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Questions and Answers
What wavelength corresponds to unique blue?
What wavelength corresponds to unique blue?
Which pathway is excited by green and inhibited by red?
Which pathway is excited by green and inhibited by red?
Which phenomenon involves the perception of a surrounded color shifting towards its complementary color?
Which phenomenon involves the perception of a surrounded color shifting towards its complementary color?
What happens during photopigment bleaching?
What happens during photopigment bleaching?
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Which of the following color perception processes supports the opponent mechanism theory?
Which of the following color perception processes supports the opponent mechanism theory?
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Which condition is characterized by total colour blindness and the presence of only one type of cones or only rods?
Which condition is characterized by total colour blindness and the presence of only one type of cones or only rods?
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Protanopia is categorized under which type of color vision deficiency?
Protanopia is categorized under which type of color vision deficiency?
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In the context of colour perception, the term 'opponency' refers to which of the following?
In the context of colour perception, the term 'opponency' refers to which of the following?
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Which type of color vision deficiency is caused by missing S-cones?
Which type of color vision deficiency is caused by missing S-cones?
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What experimental technique allows a person to cancel out the perception of a particular color by adding light of another color?
What experimental technique allows a person to cancel out the perception of a particular color by adding light of another color?
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Which of the following best describes anomalous trichromacy?
Which of the following best describes anomalous trichromacy?
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The mechanisms for colour opponency include distinctions between which of the following pairs?
The mechanisms for colour opponency include distinctions between which of the following pairs?
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What is the primary function of cones in the human eye?
What is the primary function of cones in the human eye?
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What happens with achromatic light?
What happens with achromatic light?
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What is the principle of univariance regarding photoreceptors?
What is the principle of univariance regarding photoreceptors?
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How does additive color mixing work?
How does additive color mixing work?
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Which type of color vision deficiency involves having only two types of cones?
Which type of color vision deficiency involves having only two types of cones?
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What defines spectral reflectance?
What defines spectral reflectance?
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What is the main distinguishing factor between additive and subtractive color mixing?
What is the main distinguishing factor between additive and subtractive color mixing?
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In the context of color perception, what role does saturation play?
In the context of color perception, what role does saturation play?
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Which statement best describes the function of the color circle?
Which statement best describes the function of the color circle?
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Cortical achromatopsia is caused by genetic factors affecting the cones in the eyes.
Cortical achromatopsia is caused by genetic factors affecting the cones in the eyes.
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What are the two types of monochromacy?
What are the two types of monochromacy?
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Hue cancellation is an experimental technique used to cancel out a particular color by adding light of another ______.
Hue cancellation is an experimental technique used to cancel out a particular color by adding light of another ______.
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Match the following types of dichromacy with the type of cones that are missing:
Match the following types of dichromacy with the type of cones that are missing:
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What is the role of the +S-ML pathway?
What is the role of the +S-ML pathway?
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Colour contrast involves the perception of a surrounded color as shifted toward its complementary color.
Colour contrast involves the perception of a surrounded color as shifted toward its complementary color.
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What is chromatic adaptation?
What is chromatic adaptation?
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The wavelength for unique yellow is _____ nm.
The wavelength for unique yellow is _____ nm.
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Match the following pathways with their excitation and inhibition properties:
Match the following pathways with their excitation and inhibition properties:
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Which of the following correctly describes the visible light spectrum for humans?
Which of the following correctly describes the visible light spectrum for humans?
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Achromatic light is perceived as colorless.
Achromatic light is perceived as colorless.
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What are the three primary additive colors?
What are the three primary additive colors?
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The ______ is the color most closely associated with the wavelength of light.
The ______ is the color most closely associated with the wavelength of light.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which phenomenon describes the perception of different colors despite different physical stimuli?
Which phenomenon describes the perception of different colors despite different physical stimuli?
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Most humans have two types of cones in their eyes.
Most humans have two types of cones in their eyes.
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What principle explains that a single type of photoreceptor cannot distinguish between different wavelengths of light?
What principle explains that a single type of photoreceptor cannot distinguish between different wavelengths of light?
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___ is the perceived intensity of light.
___ is the perceived intensity of light.
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What limits the ability to match wavelengths with only two primary colors?
What limits the ability to match wavelengths with only two primary colors?
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What do parvocellular layers primarily process?
What do parvocellular layers primarily process?
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Lightness constancy refers to the perception of a surface maintaining the same color regardless of the light conditions.
Lightness constancy refers to the perception of a surface maintaining the same color regardless of the light conditions.
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What is the term for the probability that a cone's photopigment will absorb a photon of light at a given wavelength?
What is the term for the probability that a cone's photopigment will absorb a photon of light at a given wavelength?
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The tendency to see a surface as maintaining the same lightness under different illumination levels is known as ______.
The tendency to see a surface as maintaining the same lightness under different illumination levels is known as ______.
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Match the following types of pathways with their functions:
Match the following types of pathways with their functions:
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Which layer of the striate cortex receives input from the parvocellular pathway?
Which layer of the striate cortex receives input from the parvocellular pathway?
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What phenomenon describes the tendency to perceive a color as the same under varying light conditions?
What phenomenon describes the tendency to perceive a color as the same under varying light conditions?
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Which statement is true regarding the function of double opponent cells in V1?
Which statement is true regarding the function of double opponent cells in V1?
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Which layers of the LGN process color information from the S-ML pathway?
Which layers of the LGN process color information from the S-ML pathway?
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What aspect of surface perception is involved in lightness constancy?
What aspect of surface perception is involved in lightness constancy?
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Study Notes
Monochromacy
- A rare condition where individuals experience total color blindness.
- Only have one type of cone, or only rods.
- Rod monochromacy: Only rods, no cones. This leads to poor spatial acuity and no color vision.
- Cone monochromacy: Have rods and one type of cone.
Dichromacy
- Individuals have only two cones.
- Three types depending on which cone is missing:
- Protanopia (X-linked): L-cones are missing.
- Deuteranopia (X-linked): M-cones are missing.
- Tritanopia: S-cones are missing.
Anomalous Trichromacy
- L and M cones are too close together.
- This makes it difficult to differentiate between their responses.
- Results in difficulty distinguishing certain colors.
Cortical Achromatopsia
- Loss of color vision due to brain damage.
- Damage to color-processing areas in the brain.
Color Opponency
- No single cone can correctly signal for color.
- Three mechanisms (distinct from cone types) result in color opponency:
- Red/green
- Blue/yellow
- Black/white
Hue Cancellation:
- An experimental technique to cancel out the perception of a specific color.
- Achieved by adding light of another color.
Color Vision:
- The ability to see differences between lights of different wavelengths.
- Objects don't have color, it's how our eyes interact with light reflected from surfaces.
Light and Color
- Electromagnetic Spectrum: Range of all electromagnetic radiation.
-
Visible Light: The only wavelengths that humans perceive (400 nm - 700 nm).
- Gamma waves: Very high energy.
- Radio waves: Very low energy.
-
Light is an electromagnetic wave.
- Different wavelengths are perceived as different colors.
-
Heterochromatic Light: Consists of many wavelengths.
- Perceived as the color corresponding to the dominant wavelength.
-
Achromatic light: No dominant wavelength.
- Perceived as colorless (e.g., white, gray, black).
Additive Color
- Creating different color perceptions by mixing primary colors.
- Works best with pure monochromatic light.
- Used in digital displays (screens).
Subtractive Color
- Relies on light absorption.
- Color is determined by the wavelengths absorbed.
- Used for mixing paints and inks.
Spectral Power Distribution:
- Intensity (power) of light at each wavelength in the visible spectrum.
Color Dimensions
- Hue: Color most closely associated with the wavelength of light.
- Saturation: Purity or vividness of the hue.
- Brightness: Perceived intensity of the light.
- Color Circle: 2D depiction of hues around the circumference and saturation along any radius.
- Color Solid: 3D depiction of the color circle with brightness varying vertically.
- CIE Color Space: Standardized color space where any color can be represented by coordinates (x,y).
Color & Wavelength
-
Spectral Reflectance: Proportion of light that a surface reflects at each wavelength.
- Perceived color depends on how surfaces reflect light.
- Reflectance is determined by the molecular structure of the surface.
Seeing in Color
- Primary Colors: Needed to match any other color.
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Metamers: Two physically different stimuli that are perceived as the same color.
- With three primary colors, any wavelength can be matched. Not possible with only two.
Cones and Color
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Spectral Sensitivity Function: Probability that a cone's photopigment will absorb a photon and trigger an action potential.
- Represents the likelihood of a photoreceptor responding to a given wavelength.
- One type of photoreceptor can't distinguish different wavelengths (it generates the same signal).
- To differentiate, we need different sensitivities to different wavelengths.
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Principle of Univariance: Absorption of a photon results in the same response regardless of wavelength.
- Applies to rods, meaning night vision is colorblind.
Trichromacy
- Most humans have three types of cones with different sensitivities.
- Dichromats: Other mammals have two types of cones.
- Tetrachromats: Some birds have four types of cones.
- Hedecachromats: Mantis shrimp have sixteen types of cones.
Cone Distribution in the Retina:
- L-cones: Higher concentration.
- M-cones: High concentration.
- S-cones: Lower concentration.
Color Deficiencies
-
Inherited Deficiencies:
- Unique Green: A color that appears neither yellow nor blue when green is absent.
Unique/Pure Color Wavelengths
- Unique Blue: 477 nm
- Unique Green: 510 nm
- Unique Yellow: 580 nm
- Unique Red: Does not have a specific point on the spectrum.
Opponent Ganglion Cells
- Three types of cones (S, M, L) form excitatory or inhibitory connections with ganglion cells, creating "opponent channels".
- These circuits act as the opponent mechanisms (red/green, blue/yellow).
Opponent Channels
-
+S-ML Pathway: Fires above baseline for short-wavelength light (+S), below baseline for medium and long wavelengths (-ML).
- Excited by blue.
- Inhibited by green and red.
- Spatially uniform receptive field.
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+ML-S Pathway: Fires above baseline for medium to long wavelengths (+ML), below baseline for short wavelengths (-S).
- Excited by green and red.
- Inhibited by blue.
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+L-M Pathway: Fires above baseline for long wavelengths (+L), below baseline for medium wavelengths (-M).
- Annular receptive fields (similar to on/off center but without inhibition).
- Excited by red
- Inhibited by green.
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+M-L Pathway: Fires above baseline for medium wavelengths (+M), below baseline for long wavelengths (-L).
- Excited by green.
- Inhibited by red.
Color Afterimages and Opponency
- Photopigment Bleaching: Photopigment molecule loses its ability to absorb light for a period after being activated by light.
- Chromatic Adaptation: Type of photopigment bleaching due to exposure to intense light within a narrow range of wavelengths.
Color Contrast
- The perception of a surrounded color as shifted towards the complement of the surrounding color.
- Provides support for opponent mechanisms.
Color Assimilation
- The perception of a surrounded color as shifted towards a noncomplementary surrounding color.
Colour Vision
- Colour vision is the ability to differentiate between light of different wavelengths.
- Objects don’t have colour but rather reflect wavelengths of light which interact with receptors in our eyes.
Light and Colour
- Electromagnetic spectrum: range of all types of electromagnetic radiation.
- Visible light: the only part of the spectrum that humans can see (400nm - 700nm)
- Light is an electromagnetic wave.
- Different wavelengths of light are perceived as different colours.
- Heterochromatic light: light with many wavelengths.
- Achromatic light: light with no dominant wavelength.
- Spectral power distribution: describes the intensity (power) of light at every wavelength within the visible spectrum.
Colour Dimensions
- Hue: colour we perceive.
- Saturation: purity of a hue.
- Brightness: perceived intensity of light.
- Colour circle: 2D representation of colours and saturation.
- Colour solid: 3D depiction of the colour circle with brightness represented on the vertical axis.
- CIE colour space: 3D representation of all colours.
Seeing in Colour
- Spectral reflectance: proportion of light reflected by a surface at each wavelength.
- Perceived colour depends on how an object reflects light.
- Molecular structure of a surface determines its reflectance.
- Metamers: 2 physically different stimuli that appear identical.
Cones and colour
- Spectral sensitivity function: probability that a cone's photopigment will absorb a photon of light at any given wavelength and produce an action potential.
- A single type of photoreceptor cannot distinguish between different wavelengths of light.
- Principle of univariance: absorption of a photon of light always produces the same response, regardless of wavelength.
- Trichromacy: theory that most humans have 3 types of cones with different sensitivities.
- Dichromacy: only have 2 types of cones.
- Tetrachromacy: have 4 types of cones.
- At least 2 cones with different sensitivities need to be stimulated to perceive colour.
- Cone distribution in the retina:
- Higher density of L-cones.
- High density of M-cones.
- Lower density of S-cones.
-
Colour Deficiencies
- Monochromacy (achromatopsia): Total colour blindness.
- Dichromacy: Only have 2 types of cones.
- Anomalous trichromacy: L and M cones are too close together, making it difficult to differentiate between their responses.
- Cortical Achromatopsia: Loss of colour vision due to brain damage.
Colour Opponency
- Opponent channels: 3 distinct mechanisms that create opponency between:
- Red/Green
- Blue/Yellow
- Black/White
- Hue cancellation: Technique that cancels out a colour perception by adding another colour.
- Unique green
- Unique blue
- Unique yellow
- Unique red
Opponent Ganglion Cells
- S= short wavelength
- M= medium wavelength
- L= long wavelength
- S-ML Pathway: Responds to short-wavelength light positively (+S) and medium-long wavelength light negatively (-ML), excited by blue, inhibited by green and red.
- +ML-S Pathway: Responds to medium-long wavelength light positively (+ML) and short wavelength light negatively (-S), excited by green and red, inhibited by blue.
- +L-M Pathway: Responds to long-wavelength light positively (+L) and medium-wavelength light negatively (-M) with an annular receptive field, excited by red, inhibited by green.
- +M-L Pathway: Responds to medium-wavelength light positively (+M) and long-wavelength light negatively (-L) , excited by green, inhibited by red.
- Colour afterimages and opponent cells are a result of photopigment bleaching and chromatic adaptation.
Colour Contrast and Assimilation
- Colour contrast: When a colour is perceived as shifted towards the complement of a surrounding colour.
- Colour assimilation: When a colour is perceived shifted towards a non-complementary colour.
Spectral Power Distribution
- Describes the intensity or power of light at each wavelength within the visible spectrum.
CIE Colour Space
- A standardized system for representing colors, where any color can be defined using a pair of (x,y) coordinates.
Spectral Sensitivity Function
- Represents the probability of a cone's photopigment absorbing a photon of light at any given wavelength and triggering an action potential.
- Indicates the likelihood of a cone generating an action potential for a specific wavelength.
Colour Perception
- A single type of photoreceptor cannot distinguish between different wavelengths of light.
- Photoreceptors will produce the same neural signal for different wavelengths.
- Color perception depends on the relative activity of different types of cones.
Colour Assimilation
- The perception of a surrounded color being shifted towards a non-complementary surrounding color.
- An example of how color perception is influenced by its context.
Colour Constancy
- The tendency to perceive a surface as having the same color under different lighting conditions.
- A remarkable ability of the visual system to maintain stable color perception despite varying light sources.
Lightness
- The perceived reflectance of a surface.
- A measure of how bright a surface appears.
Lightness Constancy
- Tendency to perceive a surface as having the same lightness, even when illuminated by significantly different amounts of light.
- Another example of the visual system's ability to maintain stable perception despite changing conditions.
Color Processing in the LGN
- Parvocellular layers process the +L-M pathway (red-green opponent channel).
- Koniocellular layers process the +S-LM pathway (blue-yellow opponent channel).
- Magnocellular layers process luminance information but not color.
Color Processing in V1
- Parvocellular projections reach layer 4Cβ of the striate cortex.
- +L-M pathway information is then sent to layer 3 within the blobs.
- Koniocellular projections reach layer 4 of the striate cortex directly, also targeting the blobs.
- Double opponent cells in V1 are inhibited when the preferred center color is presented in the surround.
- These cells are crucial for detecting color differences in the environment, even under constant luminance.
Spectral Power Distribution
- Defines the intensity (power) of light at each wavelength within the visible spectrum.
CIE Colour Space
- Standardized colour space that represents any color using coordinates (x, y)
Spectral Sensitivity Function
- Represents the probability that a cone's photopigment will absorb a photon of light at a given wavelength and generate an action potential.
- Indicates the rate of action potentials triggered by different wavelengths.
Colour Perception
- A single type of photoreceptor can't distinguish between different wavelengths of light.
- Photoreceptor produces the same neural signal regardless of specific wavelength.
- Less intense light at a wavelength it's sensitive to can be perceived as the same color as more intense light at a wavelength it's less sensitive to.
Colour Assimilation
- The perception of a surrounded color is shifted towards a non-complementary surrounding color.
Colour Constancy
- The tendency to perceive a surface as having the same color despite illumination with varying spectral power distributions.
Lightness
- The perceived reflectance of a surface.
Lightness Constancy
- The tendency to see a surface as having the same lightness under illumination by varying amounts of light.
Colour Processing in the LGN
- Parvocellular layers process the +L-M pathway.
- Koniocellular layers process the +S-ML pathway.
- Magnocellular layers do not process color information, focus on luminance.
Colour Processing in V1
- Parvocellular layer projects to layer 4C𝛽 of the striate cortex: processes +L-M pathway.
- Sends axons to layer 3 within the blobs.
- Koniocellular layers project directly to layer 4 of the striate cortex: processes +S-ML pathway.
- Projects directly to within the blobs.
Double Opponent Cells in V1
- Inhibited if the preferred center color is presented in the surround.
- Ideal for detecting color differences in the environment even without luminance differences.
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Description
Explore the various types of color vision deficiencies like monochromacy, dichromacy, and anomalous trichromacy. Understand the implications of each condition and how they relate to the brain's processing of color. This quiz delves into the physiological and neurological aspects of color blindness.
