Optical Illusions

An illusion is the distorted perception of a stimulus. They are not to be confused with hallucinations, which are false perceptions when there is no presence of a stimulus, in contrast, illusions are the misinterpretation of a true sensation (Illusion Wikipedia). Illusions are mundane phenomena, and are experienced by nearly everyone in similar ways where hallucinations are a personal experience and are typically limited to people who are mentally ill or under the influence of certain drugs (Hallucination Wikipedia). Some illusions occur automatically because it is in our biological nature to perceive things in a particular way, for example objects that are farther away appear smaller than closer objects.

Other illusions can be shown by displaying certain visual tricks that we know will cause an illusion because we have knowledge of how our bodies interpret stimuli (Illusion Wikipedia). Illusions give us an understanding as to how our brain organizes and translates stimuli. They help explain and support the Laws of Perceptual Organization defined in Gestalt Psychology. These laws explain how we visualize the world around us and will later be talked about in more detail (Gleitman, Gross and Reisberg). There are more illusions than just optical; they can occur with all of your senses such at auditory illusions (sound) and tactile illusions (touch) (Illusion Wikipedia). Optical illusions are however the most notorious and understood; there are various different kinds of optical illusions and in my research I looked closely at the boundary extension illusion, the moon illusion, motion illusion, and autokinetic illusions, which are all optical illusions. I also researched many supported theories and explanations of why illusions occur.

We do not just “receive” visual information, we interpret it. The interpretation is an essential part of our perception and aids us in perceiving the world around us correctly. The role of interpretation becomes especially clear when we misinterpret the information that is around us and end up misperceiving the world (Gleitman, Gross and Reisberg).Gestalt Psychology, which is the idea that when we see things we have the biological tendency to organize them into certain ways that make sense to us, is a very good explanation of why we see some optical illusions. There are six fundamental principles in Gestalt Psychology that explain how we visually organize things. The first principle is similarity, this is the idea that we group together objects that are similar to one another. Figure 1.1 demonstrates similarity, because we group the circles together and the squares together we see a “t” made of squares rather than seeing the picture as columns or rows. The second principle is proximity, it explains that when objects are close together we tend to pair them apart and when they are separated we see them individually. Because of the principle of proximity when you look at figure 1.2 you will see one big square rather than nine individual squares, but if these squares were separated we would see them exclusively.

The third principle is good continuation, it is the notion that we are apt to see contours continue smoothly along their original course (Gleitman, Gross and Reisberg). Figure 1.3 exhibits good continuation because instead of seeing four lines meeting in the middle we see two crossed lines. The fourth Gestalt principle is closure; we perceive contours that don’t actually exist. When figures have gaps we illusively close those gaps by perceiving that the contours continue along their original path. In figure 1.4 we form a panda bear even though there are no actual contours that physically exist making a panda. The fifth principle is simplicity, stating that we translate images into our mind in the simplest way possible.

In figure 1.5 you see two rectangles that are crossed instead of seeing a single 12-sided irregular polygon. The sixth Gestalt principle, figure-ground, is a little more complicated than the others; this principle of visual organization is the separation of the object from its setting (Gleitman, Gross and Reisberg). When a person looks at a picture they are able to immediately see which is the figure and with is the ground, it happens with simple and completely unfamiliar objects. Because you can recognize a figure with such ease it seems like this recognition is somehow identified by the stimulus itself and isn’t an element of your interpretation. However, the truth is that the identification of the figure is up to you, along with all other parts of perceptual organization. This becomes obvious when you realize there is more than one way to interpret a stimulus (in this case a picture). In figure 1.6 you instantly see the unfamiliar white splotch as the figure and the black as the background but if you look more closely the image can also be interpreted as two faces (Gleitman, Gross and Reisberg).

A very common optical illusion probably everyone has experienced in their lifetime is the “Moon Illusion” which is how the moon appears to be larger when it’s at the horizon than it does when it’s higher up in the sky even though the moon is always the same size and the same distance away from Earth. It is not yet completely understood why the moon illusion occurs but there are many theories that explain it well. The moon illusion is thought to be connected to the visual angle illusion theory, which states that we perceive objects that are the same distance away but at different angles as different sizes, the size does not actually change though (Egan). I you held a ping pong ball about 25 inches away from you next to the moon at the horizon and then later held that same ping pong ball 25 inches away from yourself up next to the moon that was up high in the sky you will see that the moon is that same size as it was at the horizon (Egan). It’s also made certain that the moon is indeed the same size no matter where it is in the sky because of photographs; a photograph of the moon in different angles of the sky taken from the same spot will have the same sized moon in each picture (Egan).

Another group especially common optical illusions are “Motion Illusions”. There are several different kinds of Motion illusions, and they are also often referred to as Autokinetic Illusions, the two terms can be used interchangeably (Hoots). If you ever rode a school bus as a child or been next to a big bus in a car you’ve probably experienced the illusion of moving backward when really you’re just watching the bus next to you move forward; this particular Autokinetic Illusion is referred to as induced motion. You also encounter induced motion when you are watching a movie scene of say a car and really the movie makers are making the scene outside the windows move instead of the car to give you the illusion that the car is moving.

Another common Motion Illusion is the “motion aftereffect,” this happens when you have been looking at a moving stimuli for an extended period of time and you shift your vision to a still object and it appears to be moving in the opposite direction of the moving stimuli you were previously looking at. For example, if you stare at a spinning black and white spiral for a while and then look at a person’s face it will appear to move like the spiral or have the illusion of getting bigger and smaller. The last Motion Illusion I want to elaborate on is called “optical art”, this is when artists can arrange black and white patterns in a way that they appear to be moving. If you look at figure 2.1 you will see that the black and white patterned picture appears to be moving thought it is a still picture. The reason for this is thought to be due to optical flow, which is a mathematical approach to explaining how we visualize (Ozeki, Keisuke and Keiichiro).

The last illusion I researched was the Boundary Extension Illusion. This is the proposal that when we look at a picture of an object, but are not shown much of the background, when we are asked to explain or draw what we saw we often imagine that we saw more than we did and make up the background. The unusual thing about the Boundary Extension illusion is that the extensions that the people remember and/or draw are typically what actually lie beyond the picture. Another thing about the Boundary Extension Illusion is that it usually only occurs when the initial picture the person looks at contain a background surface (Blumenthal). For example, if you look at an object and the background is just white, when you recall what you saw or draw it you will make the background white again or plain, whereas if you saw a picture with a background you would add more to the picture that you couldn’t see. Figure 3.1 demonstrates this very well, the person who saw the picture of the trash and the area a little behind the fence added the house and tree where the person who just saw the fence didn’t any “extended boundaries” (Blumenthal).

Illusions are a very fascinating a peculiar thing and it’s incredible that most everyone experiences them. I think what makes illusions so intriguing to people if the fact that they are so bizarre but every person experiences them in a conventional way and also that they are very difficult to explain. Gestalts principles of visual organization are a good fundamental basis of knowledge to have if you want to understand on a deeper level why and how optical illusions occur. The way we are biologically made to perceive things sometimes causes us to misperceive how things really are and it’s important to keep this idea in mind. Not everything is quite how it seems.