Analysis of Table Illusion: Importance of Legs and Frame
Kaitlin McDaniel, Ashleigh Ocenasek, Margaret Ryder, 10akocen@alma.edu, Alma College
In the following experiment we tested Roger N. Shepard's table illusion, as seen in figure 1, to analyze strengthening factors. The two tables are the exact same size; yet, multiple variables are affecting the image and creating the illusion of different sizes. Because the tables are positioned vertically and horizontally to each other, it creates the illusion that the table on the left is longer and narrower while the table on the right looks wider. This is due to the fact that the vertical line appears to be bisecting the horizontal line creating the vertical horizontal illusion (Wolfe et. al 2004). However, the fact that the tables have legs gives them depth and also strengthens the illusion. Therefore, we will strip the legs and other 3D effects to determine if the illusion is weakened. When the illusion is seen as just two parallelograms the depth should disappear and the images will reveal more true sizes (Mitchell et. al 2005). The final factor we are testing is framing. It appears as if the illusion is also being strengthened by the surrounding frame. There are different distances between each table and the surrounding frame so it may be contributing to the illusion of different table sizes. The horizontal plane of the image is enlarged because there is more space in between the image and the frame compared to the vertical image (NSF 1996). Framing also creates an illusion because as the vertical table fills more of the frame, it appears longer (Houck 1972). Therefore, we tested participants to determine whether or not the 3D effects and the frame affect the illusion. Obviously, the arrangement of the tables is producing the illusion, but the fact that the human eye is interpreting a two dimensional image as three dimensional giving it depth may also strengthen the illusion. Yet, the frame that surrounds the image may also be strengthening the illusion based on the framing effect referred to above (NSF 1996). Within this experiment, the 3D effects and the frame are being tested to measure there strength on the illusion.
Methods
Participants
Sixteen Alma college students ranging in age from eighteen to twenty two, volunteered to participate in our study. We explained the process of the experiment to them but not the purpose of the experiment. In order to receive accurate data, participants were not told that the tables were the same size nor were they told that we were testing the factors that create the illusion of different sizes. These students were not rewarded in any way, and they completed the study at their own pace.
Materials
Four different versions of the table illusion were presented to the participants on a twenty inch computer screen on a Macintosh computer. The first table had legs and a frame; the second table had legs and no frame; the third table had no legs and no frame; the fourth table had a frame and no legs. In each image, the bottom line on the right table was adjustable. When the participant held the mouse down and moved it up, the line would move up making the table width narrower. When the mouse was moved down, the line would move and expand the width of the table. The four different images were show to each participant twice in random sequence during three different cycles.
Procedures
The participants sat at the computer at a comfortable distance and were shown the different images in the three cycles. During each image, they were told to adjust the width of the right table until it appeared to be the same width as the table on the left. The participants were shown the four different images in order to test whether or not the 3D effects or framing would make them err in their adjustments. If the 3D effects and the frame strengthened the illusion, then the participants would adjust the right table to make it narrower. In reality, no adjusting is ever needed because the tables are the same size
Figure 1. Legs and Frame
This was the original Illusion shown to the participants.
Figure 2. Legs and No Frame
This was another stimulus shown to the participants. It is the original illusion without the frame
Figure 3. No Legs and No Frame
This was the third illusion presented to the participants.
Figure 4. Frame and No Legs
This was the fourth illusion shown to participants.
Results
The results from the experiment indicated that the original illusion, that contained 3D legs and the frame created the most illusion. Then, the second table with legs and no frame was weakened. However,tables with no legs were the weakest of the illusions and the frame did not seem to make any difference between the two.
Figure 5. Graph.
The graph shows that image Legs and Frame shows the most illusion. Image Legs and No Frame shows some illusion but less than Legs and Frame. Image No Legs and No Frame had the least illusion.
Discussion
Based on the results, the three dimensional characteristics of tables 1 and 2 gave the table its depth and strengthened the illusion. The legs of these tables made them appear less similar than the really are. The legs gave the illusion of narrowness on the left table, but wideness on the right table making the table tops appear as different sizes. However, in the tables without legs, the lack of legs allowed the participants to only judge the sizes of the rectangles instead of the legs and the tables together; thus, reducing the strength of the illusion. In conclusion, the illusion was created by the vertical horizontal illusion based on the placement of the tables (Wolfe et. al 2004). It is partially explained by the confusion theory and the Delbeouf theory. The participants judged the size of the tables based on the legs instead of the table tops; therefore, they were comparing the wrong areas of the illusions. Then, the space in between the legs on the left table looks more narrow making the table top look more narrow, and the space in between the legs of the right table looks wider making the table top look wider. The table tops assimilated to the placement of the legs looking more similar to the space of the leg width rather than their real width expressing the Delbeouf theory. The frame on the table with legs did strengthen the illusion because the vertical table took up more space in the frame so it made it appear larger (Houck 1972). Even though all of these factors affected the illusion, the frame on the table without legs did not have enough strength to truly affect the strength between the two figures without legs
References
Houck, Robert L. "Influence of a visual frame and vertical-horizontal illusion on shape
and size perception." Journal of Experimental Psychology 96 (1972): 273-279.
Mitchell, Peter, et. al. "Human Perception and Performance." Journal of Experimental
Psychology 31 (2005): 996-1003.
"The MindŐs Eye: Finding Truth in Illusion." National Science Foundation. June 1996.
Frontiers. 6 March 2007.
http:// www.nsf.gov/news/frontiers_archive/6-96/6illusio.jsp
Wolfe, Uta, et. al. "Distortions of perceives length in the
Frontoparallel plane: Tests of perspective theories." Perception and
Psychophysics 67 (2005): 967-979.
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