Home heating is a major factor in worldwide energy use. Our system, PreHeat, aims to more efficiently heat homes by using occupancy sensing and occupancy prediction to automatically control home heating. We deployed PreHeat in five homes, three in the US and two in the UK. In UK homes, we controlled heating on a per-room basis to enable further energy savings. We compared PreHeat's prediction algorithm with a static program over an average 61 days per house, alternating days between these conditions, and measuring actual gas consumption and occupancy. In UK homes PreHeat both saved gas and reduced MissTime (the time that the house was occupied but not warm). In US homes, PreHeat decreased MissTime by a factor of 6-12, while consuming a similar amount of gas. In summary, PreHeat enables more efficient heating while removing the need for users to program thermostat schedules.

The impact of interruptions on workflow and productivity has been extensively studied in the PC domain, but while fragmented user attention is recognized as an inherent aspect of mobile phone usage, little formal evidence exists of its effect on mobile productivity. Using a survey and a screenshot-based diary study we investigated the types of barriers people face when performing tasks on their mobile phones, the ways they follow up with such suspended tasks, and how frustrating the experience of task disruption is for mobile users. From 386 situated samples provided by 12 iPhone and 12 Pocket PC users, we distill a classification of barriers to the completion of mobile tasks. Our data suggest that moving to a PC to complete a phone task is common, yet not inherently problematic, depending on the task. Finally, we relate our findings to prior design guidelines for desktop workflow, and discuss how the guidelines can be extended to mitigate disruptions to mobile taskflow.

Technology makes it possible to share many different types of information with coworkers. We conducted a large-scale survey (N=549) to better understand current sharing among coworkers, how people stay aware of collocated and remote coworkers, and whether their willingness to share different types of awareness information changes based on the location in which the information is displayed. Contrary to our expectations, the display location did not greatly affect what respondents were willing to share. Our results also suggest considerations for researchers building situated displays, as respondents had concerns about unintended viewers and encouraging people to visit their personal space when they were not present.

Although domestic computer use is increasing, most efforts to reduce energy use through improved power management have focused on computers in the workplace. We studied 20 households to understand how people use power management strategies on their home computers. We saw computers in the home, particularly desktop computers, are left on much more than they are actively used suggesting opportunities for economic and energy savings. However, for most of our participants, the economic incentives were too minor to motivate them to turn off devices when not in use, especially given other frustrations such as long boot up times. We suggest research directions for home computer power management that could help users be more green without having to dramatically change their home computing habits.

Repetitive strain injuries and ergonomics concerns have become increasingly significant health issues as a growing number of individuals frequently use computers for long periods of time. Currently, limited software mechanisms exist for managing ergonomics; the most well-known are packages that schedule and recommend typing breaks. Yet despite the proven benefits of taking breaks, such packages are rarely adopted due to the over-head of introducing periodic interruptions into a user's workflow. In this paper, we describe SuperBreak, a break-reminder package that provides hands-free interactions during breaks, with the goal of encouraging users to take more breaks and enhancing the benefits of those breaks. In a field study of 26 knowledge workers, 85% preferred SuperBreak over a traditional break-reminder system, and on average participants took a higher percentage of the interactive breaks suggested to them. Our results highlight the value of interactivity for improving the adoption and retention of ergonomic break practices.

Software can now track which computer applications and documents you use. This provides us with the potential to help end-users recall past activities for tasks such as status reporting. We describe findings from field observations of eight participants writing their status reports. We observed interesting trends, including the reliance on memory triggers, which were either retrieved from explicit self-reminders, from implicit breadcrumbs left while performing their tasks or directly from memory. Participants perceived spending relatively short amounts of time composing their status reports, suggesting that any technology solution must offer dramatic improvements over current practice.

Modern development environments provide many features for navigating source code, yet studies show the developers still spend a tremendous amount of time just navigating. Since existing navigation features rely heavily on memorizing symbol names, we present a new design, called code thumbnails, intended to allow a developer to navigate source code by forming a spatial memory of it. To aid intra-file navigation, we add a thumbnail image of the file to the scrollbar, which makes any part of the file one click away. To aid interfile navigation, we provide a desktop of file thumbnail images, which make any part of any file one click away. We did a formative evaluation of the design with eleven experienced developers and present the results

The dominant paradigm for searching and browsing large data stores is text-based: presenting a scrollable list of search results in response to textual search term input. While this works well for the Web, there is opportunity for improvement in the domain of personal information stores, which tend to have more heterogeneous data and richer metadata. In this paper, we introduce FacetMap, an interactive, query-driven visualization, generalizable to a wide range of metadata-rich data stores. FacetMap uses a visual metaphor for both input (selection of metadata facets as filters) and output. Results of a user study provide insight into tradeoffs between FacetMap's graphical approach and the traditional text-oriented approach.

The continuing trend toward greater processing power, larger storage, and in particular increased display surface by using multiple monitor supports increased multi-tasking by the computer user. The concomitant increase in desktop complexity has the potential to push the overhead of window management to frustrating and counterproductive new levels. It is difficult to adequately design for multiple monitor systems without understanding how multiple monitor users differ from, or are similar to, single monitor users. Therefore, we deployed a tool to a group of single monitor and multiple monitor users to log window management activity. Analysis of the data collected from this tool revealed that usage of interaction components may change with an increase in number of monitors, and window visibility can be a useful measure of user display space management activity, especially for multiple monitor users. The results from this analysis begin to fill a gap in research about real-world window management practices.

Our studies have shown that as displays become larger, users leave more windows open for easy multitasking. A larger number of windows, however, may increase the time that users spend arranging and switching between tasks. We present Scalable Fabric, a task management system designed to address problems with the proliferation of open windows on the PC desktop. Scalable Fabric couples window management with a flexible visual representation to provide a focus-plus-context solution to desktop complexity. Users interact with windows in a central focus region of the display in a normal manner, but when a user moves a window into the periphery, it shrinks in size, getting smaller as it nears the edge of the display. The window "minimize" action is redefined to return the window to its preferred location in the periphery, allowing windows to remain visible when not in use. Windows in the periphery may be grouped together into named tasks, and task switching is accomplished with a single mouse click. The spatial arrangement of tasks leverages human spatial memory to make task switching easier. We review the evolution of Scalable Fabric over three design iterations, including discussion of results from two user studies that were performed to compare the experience with Scalable Fabric to that of the Microsoft Windows XP TaskBar.

We describe a real-time system for detecting pointing gestures and estimating the direction of pointing using stereo cameras. Previously, similar systems were implemented using color-based blob trackers, which relied on effective skin color detection; this approach is sensitive to lighting changes and the clothing worn by the user. In contrast, we used a stereo system that produces dense disparity maps in real-time. Disparity maps are considerably less sensitive to lighting changes. Our system subtracts the background, analyzes the foreground pixels to break the body into parts using a robust mixture model, and estimates the direction of pointing. We have tested the system on both coarse and fine pointing by selecting the targets in a room and controlling the cursor on a wall screen, respectively.

Background maintenance is a frequent element of video surveillance systems. We develop Wallflower, a three-component system for background maintenance: the pixel-level component performs Wiener filtering to make probabilistic predictions of the expected background; the region-level component fills in homogeneous regions of foreground objects; and the frame-level component detects sudden, global changes in the image and swaps in better approximations of the background. We compare our system with 8 other background subtraction algorithms. Wallflower is shown to outperform previous algorithms by handling a greater set of the difficult situations that can occur. Finally, we analyze the experimental results and propose normative principles for background maintenance.