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After you are finished, a results window will appear:

The dependent measures are formatted in the above window as follows (you may want to print this page in order to refer to it after you are finished with the experiment):

<Lower threshold, Upper threshold>, Point of Subjective Equality

The top portion of the window contains a list of results from ascending trials on the left and descending trials on the right. For each trial, a lower and upper threshold is shown along with a calculated point of subjective equality (e.g., "Trial 1. <104%, 112%>, 108%). Below this are the average trial type results for the ascending trials (on the left) (i.e., <105%, 117%>, 111%) and the descending trials (on the right) (i.e., <104%, 120%>, 112%). Below this are the results averaged over all the trials in the experiment (i.e., <105%, 119%>, 112%).

As you can see, the illusion has an effect in both types of trials, but there seems to be little difference between type of trial (i.e., 111% verses 112%). Overall the point of subjective equality is 112%. In others words, for this particular subject, when the comparison line length was 112% of the standard line length, the two lines were maximally indistinguishable in terms of their respective lengths.

So what is your point of subjective equality? Try the experiment and see!

These pages and applets were created by Christopher Currie.
Send questions concerning this unit or applets to The IPL Development team or to
(Last update: February 2, 1998).