1
Moon Illusion in Virtual Reality The Moon Illusion The Virtual Worlds Abstract Acknowledgments This work was supported by NSF grants CCF-1117439 and CCF-1421734 People have been fascinated by the moon illusion for thousands of years. The moon on the horizon appears to be bigger to the human observer, when compared to the moon seen at the Zenith by the observer. The size of the moon doesn't change; technically the moon should be smaller on the horizon, because it is physically farther away There have been many hypotheses to try to explain the moon illusion, but most of them can be ruled out, and the few that are left are hard to prove. One fact we know for sure is that the moon illusion is psychological; if you take a photo or a video of the moon, even with the best camera in the world, you won't see the illusion. In fact, almost all of the hypotheses that think state that the moon illusion occurs because of atmospheric conditions or distance actually have it completely backward, because they make the moon appear smaller. Software and Hardware used Anton Soloviev and Toshiro Kubota (Mathematical Sciences) Susquehanna University, 514 University Avenue, Selinsgrove, PA 17870 The moon and other celestial objects, on the horizon, appear to be bigger to the average human observer, and appear to be smaller when above the observer. The visual system of the human brain is working its magic to produce these effects. Can this effect be replicated in a virtual world? On a simple computer monitor this might be impossible, but with the help of virtual reality goggles – that imitate the way that humans perceive depth and scale – this is a realistic goal. To answer the question, we have created a virtual world using a popular game engine, Unity3D, and projected it to Oculus Rift DK2 goggles. This world incorporates many aspects of reality, such as buildings, trees, clouds, lighting, and of course the moon. The Earth's natural satellite was replicated using the actual texture map of the moon and placed a couple of thousand units relative to the observer's position. The spectator will observe the moon rising from the horizon to the zenith, and will be able to compare it at different intervals. The actual size of the moon relative to the position of the observer will be unchanged. The human visual system will be tested. Currently, we have not been able to observe enlargement of the moon near the horizon in our virtual world. We can think of several possible causes. First, the environment we constructed was not realistic enough to induce realistic VR experience. The observer sees everything artificially fabricated despite improved depth and scale sensation. Therefore, the moon is just one of many weird objects, and it doesn't stand out. Second, the field of view supported by the Oculus is smaller than that of our natural vision. This introduces confined feeling to the observer and may distract the experience. Third, the distance and the size of the moon were scaled down due to computational issues, which affect motion parallax and binocular disparity of the moon. References The virtual world was created using Unity3D, a free software that is mainly used by game developers. Unity allows you to create a manipulate any object you put it in the game – whether it is an entire city, or a small toy. The lighting, rendering, shadows, and everything else imaginable can be manipulated in Unity. You can also write scripts to make objects move and interact how you please. The world is seen through virtual reality goggles, Oculus Rift Development Kit 2. DK2 uses an OLED screen designed to have low persistence and high refresh rate of 75 Hz. The camera for the DK2 does real time positional tracking of the markers on the DK2, it's an infrared camera so you won't see the markers using your eyes. Testing the Hypothesis The virtual world that was created was designed in a way to induce the illusion. We have built many different world to try to test each hypothesis on the moon illusion (we've also tried combining many different aspects of different hypotheses into one world). We know that the moon illusion cannot be induced in a planetarium, so we've tried to make the observer peer into great distances (although the fact remains that you just have a screen in front of your eyes). Familiar objects were put near and far away from the observer in order to make the observer compare these objects and experience the illusion. The landscape was designed to try to make the observer see the illusion by using geometric tricks in order to fool your brain into thinking the object is bigger. Mountains, oceans, forests, urban cities, and rural towns were all tested for the illusion, in order to invoke different feelings and references for the observer. Conclusion The results seem to indicate that the moon doesn't appear bigger near the horizon in virtual reality, observers say that the real life illusion could give about a 75% increase in size (sometimes more sometimes less), but this remains to be seen. Perhaps this can be achieved with better hardware and software in the future, or our hypotheses about the moon illusion have to be reformed and tested. If detailed enough world were to be created, seen through very advanced virtual reality goggles, there is a higher chance for the illusion to occur. However, without an intricate virtual world to fool the observer that what he is seeing is a second reality, the illusion is not likely to occur. McCready, D. (2004, November 10). Moon Illusion Explained! Retrieved July 21, 2015. Simanek, D. (2015, April 2). The Moon Illusion,An Unsolved Mystery. Retrieved July 21, 2015. Borghui, B. (n.d.). The Moon Illusion. Retrieved July 21, 2015. Kaufman, L., Kaufman J. (1999, August 23). Explaining the moon illusion. Retrieved July 21, 2015. Jewett, J. (1996). Chapter 26 - Reflection and Refraction. In Physics begins with another M--: Mysteries, magic, myth, and modern physics (p. Page 351). Boston: Allyn and Bacon. Some of the hypotheses One of the most promising hypothesis today is called Oculomotor micropsia and macropsia. It talks about the fact that our eyes try to accommodate and converge to the distance of the object that we see. A similar model is also mentioned in Arnold Trehub book, The Cognitive Brain, which talks about the fact that the information we receive from our visual sensors (our eyes) is then organized and made sense of by our brain; and the fact that we haven't evolved with the moon near us might confuse that processing of data being interpreted. The memory map hypothesis also talks about the fact that we form a map or images in our brain that we later recall and use when comparing other objects.
