If you stare at a green dot for about a minute, then turn your gaze toward a white wall, you should see a red afterimage. The experience of afterimages is a fairly common one among humans, and in this lesson we will talk about how the brain creates them.
What Is Opponent-Process Theory?
In 1874, a German physiologist researching the functions of the eye named Ewald Hering noticed that there are certain color combinations that are never seen, such as reddish-green or bluish-yellow. From this observation, he proposed opponent-process theory, which states that we perceive color in terms of opposite ends of the spectrum: red to green, yellow to blue, and white to black.
It is through this theory that we can explain afterimages, or when we keep seeing the same image after it’s vanished. For example, if you stare at something red for a minute then avert your eyes toward a white surface then you will see a green afterimage. If you stare at a blue circle you will see a yellow afterimage, and if you stare at a white dot you will see a black afterimage.You can see this more clearly from the picture here.
Stare at the white dot in the middle of the flag for about a minute. Afterwards, move your eyes to a white surface.
You should see an afterimage of the flag in the colors of red, white, and blue so that it looks like the actual American flag.
How Opponent-Process Theory Works
While other theories of color vision explain how color is processed by the eye, opponent-process theory explains how it is processed by the brain. Once information about color is detected by the retina, or the membrane in the back of the eye, that information is sent to an area of the brain called the thalamus.
The thalamus is responsible for receiving all the information from the sensory organs (eyes, ears, etc.) and forwarding that information to the correct part of the brain that processes it. In this case, the thalamus sends visual information to the visual cortex of the brain. Within the thalamus, there is a cluster of brain cells referred to as the lateral geniculate nucleus (LGN), which is responsible for the opponent-processing of colors and the afterimage effect.More specifically, these brain cells are sensitive to different colors; some are sensitive to red, some to blue, and some to white. These are the colors that activate these brain cells, while their opponent colors (green, yellow, and black respectively) are the colors that inhibit these brain cells.
Therefore, when you stare at a red circle for long enough, the cells sensitive to red are activated and stimulated for an excessive amount of time. This makes the cells fatigued, which causes the opponent color (in this case green) to be perceived when your eyes are averted from the color red, to inhibit the over-stimulated red sensitive cells.
Opponent-process theory was first proposed by Ewald Hering, a German physiologist researching the functions of the eye in 1874 and states that we perceive color in terms of opposite ends of the spectrum: specifically red to green, yellow to blue, and white to black. This theory explains afterimages, in which we see a lasting image of an object that was just seen in the opposite color that the object was originally perceived.For example, a yellow dot will leave a blue afterimage, and a red dot will leave a green afterimage. This processing of color perception occurs within the brain. The structure responsible for receiving all this sensory information is the thalamus, which contains a cluster of brain cells known as the lateral geniculate nucleus (LGN).
The LGN has cells that are stimulated by some colors (such as red) and inhibited by its opposite color (such as green), which causes afterimages.