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### Experimental Design

There will be a short number of trials; half will be an ascending type of trial, the other half will be a descending type of trial. Within each set of ascending and descending types of trials, the arrowheads on the comparison line will either be the same as the arrowheads on the standard line or they will be different. For example, if there are a total of 20 trials, 10 will be ascending types of trials (in 5 of the trials, the comparison line will have the same arrowheads as the standard; in the other 5, the arrowheads will be different); the other 10 will be descending types of trials (again, in 5 of the trials, the comparison line will have the same arrowheads as the standard, and in the other 5 trials, the arrowheads will be different). Thus the experiment has 4 conditions: 1) in an ascending type of trial, the comparison line's arrowheads will be the same as the standard's or 2) its arrowheads will be different from the standard; 3) in an descending type of trial, the comparison line's arrowheads will again be the same as the standard's or 4) its arrowheads will be different from the standard's. We are interested in the effect of these 4 different conditions on your perception of relative length. The order of presentation of these trials will be shuffled randomly.

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