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Throughout the experiment, your task will be to adjust the length of the comparison line (i.e., the lower stimulus line) so that its main line segment (i.e., the straight line segment without the arrowheads) matches the length of the standard line's main line segment (see figure 1 below). You will be presented with three buttons, "increase," "decrease," and "next trial." During the trial, you will be able to either lengthen or shorten the comparison line: clicking a mouse button will change the length of the comparison line by one unit; holding the button down will change its length continuously. When you think the comparison main line segment matches the standard main line segment, press the "next trial" button to end the current trial and begin a new one. 

figure 1

Below are two links. Do the "practice experiment" first. This has about 8 trials and will familiarize you with the procedure. Then choose one of the experiment links, either the experiment with 24 trials or the experiment with 32.

Do this first: practice the experiment

Do one of these next:

24 Trial Experiment

32 Trial Experiment

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(Last update: February 2, 1998).