1. Distance Perception in Real and Virtual Environments
Jodie M. Plumert
Department of Psychology
Joseph K. Kearney
James F. Cremer
Department Of Computer Science
University of Iowa

2. Virtual Environments as Laboratories for Studying Behavior
Gaining widespread acceptance
Driving (Uc, Rizzo, Shi, Anderson, and Dawson, 2004;
Lee, McGehee, Brown, & Reyes, in press)
Bicycling (Plumert, Kearney, & Cremer, 2004)
Navigating (Murray, Bowers, West, Pettifer, & Gibson, 2000;
Warren, Tarr, & Kaebling, NEVLab;
Bowman, Davis, Badre, & Hodges, 1999)
Advantages
Near natural
Highly controlled
Safe
Issues
Are virtual environments “real” enough?
How well do people perceive distance in VE?
State purpose of this study
Uc EY, Rizzo M, Shi Q, Anderson SW, Dawson J. Driver Route-Following and Safety Errors in Early Alzheimer’s Disease. Neurology; 2004
Lee, J.D., McGehee, D.V., Brown, T.L., & Reyes, M.L., (In press), "Collision Warning Timing, Driver Distraction, and Driver Response to Imminent Rear End Collisions in a High-Fidelity Driving Simulator, Human Factors (in press)
Navigation, Wayfinding and Place Experience within a Virtual City
Murray et al, Presence, 2000
Landmarks vs. Path Integration in Virtual Reality,
Vlada Aginsky, Andrew P. Duchon, William H. Warren, & Michael J. Tarr Paper presented at the 7th Annual Workshop on Object Perception and Memory (OPAM), November 1999
Bowman, D., Davis, E., Badre, A., and Hodges, L. Maintaining Spatial Orientation during Travel in an Immersive Virtual Environment.
Also hostage rescue, firefighting

3. Gap Acceptance in the Hank Bicycle Simulator

4. Perceiving Distance in the Real World
How well do people perceive absolute distance from self? (egocentric distance)
Visually guided judgments
Matching depth/frontal intervals
(Gilinsky, 1951, Harway, 1963, Loomis et al., 1992)
People typically underestimate distance
Visually directed action
Walking to target with eyes closed
(Loomis et al., 1992, Philbeck & Loomis, 1997, Rieser et al., 1990)
People quite accurate up to 20 m.
People tend to underestimate beyond 20 m.

5. Perceiving Distance in Virtual Worlds
Distance perception with HMDs
Triangulation (Loomis & Knapp, 2003)
People view a target, turn and walk a short distance, then point back at target.
Pointing errors indicated that people undershot distances.
Blindfolded walking (Whitmer & Sadowski, 1998)
Compared blindfolded walking in a real hallway with blindfolded walking on a treadmill in a virtual hallway.
Mean error similar, but unsigned relative error greater in virtual than real environment.
People made greater errors in both environments when they experienced the virtual environment first.
Distance perception with large screen immersive display systems (LSIDs)?

6. General Methods Real Environment Virtual Environment
Standard university building
Targets were real people
Virtual Environment
Model of real environment
Targets were billboard people

7. Virtual Environment Three 10X8 ft screens Rear projection
Electrohome DLV projectors -1280x1024 pixels/screen
Square (Cave-like) configuration
SGI Onyx with Infinite Reality Graphics

8. Experiment 1 Subjects: 24 undergraduates Procedure Measures
Baseline walking
Timed normal walking to derive estimate of walking speed
Distance estimates
Presented 6 randomly ordered distances (20, 40, 60, 80, 100, and 120 ft) in each environment (order counterbalanced)
Subjects estimated how long it would take to walk to the target by starting and stopping a stopwatch (without looking at the stopwatch)
Measures
Actual time to walk
Calculated expected time to walk each distance from baseline walking speed
Estimated time to walk
Elapsed time on a stop watch

9. Results Two primary questions:
How closely did time-to-walk estimates correspond in real and virtual environments?
How closely did time estimates in the real and virtual environments correspond to actual times?

10. Mean time-to-walk estimates: Real environment first

11. Mean time-to-walk estimates: Virtual environment first

12. Summary of Experiment 1
Time-to-walk estimates were remarkably similar across the real and virtual environments
Estimates were accurate up to ft
Time-to-walk estimates more distorted in both environments when people experienced the virtual environment first

13. Experiment 2: Sighted vs. blindfolded time-to-walk estimates
Rationale
Replicate findings from Experiment 1
Determine whether time-to-walk estimates differ with and without vision
Subjects
16 undergraduates
Procedure
Baseline walking
Sighted judgments same as Experiment 1
Blindfolded judgments
People viewed target for 5 s, put on blindfold, and started stopwatch when they imagined starting to walk
Mention also tested and 12-year-old children. Important to validate bike riding studies. Results similar to adults.

14. Mean sighted time-to-walk estimates

15. Mean blindfolded time-to-walk estimates

16. Summary of Experiment 2
Again, time-to-walk estimates in the real and virtual environment were very similar
Estimates accurate up to about 60 ft
Time-to-walk estimates very similar with and without vision

17. Conclusions Time-to-walk estimates are:
Highly similar in real and virtual environments
Accurate for distances of ft
Underestimated for distances beyond 60 ft

18. Why the Difference?
The Environment
Time-to-walk measure

19. Why the Difference? The Environment Large Screen Immersive Display
Large vertical field of view
+ Wu , Ooi, & He (2004) Show restricted VFOV lead to underestimation of distance
+ Whitmer & Sadowski (1998) suggest reduced VFOV in HMDs degrades cues to distance
- Knapp & Loomis (in press) “Limited FOV of HMD displays is not the cause of distance underestimation in VE”
- Creem-Regehr, Willemsen, Gooch, & Thompson (2003) Show restricted FOV does lead to compression if head motions allowed
Helmet Weight
Willemsen, Colton, Creem-Regehr, & Thompson (2004)
Wu et al. explanation (?)
Whitmer and Sadowski suggest HMDs degrade convergent linear perspective and relative size cues
Creem-Regehr et al also show binocular = monocular

20. Why the Difference? Time-to-walk measure
Differs from triangulation and blindfolded walking in that it involves imagined rather than real movement
New experiment to compare time-to-walk estimates with blindfolded walking
Preliminary results show similar patterns of error
Blindfolded walking ~83% of real
Imagined walking ~73% of real
Significantly different only at 20 ft

21. Acknowledgments NSF Support: INT-9724746, EIA-0130864, and IIS-0002535
Students and staff for helping with this research:
David Schwebel Pete Willemsen
Penney Nichols-Whitehead HongLing Wang
Jennifer Lee Steffan Munteanu
Sarah Rains Joan Severson
Sara Koschmeder Tom Drewes
Ben Fraga Forrest Meggers
Kim Schroeder Paul Debbins
Stephanie Dawes Bohong Zhang
Lloyd Frei Zhi-hong Wang
Keith Miller Xiao-Qian Jiang
Geb Thomas