Introduction
Although the illusion induced by this simulation can be rather complex (as you'll soon learn!), surprisingly little research has been conducted employing this illusion. Thus, when you perform the experiments suggested below, you'll be conducting original research and obtaining results that have never been published!
Tips and Hints
1. As with many other visual illusions, the images displayed by this simulation can become unpleasant, even causing visual disturbances, headaches, or nausea. Therefore, avoid staring at the image for too long an interval. Take a break every once in a while!
2. An eye-to-screen viewing distance of 30 – 50 cm is about right for most viewers, but you may adjust that to your personal tastes.
Exercises & Thought Questions:
1. Set the Offset slider to a value of 20 (you can use the slider itself or type in the value of 20 into the textfield) and click the "Go" button. Notice anything? Carefully observe the illusion and determine whether it's the same to the left or right of the point on which your vision is focused. How about above and below? Does each pair of lines behave the same -- i.e., do all pairs of lines converge or diverge, no matter where they are relative to your focus point ( = the spot you're looking at in the display)?
2. Determine whether the illusion changes depending on whether your focus point is stationary or moving (remember the Hermann Grid or Scintillating Grid illusions?)?
3. Does the illusion differ when the lines are vertical and the squares are offset vertically?
4. Do the colors of the squares affect the illusion (hint: try ? If so, can you detect any pattern in what combination(s) of colors produce the strongest illusion? The weakest? Do the colors of the squares affect the illusion when the "Vertical Lines?" option is selected (hint: try Blue and Red squares with the Offset set to 0)?
5. Does the size of the squares affect the illusion?
6. Does the degree of offset (relative to the size of the grid squares) affect the illusion?
7. Try to determine if there’s a combination of grid square size and offset that maximizes the intensity of the illusion. Does this value differ with the vertical-line version of the illusion?
8. Vary the size of the grid squares while keeping the offset at a constant percentage of the grid square size. For example, suppose you choose your offset percentage to be 20% of grid square size. You could start with a grid square size of 80 and an offset of 16 ( = 20% of 80). Then, reduce the grid square size to 70 with an offset of 14 ( = 20% of 70), and so on. Note the appearance of the illusion after each change. Does the perceived intensity of the illusion change with grid square size? Does the illusion change qualitatively (i.e., do new ‘features’ appear as you change the grid square size, or does the illusion look pretty much the same at all grid square size settings? Do existing features disappear?).
9. Do the squares appear distorted in the illusion? Or, is it only the lines?
10. Do you think having a pattern like this would have advantages for organisms trying to 'fool' a predator or, perhaps, a prey? Can you think of any animals that have a pattern that is similar to any of those you're produced during these exercises?
11. Compare your results and perceptions with those of other students. There are often noticeable and, to me, surprising differences in the way people perceive the same illusion.
12. Print out the Hering illusion figures and determine if the Hering illusion depends on whether you orient the heavy parallel lines horizontally or vertically in your visual field. What if you tip the page away from you so that the image is foreshortened?
13. Do any of the settings for square size and/or color produce visual illusions such as those produced by the Hermann Grid or Scintillating Grid illusions?
14. Go to the library or search the Web and see what you can find in the way of research articles dealing with the use of grids to investigate the function of the visual system.