Random Dot Stereograms
USD Internet Psychology Laboratory
The Random Dot Stereogram experiment requires the use of special eye-glasses that have a RED LENS covering your left eye and a BLUE LENS covering your right eye. These special eye-glasses were designed to enable you to view special stereoscopic images known as ANAGLYPHS.
The anaglyphs used in the USD Internet Sensation & Perception Laboratory are constructed using overlapping red and blue images. When you view one of these anaglyphs while wearing the special anaglyph eye-glasses the red part of the image goes only to your left eye while the blue part of the image goes only to your right eye. Hence, anaglyphs can be used to generate "retinal disparity" -- that is, a slight difference in the retinal images in our left versus right eyes. Retinal disparity is an important cue used by the binocular visual system in its attempt to reconstruct a 3D representation of the world using the 2D images presented upon the retina.
Inspect the image below (Figure 1) while wearing your anaglyph glasses. Alternately, open and close your left and right eyes and note what happens to your ability to read each line in Figure 1. Can you explain your observations?
The object of this experiment is to examine your ability to accurately judge depth using a stimulus called a random dot stereogram (or RDS). The experiment requires the use of a special pair of red-blue anaglyph glasses (described above) when viewing the RDS stimulus. The combination of the anaglyph glasses and the RDS stimulus will introduce a "mismatch" in the alignment of the images that appear across your two retinas. This mismatch, or retinal disparity, is a powerful visual cue for perceiving depth.
Demo Screen Instructions. In order to familiarize you with the nature of random dot stereograms, we have supplied a demo screen where you can sample and manipulate the amount of retinal disparity introduced by the RDS stimulus. The demo screen will display a large fusia colored square. If your anaglyph glasses are in place, you should be able to see a central subset of dots that appear to be "popping out" toward you from the background (Note: Stereoblind individuals will not be able to perceive this effect!). The two buttons toward the bottom of the screen allow you to manipulate the amount of retinal disparity. Try increasing and decreasing the amount of disparity by clicking the appropriate buttons and note the effect of the changes upon you perception of depth. Try closing one of your eyes and noting what happens to your perception of depth. Can you explain why your perception of depth changes under monocular viewing conditions? Click the button below and explore the demo before continuing to the next section.
Depth Estimation Experiment Instructions. Once you begin the experiment, you will be presented with a large rectangular box that contains two smaller random dot stereogram stimuli. The stimulus on the left is called the STANDARD STIMULUS, and always has its retinal disparity set to a value of 10. The stimulus on the right is called the COMPARISON STIMULUS. The amount of retinal disparity exhibited by the COMPARISON STIMULUS will vary from trial to trial. Your job will be to rate the magnitude and direction of the perceived depth of the COMPARISON STIMULUS relative to that of the STANDARD STIMULUS. For example: If the COMPARISON STIMULUS appeared to be popping out exactly the same distance as the STANDARD STIMULUS, then you should assign it a depth estimate of 10. Similarly, if the COMPARISON STIMULUS appears flush with the background, it should be assigned a depth rating of 0. A negative disparity value is just as likely as a positive, and should be made when a COMPARISON STIMULUS appears to be recessed behind the background. Remember that you are judging the perceived depth of the COMPARISON STIMULUS -- not the difference between the comparison and standard stimuli.
1. What is the independent variable?
2. What is the dependent variable?
3. What psychophysical method was used to collect the data?
4. Plot the psychophysical function.
5. Describe the relationship between your perception of depth and the actual physical stimulus.
Where to buy Anaglyph Glasses
Sample 3D-Anaglyph
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