Kathrin Probst

David Lindlbauer

Florian Perteneder

Michael Haller

Bernhard Schwartz

Andreas Schrempf

Exploring the Use of Distributed Multiple Monitors Within an Activity-Promoting Sit-and-Stand Office Workspace

Keywords:

Nowadays sedentary behaviors such as prolonged sitting have become a predominant element of our lives. Particularly in the office environment, many people spend the majority of their working day seated in front of a computer. In this paper, we investigate the adoption of a physically active work process within an activity-promoting office workspace design that is composed of a sitting and a standing workstation. Making use of multiple distributed monitors, this environment introduces diversity into the office workflow through the facilitation of transitions between different work-related tasks, workstations, and work postures. We conducted a background study to get a better understanding of how people are performing their daily work within this novel workspace. Our findings identify different work patterns and basic approaches for physical activity integration, which indicate a number of challenges for software design. Based on the results of the study, we provide design implications and highlight new directions in the field of HCI design to support seamless alternation between different postures while working in such an environment.

Introduction

Over the past centuries, our lives have become more and more dominated by sedentary behaviors such as prolonged sitting. Particularly in the work context (e.g., office jobs), the number of tasks focused around sitting at a computer has increased markedly in the recent years [START_REF] Miller | Steps and sitting in a working population[END_REF][START_REF] Owen | Too much sitting: a novel and important predictor of chronic disease risk?[END_REF], although a growing body of research has connected this sedentary lifestyle to a dramatic increase of health-related risk factors (e.g., for cardiovascular or musculoskeletal diseases) [START_REF] Freak-Poli | Risk of Cardiovascular Disease and Diabetes in a Working Population With Sedentary Occupations[END_REF][START_REF] Wilmot | Sedentary time in adults and the association with diabetes, cardiovascular disease and death: systematic review and meta-analysis[END_REF]. In contrast to that, a physically active work process promotes the avoidance of prolonged sedentary behavior and related degenerative phenomena. Thus, the World Health Organization (WHO) has identified the workplace as important area for setting health-promoting preventive measures with great potential to solve the problem of rapidly increasing health care costs [START_REF]Preventing Noncommunicable Diseases in the Workplace through Diet and Physical Activity: WHO/World Economic Forum Report of a Joint Event[END_REF].

Despite the growing evidence for the benefits of such workplace health promotion programs, interventions have proven to be limited though, as most of them pose demands on workforce commitment (e.g., gym classes), require employees to leave their desks for exercising, or are unlikely to be sufficient in the context of otherwise sedentary lifestyles [START_REF] Craft | Evidence that women meeting physical activity guidelines do not sit less: An observational inclinometry study[END_REF]. Rather, the accumulation of small amounts of low-intensity physical activity throughout a day provides health benefits that may even exceed those associated with more vigorous activities [START_REF] Levine | Non-Exercise Activity Thermogenesis (NEAT)[END_REF]. Based on this insight, recent approaches have focused on the motivation of reduced sitting, increased walking or standing activities (e.g., taking breaks, postural diversity, stand-up meetings) [START_REF] Healy | Reducing prolonged sitting in the workplace[END_REF], and the design of novel workspace environments that provide opportunities for integrating light activities into the daily office workflow [START_REF] Gilson | Does the use of standing "hot" desks change sedentary work time in an open plan office?[END_REF][START_REF] Levine | The energy expenditure of using a "'walk-and-work'" desk for office workers with obesity[END_REF][START_REF] Mcalpine | An office-place stepping device to promote workplace physical activity[END_REF][START_REF] Probst | Active Office: Towards an Activity-Promoting Office Workplace Design[END_REF].

Since computer technologies have become an integral part of today's office work, the integration of physical activity into the work routine however brings along a number of challenges that have been rarely addressed by the HCI community so far [START_REF] Probst | Active Office: Towards an Activity-Promoting Office Workplace Design[END_REF]. The facilitation of a physically active work process poses demands on user interface technology (e.g., ergonomics) and software (e.g., interface design, interaction metaphors, data management) that may be quite different from those addressed in the design of today's stationary work environments. Addressing these demands while simultaneously ensuring work efficiency therefore needs to be considered for the design of future systems within increasingly flexible and mobile work environments.

In this paper, we study a sit-and-stand workspace environment that is designed to promote physical activity in a computer workplace (see Fig. 1), which is composed of a traditional desk workstation and a standing table workstation facilitating execution of work-related tasks in sitting or standing posture [START_REF] Probst | Active Office: Towards an Activity-Promoting Office Workplace Design[END_REF]. It is not clear though, how users will use this novel workplace and what issues they need to overcome in order to work in a both efficient and physically active way. To get a better understanding of how people are working in such an environment and how this may imply requirements for the design of future computer systems, we performed an exploratory background study. In the remainder of this work, we present the observations of this study and the resulting implications on user behavior and HCI design. 2 Related Work

Workplace Health Promotion

Different structural elements have been proposed for the promotion of physical activity in the workplace, such as standing desks [START_REF] Gilson | Does the use of standing "hot" desks change sedentary work time in an open plan office?[END_REF], stepping devices [START_REF] Mcalpine | An office-place stepping device to promote workplace physical activity[END_REF], or "walk-andwork" workstations [START_REF] Levine | The energy expenditure of using a "'walk-and-work'" desk for office workers with obesity[END_REF], which are directly integrated into the office environment.

Especially sit-and-stand workstations have shown to offer high potential for effective workplace health intervention through variations between different postures. Previous studies showed a generally positive attitude of workers towards such workspaces [START_REF] Wilks | The introduction of sit-stand worktables; aspects of attitudes, compliance and satisfaction[END_REF], and significant reduction of musculoskeletal discomfort [START_REF] Hedge | Effects of an electric height-adjustable worksurface on self-assessed musculoskeletal discomfort and productivity in computer workers[END_REF] without any negative effects on work performance [START_REF] Husemann | Comparisons of Musculoskeletal Complaints and Data Entry Between a Sitting and a Sit-Stand Workstation Paradigm[END_REF]. While workers equipped with a sit-and-stand workspace tend to be positive about having the possibility to choose between sitting and standing, previous research also indicates that people sometimes tend to avoid standing posture because of ergonomic (e.g., workplace size), hardware-related (e.g., cable reach), or software-related (e.g., data access) constraints.

Another recent ergonomic approach for physical activity promotion [START_REF] Probst | Active Office: Towards an Activity-Promoting Office Workplace Design[END_REF] proposes a new concept of working "in-motion" and takes into account the smooth integration of hardware-and software-related structural elements to provide opportunities for office workers to seamlessly change between different work environments. Based on this work, we use a similar environment and extend it by equipping the design with a multi-monitor setup for further investigation.

Multi-Monitor Usage

Multi-monitor systems have been studied in a series of previous work. Initial evidence indicates that users can complete tasks more quickly with multiple monitors [START_REF] Czerwinski | Toward Characterizing the Productivity Benefits of Very Large Displays[END_REF], but typically experience inefficiencies or frustrations (e.g., losing the cursor, bezel problems, distal information access problems, window management problems, task management problems, configuration problems [START_REF] Robertson | The Large-Display User Experience[END_REF][START_REF] Swaminathan | Interaction Design for Large Displays[END_REF][START_REF] Tan | Effects of Visual Separation and Physical Discontinuities when Distributing Information across Multiple Displays[END_REF]) that can be addressed by alterations to basic interaction [START_REF] Hutchings | Distributed Display Environments[END_REF]. Further, a number of observations of multimonitor users provide insights on the arrangement of digital information into focal and peripheral regions [START_REF] Grudin | Partitioning Digital Worlds: Focal and Peripheral Awareness in Multiple Monitor Use[END_REF], window management [START_REF] Hutchings | Display Space Usage and Window Management Operation Comparisons between Single Monitor and Multiple Monitor Users[END_REF] and other multi-monitor usage patterns. However, while much of the recent research involving multiple monitors has focused on compact setups where monitors are placed directly next to each other, a workplace design with two separate sitting and standing workstations introduces considerably larger distances than commonly used. Since such environments have remained largely unconsidered by existing HCI research, we performed a background study to explore the usage in a real-world scenario, and provide insights into the user experience of working on a computer in sitting and standing posture. We analyze (1) the effects of such a distributed multiple monitor environment on user behavior, user interaction, usage patterns, and (2) how these may inform HCI design for supporting the concept of working while alternating between different work-related tasks, work postures, and corresponding workstations.

3

Concept & Method

In accordance to a recently proposed activity-promoting workplace design [START_REF] Probst | Active Office: Towards an Activity-Promoting Office Workplace Design[END_REF], the basic concept of the present study involved providing participants with two workstations (see Fig. 1) for execution of work-related tasks in sitting or standing posture, which consisted of two height-adjustable desks1 (Fig. 2, left) and two active seats: a swopper2 active chair (Fig. 2, middle) that supports dynamic sitting through 360° tilting and vertical up-and-down flexibility, and a muvman chair3 (Fig. 2, right) that can be used as a leaning chair to support working in standing posture. In the background study, we were interested in understanding several aspects of working within the proposed sit-and-stand workplace environment:  How do participants organize the physical and hardware-related configuration of the workstations within the workspace, and how do people make use of the individual workstations within the environment (workspace configuration)?  How do participants distribute their daily work time and work tasks among workstations within the workspace, and how is the usage influenced by the concept of working in different postures (workstation usage, switching behavior)?  How well is this specific setup supported through current operating systems and software applications? Which problems and challenges arise (software support)?

Participants

Five unpaid volunteers from the local university participated in a 4-week background study of their daily work activities within an activity-promoting workplace environment. All participants (4 male, 1 female; age 25-40) were experienced computer users, full-time employed as researchers in the field of computer science, ready to use such a setup to reduce sedentariness during the work routine. Four participants had no health problems, one participant reported on chronic back problems. All participants stated that they spent the majority of their work time (70-85%) in front of the PC, and had used multi-monitor setups for six months to three years. They replaced their existing work environments with a provided activity-promoting workstation setup.

Procedure & Setting

At the beginning of the study, all participants were provided with identical basic office furniture sets as described in the previous section. Participants were instructed to arrange these components within their office space to form a personal sit-and-stand workspace environment that consists of a sitting and standing workstation (see Fig. 1).

Participants were introduced to the adjustable features of the furniture and Ergonomics of Human System Interaction (ISO 9241). Corresponding to their individual work-related requirements, each workstation desk should be equipped with display and input devices connected to a single workplace computer to provide equal access from each workstation. Further, participants were introduced to their operating systems' native multi-monitor functionality 4 , and given free choice whether running their monitors in duplicated or extended mode throughout the course of the study.

Data Collection and Analysis

After setting up their personal workspace environments, participants' activities were observed for four subsequent weeks (20 work days). The individual workspaces were photographed, and specifications of the hardware equipment were collected. Participants reported on the time spent in sitting or standing posture, and overall work time at the end of each day. Throughout the study, six semi-structured interviews were conducted with every participant: after the first and third work day, and at the end of each work week. During the interviews, participants reported on their experience, and were assisted with suggestions for possible solutions to their reported problems. Interviews were audio-recorded (average duration 45 minutes) and affinity diagramming was used to analyze similarities, differences, and patterns in participants' behavior. In addition, a custom logging tool was installed on participants' computers, running in the background and collecting input and window events (similar to [START_REF] Hutchings | Display Space Usage and Window Management Operation Comparisons between Single Monitor and Multiple Monitor Users[END_REF]). The data was used to gain insights on how often users switched between sitting and standing workstations, and which activities they performed in these locations.

Results

Based on the data collected during interviews and logging (on average 330,000 input events per day for each participant), we drew information on participants experiences, behavior and (computing) activities during the conducted study.

In this section, we present our results according to aspects that we were primarily interested in: how did participants combine the provided furniture components with hardware-related structural elements (workstation configuration), how did they integrate the concept of working in sitting and standing posture into their work routine (workstation usage, switching behavior), and to what extent this concept is supported by current software systems (software support).

Workspace Configuration

For all five participants, the arrangement of the provided furniture components resulted in a similar sit-and-stand workspace (see Fig. 3). The tables were adjusted to participants' body height and arranged adjacent to each other, with a small gap of 10-15 cm -either at a slightly tilted angle of approximately 45° (four participants) or in straight line (one participant)-and were combined with the provided active seats to form the proposed sitting and standing workstations. Given the free choice how to combine the provided furniture with hardware components, participants further chose a similar configuration consisting of one computer (placed in a central position on the floor) with multiple connected monitors that were distributed across the tables. Four participants arranged a single monitor, keyboard, and mouse on each table (e.g., Fig. 3, left). One participant had a dual-monitor setup on one table and a front-projected tabletop-display with stylus input on the other (Fig. 3, right). All computers ran Microsoft Windows operating system (one with Windows 8, three with Windows 7, and one with Windows XP).

Workstation Usage

During the study period, participants reported an average daily work time of 7.4 hours (SD = 1.86), of which they spent the major part of 6.0 hours (SD = 1.97) within their personal office workspace. During that time, their main work tasks (Fig. 4, left) included software development, reading/writing (e.g., reports, articles, presentations), research/browsing, data analysis (e.g., statistics), communication (e.g., e-mail, telephone), meetings, and other (e.g., design, graphics, measurement) activities. The average distribution of the reported sitting and standing times shows that all five participants made use of the opportunity to incorporate the concept of working in different postures into their regular office workflow. They reported spending on average 22.5% (SD = 21.1%) of their daily office time in standing posture (Fig. 4, right). Given the relatively high variations, the participants' comments during the interviews provide further insights on a spectrum of different approaches for utilizing the novel sit-and-stand workspace. In-depth reports on the different aspects contributing to the above reported distribution are discussed in detail in the remainder of this chapter.

Participants' Overall Experience

To provide a brief overview of participants' overall experience, we present their basic approaches, behaviors and usage patterns over the course of the study-along with the daily sitting and standing times (average indicated through a horizontal line) that are depicted for each participant individually.

P1 used two monitors in extended mode, spent most of his work time using the primary screen at the sitting workstation, and switched to standing posture at rare intervalsvirtually treating it as an independent unit that provided him with a scope for handling specific work tasks in isolation. Along with that, nevertheless, he experienced limitations during cross-monitor interaction (e.g., losing the mouse cursor during drag interactions) and during window switching (e.g., no taskbar on the secondary screen)-which did not encourage him to make use of the standing workstation on a more regular basis.

P2 used two monitors in extended mode, mainly working at the primary screen at the sitting workstation, and switching to the standing workstation multiple times throughout a day to break up sitting periods from time to time. By doing so, however, he experienced a range of problems with inconsistent window placement, during cross-monitor interaction (e.g., effort of dragging windows), and during window switching (e.g., no taskbar on the secondary screen). Therefore, after the second week of the study, he started to use the operating systems' native multi-monitor support-which enabled him to relocate the primary screen during workstation switches, and dissolved most previously existing problems.

P3 used two monitors in duplicated mode, spent most time at the sitting workstation, and tried to develop a routine to integrate working in standing posture into his workflow.

After initially taking the opportunity to perform short email or browsing tasks at the standing workstation, he finally took a rather opportunistic approach of occasionally alternating his work posture at logical points within a task. He appreciated the convenience of switching between the duplicated monitors without effort, but raised concerns on peripheral distraction and privacy. To avoid these problems, he sometimes used the native multi-monitor support, but considered this as additional effort to some extent.

P4 used two monitors in duplicated mode, spent approximately equal amounts of his work time in sitting and standing posture, and alternated his work posture on a regular basis throughout a day. Having chronic back problems, he felt that this was a possibility to relieve the pressure on the spine, and appreciated the flexibility to switch between the duplicated monitors whenever he wanted. Over the course of the study, some distinctive patterns started to evolve from his day-to-day work, as he tended to start the day with checking e-mails in standing posture, to work in sitting posture after lunch break, and to perform certain work tasks at one of the workstations (e.g., collaborative settings in standing posture, cognitive demanding tasks in sitting posture).

P5 used two monitors and a tabletop projection in extended mode, using the dual-monitor setup at the sitting workstation and the tabletop-setup at the standing workstation for debugging of pen-based input. During programming, he found that this worked well for him, as he perceived the high-frequent regular switches as a welcome change. Due to the distinct separation of coding and debugging views and the pen input, he did not have to take any additional effort for dragging windows or moving the mouse cursor. Over time, however, he did not have any opportunity to work in standing posture besides of this specific implementation task and ended up spending the majority of the time seated.

Switching Behavior

During a work day, the logged data shows that participants switched on average 6.27 times (SD = 8.47) between the sitting and standing workstations at intervals of 1.13 hours (SD = 1.12), with an average duration of 1.82 hours (SD = 1.88) in sitting and 0.44 hours (SD = 0.36) in standing posture. Comments from the interviews provide evidence for a variety of factors related to participants' physical and emotional personal condition, subject and progress of the current work task, or hardware-and software-related workspace configuration that were perceived to influence participants' switching behavior in a positive (encouraging) or negative (limiting) way. These reported influencing factors are discussed in detail in the remainder of this section and summarized in Table 1. Participants stated to appreciate the possibility to bring diversity into their daily office routine by alternating between sitting and standing posture. This was especially true for P4, who had chronic spinal problems and he felt that regular posture changes relieved his back pain fundamentally. Besides of that, four participants (P1-P4) noted their switching behavior being dependent on personal habits to a certain extent. P4 for example, started nearly every work day in standing posture as he was generally feeling energized in the morning, and P1/P3 stated to rarely work in standing posture as they were not used to this kind of bodily load. Two participants (P2, P3) reported limited number of postural switches (i.e., preference of sitting posture) in situations of high emotional stress when they were feeling anxious or impatient.

Work Task. Besides the triggers related to participants' personal condition, most of them (P1-P4) also stated that the start of a new task or switching the current task was commonly associated with postural changes. To find additional opportunities for switching their workstations on a frequent basis, two participants (P3, P5) further started to introduce direct association of workstations with particular tasks. P3 for example, was initially taking occasional breaks from his mainly seated day by performing short e-mail or browsing tasks at the standing workstation. P5 used the dualmonitor setup on the sitting workstation for his common work, and the projector-setup on the standing workstation for debugging activities. Along with that, however, they oftentimes ran into situations when their work tasks were not diverse enough to support a regular switching behavior. Given that, P5 tried to find additional tasks that he considered suitable to be performed at the standing workstation (e.g., reading on printed paper), while P3 changed his usage pattern after the first week of the study, thenceforth (similar to P2 and P4) rather changing his posture at logical breakpoints in-between the current task (e.g., at the end of a paragraph in a text). Limitations for switching behavior, on the other hand, were indicated by three participants (P2-P4) tending to avoid standing posture for tasks with relatively high cognitive demand (e.g., programming), and two participants (P1, P3) showing deep task involvement that made them simply "forget" about changing their posture when they were completely focused on the current task.

Workspace Configuration. Another interesting finding reveals that all participants pointed out the suitability of the standing workstation for collaborative activities. For typical settings in small groups of 2-4 people (e.g., discussions, showcasing), participants highlighted the affordances of the standing posture such as equal sight on the display surface and being at equal eye level. Closely related to that, the accessibility of the standing desk encouraged most participants (P2-P4) to use it as a first entrypoint after leaving the workspace temporarily for external activities (e.g., meetings, breaks). On the other hand, some participants (P3-P5) noted situations where physical constraints (e.g., hardware components, notes on printed paper) turned out as limitations to their switching behavior, and all participants consistently reported that software limitations (e.g. relocation of on-screen content) had a considerable effect on their switching behavior-which is discussed in detail within the following section.

Software Support

The analysis of the collected logging data shows that participants actively used their workplace PCs (incoming mouse, keyboard, or pen input events) on average 4.98 hours per day. Throughout a work day, participants used 5-12 different software programs (Fig. 5, left), which included programming, text editing/viewing (e.g., text processor, PDF viewer), web browser, spreadsheet, communication (e.g., e-mail client, instant messenger), media (e.g., graphics/video/audio editor), and other (e.g., file browser) applications. The reported sitting/standing times (see Fig. 4, right) are largely confirmed by the logging data (Fig. 5, right), showing on average 20.61% (SD = 21.42%) of the input time being recorded at the standing workstation. In addition to participants' different motivations for workstation switching, the distribution of monitors within the workspace had a major effect on their behavior. With a relatively large gap (80-150cm) between monitors spread across the sitting and standing tables, all participants reported to perceive the workstations more or less as two separate units-feeling that they could use either the one or the other, but not both at the same time. As a result, two participants (P3, P4) decided to run their monitors in duplicated display mode, while the other three (P1, P2, P5) ran their setup in extended mode, and two participants (P2, P3) changed to a hybrid relocated display mode in the course of the study by manually switching the display configuration. Participants' experienced software support issues are discussed in the remainder of this section and summarized in Table 2.

Table 2. Reported software support issues and their occurrences per participant.

Issue P1 P2 P3 P4 P5

Primary/Secondary Screen Distinction

   Window Placement Inconsistency    Cross-Monitor Interaction   Content Relocation Effort     Peripheral Distraction   Privacy  Waste of Resources     
Extended Screen. In contrast to regular multi-monitor setups, the display units in our participants' setups were non-adjacent [START_REF] Swaminathan | Interaction Design for Large Displays[END_REF]. Consequently, none of them exhibited patterns like using the display space as a whole (e.g., straddling a window across monitors), using the two monitors in direct support of each other (e.g., reading on one screen while writing a text on the other), or for displaying peripheral information (e.g., at-a-glance e-mail notifications) [START_REF] Grudin | Partitioning Digital Worlds: Focal and Peripheral Awareness in Multiple Monitor Use[END_REF]. Instead, participants used the two screens in a rather separate fashion, thereby experiencing a variety of problems that had a major influence on their usage of the single workstations.

While the inherent primary/secondary screen distinction makes sense in a traditional extended desktop setting, this multi-monitor usage paradigm did not hold for the present setup. Two of the three extended screen users (P1, P2) reported window management limitations due to the taskbar, start menu, and task switching overview being displayed on the primary screen only. Consequently, while working on the secondary screen, they experienced difficulties to manage multiple windows without the visual feedback and one-click access functionality of these interface elements. As a result, P2 started to prepare well-defined work packages that did not require extensive window switching activities before switching to the secondary monitor at the standing workstation. P5 in contrast, reported to benefit from recently added multi-monitor support in the latest Windows version (Windows 8) providing him with the possibility to put a separate taskbar on each individual screen. A problem that however applied to all three extended screen users was the missing visual feedback of the quick-access task switcher (Alt+Tab5 ) being located on the primary screen by default.

Another issue reported by all extended screen users was the problem of window placement inconsistency. Most applications' inherent memory mechanisms [START_REF] Hutchings | Consistency, Multiple Monitors, and Multiple Windows[END_REF] to open application windows on their last known location were holding only as long as people kept running a program at the same workstation (e.g., P5). Whenever participants were transitioning between workstations though, windows that continued to appear on the same (but not necessarily current) screen had a rather detrimental effect. P1/P2 for example, reported that applications were frequently launched on the screen that they were currently not working at, that pop-up windows (e.g., notifications, file dialogs) easily went unnoticed on the second screen, and P5 experienced similar problems whenever he performed debugging tasks while sitting in some exceptional cases.

Associated with the above mentioned issues, participants oftentimes ran into situations when they had to apply cross-monitor interactions to shift digital content (e.g., windows, folders, icons) from one screen to anotherthereby traversing the distance between the monitors by moving the mouse at one workstation to reach to a screen area on the other. Since the physical distribution introduced visual discontinuities [START_REF] Tan | Effects of Visual Separation and Physical Discontinuities when Distributing Information across Multiple Displays[END_REF], two participants (P1, P2) reported difficulties in navigating the mouse cursor, or reading text on the distant screen. Losing the mouse cursor [START_REF] Robertson | The Large-Display User Experience[END_REF] was reported to frequently occur in situations when the cursor was "left behind" during workstation switches, or when "disappearing" out of sight along the screens edges.

Finally, the need to associate changes in posture with interactions for digital content relocation was considered as a major limitation. Two participants (P1, P2) stated that they perceived it as annoying to bring windows from one side to the other during workstation switches. For P3 and P4, this additional effort was one main reason why they had decided to run the monitors in their workspace in duplicated display mode: "It's not the same as having two monitors on one desk. If the other monitor is far away and you're trying to see when you're trying to pass a window from one screen to the other, this is not so easy to do. (…) That's why I couldn't imagine working with the monitors in extended mode." (P3). Duplicated Screen. Participants who used the setup in duplicated display mode (P3, P4) did not experience the same problems as extended screen users. By virtually having a single screen replicated on the extended monitor, they did not have to deal with discrepancies between primary and secondary screen, losing the mouse cursor, or the effort of moving digital objects from one screen to another. Having the exactly same view on all monitors, they were flexible to switch between the sitting and standing workstations at any desired point during task execution. Apart from that, duplicated screen users experienced other problems, though.

Having screen contents duplicated between workstation, participants reported feeling slight distraction due to on-screen interactions (e.g., mouse cursor movement, window pop-up) being visible on the monitor within their peripheral vision. Closely related to this issue, one participant (P3) raised minor privacy concerns due to on-screen activities being observable for other people within the office space. While this was not a problem for P4, whose monitors were not visible from within the office space, the three extended screen users stated that privacy was a considerable reason why they had decided not to run their setups in duplicated mode.

A major concern however, was the waste of resources in terms of screen real estate and energy consumption, which was similarly indicated by the three extended screen users. By using only one of the two available monitors at a time, participants could not make use of a large part of their available screen space: "If I could work on both monitors at the same time, if I could control them in a better way… that would be much better. To be flexible to change between the two workstations, I should be able to make it feel more like one. (…) In terms of digital communication, it could be smoother, more continuous-instead of totally separated." (P1). Relocated Screen. To avoid the disadvantages of both duplicated and extended display mode in the present multi-monitor setting, P2 and P3 started using the Windows native keyboard shortcut Win+P for second screen projection after the first two weeks of the study. In this special usage scenario, postural changes were associated with pressing the keyboard shortcut to relocate the primary screen between sitting and standing workstation monitors-which resolved issues regarding primary/secondary screen, window placement, and cross-monitor interaction, and dissolved concerns about peripheral distraction, privacy, and energy consumption. Especially for P2, the new functionality changed his workstation switching behavior fundamentally, encouraging him to change his work posture at arbitrary points during a task. However, the major problem of losing a large part of available screen real estate remained unsolved.

Other remaining problems in this configuration were for example the monitor's latency to display content after enabling it with the shortcut. Further, it was not always clear which workstation would be enabled after pressing the keyboard shortcut, and which monitor would be turned on when participants returned to the workstation after prolonged inactivity (e.g., absence from the workspace due to external meetings). Furthermore, P2 felt like the black screen on the unused workstation was a minor barrier compared to an activated monitor, and P3 rarely made use of the screen relocation function because he considered this as additional effort to some extent.

Discussion & Implications

Based on the described observations, we draw the following implications for the support of environments similar to the studied sit-and-stand workspace design.

Basic Approaches for Physical Activity Integration

From the findings of the study, we identify two basic approaches that were followed to incorporate the concept of working different postures into the daily office work:

 Task-Driven approaches are based on the concept of associating a work task with a specific workstation, thus implicitly motivating people to take up different postures throughout a work day. P5 for example, associated debugging activities with the standing workstation, P4 preferred the execution of collaborative tasks in standing posture, and P3 initially handled e-mail activities at the standing table.  Self-Determined approaches are in contrast based on the concept of performing any work tasks at any workstation, leaving the participants free to change their posture at all times. P3 for example, proceeded to alternate between the sitting and standing posture every once in a while, or P4 always changed his work posture whenever he felt the desire to break continuous sitting or standing periods. Considering the experience of participants following a rather task-driven switching behavior, it becomes evident that this approach is strongly dependent on the daily work activities. While participants stated to perceive postural changes as rather natural side effect of their regular office work, it is on the other hand not suitable for tasks that are not performed on a regular basis. Self-determined switching behavior turned out as a flexible approach that leaves people free to carry out their work in any posture, but is on the other hand associated with a certain cognitive demand and might not work during phases of high involvement in the ongoing task. From the analysis of participants' switching patterns, we see that self-determined approaches resulted in significantly longer standing periods (Fig. 6, bottom), while task-driven approaches resulted in a higher number of switches (Fig. 6, top) during a work day.

Since both approaches have their pros and cons, and participants tended to not exhibit one of these two approaches exclusively, we think that it is essential to support a hybrid solution: while the task-driven approach has high potential to achieve an implicitly motivating effect, users should at the same time not be limited to exclusive association of task and workstation, but rather be able to switch in a self-determined manner whenever task-driven approaches are not applicable or undesirable. Furthermore, while our logging data confirmed findings on equal data-entry performance in any posture [START_REF] Husemann | Comparisons of Musculoskeletal Complaints and Data Entry Between a Sitting and a Sit-Stand Workstation Paradigm[END_REF], participants in our study oftentimes preferred the sitting workstation, mainly due to reasons of personal habit or convenience. Especially for participants with self-determined switching behavior, we think that subtle reminding mechanisms (e.g., ambient displays [START_REF] Haller | Finding the right way for interrupting people improving their sitting posture[END_REF]) can assist the adoption of a sustainable behavior change. For a task-driven approach, this may not be needed as long as the daily work routine consists of a diverse range of tasks. This is where assignment mechanisms (e.g., intelligent window arrangement algorithms [START_REF] Henderson | Rooms: The Use of Multiple Virtual Workspaces to Reduce Space Contention in a Window-Based Graphical User Interface[END_REF]) can provide assistance for users to achieve a balanced task distribution among individual workstations.

Supporting Distributed Multi-Monitor Usage

Considering the study results, we see that physical separation introduced with distribution of multiple monitors across the work environment fundamentally changed the way people perceived and handled them. Although the monitors were connected to one machine, enlarged distances coupled with differences in height and relative orientation to the user introduced visual discontinuities [START_REF] Tan | Effects of Visual Separation and Physical Discontinuities when Distributing Information across Multiple Displays[END_REF], which presented major barriers to associated multi-monitor interaction. In contrast to adjacent multi-monitor setups, where users slightly rotate their neck to cover the increased screen space [START_REF] Swaminathan | Interaction Design for Large Displays[END_REF], the physical gaps in the present setup required them to additionally change their orientation or even physical location to switch focus between screen content spread across different monitors. To make effective use of both workstations, we identify a variety of challenges for designing future systems to support the physical distribution through exclusive, supportive, or peripheral multi-monitor usage [START_REF] Grudin | Partitioning Digital Worlds: Focal and Peripheral Awareness in Multiple Monitor Use[END_REF]:

 Exclusive usage implies the association of the physical distribution with corresponding logical separation-virtually treating the monitor(s) and input devices at each workstation as a single logical unit. The basic functionality of the Win+P display switching mechanism could be extended or automated to activate a workstation monitor whenever the corresponding mouse or keyboard are operated. Although exclusive monitor usage solves certain problems described earlier (e.g., window placement inconsistency, cross-monitor interaction), a major drawback remains. Participants expressed the desire to make use of the secondary monitor, since they felt like they were not using the full potential of their workstations. Concerns were raised that having two monitors but only having one in use was perceived as waste of resources (basically losing half of their working area).

 Supportive usage implies the association of the physical distribution with corresponding visual separation, thereby treating the displays at each workstation as visually isolated spaces. Digital barriers can serve as a basis for the restriction of mouse cursor movement [START_REF] Benko | Pointer Warping in Heterogeneous Multi-Monitor Environments[END_REF], border snapping mechanisms, or consistent placement of windows on the current screen. The effort of moving digital objects between monitors was identified as major barrier for fluent transitions from one workstation to another, implying the need to support effortless window management mechanisms such as grouping [START_REF] Smith | GroupBar: The TaskBar Evolved[END_REF], switching, or relocating [START_REF] Baudisch | Drag-and-Pop and Drag-and-Pick: techniques for accessing remote screen content on touch-and pen-operated systems[END_REF][START_REF] Biehl | ARIS: An Interface for Application Relocation in an Interactive Space[END_REF] digital content on the individual screens.

 Peripheral usage implies the adaption of the user interface and interactions, since participants avoided interactions with the secondary monitor due to non-optimal mouse support and poor visibility of digital content across the distance in extended display mode. In response to that, interface elements on the distant screen could be enlarged and simplified to achieve a good readability, or convenient access to these elements should be supported through novel (multi-modal) interaction styles.

Essentially, users need to be able to equally access both workstations and the switching process needs to be effortless and seamless to maintain their motivation for the adoption of a physically active work process. Some participants were favoring the workstation with the primary screen (thus not switching workstations) because of existing software limitations. Avoiding these limitations to provide users with a seamless switching experience is a very important factor for this kind of activity-promoting office environments, though. Therefore, it seems crucial to gain knowledge about the user's activity (e.g., the currently used workstation) and properties of the surrounding environment (e.g., presence of other people). Based on that knowledge, an intelligent office space could for example respond to a user's activity by bringing digital objects into his focus of attention automatically [START_REF] Brumitt | EasyLiving: Technologies for Intelligent Environments[END_REF].

Conclusion & Future Work

In this paper, we presented a background study with five office workers, who were carrying out their daily work tasks within a sit-and-stand workspace environment that follows the concept of integrating light activity into the daily work routine by providing the opportunity to work in sitting and standing posture [START_REF] Probst | Active Office: Towards an Activity-Promoting Office Workplace Design[END_REF]. Prior research in the field of multi-monitor usage is extended through the discussion of user behavior associated with the concept of working "in-motion". We indicated a number of challenges originating from user requirements within such an environment and discussed effects of different influencing factors on participants' workstation switching behavior. We identified two basic approaches for physical activity integration, and concluded that the situation-related support of both task-driven and self-determined patterns has high potential to provide users with a seamless switching experience. In a distributed multi-monitor setup, however, the physical separation of the individual displays has to be handled in a different way than in regular adjacent multi-monitor setups. Observations from our study showed that the distribution of monitors fundamentally changed the way people perceived and used them, and therefore experienced a variety of problems associated with running the monitors in extended, duplicated, or relocated mode. We highlighted resulting implications for the HCI design of future systems to support the seamless alternation of postures while working in such an environment.

Based on the findings of this study, future work will focus on the development of novel user interfaces and interaction techniques that provide an optimal interaction for exclusive, supportive and peripheral usage of distributed multi-monitor setups. Sensing methods will be developed on multiple levels to gain knowledge about the user's activity within the office workspace.

Another interesting insight provided by the presented study was that especially the standing workstation can be a great addition for collaboration and communication within an office space, which will also be addressed through the development of specific software support for such collaborative settings. Based on the findings on users' workplace switching behavior, we will examine these patterns more closely including the possibility to use and trigger them to promote workplace switching. Finally, future research will include additional studies with a larger number of participants and more diverse hardware setups (including e.g. notebooks and other mobile devices), and the investigation of challenges arising with the utilization of these setups within activitypromoting office environments.

Fig. 1 .

 1 Fig.1. A sit-and-stand workplace design integrating the concept of working in sitting and standing posture into the daily office workflow.

Fig. 2 .

 2 Fig.2. As part of the study concept, participants were provided with two height-adjustable desks (left), a swopper active seat (middle), a muvman standing chair (right).

Fig. 3 .

 3 Fig.3. Two participants' arrangements of their personal sit-and-stand workspace.

Fig. 4 .

 4 Fig.4. Participants' reported daily work tasks (left) and sitting/standing times (right).

Fig. 5

 5 Fig.5 Participants' logged software usage (left) and sitting/standing times (right).

Fig. 6 .

 6 Fig.6. Example distributions of computing events for task-driven (P5, top) and self-determined (P4, bottom) switching between sitting (gray) and standing (black) workstation.

Table 1 .

 1 Reported influencing factors with encouraging (+) or limiting (-) effects.

	Category	Influencing Factor	P1	P2	P3	P4	P5
	Personal Condition	Physical Discomfort Personal Habits Emotional Stress	+ -	+ -	+ --	+ +	+
		New/Other Task	+	+		+	+
		Workstation Association	+	+			+
	Work Task	Logical Breakpoint		+	+	+
		Cognitive Demand		-	-	-
		Task Involvement	-		-
		Collaboration	+	+	+	+	+
	Workspace	Accessibility		+	+	+
	Configuration	Physical Constraints			-	-	-
		Software Limitations	-	-	-	-	-

Personal Condition. One consistent finding applicable for all participants is that physical discomfort of prolonged sitting (e.g., back muscle tension) or standing (e.g., fatigue, aching feet) was the main trigger to switch from one workstation to another.

http://actiforce.eu/nc/products/steelforce

http://www.swopper.de/en/swopper

http://www.swopper.de/en/muvman

The systems' multi-monitor settings could be accessed and changed by pressing Win+P. http://windows.microsoft.com/en-US/windows7/Connect-to-a-projector

http://support.microsoft.com/kb/79869

Acknowledgements. We would like to thank Dr. Sheelagh Carpendale and the InnoVis group at the University of Calgary for their ideas and advice. Funding for this research was provided by the Austrian Research Promotion Agency GmbH (FFG) within the Bridge project #2579917.


Martin Henschke
email: martin.henschke@anu.edu.au

Tom Gedeon
email: tom.gedeon@anu.edu.au

Richard Jones
email: richard.jones@anu.edu.au

Sabrina Caldwell
email: sabrina.caldwell@anu.edu.au

Dingyun Zhu
email: dingyun.zhu@anu.edu.au

Wands are Magic: a comparison of devices used in 3D pointing interfaces

Keywords: "magic wand", "3D mouse", "hand gesture", "fatigue", "user satisfaction"

In our pilot study with 12 participants, we compared three interfaces, 3D mouse, glove and wand in a 3D naturalistic environment. The latter two were controlled by the same absolute pointing method and so are essentially identical except for the selection mechanism, grasp action versus button. We found that the mouse performed worst in terms of both time and errors which is reasonable for a relative pointing device in an absolute pointing setting, with the wand both outperforming and favored by users to the glove. We conclude that the presence of a held object in a pointing interface changes the user's perception of the system and magically leads to a different experience.

Introduction

Tasks that are typically accomplished by human beings can be separated into two broad categories: tasks achieved through physical manipulation of objects, such as chopping wood with an axe or writing with a pen and paper, and communication with other people, commonly done both using words and a series of communicative gestures. When not operating physical tools, gestures are usually a form of communication and often intertwined with spoken language [START_REF] Cassell | A Framework For Gesture Generation and Interpretation[END_REF]. Although operating computers can be considered a form of communication, typical day-to-day interactions with a standard desktop or laptop computer fall into the physical object category. Interfaces that use motion or body capture allow users to perform these sorts of tasks without requiring a device to be held, with interfaces implementing gestures or methods of interaction found in both categories. The challenge of making these interfaces sufficiently ubiquitous remains formidable, and in the meantime it remains unclear if such interfaces are superior or preferred by users to an object-based interface, in a comparable setting. The ergonomic factors relating to these devices, namely how much physical strain or fatigue they cause with continued use, remain an issue in interface design [START_REF] Nielsen | A Procedure for Developing Intuitive and Ergonomic Gesture Interfaces for HCI. Gesture-Based Communication in Human-Computer Interaction[END_REF], and merit further study.

Our pilot study used a series of pointing interaction methods in a 3D interface, comparing operating an interface while holding a physical object to performing interactions in the absence of one. We wish to determine if there are any changes in the mode of operation, the severity and locality of discomfort caused by their operation and the preferences of the users.

Background

The MIT Media Room [START_REF] Bolt | Put-that-there": Voice and gesture at the graphics interface[END_REF] is a seminal example of an object-free interface, in which users would use a combination of spoken language and pointing gestures at a large projected display to create and modify the state of various shapes in a scene. A similar system, using a 3D spatial environment and gesture interface captured interactions with a specially designed glove and camera system [START_REF] Maggioni | A novel gestural input device for virtual reality[END_REF]. [START_REF] Kjeldsen | Toward the use of gesture in traditional user interfaces[END_REF] presented a camera-based pointing system applied directly to performing mouse tasks on a standard desktop computer [START_REF] Kjeldsen | Toward the use of gesture in traditional user interfaces[END_REF]. Another similar system provided a means of absolute pointing through capture of the user's entire arm and projecting a line from the user's shoulder to their fingertip [START_REF] Fukumoto | Finger-Pointer": Pointing interface by image processing[END_REF]. The system used multiple cameras to make any form of device such as a glove or sensor unnecessary.

Research into the ergonomics or feasibility of such systems remains limited, though study into developing ergonomic gestures has been conducted [START_REF] Nielsen | A Procedure for Developing Intuitive and Ergonomic Gesture Interfaces for HCI. Gesture-Based Communication in Human-Computer Interaction[END_REF]. An assessment of performance of gesture interfaces in VR environments reported the interfaces were almost four times slower than using a traditional mouse system, and fatigue was a common complaint [START_REF] Cabral | On the usability of gesture interfaces in virtual reality environments[END_REF]. A study comparing Wii remote and Kinect interfaces found a hands free interface performed tasks faster and was preferred by users to the Wii interface, which used in-built accelerometers rather than arm movements for tracking [START_REF] Francese | Wiimote and Kinect: gestural user interfaces add a natural third dimension to HCI[END_REF]. Another study, looking specifically at the ergonomic considerations of interfaces with and without physical objects indicated that performing a task with a 'virtual object' was more difficult and fatigue-inducing than an equivalent one performed with a real object. The trial found users extended their fingers earlier and farther with the virtual object, making it the more fatiguing of the two interactions [START_REF] Kim | Analysis on virtual interaction-induced fatigue and difficulty in manipulation for interactive 3D gaming console[END_REF].

3

The System

We have developed a 3D pointing interface, in which users are able to select, grab and drag objects in a virtual space by pointing and performing interactions with the given device. The interface makes use of an absolute pointing system, in which both the user's position in the work area and the screen's position and dimensions are used to determine where user is pointing. The system works by having the user physically point at the display surface with their hand. From here, capturing user input involves detecting the position of the user's forearm and hand to construct a 3D vector, which is then projected forward to the 2D plane on which both the Kinect and the display surface rest. This provides a 2D point on the plane where the user is pointing at any given point in time. The system allows for a relatively flexible definition of pointing, with different arm orientations and holding the device in different ways possible.

Our pilot makes use of a total of three different interaction methods. The first is a wired glove interface as an approximation of operating a user interface without physically manipulating a device. It operates using an Essential Realities P5 Wired Glove, weighing 82g for tracing finger movements and a Microsoft Kinect that tracks general body movements. The second is a Wand interface, operating with Kinect in the same way as the Wired Glove interface, but with a hand-held controller in place of a glove. The controller is from a Nintendo Wii, and is identical to a standard Wii Remote controller, except that it has a slimmer, longer and more cylindrical profile, weighing 78g. The controller is only used for button presses as position information is acquired from the Kinect. An OnmiMotion Air Mouse, weighing 65g, is used for our third device, using a relative pointing system in contrast to the other two devices. This gyroscopic mouse is similar to a standard desktop mouse in appearance, but moves the cursor through rotating the body of the mouse rather than laser tracking.

Experiment

The general research question of this paper is does the absence of a physical object of manipulation impact how the user interacts with an interface? We define a physical object in this context as one that is held rather than worn, and is manipulated in-hand.

We are looking at three particular aspects of this question: user performance, induced fatigue and preference. A 3D visualization was conducted for the experimental trials, designed to have the appearance of being performed in a Gothic château, with the tasks themselves resembling ones being accomplished by casting magic spells. This allowed users to treat each device as operating according to their own expectations, and adopt an approach that felt contextually natural in operating the devices. A total of three separate kinds of tasks were performed:  A selection task, in which the user was required to select a ghost on the screen by pointing at it and performing a selection. For the glove, this was achieved by quickly tapping the index finger down and back up again, and for the wand this was done by pressing the 'A' button on the shaft of the device. For the mouse, the left mouse button was used. The position and size of the targets was randomized. Nine selections were performed per trial.  A select-drag task, in which the user was required to select a key, randomly placed near the bottom of the display, then 'grab' the object and drag it over a lock. In the case of the glove, the grab was performed by forming a fist, and in the case of the wand it was by pulling a trigger beneath the device. Six drag tasks were performed per trial.  A select-drag-drop task, in which the user was required to select a firefly and drag it to a cage, then release it. The target area remained the same for each task, but the positions of the selectable objects were randomized. Six of these tasks were performed per trial. The trials presented the tasks consecutively with a brief break between each task explaining what needed to be done before it was begun. At the end of each sequence of tasks, the participant was given a 5-10 minute break to rest their arm before continuing with the next interface device.

During the task completion phase of the experiments, the mouse cursor is hidden from participants, as our trial is designed for a naturalistic environment without relative location cues, and could be used in a natural environment. Selection gestures are accompanied with a small burst of stars at the area pointed to, so users know where their gesture was directed.

Over the course of the trials, the system keeps track of every button press and gesture, the position of the pointing location and a time signature. Video from the Kinect was captured, to observe the movements each user makes when operating each interface. At the end of each trial, the user was also queried on the discomfort felt in their arms, and asked where specifically the discomfort, if any, was located and how severe it was on a scale of 0 to 10. At the end of each trial, the user was also asked to fill out a short questionnaire about the device they had just used, using a combination of Likert-scale questions and short written answers.

Results

The trial was run with 12 participants, 8 male, and 4 female, between the ages of 21 and 36, with a mean age of 25. All participants were computer science students, and reported regular computer use. Of those, 9 reported familiarity with the Kinect. Other gesture capture technologies such as the Nintendo Wii were also familiar to participants, with 1 participant having never used any motion capturing devices.

The relationship between the number of incorrect selections made and the time taken to complete the trial demonstrates a moderate to strong trend for most users, so these values are used as a measure of how accurately and easily each participant was able to use each device. Performance between the glove interface and wand were roughly equivalent in terms of accuracy, but users on average took substantially longer in performing operations with the glove. The mouse was on average the poorest performing device, but also the device with the greatest level of variance. The wand can be seen here as having generally the best and most consistent performance, though all devices are demonstrated as being able to perform quickly and with relatively few errors.

During the trial, a variety of arm positions were adopted. The method of control and orientation of the arm was consistent enough between participants to be separated into three categories, ordered from lowest induced fatigue to highest:

 The shoulder at rest, with the elbow kept at the side and the forearm extended pointing at the display. Holding the device in this manner, users typically made wrist and small forearm movements to control the interface.  The shoulder partially at rest, the elbow out from the side and bent, with the forearm raised and the wrist bent to face the device to the display. Forearm rotation and wrist movements were the primary method of interaction.  The arm fully extended with the elbow locked. The user moves the entire arm at the shoulder in this position.

While users typically kept a consistent arm orientation for the trials, it was not uncommon for them to change positions. This was most commonly moving from an outstretched arm to a relaxed or partially relaxed arm, likely to combat fatigue, or from a relaxed or partially relaxed arm to an outstretched arm, usually due to issues with accuracy. Figure 3 shows the prevalence of various orientations with each device, by counting the number of times and the duration of the trial during which the stance appeared for all participants.

On average, the glove interface was reported to be the most fatiguing by participants (µ = 4, σ = 1.9), followed by the wand (µ = 2.4, σ = 2.2) with the mouse being the least stressful to use (µ = 1.3, σ = 2.5). 2, with no significant difference between the wand and mouse (p > 0.05), but more pronounced variation between the glove and all other devices. This confirms the glove as being the most fatigue-inducing device to operate. In the questionnaire, users were asked to grade each interface system on a sevenlevel Likert scale, how natural, intuitive, learnable, reactive, accurate and generally easy to use the interface was perceived to be. Of those, only two yielded a statistically significant result in non-parametric analysis. In both instances, pair-wise analysis revealed no significant difference between the glove and mouse. The wand however was found to be more intuitive than the glove (p=0.016) and the mouse (p=0.018). The wand was also found to be easier and quicker to learn than the glove (p=0.024). The fact that all other results lacked a clear correlation suggested personal preference played a large part in these reports.

Users were also asked to rank each interface in terms of preference, and provide comments as to those rankings. The results of this are shown in Figure 3, indicating a general preference for the wand interface. Comments justifying this preference referenced the wands appearance or comfortable grip or being easier to press buttons than on the mouse or with finger gestures with the glove. When the mouse was preferred over the wand, it was typically due to being the less strenuous to operate, with com-plaints of the mouse being its unpredictable behavior and difficulty in reaching buttons. Preferences for the glove were reported as being the more natural of the interfaces, while complaints included a poor responsiveness and fatiguing to use. Our expectations were that users would find differences in induced fatigue and preference between the devices, but pronounced differences in performance and speed were not expected. The results suggest the presence of an object held in the user's hand has a profound impact on how users view the system, and the amount of effort users expended.

The results from observations suggest that interfaces with a physical object held in hand tended to encourage users to use a less direct form of pointing, performing pointing with the upper arm fully or partially at rest, and the elbow at the side, while having no object encouraged users to keep their arms fully extended. This fits the natural analogue of attempting to point to an object with your hand, in which the user raises it and looks down their arm towards their index finger, where the wand was interpreted much more generally and had more varied usage patterns. A generally larger number of changes in posture were seen with wand users; they would find configurations they liked rather than what they felt was necessary. The wand was observed to also be subject to in-hand manipulation; users were observed turning or rotating the device within the palm of their hand rather than performing the equivalent rotation with their wrist or forearm. This rather counter-intuitively seems to be accompanied with a better performance index for the wand. Less physical movement by the user is required overall to move the pointer to the desired area, but as the region of selection is far smaller, inaccuracy was expected to be higher. This may be attributed to the fact that selection and grabbing was reported to be much easier with the wand and mouse when compared to the glove. Users on average seemed to exert more energy attempting to perform selections and grabs, as the glove required a strong, deliber-ate motion to select an object on screen compared to the other two. That a strong correlation can be seen between increasingly extended arm, trial length and fatigue matches expectations, and remains an important consideration in interface design.

The poor results for the mouse can largely be attributed to the absence of a visible cursor and the use of rotation as opposed to lateral motion as with a desktop mouse. Overshooting targets and quickly clicking to inform the user where the cursor was occurred regularly in the trials.

The variation in user preference may reflect the background of participants. Comments such as 'familiarity with the Wii may have been useful' appeared in the questionnaire, despite the fact the system functions quite differently to the Wii, but the method in which users operated the interface may have reflected that experience. Preferences for any given device appears to be heavily influenced by those users found to perform most effectively, though there were some instances where this was supplanted by familiarity with that device, particularly with the mouse.

This trial has indicated substantial nuances in the problem that merit further investigation. Controlling and examining each of the findings in this paper in more detail will be the focus of later experiments. Running trials for extended periods of time and encompassing more complex interactions will be performed in future work.

Fig. 1 .

 1 Fig. 1. Selecting a firefly in the select-drag-drop trial using the P5 Wired Glove

Fig. 2 .Fig. 3 .

 23 Fig. 2. From left to right: shoulder at rest, partially extended forearm, fully extended arm

Fig. 4 .

 4 Fig. 4. Sum of rankings given by each user to the three interface devices

Table 1 .

 1 Mean and Standard Deviations for time and errors in completing selection tasks for each device (time in seconds)

		Glove		Mouse		Wand
		Time	Errors	Time	Errors	Time	Errors
	µ	136.8s	50.3	149.0s	71.5	79.7s	45.8
	σ	62.1	18.4	81.3	33.8	33.8	20.7

Table 2 .

 2 Distribution-free analysis of questionnaire results pertaining to immediate and continually induced fatige from each device

		Immediate Fatigue	Continuous Fatigue
	Non-parametric test	χ 2 =7.023, p=0.03	χ 2 =11.286, p=0.004
	Pair-wise Glove vs. Wand	p = 0.008	p = 0.015
	Pair-wise Glove vs. Mouse	p = 0.04	p = 0.005
	Pair-wise Wand vs. Mouse	p = 0.55	p = 0.232