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Color Harmony and the Opponent-Process Channel Theory

Color Harmony and the Opponent-Process Channel Theory. Christina Lewis Psych 159. TRICHROMATIC THEORY Thomas Young and Hermann von Helmholtz, 18’th-19’th century. Opponent-Process Theory 1878 Ewald Hering

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Color Harmony and the Opponent-Process Channel Theory

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  1. Color Harmony and the Opponent-Process Channel Theory Christina Lewis Psych 159

  2. TRICHROMATIC THEORYThomas Young and Hermann von Helmholtz, 18’th-19’th century

  3. Opponent-Process Theory • 1878 Ewald Hering • Certain color combinations don’t exist (we never see them), such as reddish-green or yellowish-blue • Three receptor types, each with opposing pairs: red green, blue yellow, black white

  4. Opponent Neurons • Excitatory response to some wavelengths and inhibitory response to others • Red-Green receptors cannot send information about both colors at the same time • Responses to one color of an opponent channel are antagonistic to those to the other color. • **More efficient, given that for the cones, responses to certain wavelengths overlap. Differences are more important.

  5. CONES  BIPOLAR CELLS  GANGLION CELLS PARVOCELLULAR MAGNOCELLULAR Processes differences between L & M Cones, Red – Green differences Processes difference between S cones, blue-yellow differences Intensity of light

  6. How it Works Red-Green Channel: The difference between long-wavelength and middle-wavelength cone signals. Yellow-Blue Channel: The difference between short wavelength cones and the sum of the other two cones. *Luminance Channel*: Based on inputs from all the colors. Detects the difference in brightness of color information.

  7. ISOLUMINANCE DIFFERENT COLORS - SAME BRIGHTNESS

  8. This is a very bad words-on-background color-pair, because there is very little difference between the luminance of the color dark-blue and the luminance of the color black. Youhellohavepsychnoclassproblemthisreadingisonlyathereadinggreentestwords.

  9. BAD BADBAD DON’T DO THIS IN YOUR FUTURE POWERPOINTS

  10. Implications • Color-opponent channels: • Color is good for SEPARATING OBJECTS • Separating regions • Luminance Channel: • Contrast transmits SHAPE INFORMATION (**edges**) • Fine detail

  11. Other Important Properties of Opponent Channels • Luminance > Purely Chromatic Information: • (for many aspects of vision including): • Stereoscopic depth: Cannot detect differences in depth based purely on color channel information

  12. Other Important Properties of Color Channels • Motion Perception: • Luminance > Purely Chromatic Information • If gratings of different colors but equal luminance are moving, we detect the speed much slower (or for some humans, completely immobile) as compared to a grating of very large contrast difference (for example a black and white or black and yellow grating).

  13. After-Images-Fatigue of one color receptive causes stimulation of its opponent color in the pair

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