Color Harmony and the Opponent-Process Channel Theory

Color Harmony and the Opponent-Process Channel Theory

Christina LewisPsych 159

TRICHROMATIC THEORY Thomas Young and Hermann von Helmholtz, 18’th-19’th

century

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

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.

CONES BIPOLAR CELLS GANGLION CELLS

PARVOCELLULAR MAGNOCELLULAR

Processes differences between L & MCones, Red – Green differences

Processes difference between S cones, blue-yellow differences

Intensity of light

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.

ISOLUMINANCE DIFFERENT COLORS - SAME BRIGHTNESS

Youhellohavepsychnoclassproblemthisreadingisonlyathereadinggreentestwords.

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.

BAD BAD BAD DON’T DO THIS IN YOUR FUTURE POWERPOINTS

Implications•Color-opponent channels:•Color is good for SEPARATING OBJECTS• Separating regions

• Luminance Channel:•Contrast transmits SHAPE INFORMATION

(**edges**)• Fine detail

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

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).

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