### Instructions for Ratios of Differences in Darkness

In this experiment you are asked to consider the difference in darkness
between two dot patterns and compare that with the difference in darkness between
two other dot patterns. Your task is to estimate the ratio of the first difference
(on the left) to the second difference (on the right).
You will make your judgments using the following scale for judging ratios of
differences:

12.5=the difference on the left is 1/8 as large as the difference on the right

25=the difference on the left is 1/4 as large as the difference on the right

50=the difference on the left is 1/2 as large as the difference on the right

100=the difference on the left is equal to the difference on the right

200=the difference on the left is twice the difference on the right

400=the difference on the left is four times the difference on the right

800=the difference on the left is eight times the difference on the right

Feel free to use numbers in between or more extreme to reflect your judgment of the
ratio of the darkness difference between the two patterns on the left as a ratio of the
darkness difference between the two patterns on the right.

Look at the first warmup, W1
below. Notice that the two differences are the same. In that case, the ratio of the
two differences would be 1, so you should type the number 100 in the space provided
next to that trial. Look at trial W2. This represents a large difference on the left,
divided by a small difference on the right. You should respond with a number greater than
100. But how large does the ratio of the two differences in subjective
darkness seem to you? Is the first difference twice as great, three times as great,
four times as great, six times as great, eight times as great, or what? You would
enter a number that is 100 times the ratio. Now look at warmup W3. Here the
difference on the left is less than that on the right, so the ratio is less than
1, so you will use a number less than 100 here. If you thought the difference
between the two patterns on the left is 1/2 as great as the difference on the right,
you would type 50; if the difference on the left seems 1/4 the difference on the right,
type 25, and so on.

#### Warmup Trials Ratios of Differences in Darkness