Ch. 9 pt. 1&2&3

• Cerebral Achromatopsia is a type of color-blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina
• Damage to the ventro-medial occipital and temporal lobes can lead to cerebral achromatopsia
• Colour Deficiency or Congenital achromatopsia occurs at birth due to the genetic absence of one or more types of cone receptors
• Most people born partially color blind are not disturbed by their decreased color perception compared to "normal" as they have never experienced color as a person with normal color vision does
• People with color deficiency have difficulty distinguishing between certain colors, such as red and green
• Color perception has signaling functions that help us identify and classify things, aiding in perceptual organization
• The ability to detect colored food suggests that monkey and human color vision may have evolved to detect fruit
• Knowing the colors of familiar objects helps us recognize these objects
• Color can be a cue to emotions signaled by facial expressions
• Participants were more likely to rate a face as expressing disgust when colored green and as expressing anger when red
• Newton's Experiment involved splitting white sunlight into its spectrum of colors using a prism
• Newton concluded that light in each part of the spectrum is defined by different physical properties, giving rise to our perception of different colors
• Wavelengths from about 400 to 450 nm appear violet, 450 to 490 nm appear blue, 500 to 575 nm appear green, 575 to 590 nm appear yellow, 590 to 620 nm appear orange, and 620 to 700 nm appear red
• Selective Reflection results in chromatic colors when some wavelengths are reflected more than others, while achromatic colors occur when light is reflected equally across the spectrum
• Selective Transmission means that only some wavelengths pass through an object or substance
• Additive color mixing involves mixing lights, where blue and yellow lights projected together on a white surface are perceived as white
• Spectral Colors are evoked by monochromatic light, while Non-Spectral Colors are mixtures of other colors that do not appear in the spectrum
• Humans can differentiate between about 2.3 million different colors
• Hues include red, orange, yellow, green, blue, and violet
• Saturation refers to the intensity of color, while Value is the light-to-dark dimension of color
• The Trichromatic Theory of Color Vision proposes that color vision is based on three principal colors and three different receptor mechanisms
• Color perception is based on the response of the three different types of cones in the retina
• Monochromatism is a rare form of color blindness where individuals have no functioning cones, leading to vision created only by rods
• Protanopia affects 1% of males and 0.02% of females, where individuals are missing the long-wavelength pigment
• Deuteranopia affects about 1% of males and 0.01% of females, where individuals are missing the medium wavelength pigment
• Tritanopia is very rare, affecting about 0.002% of males and 0.001% of females, where individuals are missing the short wavelength pigment
• Anomalous trichromats need three wavelengths to match any wavelength, but mix these wavelengths in different proportions from a normal trichromat
• The Opponent-Process Theory of Color Vision proposes that color vision is caused by opposing responses generated by blue and yellow, and by green and red
• Hue Cancellation Experiments: procedure in which a subject is shown a monochromatic reference light and is asked to remove, or "cancel", the one of the colours in the reference light by adding a second wavelength

  • used for research on opponent-process theory
• Opponent Neurons respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other
• Hue cancellation experiments help determine the amount of blue and yellow in a light to cancel out perceptions of blueness
• • Trichromatic Theory explains the responses of cones in the retina
  • Opponent-Process Theory explains neural responses for cells connected to the cones further in the brain
• Color vision deficiencies, such as;

  • Achromatopsia: inability to perceive colors, seeing the world in shades of gray
  • Color Weakness: commonly referred to as color blindness, where one is missing one type of cone, affecting colour discrimination
• Importance is placed on the brain's role in color perception, specifically the ventral medial occipital cortex and temporal lobes

  • Damage to these areas can result in achromatopsia, underscoring the brain's pivotal role in interpreting colors
• Isaac Newton's experiments with prisms led to the understanding of white light as composed of the spectrum of colors
• Different materials absorb, reflect, or transmit light wavelengths, contributing to our perception of their colour
• Concept of Scattering: the process by which small particles in the atmosphere deflect light in different directions

  • Explains why the sky appears blue, as molecules scatter shorter (blue) wavelengths of sunlight more than longer wavelengths, making the sky predominantly seen as blue from the Earth's surface
• Theory proposed by Young and Helmholtz: suggests that colour vision is based on the activation of three types of cone photoreceptors in the retina -

  1. sensitive to short
  2. medium
  3. long wavelengths

  The mixing of these basic colors in various proportions allows for the perception of the wide range of colours
• Maxwell's Color-Matching Experiments: evidence supporting the trichromatic theory, showing that any color can be matched through the adjustment of the intensities of three primary lights
• Trichromatic theory of Colour Vision: human eye perceives color through the response of three types of cone cells, each sensitive to a specific range of wavelengths corresponding to red, green, and blue light

  • Explains how the combination of these three colors in varying intensities can produce the perception of a wide spectrum of colors