Hearing + Color vision Flashcards
1
Q
Describe what happens with mixing lights
A
- 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
2
Q
Summarize the connection between wavelength and color
A
- 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)
3
Q
Isaac Newton described the visible spectrum in his experiments in terms of what 7 colors?
A
- 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)
4
Q
What are spectral colors?
A
Colors that appear in the visible spectrum
5
Q
Why do modern vision scientists tend to exclude indigo from the list of spectral colors?
A
Because humans actually have a difficult time distinguishing it from blue and violet
6
Q
What are non-spectral colors?
A
- 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
7
Q
How many colors are humans estimated to be able to discriminate between?
A
A conservative estimate is that we can tell the difference between about 2.3 million different colors
8
Q
What’s an example of something that highlights the enormous amount of colors we can differentiate
A
- 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
9
Q
How can we perceive millions of colors when we can describe the visible spectrum in terms of only 6 or 7 colors?
A
Because there are 3 perceptual dimensions of color, which together can create the large number of colors we can perceive
10
Q
What are the 3 perceptual dimensions of color?
A
- Hue
- Saturation
- Value
11
Q
What’s hue?
A
- The experience of a chromatic color, such as red, green, yellow, or blue, or combinations of these colors
- AKA chromatic colors
12
Q
What’s saturation?
A
- 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
13
Q
What happens when hues become desaturated?
A
They can take on a faded or washed-out appearance
14
Q
What does desaturated mean?
A
- Low saturation in chromatic colors as would occur when white is added to a color
- Ex: pink isn’t as saturated as red
15
Q
What’s value?
A
- AKA lightness
- The light-to-dark dimension of color
- Value decreases as the colors become darker
16
Q
What’s lightness?
A
The perception of shades ranging from white to gray to black
17
Q
What’s a color solid?
A
- 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
18
Q
What’s the Munsell color system?
A
- 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
19
Q
How did Newton explain the retinal basis of color vision through his prism experiment?
A
- 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
20
Q
How did Thomas Young expand on Newton’s explanation of the retinal basis of color vision through his prism experiment?
A
- 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
21
Q
What’s the theory of trichromacy of color vision?
A
- 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
22
Q
Who conducted experiments to prove Thomas Young’s theory of trichromacy of color vision?
A
- 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
23
Q
The trichromacy of color vision is supported by the results of what kind of behavioural procedure?
A
A psychophysical procedure called color matching
24
Q
What’s color matching?
A
A procedure in which observers are asked to match the color in one field by mixing 2 or more lights in another field
25
Q
Describe the procedure of color matching
A
- The experimenter presents a reference color that is created by shining a single wavelength of light on a “reference field”
- The observer then matches the reference color by mixing the wavelengths of light in a “comparison field”
- Ex: an observer could be shown a 500-nm light in the reference field and then be asked to adjust the amounts of 420-nm, 560-nm, and 640-nm lights in the comparison field, until the perceived color of the comparison field matches the reference field (bipartite field)
- In a color-matching experiment, a wavelength in one field is matched by adjusting the proportions of 3 different wavelengths in another field
- This result is interesting because the lights in the 2 fields are physically different (they contain different wavelengths) but they are perceptually identical (they look the same) -> metamerism
26
Q
What was Maxwell’s key finding for his color-matching experiments?
A
- That any reference color could be matched provided that observers were able to adjust the proportions of 3 wavelengths in the comparison field
- 2 wavelengths allowed participants to match some, but not all, reference colors, and they never needed 4 wavelengths to match any reference color
- Based on the finding that people with normal color vision need at least 3 wavelengths to match any other wavelength, Maxwell reasoned that color vision depends on 3 receptor mechanisms, each with different spectral sensitivities
27
Q
The discovery of 3 types of cones in the human retina was made using what technique?
A
- Microspectrophotometry
- This made it possible to direct a narrow beam of light into a single cone receptor
- By presenting light at wavelengths across the spectrum, it was determined that there were 3 types of cones, with the absorption spectra
- This discovery provided physiological support for the trichromacy that was based on the results of Maxwell’s color matching experiments
- These new measurements were important because they were not only consistent with trichromacy as predicted by color matching, but they also revealed the exact spectra of the 3 cone mechanisms, and, revealed the large overlap between the L and M cones
28
Q
What’s microspectrophotometry?
A
- A technique in which a narrow beam of light is directed into a single visual receptor
- This technique makes it possible to determine the pigment absorption spectra of single receptors
29
Q
Describe the absorption spectra of the 3 cone pigments
A
- The short-wavelength pigment (S), absorbed maximally at 419-nm
- The middle-wavelength pigment (M), at 531-nm
- The long-wavelength pigment (L), at 558-nm
30
Q
What’s adaptive optical imaging?
A
- Another advance in describing the cones
- A technique that makes it possible to look into a person’s eye and take pictures of the receptor array in the retina (showed how the cones are arranged on the surface of the retina)
- This was an impressive achievement, because the eye’s cornea and lens contain imperfections called aberrations that distort the light on its way to the retina
- This method creates a sharp image by first measuring how the optical system of the eye distorts the image reaching the retina, and then taking a picture through a deformable mirror that cancels the distortion created by the eye
- The result is a clear picture of the cone mosaic, which shows foveal cones
- Colors are added after the images are created to distinguish the long- (red), medium- (green), and short-wavelength (blue) cones
31
Q
What are abberations?
A
Imperfections on the eye’s cornea and lens that distort light on its way to the retina
32
Q
Can optometrists see our cones?
A
- No, they would need adaptive optical imaging
- When your optometrist or ophthalmologist uses an ophthalmoscope to look into your eye, they can see blood vessels and the surface of the retina, but the image is too blurry to make out individual receptors -> this is usually due to abberations
33
Q
What’s a cone mosaic?
A
Arrangement of long- (red), medium- (green), and short-wavelength (blue) cones in a particular area of the retina
34
Q
How is short-wavelength light, which appears blue in the spectrum, signaled in the receptors?
A
It’s signaled by a large response in the S receptor, a smaller response in the M receptor, and an even smaller response in the L receptor
35
Q
How is yellow signaled in the receptors?
A
Yellow is signaled by a very small response in the S receptor and large responses in the M and L receptors
36
Q
How is white signaled in the receptors?
A
White is signaled by equal activity in all the receptors
37
Q
Other than the varying wavelengths stimulating our receptors, what other factors affect our perception of color?
A
- Our state of adaptation
- The nature of our surroundings
- Our interpretation of the illumination
38
Q
What’s metamerism?
A
- The situation in which 2 physically different stimuli are perceptually identical
- In vision, this refers to 2 lights with different wavelength distributions that are perceived as having the same color
39
Q
What are the 2 identical fields in a color-matching experiment called?
A
Metamers
40
Q
What are metamers?
A
- 2 lights that have different wavelength distributions but are perceptually identical
- The reason metamers look alike is that they both result in the same pattern of response in the 3 cone receptors
- Ex: when the proportions of a 620-nm red light that looks red and a 530-nm green light that looks green are adjusted so the mixture matches the color of a 580-nm light, which looks yellow, the 2 mixed wavelengths create the same pattern of activity in the cone receptors as the single 580-nm light
- The 530-nm green light causes a large response in the M receptor, and the 620-nm red light causes a large response in the L receptor
- Together, they result in a large response in the M and L receptors and a much smaller response in the S receptor
- This is the pattern for yellow and is the same as the pattern generated by the 580-nm light
- Thus, even though the lights in these 2 fields are physically different, the 2 lights result in identical physiological responses so they are identical as far as the brain is concerned and they are therefore perceived as being the same
41
Q
What’s monochromatism?
A
- Rare form of color blindness in which the absence of cone receptors results in perception only of shades of lightness (white, gray, and black), with no chromatic color present
- Usually hereditary and occurs in only about 10 people out of 1 million
- Monochromats usually have no functioning cones, so their vision is created only by the rods
- Their vision, therefore, has the characteristics of rod vision in both dim and bright lights so they see only in shades of lightness (white, gray, and black)
- A person with normal color vision can experience what it’s like to be a monochromat by sitting in the dark for several minutes
- When dark adaptation is complete, vision is controlled by the rods, which causes the world to appear in shades of gray
- Because monochromats perceive all wavelengths as shades of gray, they can match any wavelength by picking another wavelength and adjusting its intensity
- Thus, a monochromat needs only one wavelength to match any wavelength in the spectrum
42
Q
Why is color vision not possible in a person with just one receptor type?
A
- We can understand this by considering how a person with just one pigment would perceive 2 lights, one 480 nm and one 600 nm, which a person with normal color vision sees as blue and red
- The absorption spectrum for the single pigment indicates that the pigment absorbs 10% of 480-nm light and 5% of 600-nm light
- When light is absorbed by the retinal part of the visual pigment molecule, the retina changes shape (isomerization)
- The visual pigment molecule isomerizes when the molecule absorbs one photon of light
- This isomerization activates the molecule and triggers the process that activates the visual receptor and leads to seeing the light
- If the intensity of each light is adjusted so 1,000 photons of each light enter our one-pigment observer’s eyes, the 480-nm light isomerizes 1000 x 0.10 = 100 visual pigment molecules and the 600-nm light isomerizes 1000 x 0.05 = 50 molecules
- Because the 480-nm light isomerizes 2x as many visual pigment molecules as the 600-nm light, it will cause a larger response in the receptor, resulting in perception of a brighter light
- But if we increase the intensity of the 600-nm light to 2,000 photons, then this light will also isomerize 100 visual pigment molecules
- When the 1,000 photon 480-nm light and the 2,000 photon 600-nm light both isomerize the same number of molecules, the result will be that the 2 spots of light will appear identical
- Thus, by adjusting the intensities of the 2 lights, we can cause the single pigment to result in identical responses, so the lights will appear the same even though their wavelengths are different
- A person with only one visual pigment can match any wavelength in the spectrum by adjusting the intensity of any other wavelength and sees all of the wavelengths as shades of gray
- Thus, adjusting the intensity appropriately can make the 480-nm and 600-nm lights (or any other wavelengths) look identical
43
Q
What does a person need to perceive chromatic color?
A
More than one type of receptor
44
Q
What does it mean to be color blind?
A
- A condition in which a person perceives no chromatic color
- This can be caused by absent or malfunctioning cone receptors or by cortical damage
45
Q
Why does the difference in the wavelengths of light not matter?
A
- Because of the principle of univariance, which states that once a photon of light is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost
- Absorption of a photon causes the same effect, no matter what the wavelength is
- Any two wavelengths can cause the same response by changing the intensity
- An isomerization is an isomerization no matter what wavelength caused it
- Univariance means that the receptor doesn’t know the wavelength of light it has absorbed, only the total amount it has absorbed
- Thus, by adjusting the intensities of 2 lights, we can cause a single pigment to result in identical responses, so the lights will appear the same even though their wavelengths are different
46
Q
What are dichromats?
A
- A person who has a form of color deficiency
- People with just 2 types of cone pigment
- They see chromatic colors, just as our calculations predict, but because they have only 2 types of cones, they confuse some colors that trichromats can distinguish
- ## Dichromats can match any wavelength in the spectrum by mixing 2 other wavelengths
47
Q
What are trichromats?
A
- A person with normal color vision
- Trichromats can match any wavelength in the spectrum by mixing 3 other wavelengths in various proportions
48
Q
What are ways of determining the presence of colour deficiency?
A
- By using the color-matching procedure to determine the minimum number of wavelengths needed to match any other wavelength in the spectrum
- With a color vision test that uses stimuli called Ishihara plates
49
Q
What are Ishihara plates?
A
- A display of colored dots used to test for the presence of color deficiency
- The dots are colored so that people with normal (trichromatic) color vision can perceive numbers in the plate, but people with color deficiency cannot perceive these numbers or perceive different numbers than someone with trichromatic vision
50
Q
What’s a unilateral dichromat?
A
- A person who has dichromatic vision in one eye and trichromatic vision in the other eye
- People with this condition (which is extremely rare) have been tested to determine what colors dichromats perceive by asking them to compare the perceptions they experience with their dichromatic eye and their trichromatic eye
- Both of the unilateral dichromat’s eyes are connected to the same brain, so this person can look at a color with his dichromatic eye and then determine which color it corresponds to in his trichromatic eye
51
Q
What do we need to do too determine what a dichromat perceives compared to a trichromat?
A
We need to locate and experiment on a unilateral dichromat
52
Q
What are the 3 major forms of dichromatism?
A
- Protanopia
- Deuteranopia
- Tritanopia
53
Q
What are the 2 most common kinds of dichromatism?
A
- Protanopia and Deuteranopia
- These are inherited through a gene located on the X chromosome
- They result in the same perception of blues, greys and yellows
54
Q
Why are males more likely than females to have a colour deficiency?
A
- Because both Protanopia and Deuteranopia are inherited through a gene located on the X chromosome
- Males (XY) have only one X chromosome, so a defect in the visual pigment gene on this chromosome causes color deficiency
- Females (XX), on the other hand, with their 2 X chromosomes, are less likely to become color deficient because only one normal gene is required for normal color vision
- These forms of color vision are therefore called sex-linked because women can carry the gene for color deficiency without being color deficient themselves
- Thus, many more males than females are dichromats
55
Q
What’s protanopia?
A
- A form of dichromatism in which a protanope is missing the long-wavelength pigment (no red), and perceives short-wavelength light as blue and long-wavelength light as yellow
- This affects 1% of males and 0.02% of females
- Results in the perception of colors as only blues and yellows (no red)
- As a result, a protanope perceives short-wavelength light as blue, and as the wavelength is increased, the blue becomes less and less saturated until, at 492 nm, the protanope perceives gray
- The wavelength at which the protanope perceives gray is called the neutral point
- At wavelengths above the neutral point, the protanope perceives yellow, which becomes less intense at the long wavelength end of the spectrum
56
Q
What’s deuteranopia?
A
- A form of dichromatism in which a person is missing the medium-wavelength pigment (no green)
- A deuteranope perceives turquoise at short wavelengths, sees yellow at long wavelengths, and has a neutral point at about 498 nm
- This affects about 1% of males and 0.01% of females and results in the perception of colour as blues and yellows
57
Q
What’s tritanopia?
A
- A form of dichromatism in which a person is missing the short-wavelength pigment
- A tritanope sees blue at short wavelengths, red at long wavelengths
- Very rare -> affecting only about 0.002% of males and 0.001% of females
- A tritanope sees colors and the spectrum as blues, greys and reds and sees the spectrum the same
- Has a neutral point at 570 nm
58
Q
Other than monochromatism and dichromatism, what’s another prominent type of colour deficiency?
A
Anomalous trichromatism
59
Q
What’s anomalous trichromatism?
A
- A type of color deficiency in which a person needs to mix a minimum of 3 wavelengths to match any other wavelength in the spectrum but mixes these wavelengths in different proportions than a trichromat
- They are not as good as a trichromat at discriminating between wavelengths that are close together
60
Q
What’s Hering’s opponent-process theory of color vision?
A
- Theory originally proposed by Hering, which claimed that our perception of colour is determined by the activity of 3 opponent mechanisms: a blue–yellow mechanism, a red–green mechanism and a white-black mechanism
- The responses to the 2 colours in each mechanism oppose each other, one being an excitatory response and the other an inhibitory response
- These responses were believed to be the result of chemical reactions in the retina
- This theory also includes a black–white mechanism, which is concerned with the perception of brightness
- He picked these pairs of colors based on phenomenological observations—observations in which observers described the colors they were experiencing
- This was based on his observation that if you stare at something that’s coloured, you’re going to see something that’s coloured differently
61
Q
What are the 2 types of behavioural evidence for opponent-process theory?
A
- Phenomenological
- Psychophysical
62
Q
Describe the phenomenological evidence for Hering’s opponent-process theory
A
- This evidence is based on colour experience
- This evidence was central to Hering’s proposal of opponent-process theory
- His ideas about opponent colours were based on people’s colour experiences when looking at a colour circle
- Hering identified 4 primary colors (red, yellow, green, and blue) and proposed that each of the other colors are made up of combinations of these primary colors
- This was demonstrated using a procedure called hue scaling, in which participants were given colors from around the hue circle and told to indicate the proportions of red, yellow, blue, and green that they perceived in each color
- One result was that each of the primaries was “pure”
- Ex: there’s no yellow, blue, or green in the red
- The other result was that each of the intermediate colors like purple or orange were judged to contain mixtures of 2 or more of the primaries
- Results such as these led him to call the primary colors unique hues
- He proposed that our color experience is built from the 4 primary chromatic colors arranged into 2 opponent pairs: yellow–blue and red–green
- To these chromatic colors, Hering also considered black and white to be an opponent achromatic pair
63
Q
What’s a colour circle?
A
- Perceptually similar colors located next to each other around its perimeter and arranged in a circle
- In the color circle, colors across from each other are complementary colors
- The difference between a color circle and a color solid is simply that the color circle focuses only on hue, without considering variations in saturation or value
- Hering’s colour circle has colors on the left appear blueish, colors on the right appear yellowish, colors on the top appear reddish, and colors on the bottom appear greenish
- Lines connect opponent colors
64
Q
What are complementary colours?
A
Colours which when combined cancel each other to create white or gray
65
Q
What are the 4 primary colours that Hering identified?
A
- Red
- Yellow
- Green
- Blue
- He referred to these as unique hues
66
Q
What’s hue scaling?
A
Procedure in which participants are given colors from around the hue circle and told to indicate the proportions of red, yellow, blue, and green that they perceive in each color
67
Q
What are the 3 reasons why Hering’s phenomenological opponent-process proposal wasn’t widely accepted?
A
- Its main competition, trichromatic theory, was championed by Helmholtz, who had great prestige in the scientific community
- Hering’s phenomenological evidence, which was based on describing the appearance of colors, couldn’t compete with Maxwell’s quantitative color mixing data
- There was no neural mechanism known at that time that could respond in opposite ways
68
Q
Describe the psychophysical evidence for Hering’s opponent-process theory
A
- The idea of opponency was given a boost in the 1950s by Leo Hurvich and Dorthea Jameson’s (1957) hue cancellation experiments
- The purpose of the hue cancellation experiments was to provide quantitative measurements of the strengths of the B–Y and R–G components of the opponent mechanisms
- Through these, they found that blue opposes yellow and that green opposes red
- Hurvich and Jameson’s hue cancellation experiments were an important step toward acceptance of opponent-process theory because they went beyond Hering’s phenomenological observations by providing quantitative measurements of the strengths of the opponent mechanisms
69
Q
Describe the method of hue cancellation
A
- Procedure in which a subject is shown a monochromatic reference light and is asked to remove, or “cancel,” the one of the colors in the reference light by adding a 2nd wavelength
- Ex: We begin with a 430-nm light, which appears blue
- Hurvich & Jameson (1957) reasoned that since yellow is the opposite of blue and therefore cancels it, they could determine the amount of blueness in a 430-nm light by determining how much yellow needs to be added to cancel all perception of “blueness”
- Once this is determined for the 430-nm light, the measurement is repeated for 440nm and so on, across the spectrum, until reaching the wavelength where there is no blueness
- This method was then used to determine the strength of the yellow mechanism by determining how much blue needs to be added to cancel yellowness at each wavelength
- For red and green, the strength of the red mechanism is determined by measuring how much green needs to be added to cancel the perception of redness, and the strength of the green mechanism, by measuring how much red needs to be added to cancel the perception of greenness
70
Q
Describe the physiological evidence for Opponent-Process Theory
A
- Even more crucial for the acceptance of opponent-process theory was the discovery of opponent neurons that responded with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
- In an early paper that reported opponent neurons in the lateral geniculate nucleus (LGN) of the monkey, Russell DeValois (1960) recorded from neurons that responded with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
- Later work identified opponent cells with different receptive field layouts (circular single opponent, circular double opponent, and side-by-side single opponent)
- This provided physiological evidence for the opponency of color vision
- The opponent neurons can be created by inputs from the 3 cones
- Ex: the L-cone sends excitatory input to a bipolar cell, whereas the M-cone sends inhibitory input to the cell. This creates an +L –M cell that responds with excitation to the long wavelengths that cause the L-cone to fire and with inhibition to the medium wavelengths that cause the M-cone to fire
- Ex: the +S –ML cell also receives inputs from the cones. It receives an excitatory input from the S cone and an inhibitory input from cell A, which sums the inputs from the M and L cones
- Opponent responding has also been observed in a number of cortical areas, including the visual receiving area (V1)
71
Q
What are the 3 different receptive field layouts for opponent cells?
A
- Circular single opponent
- Circular double opponent
- Side-by-side single opponent
72
Q
What kind of colour display do circular single opponent cells and side-by-side single opponent cells respond to?
A
Large areas of colour
73
Q
What kind of colour display do circular double opponent cells respond to?
A
Colour patterns and borders
74
Q
What are opponent neurons?
A
A neuron that has an excitatory response to wavelengths in one part of the spectrum and an inhibitory response to wavelengths in the other part of the spectrum
75
Q
Describe how researchers questioned the idea of unique hues
A
- The proposed specialness of unique hues led researchers who first recorded from opponent neurons to give them names like +B –Y and +R –G that corresponded to the unique hues
- The implication of these labels is that these neurons are responsible for our perception of these hues
- One argument against the idea of a direct connection between the firing of opponent neurons and perceiving primary or unique hues is that the wavelengths that cause maximum excitation and inhibition don’t match the wavelengths associated with the unique hues
- And recent research has repeated hue scaling experiments, using different primaries—orange, lime, purple, and teal—and obtained results similar to what occurred with red, green, blue, and yellow
- That is, orange, lime, purple, and teal were rated as if they were “pure” (ex: orange was rated as not containing any lime, purple, or teal)
- Opponent neurons are certainly important for color perception, because opponent responding is how color is represented in the cortex
- But perhaps, the idea of unique hues may not be helping us figure out how neural responding results in specific colors
- Apparently, it’s not as simple as +M –L equals +G –R, which is directly related to perceiving green and red
76
Q
If responses of +M –L neurons can’t be linked to the perception of green and red (or Hering’s unique hues), what is the function of these neurons?
A
- One idea is that opponent neurons indicate the difference in responding of pairs of cones to different wavelengths
- We can understand how this works at a neural level where we see how a +L –M neuron receiving excitation from the L-cone and inhibition from the M-cone responds to 500-nm and 600-nm lights
-Ex: if the 500-nm light results in an inhibitory signal of
–80 and an excitatory signal of +50, the response of the +L –M neuron would be –30 (meaning the action of the 500-nm light on this neuron will cause a decrease in any ongoing activity). And if the 600-nm light results in an inhibitory signal of –25 and an excitatory signal of +75, the response of the +L –M neuron would be +50 (this wavelength causes an increase in the response of this neuron) - This “difference information” could be important in dealing with the large overlap in the spectra of the M and L cones
77
Q
How have neurons with side-by-side receptive fields been used to provide evidence for a connection between color and form?
A
- These neurons can fire to oriented bars even when the intensity of the side-by-side bars is adjusted so they appear equally bright
- In other words, these cells fire when the bar’s form is determined only by differences in color
- This evidence has been used to support the idea of a close bridge between the processing of color and the processing of form in the cortex
- Thus, when you look out at a colorful scene, the colors you see are not only “filling in” the objects and areas in the scene but may also be helping define the edges and shapes of these objects and areas
78
Q
How was the idea of brain area specialized for colour popularized?
A
- It was popularized by Semir Zeki based on his finding that many neurons in a visual area called V4 respond to colour
- However, additional evidence has led many researchers to reject the idea of a “colour center” in favour of the idea that colour processing is distributed across a number of cortical areas
79
Q
Describe Rosa Lafer-Sousa and coworkers (2016) study on the brain areas specialized in processing colour vision
A
- They scanned participants’ brains while they watched 3-second video clips that contained images (both coloured and BW) -> these images included faces, places, bodies and objects
- From looking at the participants’ brains, they found that areas that responded to colour were sandwiched between areas that responded to faces and places
- Faces, colour, and places are associated with different areas that are located next to each other in the brain
80
Q
What’s evidence that colour and shape/form are processed idependently?
A
- The independence of shape and color is indicated by some cases of brain damage
- Patient D.F. who could mail a card but couldn’t orient the card or identify objects was described to illustrate a dissociation between action and object perception
- Despite her difficulty in identifying objects, her colour perception was unimpaired
- Another patient, however, had the opposite problem with impaired color perception but normal form perception
- This double dissociation means that color and form are processed independently
81
Q
Sunlight contain what kind of energy for the different wavelengths?
A
Sunlight contains approx. equal amounts of energy at all wavelengths, which is a characteristic of white light
82
Q
Incandescent bulbs contain what kind of energy for the different wavelengths?
A
It contains much more energy at long wavelengths (which is why they look slightly yellow)
83
Q
LED bulbs contain what kind of energy for the different wavelengths?
A
LED bulbs emit light at substantially shorter wavelengths (which is why they look slightly blue)
84
Q
How was the idea that colour is not a property of wavelengths asserted by Isaac Newton in his Opticks (1704)?
A
- Newton’s idea was that the colours we see in response to different wavelengths aren’t contained in the rays of light themselves, but that the rays “stir up a sensation of this or that color”
- Light rays are simply energy, so there’s nothing intrinsically “blue” about short wavelengths or “red” about long wavelengths, and we perceive colour because of the way our nervous system responds to this energy
85
Q
In cases such as color vision, hearing, taste, and smell—the very essence of our perceptual experience is created by what?
A
The nervous system
86
Q
Our perception of color is determined by the action of what?
A
3 different types of cone receptors
87
Q
The foundations of what are present at about 4 months of age?
A
- The foundations of trichromatic vision
- There’s also evidence that colour vision continues to develop into the teenage years
88
Q
What does hearing provide us with that vision cannot?
A
- Unlike vision, which depends on light traveling from objects to the eye, sound travels around corners to make us aware of events that otherwise would be invisible
- Ex: in my office in the psychology department, I hear things that I would be unaware of if I had to rely only on my sense of vision: people talking in the hall; a car passing by on the street below; an ambulance, siren blaring, heading up the hill toward the hospital
- If it weren’t for hearing, my world at this particular moment would be limited to what I can see in my office and the scene directly outside my window
- Without hearing I would be unaware of many of the events in my environment
89
Q
How does our ability to hear events that we can’t see serve as an important signaling function for both animals and humans?
A
- For an animal living in the forest, the rustle of leaves or the snap of a twig may signal the approach of a predator
- For humans, hearing provides signals such as the warning sound of a smoke alarm or an ambulance siren, the distinctive high-pitched cry of a baby who is distressed, or telltale noises that indicate problems in a car engine
- Hearing not only informs us about things that are happening that we can’t see, but it also adds richness to our lives through music and facilitates communication by means of speech
90
Q
What does the question “If a tree falls in the forest and no one is there to hear it, is there a sound?” demonstrate?
A
This question shows that we can use the word sound both as a physical stimulus and as a perceptual response
91
Q
What’s sound?
A
- The perceptual experience of hearing
- The statement “I hear a sound” is using sound in this sense
92
Q
What are the 2 definitions for sound?
A
- Physical definition: Sound is pressure changes in the air or other medium
- Perceptual definition: Sound is the experience we have when we hear
- Ex: “the piercing sound of the trumpet filled the room” refers to the experience of sound, but “the sound had a frequency of 1,000 Hz” refers to sound as a physical stimulus
93
Q
When does a sound stimulus occur?
A
A sound stimulus occurs when the movements or vibrations of an object cause pressure changes in air, water, or any other elastic medium that can transmit vibrations
94
Q
Describe the example of the process of the creation of a sound stimulus through a loudspeaker
A
- A loudspeaker is a device for producing vibrations to be transmitted to the surrounding air
- In extreme cases, such as standing near a speaker at a rock concert, these vibrations can be felt, but even at lower levels, the vibrations are there
- The speaker’s vibrations affect the surrounding air
- When the diaphragm of the speaker moves out, it pushes the surrounding air molecules together, a process called compression, which causes a slight increase in the density of molecules near the diaphragm
- This increased density results in a local increase in the air pressure above atmospheric pressure
- When the speaker diaphragm moves back in, air molecules spread out to fill in the increased space, a process called rarefaction
- The decreased density of air molecules caused by rarefaction causes a slight decrease in air pressure
- By repeating this process hundreds or thousands of times a second, the speaker creates a pattern of alternating high- and low-pressure regions in the air, as neighbouring air molecules affect each other
- This pattern of air pressure changes, which travels through air at 340 meters per second (and through water at 1,500 meters per second), is called a sound wave
95
Q
What’s a sound wave?
A
- Pattern of pressure changes in a medium
- Most of the sounds we hear are due to pressure changes in the air, although sound can be transmitted through water and solids as well
96
Q
What’s the process of compression?
A
When the diaphragm of the speaker moves out, it pushes the surrounding air molecules together, which causes a slight increase in the density of molecules near the diaphragm
97
Q
What’s the process of rarefaction?
A
- When the speaker diaphragm moves back in, air molecules spread out to fill in the increased space
- The decreased density of air molecules caused by rarefaction causes a slight decrease in air pressure
98
Q
Does the traveling sound wave cause air to move outward from the speaker into the environment?
A
- Yes
- However, although air pressure changes move outward from the speaker, the air molecules at each location move back and forth but stay in about the same place
- What is transmitted is the pattern of increases and decreases in pressure that eventually reach the listener’s ear
99
Q
What’s a pure tone?
A
- A tone with pressure changes that can be described by a single sine wave
- A simple kind of sound wave
- A pure tone occurs when changes in air pressure occur in a pattern described by a mathematical function called a sine wave
- Tones with this pattern of pressure changes are occasionally found in the environment
- Ex: a person whistling or the high-pitched notes produced by a flute are close to pure tones
- Tuning forks, which are designed to vibrate with a sine-wave motion, also produce pure tones
- For laboratory studies of hearing, computers generate pure tones that cause a speaker diaphragm to vibrate in and out with a sine-wave motion. This vibration can be described by noting its frequency and its amplitude
- Pure tones are important because they are the fundamental building blocks of sounds, and have been used extensively in auditory research
- They’re rare in the environment
100
Q
What’s frequency?
A
- The number of times/cycles per second that pressure changes of a sound stimulus repeat
- Frequency is measured in Hertz, where 1 Hertz is one cycle per second
- Humans can perceive frequencies ranging from ~20 Hz to ~20,000 Hz, with higher frequencies usually being associated with higher pitches
101
Q
What’s amplitude?
A
- In the case of a repeating sound wave, such as the sine wave of a pure tone, amplitude represents the pressure difference between atmospheric pressure and the maximum pressure of the wave
- The size of the pressure change
- The range of amplitudes we can encounter in the environment is extremely large, ranging from a whisper to a jet taking off
- The amplitude of a sound wave is associated with the loudness of a sound
102
Q
What’s a Hertz (Hz)?
A
- The unit for designating the frequency of a tone
- One Hertz equals one cycle per second
103
Q
What kind of frequencies are associated with what kind of pitches?
A
- Higher frequencies are associated with the perception of higher pitches
- Lower frequencies are associated with the perception of lower pitches
104
Q
What would the difference in pressure between the high and low peaks of the sound wave indicate?
A
A sound’s amplitude
105
Q
What kind of amplitude is associated with what kind of loudness?
A
- Larger amplitude is associated with the perception of greater loudness (louder)
- Smaller amplitude is associated with the perception of smaller loudness (softer)
106
Q
Give an example of how large the range of amplitudes is
A
- If the pressure change plotted, in which the sine wave representing a near-threshold sound like a whisper is about 1/2-inch high on the page, then in order to plot the graph for a very loud sound, such as music at a rock concert, you would need to represent the sine wave by a curve several miles high
- Because this is somewhat impractical, auditory researchers have devised a unit of sound called the decibel (dB), which converts this large range of sound pressures into a more manageable scale
107
Q
What’s a decibel (dB)?
A
- Unit of sound
- Converts the large range of sound pressures into a more manageable scale
- Unit that indicates the pressure of a sound stimulus relative to a reference pressure: dB = 20 log (p/po) where p is the pressure of the tone and po is the reference pressure
- Uses logarithms to shrink the large range of sound pressures
- Ex: The range of sound pressures encountered in the environment ranges from 1 to 10,000,000, which in powers of 10 is a range of 7 log units
- Multiplying sound pressure by 10 causes an increase of 20 dB
- When the sound pressure increases from 1 to 10,000,000, the dBs increase only from 0 to 140
- This means that we don’t have to deal with graphs that are several miles high
108
Q
What term is used when specifying the sound pressure in decibels?
A
- When specifying the sound pressure in decibels, the notation SPL, for sound pressure level, is added to indicate that decibels were determined using the standard pressure of 20 micropascals
109
Q
What’s sound pressure level (SPL)?
A
A designation used to indicate that the reference pressure used for calculating a tone’s decibel rating is set at 20 micropascals, near the threshold in the most sensitive frequency range for hearing
110
Q
What’s level/sound level?
A
The pressure of a sound stimulus, expressed in decibels
111
Q
What’s a periodic waveform?
A
For the stimulus for hearing, a pattern of repeating pressure changes
112
Q
What’s the fundamental frequency of a tone?
A
- The first harmonic of a complex tone; usually the lowest frequency in the frequency spectrum of a complex tone
- The tone’s other components, called higher harmonics, have frequencies that are multiples of the fundamental frequency
113
Q
Complex tones are made up of what?
A
- Of a number of pure tone (sine-wave) components added together
- Each of these components is called a harmonic of the tone
114
Q
What’s a harmonic?
A
Pure-tone components of a complex tone that have frequencies that are multiples of the fundamental frequency
115
Q
What’s the first harmonic?
A
- A pure tone with frequency equal to the fundamental frequency of a complex tone
- Usually called the fundamental of the tone
116
Q
What are higher harmonics?
A
- Pure tones with frequencies that are whole-number (2, 3, 4, etc.) multiples of the fundamental frequency
- Ex: meaning that the second harmonic of a complex tone has a frequency of 200 x 2 = 400Hz, the third harmonic has a frequency of 200 x 3 = 600Hz, and so on
- These additional tones are the higher harmonics of the tone
117
Q
What does adding the fundamental and the higher harmonics together result in?
A
Results in the waveform of the complex tone
118
Q
What’s a frequency spectra?
A
- A plot that indicates the amplitudes of the various harmonics that make up a complex tone
- Each harmonic is indicated by a line that’s positioned along the frequency axis, with the height of the line indicating the amplitude of the harmonic
- Frequency spectra provide a way of indicating a complex tone’s fundamental frequency and harmonics that add up to the tone’s complex waveform
119
Q
Do all the harmonics need to be present for the repetition rate in a complex waveform to stay the same?
A
- No, not all the harmonics need to be present for the repetition rate to stay the same
- Ex: if we remove the first harmonic of a complex tone
- Removing a harmonic changes the tone’s waveform, but the rate of repetition remains the same
- Even though the fundamental is no longer present, the 200-Hz repetition rate corresponds to the frequency of the fundamental
- The same effect also occurs when removing higher harmonics
- If the 400-Hz second harmonic is removed, the tone’s waveform changes, but the repetition rate is still 200
- The spacing between harmonics equals the repetition rate
- When the fundamental is removed, this spacing remains, so there’s still information in the waveform indicating the frequency of the fundamental
120
Q
What’s the fundamental?
A
A pure tone with frequency equal to the fundamental frequency of a complex tone
121
Q
How can we measure the physical aspects of the sound stimulus?
A
By a sound meter that registers pressure changes in the air
122
Q
What are 2 perceptual dimensions of sound?
A
- Loudness -> involves differences in the perceived magnitude of a sound, illustrated by the difference between a whisper and a shout
- Pitch -> involves differences in the low to high quality of sounds, illustrated by what we hear playing notes from left to right on a piano keyboard
123
Q
What’s the threshold of sound?
A
The smallest amount of sound energy that can just barely be detected
124
Q
What’s loudness?
A
- The perceived intensity of a sound that ranges from “just audible” to “very loud”
- The quality of sound that ranges from soft to loud
- For a tone of a particular frequency, loudness usually increases with increasing decibels
- The perceptual quality most closely related to the level or amplitude of an auditory stimulus, which is expressed in decibels
- Decibels are often associated with loudness, which indicates that a sound of 0 dB SPL is just barely detectible and 120 dB SPL is extremely loud (and can cause permanent damage to the receptors inside the ear)
125
Q
Describe how S. S. Stevens used the magnitude estimation procedure to determine the relationship between level in decibels (physical) and loudness (perceptual)
A
- In this experiment, loudness was judged relative to a 40-dB SPL tone, which was assigned a value of 1
- Thus, a pure tone that sounds 10x louder than the 40-dB SPL tone would be judged to have a loudness of 10
- He found that increasing the sound level by 10 dB (from 40 to 50) almost doubles the sound’s loudness
126
Q
Is loudness only dependent on decibels?
A
- Loudness depends not only on decibels but also on frequency
- One way to appreciate the importance of frequency in the perception of loudness is to consider the audibility curve
127
Q
What’s the audibility curve?
A
- A curve that indicates the sound pressure level (SPL) at threshold for frequencies across the audible spectrum
- This audibility curve, which indicates the threshold for hearing VS frequency, indicates that we can hear sounds between about 20 Hz and 20,000 Hz and that we are most sensitive (the threshold for hearing is lowest) at frequencies between 2,000 and 4,000 Hz, which happens to be the range of frequencies that is most important for understanding speech
- At intensities below the audibility curve, we can’t hear a tone
128
Q
What does it mean for sounds to have low/high thresholds?
A
- Some frequencies have low thresholds -> it takes very little sound pressure change to hear them
- Other frequencies have high thresholds -> large changes in sound pressure are needed to make them heard
129
Q
What’s the auditory response area?
A
- The psychophysically measured area that defines the frequencies and sound pressure levels over which hearing functions (we can hear tones that fall within this area)
- This area extends between the audibility curve and the curve for the threshold of feeling (tones with these high amplitudes are the ones we can “feel”; they can become painful and can cause damage to the auditory system)
