Helmut Krueger

Physical and Virtual Tools: ActivityTheory Applied to the Design of Groupware

Activity theory is based on theconcept of tools mediating between subjects andobjects. In this theory, an individualscreative interaction with his or hersurroundings can result in the production oftools. When an individuals mental processesare exteriorized in the form of tools – termedobjectification – they become more accessibleto other people and are therefore useful forsocial interaction. This paper shows how ourunderstanding of activity theory has shaped ourdesign philosophy for groupware and how we haveapplied it. Our design philosophy and practiceis exemplified by a description of the BUILD-ITsystem. This is an Augmented Reality system wedeveloped to enhance group work; it is a kindof graspable groupware which supportscooperative planning. The system allows a groupof people, co-located around a table, tointeract, by means of physical bricks, withmodels in a virtual three-dimensional (3D)setting. Guided by task analysis, a set ofspecific tools for different 3D planning andconfiguration tasks was implemented as part ofthis system. We investigate both physical andvirtual tools. These tools allow users toadjust model height, viewpoint, and scale ofthe virtual setting. Finally, our designpractice is summarized in a set of designguidelines. Based on these guidelines, wereflect on our own design practice and theusefulness of activity theory for design.

In pursuit of desktop evolution: User problems and practices with modern desktop systems

This study deals with the problems users encounter in their daily work with computers and the typical practices that they employ. Sixteen daily computer users were interviewed about their habits and problems that they encountered during document classification and retrieval. For both these areas, we provide an overview of identified user practices and a citation-based analysis of the problems users encountered, including those related to the use of the screen real estate (the actual desktop). Two types of problems were identified: (1) Problems that concern the actual use of the system installed on the computer. (2) Problems that arise when people realise that they are using a system that does not allow for the desired work or organizational functions sought. We were able to show that skill continues to be an important factor with respect to the ease of using todays systems. We suggest the following necessary improvements for the evolution of personal information systems: A storage facility that represents the users view of information; replacing pure technical file metadata with more user-friendly attributes; and introduction of annotations as a new information type.

Stress Sensitivity of Piezoelectric Ceramics: Part 1. Sensitivity to Compressive Stress Parallel to the Polar Axis

Measurements are reported of the change in permittivity, loss, and the piezoelectric constants, d31 and d32, for piezoelectric ceramic transducer materials subjected to high stress perpendicular to the polar axis (T1) Ceramics useful for high‐power applications (PZT‐4 and PZT‐8) and some donor‐doped ceramics of high sensitivity but with high losses that make such applications unwise (PZT‐5A and PZT‐5H) were tested. Permittivity generally decreased with stress, T1, opposite to results with parallel stress, T3. The piezo‐electric coefficient d31 (in the direction of stress application) decreases markedly with stress, while d32 (in the direction perpendicular to the stress and the polarization) generally rises. The effects are less severe for the “hard” ceramics. A permanent change in pseudocrystal symmetry from ∝ m to 2mm is observed for the donor‐doped ceramics, even at relatively low stress levels (5 kpsi).

Continuous, intermitted and sporadic motor unit activity in the trapezius muscle during prolonged computer work

The Cinderella hypothesis postulates the continuous activity of specific motor units (MUs) during low-level muscle contraction. The MUs may become metabolically overloaded, with the subject developing muscle pain and strain. The hypothesis requires MUs that are active for a time long enough to actually damage muscle fibers. The aim of this study was to determine if there are continuously active MUs in the right trapezius muscle during normal computer work using a computer mouse. Fourteen healthy subjects executed an interactive computer-learning program (ErgoLight) for 30 min. Six-channel intramuscular EMG and two-channel surface EMG signals were recorded from two positions of the trapezius muscle. Decomposition was achieved with automated, multi-channel, long-term decomposition software (EMG-LODEC). In two out of the 14 subjects, three MUs were continuously active throughout the 30 min. Although the majority of the MUs were active during only part of the experimental session, an ordered on-off behavior (e.g. substitution) pattern was not observed. As long-lasting activity was verified in some subjects, the results support the Cinderella hypothesis. However, it cannot be concluded here how long the MUs could stay active. If continuous activity overloads low threshold MUs, the potential exists for selective fibre injuries in low threshold MUs of the trapezius muscle in subjects exposed to long-term computer work.

Long-term effects of supervised physical training in secondary prevention of low back pain

Background and objectives: In the last few years, several studies have focused on short-term treatment effects of exercise therapy. However, there is a lack of knowledge concerning the long-term treatment effects recorded after several years. Hence, this study was performed to investigate the short- and long-term effects of supervised physical training on functional ability, self-rated pain and disability in secondary prevention of low back pain. Methods: One hundred and eighty-three hospital employees with chronic low back pain were randomly assigned either to back school (comparison group), or three-months supervised physical training including a back school (exercise group). Various measurements of functional ability were performed and subjects completed questionnaires on self-rated pain, disability, and general well-being before treatment, immediately after intervention, and at six-months follow-up. At one-year and at ten-years follow-up participants evaluated treatment effectiveness. Results: Out of 183 employees, 148 completed the program. Participation at follow-ups ranged from 66 to 96%. Supervised physical training significantly improved muscular endurance and isokinetic strength during a six-months follow-up, and effectively decreased self-rated pain and disability during a one-year follow-up. At ten-years follow-up the subjects’ assessment of the effectiveness of treatment was significantly better in the exercise group. Conclusions: Supervised physical training effectively improved functional capacity and decreased LBP and disability up to one-year follow-up. The subjects’ positive evaluation of the treatment effect at ten-years follow-up suggests a long-term benefit of training.

BUILD-IT: a planning tool for construction and design

It is time to go beyond the established approaches in humancomputer interaction. With the Augmented Reality (AR) design strategy humans are able to behave as much as possible in a natural way: behavior of humans in the real world with other humans and/or real world objects. Following the fundamental constraints of natural way of interacting we derive a set of recommendations for the next generation of user interfaces: the Natural User Interface (NUI). The concept of NUI is presented in form of a runnable demonstrator: a computer vision-based interaction technique for a planning tool for construction and design tasks.

CRT versus LCD: A pilot study on visual performance and suitability of two display technologies for use in office work

Cathode ray tube (CRT) display and liquid crystal display (LCD) were compared for their suitability in visual tasks. For this purpose visual performance was assessed by means of a search task carried out using both displays with different levels of ambient light. In addition, suitability was rated subjectively by users of visual display units (VDUs). Error frequency for search tasks carried out using LCD were significantly smaller when compared to error frequency for tasks at CRT. LCD gave rise to 34% less errors than did CRT. Reaction time in search task was found to be significantly shorter using LCD when tasks were carried out in darkness. Subjective rated suitability of LCD was scored twice as high as suitability of CRT. Results indicate that LCD used in this experiment may give better viewing conditions in comparison to CRT display.

Direction of gaze and comfort: discovering the relation for the ergonomic optimization of visual tasks.

Perceived exertion caused by the extraocular muscles was assessed as a function of the direction of gaze and recorded in 114 subjects using a psychometric method. The results confirm statements in the literature that maximum comfort is achieved when gaze is aimed downwards. We found mi correlations between perceived exertion and age or viewing distance. The relationship is relevant to ergonomics, for example in tens lining and workplace layout.

Performance effects of reduced proprioceptive feedback on touch typists and casual users in a typing task

Abstract This study examined performance and acceptance effects of lack of kinesthetic and tactile feedback from the keyboard in a typing task with two subject groups of differing skill level: touch typists and casual users. Subjects’ objective performance (e.g., speed, accuracy, throughput) and subjective acceptance (questionnaire) was evaluated for both a conventional full travel keyboard and a prototype piezoelectric flat keyboard which lacked familiar kinesthetic and tactile feedback. Any performance decrement present with the flat keyboard was expected to diminish with practice for the touch typists due to transfer and adaptation of typing skills. Performance for both subject groups was significantly higher with the conventional keyboard and touch typists’ performance was more adversely affected by the flat keyboard than casual users’. No performance improvement with practice was found for one subject group relative to the other or for one keyboard relative to the other. It was concluded the touch ty...

Exploring Brick-Based Navigation and Composition in an Augmented Reality

BUILD-IT is a planning tool based on computer vision technology, supporting complex planning and composition tasks. A group of people, seated around a table, interact with objects in a virtual scene using real bricks. A plan view of the scene is projected onto the table, where object manipulation takes place. A perspective view is projected on the wall. The views are set by virtual cameras, having spatial attributes like shift, rotation and zoom. However, planar interaction with bricks provides only position and rotation information. Object height control is equally constrained by planar interaction. The aim of this paper is to suggest methods and tools bridging the gap between planar interaction and three-dimensional control. To control camera attributes, active objects, with intelligent behaviour are introduced. To control object height, several real and virtual tools are suggested. Some of the solutions are based on metaphors, like window, sliding-ruler and floor.