The Main Results Are Calculated

(You may want to print this page in order to refer to it after you are finished with the experiment. )  At the end of the experiment, the applet will measure the effect of the illusion in each of the four experimental conditions. There are many ways such an effect can be measured. One way is the following:

• First, calculate the absolute difference between the length of the standard and comparison line (i.e., | Standard - Comparison | ).
• Second, divide this difference by the length of the standard line (i.e., | Standard - Comparison | / Standard).
• Third, multiply the result by 100 to convert from proportion to percent.

This gives a measure of the effect of the illusion under a certain set of conditions. For example, let’s say the standard line was 200 units throughout the experiment. At the end of an “ascending, different arrowhead” type of trial, you set the comparison line to be 190 units. Although the comparison and standard lines appeared to be the same length, in reality, the comparison line was 10 units shorter than the standard. We calculate the effect by:

• First, take the absolute value of the difference (i.e., | 200 - 190 | = 10).
• Second, divide this difference by the length of the standard (i.e., 10 / 200 = 0.05).
• Third, multiply this proportion by 100 to get 5%.

In other words, the effect of this type of trial on your perception of relative length was that you overestimated how long the comparison line was relative to the standard by 5% of the length of the standard.

After you are finished, the first results window (see an example) will appear.