Eye Tracking With Stereoscopic Images

1. Eye Tracking With Stereoscopic Images Eamon Moore, Punit Seth, Dhaval Shah Clemson University

2. Introduction • Stereoscopic image – optical illusion of depth seen by focusing ones eyes in front of or behind an image [7] • Each eye views an image differently which gives the perception of depth.

3. Eye Tracking • Eye Trackers – Can be used to track eye movements and gaze coordinates • Gaze coordinates – Helps in understanding why some people see stereo images and some do not

4. Divergence and Convergence • Divergence and Convergence – the methods that people use to view stereograms • Divergence – Moving your eyes outward in the opposite direction • Convergence – Moving your eyes inward

5. Why Use Stereograms? • Marketers and researchers – Attempts are being made to utilize ones ability to see three-dimensional images and use them in advertising. • Stereograms can enhance vividness, clarity, realism, and depth.

6. The Experiment • Analyzing the behavior of the eyes to view stereograms [dependant variable] • Convergence • Divergence • Looking for significant differences in Placebo and Experimental group [independent variable]

7. Hypothesis • Null Hypothesis – There will be no significant change in the distance of the eyes when viewing stereograms, regardless of experimental condition. • Alternate Hypothesis – There will be significant results that indicate divergence of the eyes in both conditions.

8. Background • Brain processing – The brain accepts two images that are seen by each eye and creates a completely different three-dimensional picture called stereo [6]. Figure 1: Image processing • Stereo allows you to see objects as solids in dimension of width, height, and depth.

9. When Stereoscopy Started • Idea of stereoscopy preceded photography • Paintings were made by Giovanni Porta in the late 1500s by placing images side by side. This showed his understanding of binocular vision.

10. Three-Dimensional Glasses • Three-Dimensional Glasses – red filter for left eye, blue filter for right eye [11] • When looked at images that have depth, a three-dimensional image could be seen. Figure 2: Red-blue Stereo Image

11. Modern Stereogram • First modern stereogram created in 1959 by Julesz [11] • Original image viewed by left eye • Modified version of original image viewed by right eye • Brain fuses both images creating the final image Figure 3: Modern Stereogram

12. Single Image Stereogram • Created in 1979 by a student of Julesz, Tyler • Found that the offset idea could be applied to a single image to create a black and white random dot stereogram Figure 4: Single Image stereogram

13. Colored Stereogram Program • In 1991 Smith improved on the research of Julesz by creating stereogram modeling software. • Eliminated the need for dots and provided color

14. Tracking of Eye Movements and Visual Attention • Study conducted by Neuroinformatics Group, Bielefield University [8] • Concentrated on vergence eye movements using stereograms similar to the ones used in this experiment Figure 5: Coarse Granularity Image (left) ; Stereogram (right)

15. Neuroscience Institute • Gave insight about vergence eye movements • Discussed dynamics of horizontal and vertical vergence • Study indicated that horizontal eye movements were of more importance.

16. Program to Create Stereograms • School of Electrical and Electronic Engineering at the University of Nottingham [3] • Created program that produces stereograms • Examined how stereograms were viewed

17. Experimental Design

18. Apparatus Tobii Eye Tracker [16] – Video-based combined pupil and corneal reflection eye tracker 2.4 GHz 256 MB RAM Windows XP Red Hat Linux Release 9, Version 2.4.20 Sampling Rate = 50 Hz Accuracy = 1º visual angle Figure 6: Tobii System

19. Experimental Design • Between subjects • Two conditions : • Experimental group – Stereogram • Placebo group – Nonstereo Image • 10 Participants

20. Stimulus - Control Image

21. Stimulus - Stereogram

22. The Hidden Image

23. Stimulus – Nonstereo Image

24. Salient Features • Reduced calibration points • An organized file structure • Validity = 0 • Timer • Shortcut keys • Analysis option

25. Algorithm • Record XL, XR, YL, YR. • Distance = • Control distance • Experimental distance

26. Algorithm If (Experimental distance < Control distance) If (XL < XR) Convergence Else Convergence with crossover. else If (Experimental distance > Control distance) Divergence else No difference.

27. Data Analysis

28. Data Analysis – Experimental Group (Individual)

29. Data Analysis – Placebo Group (Individual)

30. Data Analysis – Experimental Group (Aggregate)

31. Data Analysis – Placebo Group (Aggregate)

32. One Way Analysis of Variance (ANOVA) • Assumptions of an ANOVA • Independence • Homogeneity of Variance • Normality

33. Descriptive Statistics • Randomly Assigned Groups • Placebo • - Five Men • Experimental • - Three Men, Two Women

34. ANOVA • Not a significant difference between the Placebo (M = -36.048, • S = 86.891) and Experimental Group (M = -230.949,S = 225.562)

35. ANOVA and Power Analysis • Post Hoc G-Power Analysis • power of .1077 indicates approximately 11 percent chance • that the null hypothesis could have been rejected.

36. Discussion

37. Discussion • Stereograms are viewed by using • convergence regardless of stimuli. • No significant results • Experimental group shows trend towards • divergence near the end. • Placebo group shows a lesser trend • towards convergence

38. Experimental Group (Aggregate)

39. Placebo Group (Aggregate)

40. Limitations • Low Power • - Priori Power Analysis • Tobii Eye Tracker • Stereograms are harder to view on a • computer screen.

41. Future Work • Larger sample size • Introduce Z coordinate for the distance from the screen • Measure characteristics such as the diameter of the pupil while studying its behavior.

42. Conclusion • Our hypothesis was incorrect; however, we were correct in believing both groups would behave similarly. • Stereograms are viewed by converging ones eyes; however, a higher power study may prove otherwise. • More research can now be conducted to understand how stereograms can be used for advertising, marketing, and other practical applications.

43. Acknowledgements • Dr. Andrew Duchowski, PhD., Associate Professor, Clemson University. • Ms. Puja Seth, M.A. Doctoral Student, University of Georgia • Mr. Jacob Hicks Undergraduate Student, Clemson University.

44. References [1] Academy of Marketing Science Review. Three-Dimensional Stereographic Visual displays in Marketing and Consumer Research. Available at: http://www.vancouver.wsu.edu/amsrev/theory/holbrook11- 97t.htm. Last Accessed: 10 October, 2004. [2] Annals of the New York Academy of Sciences 2002. Binocular Eye Movement Responses to Dichoptically Presented Horizontal and/or Vertical Stimulus Steps. Available at: http://www.annalsnyas.org/cgi/content/full/956/1/487. Last Accessed: December 2, 2004. [3] BBC, Nottingham. SIRDS: An optical illusion. Available at: http://www.bbc.co.uk/nottingham/features/2003/08/sirds.shtml#what Last Accessed: December 2, 2004. [4] CIT,Cornell University. How To See A Magic Eye Poster. Available At: http://instruct1.cit.cornell.edu/courses/psych470/To_Be_Edited/How%20To%20See%20A%20Magic%20Eye%20Poster%20(MVW).doc. Last Accessed: December 2, 2004. [5] C. Rashbass & G. Westheimer J. Physiol. Disjunctive Eye Movements. 159, 339-360, 1961 [6] Cooper, Rachel. What is Stereo Vision?. 2004. Available At: http://www.vision3d.com/stereo.html. Last Accessed:16 September 2004. [7] Dictionary.com. Available at: http://dictionary.reference.com/search?q=stereogram Last Accessed: December 2, 2004. [8] Essig, Kai and Ritter, Helg. Tracking of Eye Movements and Visual Attention. Available at: http://www.techfak.uni-bielefeld.de/ags/ni/projects/eyetrack/eye_autostereo.html. The Neuroinformatics Group. Bielefeld University. Last Accessed: 10 October, 2004.

45. References [9] Faul, F., & Erdfelder, E. (1992). G-Power: A priori, post- hoc, and compromise power analyses for MS-DOS (computer program). Bonn, FRG:Bonn University, Department of Psychology. [10] History of Photography and the Camera. Available At: http://inventors.about.com/library/inventors/blphotography.htm Last Accessed: December 2, 2004. [11] Magic Eye Inc®. Frequently Asked Questions. 2004. Available at: http://magiceye.com/faq.htm. Last Accessed: 16 September 2004. [12] Mowforth, P. et al. Vergence Eye Movements Made in Response to Spatial-Frequency-Filtered Random-Dot- Stereograms. Perception, 10, 299-304, 1981 [13] Patrick Hahn. The History of Stereograms 1996. Available At:http://www2.vo.lu/homepages/phahn/rds/history.htm. Last Accessed: December 2, 2004. [14] Robert Leggat. Stereoscopic photography 2003. Available At: http://www.rleggat.com/photohistory/history/stereosc.htm. Last Accessed: December 2, 2004. [15] Sandin, Daniel et al. The VarrierTM Auto-Stereographic Display. Available at http://www.evl.uic.edu/todd/varrier/VarrierSPIE.html. Electronic Visualization Laboratory. University of Illinois at Chicago. Last Accessed: 10 October, 2004. [16] Tobii Technology. User Manual. Available at : http://andrewd.ces.clemson.edu/courses/cpsc412/docs/UsersManual_TobiiClearView_2_1_0.pdf Last Accessed: December 2, 2004.

46. Questions