In total 31 participants completed the survey but only 29 participants were used for the results. Two participants were removed due to the incompletion of the survey and not answering the questions correctly. Data was reduced by calculating the average of each individual participants filled line responses and non-filled line responses. Then averaged all the lines without tick and averaged all the lines with ticks to get them all together.
The study intended to find a difference between perceived lines with ticks, which should have been found longer, versus a line with no ticks. The data collected was not statistically significant but did show the group with ticks had a slightly higher average (M = 4.789, SD = 9.858) than the group without ticks (M = 3.909, SD = 8.810), t = 0.358, p = 0.721, d = 0.102. This difference constitutes no strength relationship according to Cohen’s d guidelines. The study failed to reject the null hypothesis since there is no statistically significant difference between the line with ticks than without ticks.
Figure 1. The average mean and standard deviation of lines without ticks compared to lines with ticks. The error bars represent the standard deviation.
The study conducted was to provide more evidence towards the Oppel-Kundt illusion. It was hypothesized that people would perceive the line with ticks as longer than the one without ticks. Even though there was a slightly higher average in the line with ticks than the lines without ticks, it was found that there was no statistical significance. To summarize, the study provides no additional evidence for the Oppel-Kundt illusion and failed to reject the null hypothesis.
Although the study was not significant it was shown that the line with ticks had a slightly higher average than the one without ticks. As discussed above, people do perceive lines with ticks or with something in between to be longer than those that do not have anything. Milkellidou and Thompson (2014) make a good observation that it is not a consequence of a motor response bias but a perceptual illusion of length. People all see lines differently and their perception of length/depth can be one of the reasons the results in this study came out the way they did. For instance, some participants might have believed that the line with ticks was longer, others just saw it as the same length, and then there was some people that thought that all the lines looked the.
Another way of looking at this, some participants might have believed that the line with ticks instead of being perceived as longer might have been perceived the very opposite. If hypothetically I added more than nine tick marks people might have perceived the lines as longer. Now reducing the number of ticks to three or two, people can perceive the lines as shorter. The phenomenon is interesting because we see it in fashion more often than people think. When you buy clothing with lines or strips it is said that it will make you look taller or thinner. But like I said before it is all on your perception of length/depth and not a motor response bias like they initially believed.
One major limitation that may have influenced my results was some of the participants might have not understood the questions because of the way the questions were worded. They may have not had enough information to understand what was asked of them. Although all the questions were the same and the lines were changed, they might have gotten confused with what was presented. Another major limitation was my sample size was smaller than anticipated. Found it quite difficult to recruit a larger number of participants even when posting it on social media. If the sample size would have been bigger, we might have had a different outcome.
The Oppel-Kundt illusion is an interesting phenomenon that can be seen daily in people’s lives. For instance, people tend to perceive parking to be too small, but it ends up being enough to fit their car. There is more than one example when it comes to illusions and everyone has a different approach when visualizing them. Future studies can have a better chance of correcting some of the major limitations in the study above. It would be interesting to see if they have a different approach onto how people perceive the length of the line with tick versus no ticks. Potential studies can provide more evidence of this phenomenon, also they can look at it through a different approach. They can include into the study if men and women perceive the length of the lines differently, maybe longer or shorter.