Seeing Color

What happens when we see a beach ball? Find out in this video! It shows how color vision works by following a beam of sunlight as it bounces off a beach ball and enters a human eye. But our eyes are just the beginning—the real star of the story is the brain .

SHOW HIDE TRANSCRIPT

Seeing color.

What makes the ocean blue? Why does sand look tan? To understand color, we need to know a little bit about light. Light is a kind of wave, just like radio waves. The only difference between radio waves and visible light is the wavelength. X-rays, radio waves, and light waves are all part of the same electromagnetic spectrum. But only certain wavelengths can be detected by the human eye. Each of these wavelengths is a different color.

Light from the sun may not seem to have any color. But in fact, every color of the rainbow is already in sunlight. Together they make white light. Sunlight is a mixture of different colors or wavelengths. This mix of colors and white light is what lets us see colored objects. When sunlight hits a beach ball, we see only the light that bounces off of it. Different parts of the ball reflect different colors. The yellow side reflects yellow light. The blue side reflects blue light. The wavelengths that don't bounce off get absorbed as heat. Only the colors that bounce off reach your eyes.

The color of light coming from an object is what gives it color. Light travels into the eye to the retina located on the back of the eye. The retina is covered with millions of light sensitive cells called rods and cones. When these cells detect light, they send signals to the brain. Cone cells help detect colors. Most people have three kinds of cone cells. People without all three see fewer colors, sometimes called color blindness.

Some cones respond more strongly to blue light. Others pulse faster in response to green. Every color stimulates more than one cone. Their combined response produces a unique signal for each color. Millions of different colors can be distinguished this way. Each cell detects a different part of the picture. Nerve signals from the eye are sent to the brain along the optic nerve.

The brain will decode these nerve signals to create a mental image. The optic nerve carries these nerve signals to the visual cortex on the back of the head. The nerve signals arrive in the visual cortex, where an image begins to form. Various parts of the brain analyze color and shape, movement and location, and a conscious perception is created.

What happened?

Let’s go through the steps involved in seeing that beach ball: 

  1. Notice all the colors on the beach ball? They come from different paints in the plastic. Light is made up of different wavelengths, or colors, and white light is a combination of all of them. When a ray of white sunlight hits a patch of beach ball, the paint absorbs most of the wavelengths. It reflects the rest. For example, if the patch is blue, it reflects the blue wavelengths and absorbs all the others.
  2. Those reflected light waves from the Sun bounce off the beach ball, right into your eye. That’s when the action starts.
  3. At the back of your eye is a tissue called the retina. Special cells called rods and cones live in the retina. These cells are the eye’s lookouts. Their job is to spot light and let the brain know about it. Different rods and cones react to different wavelengths, or colors, of light. 
  4. When light hits the rods and cones, they send electrical signals to let the brain know. They do that through the optic nerve. Like roads and highways, nerves carry signals around the brain and body.  
  5. The optic nerve is connected directly to a part of the brain called the thalamus. Like cards and packages arriving at a sorting station, signals come into the thalamus from many senses, not just sight. The thalamus processes those signals, combining and repackaging some of them into new information. Then it sends the information to other parts of the brain. 
  6. Next, the information about the beach ball heads to the visual cortex. It’s an area way in the back of the brain that’s part of the occipital lobe. 
  7. Special cells in the visual cortex are on the lookout for different kinds of visual information. For example, some of those cells react when the object is a circle. Others react when it’s a line. Some cells react to motion, some to color, and some to various other things. So when it comes to seeing the ball, specific cells recognize each color, and other cells recognize the round shape. These signals are combined into a whole image.
  8. Information about the beach ball’s image heads out along the nerves to other parts of the brain. One place it goes is an area in the front called the prefrontal cortex. The prefrontal cortex is behind the forehead and above the eyes. That’s where the brain processes information from the senses and combines it with other kinds of information, such as memories and emotions.

Together, all this information helps us make sense of the object. We see the beach ball’s round shape and all its colors. We can tell which direction it’s moving. We understand how hard to hit it to send it into our friend’s waiting hands. And we know when to put our own hands up to catch it. For us to perceive the beach ball, so many different parts of the brain all have to work together. Think fast!

These regions are shown in the following diagram:

Diagram of the eyes and brain with the thalamus, visual cortex and optic nerve labeled.

The Museum gratefully acknowledges the Richard and Karen LeFrak Exhibition and Education Fund.

Generous support for The Nature of Color has been provided by the Eileen P. Bernard Exhibition Fund.

The Nature of Color is generously supported by Chase Private Client. 

This educational resource for The Nature of Color is made possible by the Anna-Maria and Stephen Kellen Foundation.

Image credits

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Image Credits:
colorful background by Vecteezy.