Horizontal/Vertical Illusion Experiment

This experiment will use the method of adaptation. You will be asked to match the overall length of the horizontal line [the standard stimulus] by adjusting the length of the vertical line [the comparison stimulus]. The adjustments will be fairly large at first, but will become progressively finer.

You will be presented with four series of trials. The vertical line will begin either larger or smaller than the comparison vertical. If larger, click the button "too large" until the vertical seems smaller than the horizontal, then click "too small". The adjustment size for each click will now be reduced, so continue clicking "too small" until the vertical is once more longer than the horizontal. Clicking "too large" will then reduce the adjustment size for the next set of adjustments. Each change in direction records the current height for display in the results; each series of trials will collect four reversal values, then reset the stimuli for the next series.

Heights (percent of standard width) at limits of equality

Values at turn points Means
Trial Type series number first second third fourth series trial type overall
Ascending trials 2 82 78 79 78 79 78 80
4 76 74 78 76 76
Descending trials 1 86 88 83 84 85 82
3 74 80 79 80 78

The data is presented as a graph showing the length of the vertical as a percentage of the length of the horizontal for each step of the adjustment [the heavy lines], the four values at direction changes [the lighter lines], and the mean of these four values for each of the adjustment series [dotted lines]. All the data for a series is shown in the same color.