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Page 1: A design advice tool presenting usability guidance for virtual environments-Kaur.pdf

A design advice tool presenting usability guidance forvirtual environments

Kulwinder Kaur Deol, Alistair Sutcliffe and Neil Maiden

Centre for HCI Design, City University, London

Abstract

There is a lack of design advice on how to construct usable virtual environment(VE) systems, even though major usability problems have been reported. Thispaper details the development and evaluation of a design advice tool forpresenting usability guidance to VE designers. The guidance was derived fromtheoretical work on human-computer interaction in VEs, which detailed stages ofinteractive behaviour and design requirements to support the stages. The designrequirements were translated into concrete design guidelines and a hypertext tooldeveloped to present the guidelines. The design of the tool incorporatedknowledge of design practice from studies of VE designers. The usability andutility of the tool was evaluated. Industrial designers found the tool andguidelines to be useful in highlighting usability considerations and in providing achecklist for different design elements. Areas of improvement and extensions tothe tool were suggested.

Keywords: Virtual Environments, Usability, Guidelines, Design Assistance

1 Introduction

Virtual environments provide a computer-based interface representing a three-dimensional real-life or abstract space. VEs offer new possibilities and challenges tohuman-computer interface design, but have been noted for being significantly moredifficult to design and use than 2D interfaces (Herndon et al., 1994). In our previouswork, we carried out studies of the design of VEs (Kaur et al., 1996) which showed thatdesigners lacked a coherent approach to interaction design. They appeared to be pre-occupied with difficult technical issues and thought little about supporting userinteraction. However, major interaction problems have been found with current VEs,such as disorientation, perceptual misjudgements and difficulty finding availableinteractions (COVEN, 1997; Miller, 1994). These problems result in user frustration anda low usability and acceptability for the VE (Kaur et al., 1996; Miller, 1994).

VE designers need guidance which highlights relevant usability issues and advises onhow to address them. Conventional guidance is only partially applicable to VEs and doesnot cover the range of issues and phenomena that arise in VE interaction. For example,VE users face further problems in perception, orientation and object manipulationbecause of the added spatial dimension. Movement through the VE and the locating of

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objects is a major area of potential difficulty, and the novel and more complex interfacetechnology results in additional difficulties. There is little usability guidance specificallyfor VEs and only fragmentary knowledge of user issues. Most research so far has beendirected to requirements for supporting perception and wayfinding, and the design ofviewpoint controls and user representations (e.g. Benford et al., 1995; Darken and Sibert,1996; Drucker and Zeltzer, 1994; Rushton and Wann, 1993), as well as understandingmotion sickness in immersive VEs (e.g. Oman, 1993). Although, this research may leadto detailed advice for specific parts of the VE design problem, advice on general usabilityrequirements is needed (Herndon et al., 1994) to cover the range of interaction tasks auser may be engaged in, from goal-formation to perception and action. This paperreports work towards a design adviser for VE usability. Usability guidelines weredeveloped from theoretical work on interaction in VEs. A hypertext tool was developedto present the guidelines and tested with industrial VE designers.

2 Theory

The research focused on the more basic type of VE, i.e. single-user systems modelled onreal-world phenomena, since there was little previous work in this area. The theoreticalwork and the related evaluation studies are briefly outlined here, but full details can befound in Kaur (1998). Models of interaction for VEs were developed and from thesemodels abstract usability requirements were proposed. Norman’s (1988) basic plan-based theory of action was elaborated to include required behaviours in VEs, in particularexploratory and reactive behaviours. Three inter-connected models described the majormodes of interactive behaviour:

Task action model - describing behaviour in planning and carrying out specific actionsas part of user's task or current goal/intention. Requirements for 3D actions includedthe need to approach and orient as required to action objects, and the possibility ofobject inspection rather than manipulation actions.Explore navigate model - describing opportunistic and less goal-directed behaviourwhen the user explores and navigates through the environment. The user may have atarget in mind or observed features may arouse interest.System initiative model - describing reactive behaviour to system prompts and events,and to the system taking interaction control from the user (e.g. taking the user on apre-set tour of the environment).

The models were evaluated through user studies, comparing observed physical andmental behaviour (from verbal protocols) with that predicted in the models. Majorpredicted patterns of activity were supported and the models were refined in light of theresults (Kaur et al., 1999).

The interaction models provided a clear breakdown of interactive behaviour. The modelswere used to systematically reason about what generic properties are required in a VEdesign to support the user during each identified stage in interaction. Previous researchon human-computer interaction was used to inform required design properties, whererelevant. Forty-six design properties were identified in categories covering requirements

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for: the user task, spatial layout, viewpoint and user representation, objects, system-initiated behaviour, actions and action feedback. For example, the property identifiableobject states that an object should be easy to identify or recognise; clear navigationpathways states that areas that the user can move through should be clear; and declaredsystem control commencement/ termination states that the beginning (and end) of asession of system control (e.g. a guided tour) should be clearly cued. Use of the modelsof interaction meant that the identified set of properties could cover a broad range ofinteraction issues for VEs, including planning and task execution; exploration, navigationand wayfinding; action identification and execution; object approach and inspection; andevent interpretation and response. The design properties were evaluated in a controlledstudy where interaction success with two versions of a test application, with and withoutimplementation of the properties, was compared. Results were very encouraging andshowed a 66% reduction in usability problems and significantly improved taskperformance, with the design properties present. Analysis of detailed results provided forindividual assessments of properties.

3 Design Advice

Having shown that the theory could be applied to improve interaction, the next step wasto provide the abstract theory advice in an appropriate form for designers. Guidelines canbe useful prompts for designers, by highlighting the variety of issues that need to beconsidered. However, they need to be given with extra information, such as scopingrules and caveats, to avoid the guidance being too vague or conflicting (Reisner, 1987).Each abstract design property was translated into a concrete design guideline, whichincluded the design advice itself, motivation for the advice (based on supportinginteractive behaviour in the models), a context-of-use giving information about theapplicability of the advice for different applications, and two practical examples ofimplementation of the guideline. A tool was designed to present the guidelines in asuitable form for designers. Previous studies of VE development (Kaur et al., 1996) hadindicated that designers had varied backgrounds, but a generally poor understanding ofusability. They followed informal, iterative design approaches, with projects typicallyhaving short development times (i.e. a number of weeks). Therefore, a presentation stylewas required which would be simple to understand and allow quick, easy and flexibleaccess to the guidance.

As a result, a hypertext tool was designed to present the guidelines in a structured andaccessible form. The hypertext tool structured guidelines according to the environmentelements involved (e.g. events, objects and actions) and general development stages whenthe guidelines would apply. A manageable amount of guidance (avg. 5 guidelines) wasgiven for each element type. Development stages were defined using knowledge of theVE design process, from the designer study, and the common stages of activity found insystem development methods. The stages outlined were: define requirements, specifycomponents in VE, specify interactions, design components, design interactions, buildenvironment and evaluate environment. A demonstration version of the tool wasimplemented in HyperText Modelling Language. It included 12 guidelines chosen tocover a range of major issues for three element types: objects, actions and system control.

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The corresponding design properties had been tested in the controlled study outlinedabove and found to significantly reduce related problems. For each element type, a bulletpoint list of guidelines was given, which was linked to full descriptive texts and screen-shots illustrating examples. A navigation panel enabled rapid access to guidance fordifferent stages, although only the introduction and two design stages were available inthe demonstration version. For example, figure 1 shows the bullet point list for the objectguidelines and figure 2 shows the guideline for property identifiable object.

Figure 1: The bullet point list for the object guidelines in the tool.

Figure 2: Description of the guideline for the property identifiable object.

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4 Evaluation Study

The tool and design guidelines were tested using expert evaluation and critiquing to gaindirect qualitative feedback about their usability and utility. Four industrial VE designerswith an average (median) of 3 years experience took part in a one-day study. Thedesigners were given nine design scenarios and asked to produce paper storyboards ofdesign solutions. They worked in groups and had access to the demonstration version ofthe tool throughout. The scenarios included five for designing original elements (objects,actions and system controls) from given requirements, two for re-designing elementschosen by the designers from their previous experiences, and two for re-designingelements from given descriptions of a current design (including the usability problemswith the design). For example, designers were asked to design a corridor object withaccessible and inaccessible doors and re-design the action of drawing a blind, which userscurrently had difficulty working out how to do. Scenarios chosen by designers includedthe action of adding a new card to a personal computer. After all scenarios had beencompleted, designers filled in retrospective questionnaires eliciting their views about theguidance and tool, and took part in a discussion session.

A simple scoring scheme was used to score the completed storyboards of designsolutions, to give a general indication of usability. The solutions were assessed for howwell each relevant guideline in the tool had been incorporated in the design solution.Individual scores for guidelines were either 0 – for no consideration of the associatedusability issues, 1 - for a partial or inadequate consideration, or 2 – for a fullconsideration of all associated usability issues. The retrospective questionnaires coveredimportant aspects of the usability and utility of HCI guidance, described in detail in Limand Long (1994). Learnability could not be covered because longitudinal data was notavailable in this one-day study.

5 Results

Usability scores given ranged from 50 to 100%, median 75%. Most individual scoreswere either 1 or 2 (53 of the 57), indicating that usually the guidelines were addressed tosome extent. Points were generally lost where designers had considered some but not allassociated usability issues with a guideline, or where there was missing information inthe storyboards.

Table 1 gives the average response to each aspect of usability and utility in theretrospective questionnaires. Responses were generally positive, with averages forindividual areas ranging from 4.75 to 6.00 (on a scale of 1 to 7, where 7 represented themost positive response). The average response for the usability questions was 5.3, andfor the questions on utility the average was 5.25. The most positive response was for thequestion on how acceptable the tool would be in practice.

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Question on avg. (1-7)Usability accessibility 5.75

understandability 5.00applicability 4.75specificity - pitched at appropriate level 5.00acceptability - compatible with design practice 6.00

Utility uncovered usability issues 5.75helped address issues 5.25helped validate usability of designs 5.25improved usability of design 4.75

Table 1: Average responses to questions on the usability and utility of the guidance tool.

In the questionnaires and during the discussion, designers commented that the tool wasuseful as a reminder of all the usability issues that needed to be considered for a designelement. Designers used the tool particularly for assessing design solutions with respectto usability, although there was often direct (copycat) reuse of techniques from theexamples given. Some changes to the design of the hypertext in the tool were suggestedas well as useful extensions to the tool. Designers wanted more example techniques forincorporating the guidelines, to enable re-use by copying. They also felt the guidancecould be extended to help address the issue of how faithfully to model reality, and thepossible trade-offs between adding support information and maintaining the realism andnaturalness of the VE.

6 Discussion

In this paper, we have outlined the development of usability guidelines for VEs, fromtheoretical work on interaction behaviour. A prototype tool was designed to present theguidelines to designers. The tool was evaluated, using design scenarios together withstoryboarding. The results were encouraging and provided useful qualitative feedbackabout the guidance and tool. The design solutions produced generally had good usabilityscores, indicating that the designers were able to incorporate interaction support in theirdesigns, through the use of the tool. Designers’ perceptions about the guidance tool werevery positive. They felt the design advice was usable and that it helped to analyse andaddress the usability of VEs. They also felt it could have an important impact on thedesign process and could fit in with current design practices. Therefore, the tool appearsto represent an effective way of delivering the theory-based knowledge to industrialdesigners. The evaluation has also highlighted some possible improvements andextensions.

Previous work had provided fragmentary knowledge about usability requirements in VEsand focused on only certain parts of the VE design problem. There were tools forconstructing the graphics for VEs, but no tools presenting design advice directly todesigners. The design properties in this research provide a more broad andcomprehensive set of requirements that are based on a theoretical model of interaction.The prototype tool represents early work towards an effective design advisor for VEusability.

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Future work includes further development of the guidance tool, by researching andincluding a range of example techniques for implementing guidelines, for varying levelsof realism constraints. For example, various techniques have been used for providingappropriate user representations, such as human bodies, block figures and detailed faces(Benford et al., 1995). Different styles could be applied to incorporate properties, such asmanipulating levels of detail and realism, using highlighting techniques for attentionaldesign or active support techniques. Further evaluation work is also planned to testcomplete versions of the guidance tool with more designers and in full developmentprojects. Our overall aim is to address problems in interaction design for VEs, throughguidance and tools based on human-computer interaction theory.

References

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COVEN (1997). D3.3: Usage evaluation of the initial applications. Public Deliverable report ofCOVEN (Collaborative Virtual Environments) ACTS Project N.AC040.

Darken R.P. and Sibert J.L. (1996). Wayfinding strategies and behaviours in large virtual worlds.In: Human Factors in Computing Systems: CHI ’96 conference, Vancouver 1996.Proceedings. New York: ACM, pp. 142-149.

Drucker S.M. and Zeltzer D. (1994). Intelligent camera control in a virtual environment. In:Graphics Interface ’94 conference, Banff, Alberta, 1994. Proceedings. Toronto: CanadianInformation Processing Society, pp. 190-199.

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Kaur K., Maiden N. and Sutcliffe A. (1996). Design practice and usability problems with virtualenvironments. In: Virtual Reality World ’96 conference, Stuttgart, Germany, 1996.Proceedings. Munich, Germany: IDG Conferences & Seminars.

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