Horizontal/Vertical Illusion Experiment – Method and Results

We’ll use the method of adaptation to really drive this point home in an experiment. As the subject, your job is to match the overall length of the horizontal line by adjusting the length of the vertical line. The adjustments might seem large at first but will become progressively finer.

Procedure: You, the subject, will be presented with four trial series. Begin each trial by pressing the “start trial” button. At first, the vertical line will be either larger or smaller than the horizontal line. It’s your job to make adjustments to the vertical line so that the lines are similar in length. For example, if the vertical line is longer than the horizontal, press the “too tall” button until the vertical line just seems smaller than the horizontal. Then press the “too small” button until the vertical line is once more the longer of the two lines. You’ll change directions like that four times. Each change in direction records the current height for display in the results.

Results: Look at the chart to interpret your results. The numbers that you see represent the heights of the vertical lines, as a percentage of the horizontal line. In other words, if you see the number 78, it means that your vertical line was only 78% of the horizontal line, when you thought they were equal. This is the nature of the illusion.