Opponent process

The color opponent process was developed by Ewald Hering, it is a color theory that states that the human visual system interprets information about color by processing signals from cone cells and rod cells in an antagonistic manner. There is some overlap in the wavelengths of light to which the three types of cones (L for long-wave, M for medium-wave, and S for short-wave light) respond, so it is more efficient for the visual system to record differences between the responses of cones, rather than each type of cone's individual response. The opponent color theory suggests that there are three opponent channels the cone photoreceptors are linked together to form three opposing color pairs: red versus green, blue versus yellow, and black versus white (the last type is achromatic and detects light-dark variation, or luminance). When people stare at a bright color for too long, for example, red, and look away at a white field they will perceive a green color. Activation of one member of the pair inhibits activity in the other.  This theory also helps to explain some types of color vision deficiency.  For example, people with dichromatic deficiencies can match a test field using only two primaries.  Depending on the deficiency they will confuse either red and green or blue and yellow. The opponent-process theory explains color vision as a result of the way in which photoreceptors are interconnected neutrally. The opponent-process theory applies to different levels of the nervous system. Once the neutral system passes beyond the retina to the brain, the nature of the cell changes and the cell responds in an opponent fashion. For example, the green and red photoreceptor might each send a signal to the blue-red opponent cell farther along with the system. Responses to one color of an opponent channel are antagonistic to those to the other color. That is, opposite opponent colors are never perceived together – there is no 'greenish red' or 'yellowish blue'. The color opponent process was developed by Ewald Hering, it is a color theory that states that the human visual system interprets information about color by processing signals from cone cells and rod cells in an antagonistic manner. There is some overlap in the wavelengths of light to which the three types of cones (L for long-wave, M for medium-wave, and S for short-wave light) respond, so it is more efficient for the visual system to record differences between the responses of cones, rather than each type of cone's individual response. The opponent color theory suggests that there are three opponent channels the cone photoreceptors are linked together to form three opposing color pairs: red versus green, blue versus yellow, and black versus white (the last type is achromatic and detects light-dark variation, or luminance). When people stare at a bright color for too long, for example, red, and look away at a white field they will perceive a green color. Activation of one member of the pair inhibits activity in the other.  This theory also helps to explain some types of color vision deficiency.  For example, people with dichromatic deficiencies can match a test field using only two primaries.  Depending on the deficiency they will confuse either red and green or blue and yellow. The opponent-process theory explains color vision as a result of the way in which photoreceptors are interconnected neutrally. The opponent-process theory applies to different levels of the nervous system. Once the neutral system passes beyond the retina to the brain, the nature of the cell changes and the cell responds in an opponent fashion. For example, the green and red photoreceptor might each send a signal to the blue-red opponent cell farther along with the system. Responses to one color of an opponent channel are antagonistic to those to the other color. That is, opposite opponent colors are never perceived together – there is no 'greenish red' or 'yellowish blue'. While the trichromatic theory defines the way the retina of the eye allows the visual system to detect color with three types of cones, the opponent process theory accounts for mechanisms that receive and process information from cones. Though the trichromatic and opponent processes theories were initially thought to be at odds, it later came to be understood that the mechanisms responsible for the opponent process receive signals from the three types of cones and process them at a more complex level. Besides the cones, which detect light entering the eye, the biological basis of the opponent theory involves two other types of cells: bipolar cells, and ganglion cells. Information from the cones is passed to the bipolar cells in the retina, which may be the cells in the opponent process that transform the information from cones. The information is then passed to ganglion cells, of which there are two major classes: magnocellular, or large-cell layers, and parvocellular, or small-cell layers. Parvocellular cells, or P cells, handle the majority of information about color and fall into two groups: one that processes information about differences between the firing of L and M cones, and one that processes differences between S cones and a combined signal from both L and M cones. The first subtype of cells is responsible for processing red–green differences, and the second process blue–yellow differences. P cells also transmit information about the intensity of light (how much of it there is) due to their receptive fields. Johann Wolfgang von Goethe first studied the physiological effect of opposed colors in his Theory of Colours in 1810. Goethe arranged his color wheel symmetrically 'for the colours diametrically opposed to each other in this diagram are those which reciprocally evoke each other in the eye. Thus, yellow demands purple; orange, blue; red, green; and vice versa: Thus again all intermediate gradations reciprocally evoke each other.' Ewald Hering proposed opponent color theory in 1892. He thought that the colors red, yellow, green, and blue are special in that any other color can be described as a mix of them, and that they exist in opposite pairs. That is, either red or green is perceived and never greenish-red: Even though yellow is a mixture of red and green in the RGB color theory, the eye does not perceive it as such. In 1957, Leo Hurvich and Dorothea Jameson provided quantitative data for Hering's color-opponent theory. Their method was called hue cancellation. Hue cancellation experiments start with a color (e.g. yellow) and attempt to determine how much of the opponent color (e.g. blue) of one of the starting color's components must be added to eliminate any hint of that component from the starting color. In 1959, Svaetichin and MacNichol recorded from the retina of fish and reported of three distinct types of cells: one responded with hyperpolarization to all light stimuli regardless of wavelength and was termed a luminosity cell. A second cell responded with hyperpolarization at short wavelengths and with depolarization at mid-to-long wavelengths. This was termed a chromaticity cell. A third cell, also a chromaticity cell, responded with hyperpolarization at fairly short wave- lengths, peaking about 490 nm, and with depolarization at wavelengths longer than about 610 nm. Svaetichin and MacNichol called the chromaticity cells Yellow- Blue and Red-Green opponent color cells. Similar chromatically or spectrally opposed cells, often incorporating spatial-opponency (e.g. red 'on' center and green 'off' surround), were found in the vertebrate retina and lateral geniculate nucleus (LGN) through the 1950s and 1960s by De Valois et al., Wiesel and Hubel, and others. After Svaetichin's lead, the cells were widely called opponent colour cells, Red-Green and Yellow-Blue. Over the next three decades, spectrally opposed cells continued to be reported in primate retina and LGN. A variety of terms are used in the literature to describe these cells, including chromatically opposed or -opponent, spectrally opposed or -opponent, opponent colour, colour opponent, opponent response, and simply, opponent cell. The opponent color theory can be applied to computer vision and implemented as the Gaussian color model and the natural-vision-processing model. Others have applied the idea of opposing stimulations beyond visual systems, described in the article on opponent-process theory. In 1967, Rod Grigg extended the concept to reflect a wide range of opponent processes in biological systems. In 1970, Solomon and Corbit expanded Hurvich and Jameson's general neurological opponent process model to explain emotion, drug addiction, and work motivation.