Vision and Perception
How Light Works
To understand vision, you must first understand the nature of light. Without light, the eye cannot function. In fact, in a situation where no light is present, you would not see anything. The eye is a highly specialized organ that transduces, or transforms, incoming light energies into signals that your brain converts into a picture of the outside world. In this interactivity, you will explore how light works. Click the player to begin.
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Structure of the Eye
Once light reaches your eye, thus begins the complex process of converting light into signals your brain can use to create an internal image of the outside world. Light enters the cornea, bends toward the pupil, is focused by the lens, and projects an image onto the retina. After cells on the retina, called rods and cones, detect light, they send signals to the visual cortex of the brain for processing.
Take a moment to view the video, Vision: Crash Course A&P 18, from eMediaVASM, and discover more details about the inner workings of your eye. As you watch, think about answers to the following questions: How do the cornea, lens, iris, pupil, and retina work together to bring light into your eye? What is the difference between rods and cones? How did your cones and rods impact the after-image of the optical illusion that contained a flag with turquoise and black stripes and black stars?
Vision Problems
Although your eye is an incredible organ, visual problems can occur. In this interactivity, you will examine some vision problems people may have, including nearsightedness, farsightedness, astigmatism, and a blind spot. Click the player to begin.
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Seeing Color
Have you ever been to a paint store and noticed colors with names like flat white, cream, and eggshell? Although the differences between these colors may be subtle, they are noticeable. You learned earlier in this topic that cones in the retina help people differentiate colors, like the ones you see in a paint store. However, all of these fine variations are comprised of just three primary colors: red, green, and blue. These colors are either reflected off of or absorbed into different objects so you perceive them to look a certain way. The idea that red, green, and blue are the primary colors that cones in your eye can detect, and that a mix of varying levels of these three colors actually creates all of the different colors you can see, is called the trichromatic theory. Furthermore, if you put all three of these colors together, you actually create white, not black.
By combining what you have learned about how light works, with information regarding the structure of the eye, you will better understand how you see colors. Take a moment to view the video, What Is Color: Physics Girl, from eMediaVASM, to delve more deeply into this concept.
Trichromatic Theory and Opponent-Process Theory
The existence of color blindness can help you understand the power of the trichromatic theory. People who are color blind, may not have enough of a certain type of cone to detect a particular color easily. In addition, although some women are color blind, most people with this condition are male, because color blindness is a sex-linked trait. Also, most people who are color blind likely have a red-green deficiency, but other colors may be easily distinguishable to them.
Like primates, early human ancestors did not have the same ability to see colors as people do today. Take a moment to view the video, Finding the Origins of Color Vision, from eMediaVASM, to discover why people can presently see the world in color when they could not always. As you watch the video, note that the researchers use an Ishihara test to determine whether the monkeys are color blind. This test is also used on humans.
Test whether you are color blind by viewing an Ishihara color test plate.
Recall the video you watched about the structure of the eye, Vision: Crash Course A&P 18, from eMediaVASM. You experienced the afterimage effect by looking for thirty seconds at the flag, and then moving your gaze quickly to a blank, white screen. The reason you saw the flag in its correct version of red, white, and blue when you looked at the white screen, is because of the opponent-process theory. The idea is that color is processed in opposing pairs of red/green, blue/yellow, and black/white. These three pairs are opposites of one another. When your eyes get used to seeing one color of the pair by stimulating the same receptor cells for a long time, and then the stimulation goes away, this leads to the brief perception of the opposite color.
Both the trichromatic theory and opponent-process theory help explain different aspects of the ways in which humans detect color. In fact, both theories work together to explain the millions of colors we see on a daily basis.
Perception
Have you ever heard the saying, "The whole is greater than the sum of its parts"? This idea is central to the movement in psychology called Gestalt. The word gestalt is German for "whole." Gestalt psychologists were primarily Germans in the late 19th and early 20th centuries. They worried psycholgists had become too focused on breaking things down into smaller parts, and as a result, might be missing the bigger picture of how things work together. Gestalt principles help explain many ways that human perception functions.
Take a moment to view the video, It's More Than An Image, from eMediaVASM, and discover how your eyes make sense of the world around you, as well as how your perception can be tricked. As you watch the video, determine answers to the following questions: How do form and color work together to help you perceive an image? How does your brain interpret perspective? Why is it difficult for computers to perceive things in the same way that humans do?
Vision and Perception Review
Now that you have learned about vision, review your knowledge in this non-graded activity. Click the player to get started.