Hearing + Color vision Flashcards
Describe what happens with mixing lights
- If a light that appears blue is projected onto a white surface and a light that appears yellow is projected on top of the light that appears blue, the area where the lights are superimposed is perceived as white
- Because the 2 spots of light are projected onto a white surface, which reflects all wavelengths, all of the wavelengths that hit the surface are reflected into an observer’s eyes
- The blue spot consists of a band of short wavelengths, so when it is projected alone, the short-wavelength light is reflected into the observer’s eyes
- Similarly, the yellow spot consists of medium and long wavelengths, so when presented alone, these wavelengths are reflected into the observer’s eyes
- When colored lights are superimposed, all of the light that’s reflected from the surface by each light when alone is also reflected when the lights are superimposed
-Thus, where the 2 spots are superimposed, the light from the blue spot and the light from the yellow spot are both reflected into the observer’s eye - The added-together light therefore contains short, medium, and long wavelengths, which results in the perception of white
- Because mixing lights involves adding up the wavelengths of each light in the mixture, mixing lights is called an additive color mixture
Summarize the connection between wavelength and color
- Colors of light are associated with wavelengths in the visible spectrum
- The colors of objects are associated with which wavelengths are reflected (for opaque objects) or transmitted (for transparent objects)
- The colors that occur when we mix colors are also associated with which wavelengths are reflected into the eye
- Mixing paints causes fewer wavelengths to be reflected (each paint subtracts wavelengths from the mixture); mixing lights causes more wavelengths to be reflected (each light adds wavelengths to the mixture)
Isaac Newton described the visible spectrum in his experiments in terms of what 7 colors?
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
- His use of 7 color terms probably had more to do with mysticism than science, however, as he wanted to harmonize the visible spectrum (7 colors) with musical scales (7 notes), the passage of time (7 days in a week), astronomy (7 known planets at the time), and religion (7 deadly sins)
What are spectral colors?
Colors that appear in the visible spectrum
Why do modern vision scientists tend to exclude indigo from the list of spectral colors?
Because humans actually have a difficult time distinguishing it from blue and violet
What are non-spectral colors?
- Colors that don’t appear in the spectrum because they are mixtures of other colors
- Ex: magenta, which is a mixture of red and blue
How many colors are humans estimated to be able to discriminate between?
A conservative estimate is that we can tell the difference between about 2.3 million different colors
What’s an example of something that highlights the enormous amount of colors we can differentiate
- If you’ve ever decided to paint your bedroom wall, you will have discovered a dizzying number of color choices in the paint department of your local home improvement store
- Major paint manufacturers have thousands of colors in their catalogs, and your computer monitor can display millions of different colors
How can we perceive millions of colors when we can describe the visible spectrum in terms of only 6 or 7 colors?
Because there are 3 perceptual dimensions of color, which together can create the large number of colors we can perceive
What are the 3 perceptual dimensions of color?
- Hue
- Saturation
- Value
What’s hue?
- The experience of a chromatic color, such as red, green, yellow, or blue, or combinations of these colors
- AKA chromatic colors
What’s saturation?
- Refers to the intensity of color
- The relative amount of whiteness in a chromatic color
- The less whiteness a color contains, the more saturated it is
- The more whiteness has been added the more saturation decreases
What happens when hues become desaturated?
They can take on a faded or washed-out appearance
What does desaturated mean?
- Low saturation in chromatic colors as would occur when white is added to a color
- Ex: pink isn’t as saturated as red
What’s value?
- AKA lightness
- The light-to-dark dimension of color
- Value decreases as the colors become darker
What’s lightness?
The perception of shades ranging from white to gray to black
What’s a color solid?
- A solid in which colors are arranged in an orderly way based on their hue, saturation, and value
- A way to arrange colors systematically within a three-dimensional color space
What’s the Munsell color system?
- Depiction of hue, saturation, and value developed by Albert Munsell in the early 1900s in which different hues are arranged around the circumference of a cylinder with perceptually similar hues placed next to each other
- Hue is arranged in a circle around the vertical
- The vertical represents value or lightness -> value is represented by the cylinder’s height, with lighter colors at the top and darker colors at the bottom
- Saturation increases with distance away from the vertical -> depicted by placing more saturated colors toward the outer edge of the cylinder and more desaturated colors toward the center
- The order of the hues around the cylinder matches the order of the colors in the visible spectrum
- The color solid therefore creates a coordinate system in which our perception of any color can be defined by hue, saturation, and value
How did Newton explain the retinal basis of color vision through his prism experiment?
- When he separated white light into its components to reveal the visible spectrum, he argued that each component of the spectrum must stimulate the retina differently in order for us to perceive color
- He proposed that “rays of light in falling upon the bottom of the eye excite vibrations in the retina. Which vibrations, being propagated along the fibres of the optic nerves into the brain, cause the sense of seeing”
- Electrical signals, not “vibrations,” are what is transmitted down the optic nerve to the brain, but Newton was on the right track in proposing that activity associated with different lights gives rise to the perceptions of different colors
- He thought each component of the spectrum must stimulate the retina differently in order for us to perceive colour
How did Thomas Young expand on Newton’s explanation of the retinal basis of color vision through his prism experiment?
- He suggested that Newton’s idea of a link between each size of vibration and each color won’t work, because a particular place on the retina can’t be capable of the large range of vibrations required
- He stated “Now, as it is almost impossible to conceive of each sensitive point on the retina to contain an infinite number of particles, each capable of vibrating in perfect unison with every possible undulation, it becomes necessary to suppose the number limited, for instance, to the three principal colors, red, yellow, and blue” (Young, 1802)
- It’s this proposal—that color vision is based on 3 principal colors—that marks the birth of what is today called the trichromacy of color vision
- However, Young’s theory was little more than an insightful idea that, if correct, would provide a solution to the puzzle of color perception
- Young had little interest in conducting experiments to test his ideas, however, and never published any research to support his theory
What’s the theory of trichromacy of color vision?
- AKA Young-Helmholtz theory
- The idea that our perception of color is determined by the ratio of activity in 3 receptor mechanisms with different spectral sensitivities
- According to this theory, light of a particular wavelength stimulates each receptor mechanism to different degrees, and the pattern of activity in the 3 mechanisms results in the perception of a color
- Each wavelength is therefore represented in the nervous system by its own pattern of activity in the 3 receptor mechanisms
Who conducted experiments to prove Thomas Young’s theory of trichromacy of color vision?
- James Clerk Maxwell (1831–1879) and Hermann von Helmholtz
- Although Maxwell conducted his experiments before Helmholtz, Helmholtz’s name became attached to Young’s idea of 3 receptors, and trichromatic theory became known as the Young-Helmholtz theory
- This has been attributed to Helmholtz’s prestige in the scientific community and to the popularity of his Handbook of Physiology (1860), in which he described the idea of 3 receptor mechanisms
The trichromacy of color vision is supported by the results of what kind of behavioural procedure?
A psychophysical procedure called color matching
What’s color matching?
A procedure in which observers are asked to match the color in one field by mixing 2 or more lights in another field