In V1, we find cells that are specific not to cones but to colors themselves. These neurons are called color-opponent cells. Color-opponent cells are excited by one color in the center and inhibited by its opponent color in the surround. A color-opponent cell may also be inhibited by one color in the center and excited by its opponent color in the surround. Color-opponent cells are red-green and blue-yellow, but never, for example, red-yellow or green-blue, consistent with Hering’s opponent processes theory. That is, these cells work in opponent pairs. There will be a cell that responds to red in the center and inhibits green in the surround, the presumed basis of simultaneous color contras.
In V1, in particular, the blobs, there is also a class of color-sensitive cells called double-opponent cells. Double-opponent cells have a center, which is excited by one color and inhibited by the other. In the surround, the pattern is reversed. Thus, if the center is excited by green and inhibited by red, the surround will be excited by red and inhibited by green. Double-opponent cells are useful in detecting colored edges—that is, where one color ends and a different color begins. Think of red berries surrounded by green leaves.
In this activity, you can interact with both single- and double-opponent cells. You will be able to interact will all the basic types of opponent cells and control the color of the stimulus filling both the center and the surround.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On the Illustration tab, you can stimulate a region of the retina and see the effect on the single cell you are recording from.
Below is a list of the ways that you can alter the model. The settings include the following:
Screen Area: the black area on the screen to the left is a screen that the
eye of your animal is seeing. The receptive field is indicated by two concentric circles in
the center of the screen.
Opponent Cell Types: choose the color opponents that the cells responds to:
R/G: red in the center and green in the surround.
G/R: green in the center and red in the surround.
B/Y: blue in the center and yellow in the surround.
Y/B: yellow in the center and blue in the surround.
Color Sets: change the color filling the receptive field. Single colors, like R for red, fill the entire receptive field with that color at full intensity. Double Colors, like red/green, fill the center with one color and the surround with the opposite. The double colors will not change the intensity of the surround or center.
Inner Color: fill the center of the receptive field with a color chosen from the color wheel or sliders below. You can adjust hue and intensity, but saturation stays at full saturation.
Outer Color: fill the surround of the receptive field with a color chosen from the color wheel or sliders below. You can adjust hue and intensity, but saturation stays at full saturation.
Pressing this button restores the settings to their default values. It also gets you a new cell, which might have a different receptive field.