In this paper we discuss the creation of visual mementos as a new application area for visualization. We define visual mementos as visualizations of personally relevant data for the purpose of reminiscing, and sharing of life experiences. Today more people collect digital information about their life than ever before. The shift from physical to digital archives poses new challenges and opportunities for self-reflection and self-representation. Drawing on research on autobiographical memory and on the role of artifacts in reminiscing, we identified design challenges for visual mementos: mapping data to evoke familiarity, expressing subjectivity, and obscuring sensitive details for sharing. Visual mementos can make use of the known strengths of visualization in revealing patterns to show the familiar instead of the unexpected, and extend representational mappings beyond the objective to include the more subjective. To understand whether people's subjective views on their past can be reflected in a visual representation, we developed, deployed and studied a technology probe that exemplifies our concept of visual mementos. Our results show how reminiscing has been supported and reveal promising new directions for self-reflection and sharing through visual mementos of personal experiences.

Although there has been widespread proliferation of creative-coding programming languages, the design of many toolkits and application programming interfaces (APIs) for expression and interactivity do not take full advantages of the unique space of mobile multitouch devices. In designing a new API for this space we first consider five major problem spaces and present an architecture that attempts to address these to move beyond the low-level manipulation of graphics giving first-class status to media objects.

There are about as many strategies for listening to music as there are music enthusiasts. This makes learning about overarching patterns and similarities difficult. In this paper, we present an empirical analysis of long-term music listening histories from the last.fm web service. It gives insight into the most distinguishing factors in music listening behavior. Our sample contains 310 histories with up to six years duration and 48 associated variables describing various user and music characteristics. Using a principal components analysis, we aggregated these variables into 13 components and found several correlations between them. The analysis especially showed the impact of seasons and a listener's interest in novelty on music choice. Using this information, a sample of a user's listening history or even just demographical data could be used to create personalized interfaces and novel recommendation strategies. We close with derived design considerations for future music interfaces.

Handheld optical projectors provide a simple way to overcome the limited screen real-estate on mobile devices. We present virtual projection (VP), an interaction metaphor inspired by how we intuitively control the position, size, and orientation of a handheld optical projector's image. VP is based on tracking a handheld device without an optical projector and allows selecting a target display on which to position, scale, and orient an item in a single gesture. By relaxing the optical projection metaphor, we can deviate from modeling perspective projection, for example, to constrain scale or orientation, create multiple copies, or offset the image. VP also supports dynamic filtering based on the projection frustum, creating overview and detail applications, and selecting portions of a larger display for zooming and panning. We show exemplary use cases implemented using our optical feature-tracking framework and present the results of a user study demonstrating the effectiveness of VP in complex interactions with large displays.

We present Cardiogram, a visual analytics system that supports automotive engineers in debugging masses of traces each consisting of millions of recorded messages from in-car communication networks. With their increasing complexity, ensuring these safety-critical networks to be error-free has become a major task and challenge for automotive engineers. To overcome shortcomings of current analysis tools, Cardiogram combines visualization techniques with a data preprocessing approach to automatically reduce complexity based on engineers' domain knowledge. In this paper, we provide the findings from an exploratory, three-year field study within a large automotive company, studying current practices of engineers, the challenges they meet and the characteristics for integrating novel visual analytics tools into their work practices.

Multi-touch screens and surfaces for manipulating digital content play a crucial role in mobile and ubiquitous computing. Augmenting these interactive surfaces with tactile feedback has been found to increase interaction speed, reduce operating errors and minimize visual and cognitive load. Communicating detailed tactile characteristics of virtual elements, however, requires complex electromechanical or electrostatic actuator setups. This increase in complexity makes tactile interfaces intricate, costly or poorly scalable. In order to provide sophisticated tactile sensations with simple actuator technology, we exploit a haptic psychophysical phenomenon called Phantom Sensation. We present a comparison of three standard tactile actuator technologies to see which one can recreate the Phantom Sensation with maximum effect. Our results show the way to a simple and scalable implementation of illusion-based tactile feedback for interactive surfaces. We explore the notion of the Phantom Sensation and its possible applications within a ubicomp scenario.

Currently available user interfaces for playlist generation allow creating playlists in various ways, within a spectrum from fully automatic to fully manual. However, it is not entirely clear how users interact with such systems in the field and whether different situations actually demand different interfaces. In this paper we describe Rush 2, a music interface for mobile touch-screen devices that incorporates three interaction modes with varying degrees of automation: Adding songs manually, in quick succession using the rush interaction technique or filling the playlist automatically. For all techniques various filters can be set. In a two- week diary study (with in-depth interaction logging) we gained insight into how people interact with music in their everyday lives and how much automation and interactivity are really necessary.

In 1992, Tani et al. proposed remotely operating machines in a factory by manipulating a live video image on a computer screen. In this paper we revisit this metaphor and investigate its suitability for mobile use. We present Touch Projector, a system that enables users to interact with remote screens through a live video image on their mobile device. The handheld device tracks itself with respect to the surrounding displays. Touch on the video image is projected onto the target display in view, as if it had occurred there. This literal adaptation of Tani's idea, however, fails because handheld video does not offer enough stability and control to enable precise manipulation. We address this with a series of improvements, including zooming and freezing the video image. In a user study, participants selected targets and dragged targets between displays using the literal and three improved versions. We found that participants achieved highest performance with automatic zooming and temporary image freezing.

We present rush as a recommendation-based interaction and visualization technique for repeated item selection from large data sets on mobile touch screen devices. Proposals and choices are intertwined in a continuous finger gesture navigating a two-dimensional canvas of recommended items. This provides users with more flexibility for the resulting selections. Our design is based on a formative user study regarding orientation and occlusion aspects. Subsequently, we implemented a version of rush for music playlist creation. In an experimental evaluation we compared different types of recommendations based on similarity, namely the top 5 most similar items, five random selections from the list of similar items and a hybrid version of the two. Participants had to create playlists using each condition. Our results show that top 5 was too restricting, while random and hybrid suggestions had comparable results.

The choices we take when listening to music are expressions of our personal taste and character. Storing and accessing our listening histories is trivial due to services like Last.fm, but learning from them and understanding them is not. Existing solutions operate at a very abstract level and only produce statistics. By applying techniques from information visualization to this problem, we were able to provide average people with a detailed and powerful tool for accessing their own musical past. LastHistory is an interactive visualization for displaying music listening histories, along with contextual information from personal photos and calendar entries. Its two main user tasks are (1) analysis, with an emphasis on temporal patterns and hypotheses related to musical genre and sequences, and (2) reminiscing, where listening histories and context represent part of one's past. In this design study paper we give an overview of the field of music listening histories and explain their unique characteristics as a type of personal data. We then describe the design rationale, data and view transformations of LastHistory and present the results from both a lab- and a large-scale online study. We also put listening histories in contrast to other lifelogging data. The resonant and enthusiastic feedback that we received from average users shows a need for making their personal data accessible. We hope to stimulate such developments through this research.

The history of songs, to which a person has listened, is a very personal piece of information. It is a rich data set that comes as a byproduct of the use of digital music players and can be obtained without interfering with the user.

Aesthetics is an unsolved problem of information visualization, because there is no satisfactory understanding of what constitutes aesthetic effect. This survey paper gives an overview of approaches to model aesthetics, starting with Birkhoffpsilas aesthetic measure and continuing to recent ones based on mathematical and information theoretical concepts. Common concepts in the different models are highlighted, such as the effects of order and complexity. Further, practical techniques for generating aesthetic visualizations are shown together with examples of recent work in this field. Finally, the paper discusses some of the key issues regarding aesthetics and the human factor in the visualization process. Empirical studies have shown a correlation between perceived aesthetics and usability, meaning that a better understanding of aesthetics could improve the usability of visualizations.