1

What is a Virtual Environment?

• Wide field presentation of computer-generated, multi-sensory information with user tracked in real time

• Computer simulation that imparts visual, auditory, and haptic sensations

• Everything user perceives is computer-generated, responds to user with sights and sounds designed to make them think they are there

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Major Types of VEs

• Non-immersive: user is outside looking in– Desktop or “fishtank”

• Immersive: user is inside looking out– Immersive Workbench: table (single surface) with

translucent rear-projection surface for image; magnetic trackers; interaction with “wand”; stereo glasses

– CAVE: multi-wall (VT’s has four) cube using rear-projected “folded optics” to display registered images in real-time; magnetic trackers; interaction with “wand”; stereo glasses

3

VEs: User-Centered Design & Evaluation

• Virtual Environments: from Mars

• Usability Engineering: from Venus

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VEs & Usability Engineering

• Goal: To get VEs and Usability Engineering on the same planet!

• Improve VE applications from a user’s perspective by

– Performing empirical studies of various aspects of VEs (e.g., devices, techniques, designs, etc.)

– Developing new usability engineering methods for VEs

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User-Centered Design & Evaluation

• Purpose of research (basic): – Design a usable VE interface– Evaluate & iteratively improve VE interaction design

• Purpose of research (meta-level): – Identify general principles and most important

parameters of VE user interface design– Identify effective techniques for VE usability

engineering

• Two projects:– Pre-screen projection– Dragon battlefield visualization system

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Pre-screen Projection VE

• What is pre-screen projection?– A new interaction technique that allows a user to

integrally pan and zoom by head movement

• Conceptual basis: Real-world metaphor– Our view of world changes as we move our head

• Gibson’s ecological approach to visual perception: humans perceive relationships between movements and changes in view

– Objects in real world appear to get larger as we move toward them

– Nearer objects visually enlarge more rapidly

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Pre-screen Projection Configuration

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Iterative Development of PSP

• Resolved numerous design decisions by numerous quick cycles of formative evaluation

• Moved on to summative evaluation to compare PSP to other pan and zoom techniques

– Mouse– Spaceball– Pre-screen Projection

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Results

• Pre-screen projection “lost” in simple averages across scenarios:

– 1. Spaceball (avg. 52.1 secs)– 2. Mouse (avg. 61.1 secs)– 3. Pre-screen projection (avg. 69.8 secs)

• Reasons: – Spaceball more suited to task of pan and zoom– Mouse more familiar

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Results

• Important finding: Order of presentation of technique affected task performance strategy

– Performance improved when user used PSP prior to another technique

– Performance on difficult tasks was better with PSP than with other techniques

• Overall, users liked PSP

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“Dragon” VE

• VE for battlefield visualization• Implemented on a Responsive Workbench• Numerous iterations of UI design

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Usability Engineering Methodologies

Expert Heuristic Evaluation: assessment by UI design experts, to determine violated usability design guidelines

Formative Evaluation: assessment with users, to iteratively determine and improve usability

Summative Evaluation: assessment with users, to determine which among several design alternatives is “best”

users perform scenarios while

“thinking out loud”

collect qualitative and

quantitative usability data

suggest user interaction

design improvements

refine user task scenarios

rep

eat.

..

develop user task scenarios

(benchmark tasks)

Formative Evaluation

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Use of Methodologies

•Preliminary observational studies revealed generic tasks:

–navigation–object manipulation–object selection–object querying–query response–object aggregation

•Focus on navigation –fundamental to all other generic tasks

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Approach

• Dragon VE was instrumentable testbed for heuristic and formative work

• Developed scenarios of benchmark user tasks

• One to three users per evaluation cycle• Based on results, iterate design• Four major cycles of evaluation

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Expert Heuristic Evaluation

• Experts assessed UI design• Initially “free play”, then structured scenarios• One or two other experts observing• Guided by framework of usability

characteristics of VEs [Gabbard & Hix 1999]

• Discovered and addressed usability problems:– Poor mapping of navigation tasks to flightstick

buttons– Missing functionality– Damping of map movement in response to

flightstick movement– Graphical and textual feedback

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Formative Evaluations

• Six sessions; formal protocol; single user per session

• User first asked to use flightstick• User then asked to perform scenarios

– Time ranged from 20 minutes to more than one hour

– Timed individual tasks; counted errors– Noted critical incidents

• Two evaluators (observers) in each session• Four major iterations of Dragon UI design

over one year

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First Iteration Results: Virtual Sandtable

Based on real-world sandtable metaphor: exo-centric map manipulation

Utilized 5 DOF (x, y, z, h, p)

+ Mapping of buttons to navigation tasks worked well

– Users wanted terrain-following capability, to “fly” over map

– Basic metaphor cumbersome

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Second Iteration Results: Point & Go

Based on real-world airplane metaphor: ego-centric flying

One gesture moves anywhere on map

Utilized 6 DOF (x, y, z, h, p, r)

+ Attempted to avoid navigation modes

– Single gesture to move around was not powerful enough to support diverse navigation tasks

– Users wanted exo-centric rotate capability

Discovered control vs. convenience trade-off

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Third Iteration Results: Modal

Based on combination of flying and sandtable metaphors

Each navigation task was separate mode

Utilized 5 DOF (x, y, z, h, p)

– Users found it cumbersome

– Too much control, not enough convenience

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Fourth Iteration Results: Integrated Navigation

Based on combination of flying and sandtable metaphors

Combined modes mapped to flightstick buttons:1) Pan & zoom

2) Pitch & heading

3) Exo-centric rotate & zoom

Fine-tuned damping and acceleration

+ Users found navigation to any location easy, and easy to switch among tasks

+ Achieved control vs. convenience compromise

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Results: Significant Navigation Variables

• Identified 27 key variables that effect VE navigation narrowed to 5 variables

User Tasks1. navigation presets 2. user scenarios

Input Devices3. navigation metaphor 4. navigation degrees-of-freedom5. gestures to trigger actions 6. speech input 7. number of flightstick buttons 8. input device type 9. movement deadspace10. movement damping 11. user gesture work volume 12. gesture mapping 13. button mapping 14. head tracking

Virtual Model15. mode switching16. mode feedback17. number of modes 18. visual navigation aids 19. dataset characteristics 20. visual terrain representation 21. visual battlefield object

representation 22. visual input device representation 23. size of battlefield objects 24. visual object relationship

representation 25. map constrained vs. floating

Presentation Devices26. visual presentation device 27. stereopsis

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Ongoing Summative Studies

• Goal: systematically examine five variables most likely to influence VE navigation

• Summative Evaluation: assessment with users, to statistically compare user

performance with different UI designs

Variable Levels1) stereopsis absent present2) visual presentation device virtual workbench desktop3) gesture mapping controls rate controls position4) navigation metaphor egocentric exocentric5) head-tracking absent present

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Conclusions

• Successful, cost-effective progression from heuristic to formative to summative evaluations

summativeevaluation

formativeevaluation

expert heuristic evaluation

usability evaluationtype

associatedcost

generalityof results

precisionof results

cheap

expensive

general

specific

low

high

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Conclusions

• VEs are great new technology• We’re still exploring whether they are just

“new” or whether they are really “better” for users

• Some good experiences:– Caterpillar backhoe design– Boeing 777 design