Introduction The Color Juxtaposition Simulation
The purpose of this exercise is to allow you to investigate a different illusion, one that familiar to artists but which appears to have received relatively little attention from established researchers in the field of perceptual psychology. Particularly when you assess the variation among individuals you will be in a very real sense conducting original research into how the eye works and how visual pathways in the brain process and integrate information arriving from the retina.
Tips and Hints
1. If moving the sliders (or typing numbers in textfields and clicking the “Go” button) has no effect on the color of the corresponding part of the display, make sure the appropriate “USE SLIDER” radio button is activated. If not, click on it and the sliders/textfields should be activated for your use.
2. As with other simulations in this series of visual illusions, I’d recommend setting the brightness and contrast controls on your monitor to their maximum settings.
3. Remember to give your overworked eyeballs frequent rests! Perhaps take turns with your lab partner(s) in performing each exercise. This would allow some ‘recovery time’ between bouts of viewing.
4. Don’t concern yourself with what you should be seeing when you view the displays produced by this illusion, and don’t worry if you don’t see the same thing as your lab partners. There’s a surprisingly large amount of interindividual variation with respect to the appearance of the illusory colors at the interface, even with respect to whether the illusion is seen at all. If you can’t see a particular illusion (or a particular feature of the illusion), or if it appears different to you than what everybody else is reporting seeing, it doesn’t mean you or your visual system are weird or inferior, just different.
5. This illusion ‘works’ best when viewed from a slightly greater distance than suggested for other illusions in this series, say 50 – 80 cm. (20 – 30 in.), but you might consider seeing if viewing distance affects your perception of it, and choose the viewing distance that works best for you.
6. Remember, you're working with light emitted by your monitor, not with light reflected from a colored surface. Thus, the primary colors are different (red, green, and blue for light as opposed to red, yellow, and blue for paint),as are the complimentary colors (yellow, cyan, and magenta, for light, as opposed to green, purple, and orange for paints).
Exercises and Thought Questions
Horizontal Interface
Do the following three exercises with the default color settings and the “Horizontal” Orientation option selected.
1. Start the simulation and gaze at the interface between the blue and brown rectangles. Do you see anything unusual at the interface? If not, tilt your head very slightly forward (drop your chin just a little) so you’re looking slightly upwards towards the screen (this produces the illusion for virtually everybody). Note the appearance of the blue and orange rectangles in the zone along the interface.
2. After gazing at the interface for 15 – 20 s, rapidly shift your eyes to a focus point about 1 – 2 cm. below the interface. Do you notice any change in the orange rectangle between your focus point and the interface? Quickly drop your focus point 1 – 2 cm at a time, several times in succession, each time noting the effect on the orange square between your focus point and the interface.
3. Repeat #2 , this time moving your focus point upward and noting any effect on the blue rectangle.
Vertical Interface
Do the following three exercises with the default color settings and the "Vertical" Orientation option selected. You may need to click the |Reset| button to revert the display to the default colors or click the |Go| button to convert the display to the vertical mode.
1. With the colors set to their default values (click the “Go” button if necessary to achieve this), click on the “Vertical” Orientation radio button, then on the “Go” button. This should produce a display with a blue rectangle on the left and an orange rectangle on the right (click the Reset button if necessary to restore the default colors). The (now vertical) interface should have an appearance similar to that you observed with the horizontal orientation (you may have to turn your head slightly to the right or left to elicit the illusory pink band).
2. Turn your head all the way to the right while keeping your vision focused on the interface. Now, slowly turn your head all the way to the left extreme while keeping your vision focused on the interface. Carefully note any changes in the appearance of the display, particularly in the regions immediately adjacent to the interface between the two differently-colored rectangles.
3. Click on the “Blue” radio button for the right panel and set the sliders for the left panel to RED = 255, GREEN = 123, and BLUE = 0 (remember to click the “USE SLIDERS?” radio button). If necessary, click the “Go” button to switch the position of the colors (make the left rectangle orange and the right rectangle blue). Now, repeat #5 and note the appearance of the illusion as you swing your head from the turned-full-right to the full left position.
Diagonal Interface
Do the following three exercises with the default color settings and the "Diagonal" Orientation option selected. You may need to click the |Reset| button to revert the display to the default colors or click the |Go| button to convert the display to the vertical mode.
1. Click on the “Diagonal” Orientation radio button, then on the “Go” button. This should produce a display with a blue triangle on the left and an orange triangle on the right (click the Reset if necessary to restore the default colors).
Effect of Different Colors
1. Repeat experiments 2 & 3 as described under the “Vertical Orientation” heading above, using different combinations of colors.
Questions
1. Compare your results with those you obtained from the Negative Afterimages simulation. Do the results make sense in that context? That is, how do the illusory colors you observed during the present exercises compare with those that characterized the negative afterimages you generated by staring at images with the same color(s)?
2. Keeping how images project on the retina and the path taken by the neurons from the retina to the brain (Fig. 11-32, p. 438 in your text), can you suggest an explanation for the effect(s) you observed as you turned your head from side to side?
3. Can you envision how the illusions engendered by this simulation could impact art, architecture, interior decorating, and the like? For example, can you suggest how an artist might take advantage of this illusion? Alternatively, can you suggest how this illusion might force compromises to avoid inadvertently evoking it in observers of a painting or occupants of a room or building?
4. With the “Vertical” option selected, repeat some of the experiments with one eye covered. Does this affect the illusion’s intensity or appearance? Repeat with the other eye covered (no, that doesn’t mean cover both eyes!).
5. Compare the results of other individuals in your lab. Is there any correlation with the perception of this illusion with the perception of other color-based illusions in this series? With the gender or handedness of the observer? If any of the observers are color-deficient, how do their perceptions of the illusion differ?
6. If you are myopic (nearsighted) and wear glasses (or contacts and are willing to remove them), try viewing the illusion without them. Note any changes, (besides the obvious blurring of the display). Would you have predicted those changes?
7. As stated earlier, there’s a surprising amount of variation among persons with respect to what they see when viewing the displays that they can produce using this simulation, ranging from different intensities of colored bands, through seeing different colors of bands along the interface, to not seeing any illusory colors at all! The following are some examples of the variation observed when individuals turned their head from side-to-side with vertical orientation of the interface during development of this simulation:
Blue left, Orange right: Most individuals see a pink band along the interface (in the orange rectangle); for most individuals, this band is most intense when viewed with the head turned to the extreme right. As the head is turned toward the left extreme, some individuals see the pink band replaced by green band in the orange rectangle, black band in the blue rectangle, but for many, the pink band simply disappears.
Red left, Green right: When viewed with the head turned to the right extreme, most observers see a narrow, intensely black band in the red rectangle and a bright green band in the green rectangle. As the head is turned to the left extreme, the black band disappears, and a narrow pale to bright yellow band develops along the interface, in the green rectangle. However, many observers see just the pale (rather than yellow) band, and a significant proportion sees no illusory colors at all!
8. The following links may prove useful to you:
a. http://eies.njit.edu/~walsh/rgb.html -- provides the RGB (and hexidecimal values, if you’re into that sort of thing……) for more than 200 colors. You can use this site to help you set the colors of the panels to values you wish to study.
b. http://webvision.med.utah.edu/Color.html -- an outrageously thorough discussion of color vision. Very informative, but a large file, so you’ll need to be patient when opening it. Very worth the time!
c. http://www.photo.net/photo/edscott/vis00010.htm -- an alternative to the previous site, this site also contains a very useful discussion of “color space”.
9. If you wish to learn more about color and how we perceive it, search the Web using the keywords “Color vision” or “Newton’s Color Wheel”.