Affect of angle changes on perception of the Zollner Illusion
Sawyer Plume 08saplum@alma.edu Alma College
Introduction
The Zollner Illusion is a simple eye illusion that is caused by several factors. One of these factors are the nine cross sectional lines on the top line of the two line illusion. One study that looked at the change in illusion from changing the degree of these lines comes from Maheux, Townsend, and Gresock(1960). In their study participants were shown cross sectional lines at degrees of 10,15,20,25,30,35,40,45,50,55,60,65,70 and 75. They then averaged the response of their participants and looked at the affect of the changing degrees. The results showed that as the degree of angle increased the the degree of the illusion decreased dramatically. The mean deviation dropped from 13 degrees with an angle of 10 degrees to a one degree illusion at 70 degrees of angle. Thus proving that the degree of the angles of the cross sectional lines have an affect on the perception of the Zollner Illusion.
MethodsHypothesis The hypothesis for this experiment is that as angles increase that is as the angle of the crossing lines become more obtuse the illusion will decrease in power.
Subjects-Test subjects for this experiment will be Alma College students. Nine-teen individuals were used in this experiment. The Zollner illusion is perceived by the majority of the population so a random selection is not needed.
Apparatus and stimuli The apparatus used for this experiment is the Eye Lines software developed by Walter Beagley of Alma College. This software allows us to manipulate the Zollner illusion and then use the manipulated Zollner images in a test. The change was measured is the degree of the Zollner illusion after changing the angles of the cross sectional lines found on the top line of this illusion. These angles were changed from 10 degrees to 110 degrees of angle from the top line of the Zollner. By comparing the averages for all of the images and subjects we were able to see where illusions strength is lowered.
Fig 1 This image shows the different angles of orientation that were presented to the test subjects. Each different degree of angle is represented by its own image. From left to right the angles are 10-degrees, 20,30,40,50,60,70,80,90,100, and 110 degrees from the top line of Zollner. This made eleven images of different angles and one control with no crossing lines.
Procedure-Nine-teen test subjects were placed 24 inches from a computer screen, which was running the Line Illusion program with the altered Zollner and a control with no crossing sectioning lines. There were twelve images that the subjects looked at and adjusted using a computer mouse until they believed the lines are parallel. All nine-teen results were then be averaged together in order to see the affect that was caused by the angle change.
Results- Upon completion of the Zollner line illusion test that was prepared on the Eye Line software of Alma College, all of the results from each of the nineteen individuals were averaged together. Each of the different degrees was represented by one image in the illusion and the adjustment made to make the lines appear parallel were recorded for all individuals for all images. The results show a large decrease in the amount of the illusion after the angles reached 40-degrees. There was a increase in the power of the illusion by .49 degrees dropping its illusion power from 1.03 at 30-degrees to .54 at 40-degrees. We then see a decline in the amount of the illusion at all other angles lower then this until we come in contact with 100-degrees and 110-degrees. At these angles the illusion actually increased in power. The degree of illusion went from .22 at 90-degrees to .46 at 100 and .49 at 110 degrees. These results are still much lower then the perceived illusion at 10, 20, and 30-degrees.
Fig 2- In this graph we see the results of the experiment added together. Notice that after the 30-degree angle the illusion lost its strength by almost half.
Discussion-The results from this experiment confirmed results that were observed by Maheux, Townsend, and Clement(1960). As the angle was made to be less acute the degree of the illusion was decreased. When we look at the data we do see areas of interest to us. For example the increase in the illusion perception from 90-degrees to 100-degrees. Although the perceived illusion was still much lower then the higher degrees of angles that were acute there is still a markable change. These could have been produced by numerous factors. First of which could have been simple human error. A person may have accidently adjusted the line to much or not have looked at the certain image as well as the rest. Another reason for this may be because of the images design. Certain designs may have been harder to decipher because the crossing lines were not placed in the same place on all images. That is in certain images the crossing lines maybe more towards one end of the line then other. It is possible that this may affect the illusion. Another possibility is if the subjects moved around during these images. By moving they would adjust their eye sight and may see the image in a different way then the last this again would through off the results. There are several ways in which this experiment could be improved. For started only a few of the test subjects actually took the test twice. This fact means that the data is only collected after one test. By these individuals not taking the test twice as was asked we are only looking at one test. If more tests were added into the experiment we could have a better idea about the results and see their average on a larger scale. Also the individuals should be placed in an area without distractions. Other subjects were in the room when this test was conducted and their communication with others could distract the subject taking the test from his object. Movement is another key area that should be reduced. A person that is moving their head is changing how they see this illusion and thus how they change the image to make it parallel.
References
"Geometric factors in illusions of direction". Maheux, Townsend, Gresock. American Journal of Psychology (1960)
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