Tag: perception

Perceptual Illusions in New York City

by Tiara Paul

While sensations reflect the raw nature of stimuli we pick up from our surroundings, perception is defined as our final experience we build of the world. Perception goes hand in hand with cognition; the way our brains process information, drawing from preexisting knowledge and identifying connections, is what impacts our interpretation of this “raw” data from our human senses. The picture below illustrates how we interpret simple sensations into more meaningful perceptions. In Chapter 4, the Gestalt principles describe how the whole is greater than the sum of the parts. For instance, we see a variety of cues (jumble of colors) but perceive with meaning (face of a friend). 

Source: https://www.youtube.com/watch?v=0SErqVGcAR0 

Illusions can be used to study perception. Cognitive illusions make us do a double take because they indicate how our expectations influence our perceptions. Typically, our perceptions help us perceive the world, but illusions fool us by tricking our natural perceptions, making us see things that do not exist or that are incorrect.  

One example is the Ames room. I went to the Museum of Illusions in New York City this past summer and took a picture in the Ames room, but it was not until Psych 100 that I understood the concept! The Ames room is an illusion whereby the room is not what we typically consider a room. It is not a rectangular cuboidal volume. Rather, the floor, ceiling, and side walls are trapezoidal in shape. Opposite walls are not parallel and adjacent walls are not perpendicular at right angles. Rather, the walls are slanted outward. The floor is not level. Rather, it is on an incline where the far left corner is lower. These features show how our natural perceptions deviate from reality. The illustration below displays the true shape of the room: an irregular quadrilateral. We perceive two figures to be standing next to each other, but in reality, one is in a farther corner of the room, resulting in a flawed perception of both size and depth. Typically, the monocular depth cue of relative size tells us that smaller objects are perceived farther away. However, the Ames Room illusion prevents us from noticing this reality. 

Source: http://editorial-ink.us/ames-room.asp 

 

The consequence of the Ames Room is that if people who are the same size stand near each other at the far corners of the room, it appears that one is extremely tiny and one is very large. In the picture below, I am standing on the far right with my friend; we are both 5’3”. On the left, the two boys are 6 feet tall, but in the Ames Room, they appear to be considerably shorter than us. 

 

Additionally, it is worth noting that in a video of the Ames Room, our idea of perceptual constancy is challenged. In this phenomenon, we perceive a stimulus as constant despite changes in sensation. Typically, with perceptual constancy, our percept is the same even though the sensations an object creates on our receptors is changing. The Ames room challenges this. 

Example: https://www.youtube.com/watch?v=hCV2Ba5wrcs  

 

For this blog post, I purposely explained the room first before showing the picture in order to reverse the normal order in which we witness illusions. Perhaps by first learning the “trick,” you were able to view the picture accurately instead of being fooled by your perceptions. In a slightly different way, relating to memories, this reflects bias. Bias is one of Daniel Schacter’s 7 Sins of Memory, whereby we align memories to our current beliefs, an example of distortion. 

In these ways, illusions allow us to understand how perceptions, our final experience as a result of processing raw sensations, works because they show how our expectations influence what we perceive. 

 

The Camera and the Eye

The 5 senses allow humans to gather data about the world we live in. This data makes up our perception, and it dictates how we think and make decisions. The 5 senses include taste, smell, feel, sight, and hearing. Humans rely heavily on their sense of sight. Two hobbies of mine include astronomy and photography and the similarities between the eye and a camera are fascinating. There are also some interesting things I have learned about how the eye works in low light through astronomy that apply to what we have learned.

Our eyes pick up light on the visible spectrum. As light enters the eye it first passes through the cornea which is a clear covering that helps protect our eye and focus the incoming light. It then goes through the pupil which is a hole that can change size depending on how much light is present. The iris is the muscle that dictates how large the pupil is. After the light goes through the pupil it then passes through the lens. The lens focuses the light and it finally reaches the retina. The retina is filled with special neurons and cells that specialize in detecting light. Together these neurons and cells make up the optic nerve which ultimately sends information to the brain telling it what we see. 

In many ways (but not all), this is how a camera works. Photography is all about how to get the proper amount of light to focus on what we want it to. In a camera, the light passes through the lens. The photographer can change how large or small the iris of the lens is. This is referred to as aperture. After passing through the lens it hits the sensor. In digital cameras, the sensor takes the light and converts it into bits of data and ultimately into an image that we can see.

The eye is similar to a wide angle lens with a small focal ratio. The eye can see a relatively large area; however, only a small portion of what we can see is in focus. The function of the retina is also very similar to an image sensor. 

The human eye works slightly different when there is plenty of light verses when there is little light. As I mentioned before, the retina contains optic nerves. These are composed of cells called rods and cones. Cones are the cells that detect detail and color; however, they work best when there is plenty of light. Cones are concentrated in the center of the retina. Rods on the other hand are not as good at detecting detail and color, but they are more sensitive to light. Rods are more evenly spaced out throughout the retina and most highly concentrated slightly off the center of the eye. 

Rods come in handy when observing the stars. Some objects are extremely faint, and when you try to look directly at them they seem to disappear. When you look just to the side of the object though, you can make out the object in your peripheral vision. This is because your rods are more concentrated in this part of your eye and are better at detecting light. This method is called “averted vision”. 

Vision is incredibly important to the way we perceive the world. The way our eyes take in light is fascinating and valuable to understand in order to make sure we can appropriately analyze our surroundings.

Sources:

Course Textbook – Chapter 4: Sensation, Perception & Vision https://askabiologist.asu.edu/rods-and-cones https://vspblog.com/camera-vs-the-human-eye/.