1. 3/23/2005 © Dr. Zachary Wartell 1 “The Perception of Distance in Simulated Visual Displays: A Comparison of the Effectiveness and Accuracy of Multiple Depth Cues Across Viewing Distances ” R. Troy Surdick, Elizabeth T. Davis, Robert A. King, Larry F. Hodges Presence, Vol 6., No. 5, October 1997, 513-531. Presentation: Revision 1.0

2. 3/23/2005 © Dr. Zachary Wartell 2 Introduction VR, AR, tele-operators: what depth cues are important? once again….

3. 3/23/2005 © Dr. Zachary Wartell 3 Definitions effective depth cue – “requires only small change in depth to produce perceptible change in perceived distance” accurate depth cue – “requires that two equidistant objects are perceived to be at the same distance”

4. 3/23/2005 © Dr. Zachary Wartell 4 Prior Work lot’s of

5. 3/23/2005 © Dr. Zachary Wartell 5 Prior Work (1)

6. 3/23/2005 © Dr. Zachary Wartell 6 Prior Work (2)

7. 3/23/2005 © Dr. Zachary Wartell 7 Prior Work (3)

8. 3/23/2005 © Dr. Zachary Wartell 8 Experiment 1: Variables IV: vary distance 1m or 2m IV: depth cues – {foreshortening,linear perspective, texture gradiant, stereopsis, relative brightness, relative height, relative size, all} DV: ability to perceive and compare relative distances of two sequentially presented stimuli

9. 3/23/2005 © Dr. Zachary Wartell 9 Experiment 1: Hypotheses 1) perspective cues & stereopsis maybe most effective 2) stereopsis, relative brightness and relative size less effective farther away 3) condition with all depth cues should be most effective 4) at 1m, perspective cues, all-cues, and stereopsis should each be more effective than rel. brightness, rel. height, rel. size 5) at 2m perspective cues, all-cues should be better than stereopsis, rel. brightness, rel. height, rel. size 6) at 2m there should be more differences in effectiveness of cues than at 1m, but accuracies should not change

10. 3/23/2005 © Dr. Zachary Wartell 10 Experiment 1: Method 10 subjects 6-7 session/sub., 2 hr/session 12-14 hr/sub. Total sub’s have normal or correct eye sight and able to see RDS

11. 3/23/2005 © Dr. Zachary Wartell 11 Experiment 1: Apparatus used chin-rest parallax adjusted for e.s. 320 x 480 pixel / eye 1m – 6.7  HVA, 10.2  VVA 2m – 3.0  HVA, 4.6  VVA greyscale (8-bit) gamma-adjusted for linear mapping of pixel value to luminance

12. 3/23/2005 © Dr. Zachary Wartell 12 Experiment 1: Stimuli target stimuli –10  below eye level –5 cm squares (2.9  and 1.4  VA @ 1,2m) background – black, linear perps. lines 2 cm apart, foresh. lines at 30 cm intervals

13. 3/23/2005 © Dr. Zachary Wartell 13 Experiment 1: Procedure {1m,2m} X {rel. size, …} (2 x 8) all sub’s test in all conditions measured sub’s IPD dark adapt for 5 minutes sub’s must fuse fusion target (4 dots in square) trial block: 1 cue cond. & 1 distance, randomize order across sub’s, 175-225 trials/block trial: std. at 1m/2m ; comparison at one of 7 or 9 distances –sub: press 0-key for next trial –display: 500 ms present (std. or comp.) 500 ms present RDS 500 ms present (comp. or std.) –Sub: 1-key if first stimulus is closer/2-key if 2 nd is closer –NO FEEDBACK GIVEN!

14. 3/23/2005 © Dr. Zachary Wartell 14 Practice Trials pilot study to determine distance range for each depth-cue/view-distance combination JND – “just noticable difference” choose closest and farthest stimuli such that they’re correctly perceived > 75% of time in practice trial range is adjusted if particular sub. performance varies too much from pilot study results

15. 3/23/2005 © Dr. Zachary Wartell 15 Results JND = (C 0.75 – C 0.25 ) / 2 C 0.75 – distance where comp. is perceived farther than std. in 75% of trials C 0.25 – distance where comp. is perceived closer than std. in 75% of trials absolute effectiveness = JND relative effectivenes = JND / {1m,2m} “Weber Fraction”

16. 3/23/2005 © Dr. Zachary Wartell 16 Results (1) Constant Error: CE = (PSE – POE) PSE – point of subjective equality POE – point of object equality accuracy = CE relative accuracy = CE / {1m, 2m}

17. 3/23/2005 © Dr. Zachary Wartell 17 Result (2): At 1m 2-Way ANOVA on Cue and Distance normality and other statistical assumption violations required alternative to ANOVA tests sign. effects: –depth cue –1m persp. cues better than others

18. 3/23/2005 © Dr. Zachary Wartell 18 Results (3): At 1m rel. brightness less effective than others rel. height and size less effective than foresh., lin. persp., texture, and all-cues

19. 3/23/2005 © Dr. Zachary Wartell 19 Result (2): At 2m sign. effects: –2m persp. cues better than others

20. 3/23/2005 © Dr. Zachary Wartell 20 Results (3): At 2m rel. brightness less effective than others rel. size less effective than foresh., lin. persp., texture,all-cues and rel. height rel. height worse than forsh.,lin. persp., texture, all-cues

21. 3/23/2005 © Dr. Zachary Wartell 21 Results (4): Effectiveness Across Distance main of dist. and interaction of dist. and cue are significant – due to changes in absolute effectiveness of some conditions (not all) pair-wise tests indicate: –rel. brightness, rel. size, rel. height each decreased in abs. effectiveness with dist. –(not true for persp. cues and all-cues) –no change in relative effectiveness for any cue

22. 3/23/2005 © Dr. Zachary Wartell 22 Results (5): Accuracy of Cues no cues differed in accuracy from others at 1m or 2m (H6) no cues differed individual in accuracy as function of dist. only sign. diff 1m,RB, CE is not 0

23. 3/23/2005 © Dr. Zachary Wartell 23 Discussion sub’s consistently perceive stimuli at simulated distances persp. cues with ground intercepts more effective than others at both distance – agrees with prior work and theory abs. effectiveness of RB & RS decrease with dist. – both agree with expectations all-cues not most effective! (but = persp. cues) –ceiling effect –maybe sub’s only attended to one cue

24. 3/23/2005 © Dr. Zachary Wartell 24 Discussion (2) 5 of 10 sub’s didn’t see stereo! separate results: sub’s with stereo seem to do worse! (but not stat. sign.)

25. 3/23/2005 © Dr. Zachary Wartell 25 Discussion (3) RB less effective as predicted at both distances (H4 & H5) perspective cues & all-cues more effective than RH & RS RH better than RS at 2m (unexpected!) –Gibsonian theory: horizon acts as reference point; perhaps

26. 3/23/2005 © Dr. Zachary Wartell 26 Experiment 2: Motivation 5 of 10 sub’s appear to get no stereopsis in display! Why? –? lack of practice – but stereo-anomalous sub’s got extra practice trials (140-270) during stage of determining each sub’s range of comparison stimuli –? short viewing duration – prior work suggests too short viewing doesn’t give brain enough time to process stereopsis, but longer viewing in this exp. would add confound of vergence –? display mis-alignment – but often stereo-anomalous sub’s succeeded stereo-seeing sub’s & display was checked daily –? lack of motivation – but sub’s new they could only move to next set of trials after reaching certain performance criterion on current block –? acc./verg. mismatch – verg. at ∞, acc. at 1m/2m, but all sub’s had same situation and 5 sub’s did see stereo

27. 3/23/2005 © Dr. Zachary Wartell 27 Experiment 2: Idea Prior work indicates sub’s may be trainable on stereo displays using smaller modeled e.s. –Does this work with Wheatstone stereoscope? –Can sub. be trained to see stereo?

28. 3/23/2005 © Dr. Zachary Wartell 28 Exp. 2: Method Subjects: 1 stereo-anomalous sub’s from exp. 1 Apparatus / Stimuli: –like exp. 1 but stereopsis cue only, distance = 1m –modeled. e.s. = {1/4,1/2,3/4} * true e.s. Method: –1 block has 10 trials at 5 comparison distances. –experimenter adjusts m.e.s. and viewing duration

29. 3/23/2005 © Dr. Zachary Wartell 29 Exp. 2: Results

30. 3/23/2005 © Dr. Zachary Wartell 30 Exp. 2: Discussion demonstrates previously stereo-anomalous sub. trained to see stereo ramification: for binocular VR/AR systems certain users need to be taught how to see stereo! future work: –large sub. pool – how many stereo- anomalous sub’s can be so trained? –what is optimum training method –trade-off of view dur. versus fraction of m.e.s. –develop training protocol

31. 3/23/2005 © Dr. Zachary Wartell 31 General Conclusions effectiveness of persp. cues w/ ground intercepts superior to others at all distances effectiveness of rel. bright. vastly interior rel. bright., rel. height, rel. size, decrease effectiveness with distance no depth cues differ in accuracy 5/10 sub’s stereo-anomalous but all other depth cues have no perception problems cost-effectiveness (circa 1997): foreshortening and ground intercepts may give adequate depth perception, but beware of screen clutter & and exact eye-level views! all-cues condition not better than just persp. cues Rel. brightness least effective some sub’s can’t see stereo in Wheatstone viewer, but can be trained

32. 3/23/2005 © Dr. Zachary Wartell 32 Thoughts? Questions? Concerns? Wheatstone stereoscopic –vergence at ∞, accommodation at {1m,2m} for 0 screen. parallax LCD Glasses + CRT –vergence = accommodation at 75cm for 0 screen. Parallax What about Titmus stereo screen and random dot stereograms? Where was vergence in these systems used to test sub’s for stereo vision?