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According to the opponent process theory, the mind can only register the presence of one color of a pair at a time because the two colors oppose one another. The same kind of cell that activates when you see red will deactivate in green light, and the cells that activate in green light will deactivate when you see red. This explains why you can't see yellowish-blue or reddish-green.

The opponent process theory of color vision, along with trichromatic theory, contributed to the current understanding of sight. This article discusses this theory, how it works, and the role it plays in our current understanding of vision.

Opponent Process Theory vs. Trichromatic Theory

The trichromatic theory of color vision suggests that people have cells that detect blue, red, and green wavelengths. These are then combined into other colors to create a visible spectrum.

While the trichromatic theory clarifies some of the processes involved in how we see color, it does not explain all aspects of color vision. The opponent process theory of color vision was developed by Ewald Hering, who noted that there are some color combinations that people never see.

For example, while we often see greenish-blue or blueish-reds, we do not see reddish-green or yellowish-blue. Opponent process theory suggests that color perception is controlled by the activity of two opponent systems: a blue-yellow mechanism and a red-green mechanism.

What Opponent Process Theory Means

The opponent color process works through a process of excitatory and inhibitory responses, with the two components of each mechanism opposing each other.

For example, red creates a positive (or excitatory) response in a cell, while green creates a negative (or inhibitory) response. When this cell is activated, it tells the brain that you are seeing red. Meanwhile, there is an opponent cell that gets a positive response to green wavelengths of light and an inhibitory response to red.

These two types of cells in a red-green receptor complex can't be activated at the same time.

Example of Opponent Process Theory

The opponent process theory helps explain the perceptual phenomena of negative afterimages. Have you ever noticed how you may see a brief afterimage in complementary colors after staring at an image for an extended period of time after staring away?

You can see this effect in action by trying out the following demonstration.

• Take a small square of white paper and place it at the center of a larger red square.
• Look at the center of the white square for approximately 30 seconds, and then immediately look at a plain sheet of white paper and blink to see the afterimage.
• What color is the afterimage? You can repeat this experiment using green, yellow, and blue.

So, how does opponent process theory explain afterimages? According to opponent process theory, staring at the red image for 30 to 60 seconds caused the white and red opponent cells to become "fatigued" (meaning they started sending weaker signals to save energy).

When you shift your focus to a blank surface, those cells no longer have the stimuli telling them to fire. When the white and red receptor cells briefly de-activate, the opposing black and green cells fire in response. As a result, you will see a brief afterimage that is black and green instead of white and red.

Modern Explanations: Complementary Color Theory

Current research has updated this explanation slightly. It seems the green receptor cells do not activate because the red cells become inhibited.

In fact, the afterimage seems to be generated in the brain's cortex, not the retina.

According to the complementary color theory, each receptor pairing registers complementary colors—there is no white/black pairing. When complementary colors are added together, they make white.

When you were staring at the red image, your brain got used to the red and suppressed the signals it was getting from red cells. When you the shifted your gaze to the white paper, your brain saw less red light than before and mentally "subtracted" red from what it is seeing.

The green cells, however, hadn't been suppressed and could send full-strength signals. White "minus" red is green, hence why you saw a flash of green.

Which Color Vision Theory Is Correct?

Although complementary colors theory is the most up-to-date, the trichromatic theory and opponent process theory help account for the complexity of color vision.

• The trichromatic theory explains how the three types of cones detect different light wavelengths.
• The opponent process theory explains how the cones connect to the ganglion cells and how opposing cells are excited or inhibited by certain wavelengths of light.
• The complementary color theory explains which wavelengths translate to which colors and how these colors are processed in the brain.

Frequently Asked Questions

• What phenomena can be explained by opponent process theory?

  Opponent process theory helps explain aspects of color vision. The activation of one type of cone cell leads to the inhibition of the other two. This opponent process is thought to be responsible for our perception of color and explains why people experience afterimages.

• How does opponent process theory explain after images?

  Opponent process theory suggests that looking at one color for a long period causes those receptor cells to become fatigued. When they begin sending weaker signals, their opposing cells fire, sending signals that cause the perception of the opposing color.

• Who first proposed the opponent process theory of color vision?

  Opponent process theory was introduced by the physiologist Ewald Herin in the late 1800s.

• Can opponent process theory explain the McCollough effect?

  The McCollough effect is a visual phenomenon in which looking at images with red horizontal lines and green vertical lines before shifting to an image of black and white lines. As a result of the initial induct with red and green lines, the black and white lines look pink. The opponent process has been implicated as a partial explanation, but the exact mechanisms behind the effect are not fully understood.

  What does opponent process theory explain?

  The opponent process theory suggests that the way humans perceive colors is controlled by three opposing systems. We need four unique colors to characterize perception of color: blue, yellow, red, and green. According to this theory, there are three opposing channels in our vision.

  What is the opponent process theory quizlet?

  The opponent process theory holds that color perception depends on receptors that make antagonistic responses to red versus green, blue versus yellow, and black versus white. The evidence now suggests that both theories are necessary to account for color vision.

  Why is the opponent process theory important?

  The theory links a person's emotions to their motivation. Research on the theory has shown relief from physical pain can bring about pleasant feelings and reduce negative ones. Opponent process theory has also been used to explain the ability to see colors.

  Which of the following is the best example of the opponent process theory quizlet?

  Which of the following is the best example of the opponent process theory? Owen is talking with his friends at lunch when he is suddenly distracted by hearing his name at a neighboring table.