression of VISPER was highly positive and participants enjoyed using it. Feedback obtained was highly valuable and directly applicable for improvements and further development.