Opponent process theory according to DeValois and DeValois (1993)

Opponent process theory works on the assumption that the ganglion cells in the eye receive information from their receptive field in a center/surround fashion. The receptive field codes either as an on-center/ off-surround or as off-center/on-surround.
This theory takes into account the following problems:

    1. Because all information about color, brightness, shape, motion, etc. must pass through the optic nerve, a neuron in the optic nerve can’t be carrying only color information – it must carry a wealth of information.
    2. S cones are less common than M and L cones. However, we do not perceive blue as less vivid than green or yellow or red – all colors appear psychologically comparable. Somehow we need to amplify the input from the S cones.
    3. How does red, green, yellow, and blue (each a separate mechanism) arise from only three cones?  (Matlin and Foley, 1997, Chapter 7)
The slides presented are how the neural coding in the eye would look for each of the opponent process receptive fields. For each slide, a V coding or a + is excitatory and a _____ or a - is inhibitory. Blue represents short wavelength cones, green represents medium wavelength cones, and red represents long wavelength cones. Black represents the ganglion cell. Each ganglion cell gets information from the bipolar cells (center) and lateral cells (surround).
S center ML surround
M center L surround
L center M surround
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How do you get the different colors from this set up? Color is processed using input from multiple ganglion cells. Remember this is similar to the cones. The cones code color based on the input from all 3 cones. If the short wavelength cones fire a lot and the medium fires less than that, and the long fires even less than that, your eye is coding that you are seeing the color blue. If the medium and the long wavelength cones fire about the same amount, but the short doesn’t fire very much, chances are you are seeing green-yellow.

This system works in the same way. Your brain is getting input from these six different ganglion cells. Based on their firing pattern, you perceive color. Take a look at this diagram.
If the brain is receiving information from the Lo, -Mo, and So, you perceive Red.
If the brain is receiving information from the Lo, -Mo, and –So, you perceive Yellow.
If the brain is receiving information from the –Lo, Mo, and -So, you perceive Green.
If the brain is receiving information from the –Lo, Mo, and So, you perceive Blue.
Light is when the Lo, Mo, and So cells are firing.
Dark is when the –Lo, -Mo, and –So cells are firing.

This shows how color and brightness information are coded using the same system. It shows how four color mechanisms arise from three cones. And it shows how the short wavelength cone information is amplified so those short wavelength colors are seen as vivid as other colors.

DeValois, R.L., & DeValois, K.K. (1993). A multistage color model. Vision Research, 33, 1053-1065.

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