Visual Illusions and YOU!

Robert T. Arrigo: Programming
Gordon Redding: Author
Additional Credits:
This module was supported by National Science Foundation Grants #9981217 and #0127561.

One of the best ways to learn about experiments is to be in one. That is what you are going to do right now. We can't tell you any details of the experiment because that could influence your responses and thus invalidate the results. But it might be a better learning experience if you have thought briefly about the experimental method and are aware of a few general considerations that go into the design of scientific experiments.

Our objective, in the present case, is to learn about the nature of human vision. How does it work? How does our visual system take the light reflected on the retina of our eyes and derive from it the rich perception of the world that we enjoy? It is a vastly complex system with many elements and dimensions. They cannot all be studied at the same time. The purpose of experiments is to isolate certain aspects of visual perception so that they can be carefully and rigorously examined. An experiment is a way of posing a very specific question to nature and forcing nature into giving an answer to that question.

The experiment you will participate in uses human beings as subjects. The reason is obvious. The part of nature we want to learn about is the human visual system. Human beings are the only things in the universe that have "human visual systems" so human beings are an obvious place to explore. (You might think it is the only place to explore, but you will discover that there are actually other alternatives -- doing experiments with other animals and even with machines sometimes have advantages over dealing directly with humans.)

This online experiment is going to measure how you respond when you see certain images. No one else can know what your experiences are like from the inside, but we can observe your behavior when you respond to visual images in various ways. The images you will see have been picked very carefully, controlling for a number of distinct properties. If the properties have been picked correctly and all other aspects of the experiment has been designed properly, then the data that is gathered from the experiment (i.e., the total responses of all of the participants) will give us information (hopefully valuable information) about some aspect of human vision.

Now it is time for you to become the subject of a vision experiment. The experiment itself will take less than 5 minutes (although there are a few pages you need to read first that could take another 5 minutes). So when you're ready, click below, and do everything that you are asked to do.

  1. After you've read all of these directions, click on the link "Do the Experiment Now!" below.
  2. A new page will open open up. In that page, scroll down to the bottom and fill in the 4 blanks (first name, middle initial, last name, date). Click "Start Experiment."
  3. The login page will pop open. If your instructor gave you a "key" (i.e., a special name, number or code) then enter that. If you were not given a key, then enter your name. Enter either your "key" or your "name" but not both. Then hit "Login".
  4. Read the instructions that come up and click on "Start Experiment"
  5. After the applet loads, go through each of the trials.
  6. When the applet instructs, click on the "I'm done" button
  7. The applet window will close, and a debriefing page will load automatically.
  8. When you've read the debriefing page, come back to this page (it will still be here) and click on "Continue the lesson" in the lower right hand corner.
Do the Experiment Now! (This is a Java Applet. If your browser doesn't support applets, try another browser or another computer.)

Before moving on to the next section, it is important that you click on "Do the Experiment Now" and complete the experiment, if at all possible. Then contine to the next page.

[NOTE TO INSTRUCTORS: Currently, this "experiment" functions only as a demonstration. We have recently moved the experiment to a new server and, in the short run, we do not have the ability to record data. However, the system is designed not only to gather annoymous data, but also to isolate only that data submitted by your students -- ultimately producing a graph that will show the extent to which your students were susceptible to the illusions. If you are interested in taking advantage of this feature, please email us and we will let you know when it is available. (David Anderson, dlanders@ilstu.edu)]

Copyright: 2000