Colour Vision
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Questions and Answers

What does the term 'saturation' refer to in the context of color dimensions?

  • The intensity or luminance of a color, from dark to light.
  • The spatial arrangement of colors based on their perceived relationships
  • The purity of a color, ranging from gray to vivid. (correct)
  • The color itself, as it changes around the color circle.

According to the CIE chromaticity diagram, where are the most saturated colors located?

  • At the center of the diagram.
  • Along the straight lines connecting any two primary wavelengths.
  • Along the perimeter of the curve, also known as the spectral locus. (correct)
  • Near the neutral or white (W) point.

What does the straight line connecting two primary wavelengths on the CIE chromaticity diagram represent?

  • The progression from dark to light.
  • The range of colors produced by mixing those two wavelengths. (correct)
  • The complementary colors of the spectrum.
  • The area where saturation is highest.

In the context of a computer monitor's color production, what does the triangle formed by the primary colors R, G, and B represent?

<p>The range of colors the monitor can produce, known as the 'gamut'. (D)</p> Signup and view all the answers

Which of the following is NOT considered a basic or primary color according to the content?

<p>ORANGE (C)</p> Signup and view all the answers

What is the primary role of the macula lutea in the eye?

<p>To absorb excess blue and UV light, acting as a natural sunblock. (B)</p> Signup and view all the answers

According to the principle of univariance, why can a single photoreceptor not differentiate between changes in wavelength and intensity?

<p>Because a single receptor responds the same way to different combinations of wavelength and intensity. (C)</p> Signup and view all the answers

What is the Purkinje effect or shift?

<p>The tendency for the peak luminance sensitivity of the eye to shift towards the blue end of the spectrum as light levels decrease. (D)</p> Signup and view all the answers

In a standard human retina, what is the approximate ratio of long (L), medium (M), and short (S) wavelength cone photoreceptors?

<p>8:4:1 (C)</p> Signup and view all the answers

What is a key distinction between additive and subtractive color mixing?

<p>Additive mixing involves the mixing of lights of differing wavelengths, while subtractive mixing involves mixing paints with different pigments. (A)</p> Signup and view all the answers

What is the consequence of the human visual system representing colour using only three cones?

<p>It means two objects can appear the same even when their spectral power distributions differ. (B)</p> Signup and view all the answers

In a colour matching experiment, what does it mean when two fields are a ‘pair of metamers’?

<p>The two fields have different spectra but are perceived the same. (B)</p> Signup and view all the answers

Why do illuminant metameric failures occur?

<p>Because colour samples match under one light source but not under another. (D)</p> Signup and view all the answers

Which statement accurately describes the distribution of blue cones in the retina?

<p>They are found predominantly in a ring around the edge of the fovea. (A)</p> Signup and view all the answers

What is the minimum number of wavelengths needed to match colors by individuals with normal colour vision?

<p>Three (B)</p> Signup and view all the answers

What condition is characterized by individuals having a reduced sensitivity to red light?

<p>Protanomaly (C)</p> Signup and view all the answers

Which type of colour deficiency is inherited as an autosomal trait?

<p>Tritanomaly (B)</p> Signup and view all the answers

What is the prevalence of congenital Deuteranomaly among affected males?

<p>5% (D)</p> Signup and view all the answers

What visual assessment tool uses pseudo chromatic plates to diagnose colour vision deficiencies?

<p>Ishihara Test (C)</p> Signup and view all the answers

Which of the following statements about monochromacy is accurate?

<p>Monochromacy results in a complete inability to see colour (B)</p> Signup and view all the answers

What is a characteristic of Tritan deficiency?

<p>Struggles to differentiate between blue and green hues (A)</p> Signup and view all the answers

Which of the following ocular conditions is not typically associated with acquired colour vision deficiency?

<p>Congenital Deuteranomaly (C)</p> Signup and view all the answers

In terms of genetic inheritance, how is congenital Protan colour vision deficiency inherited?

<p>Recessive X-linked (C)</p> Signup and view all the answers

What is the primary function of the three cone classes in colour detection?

<p>To provide the foundation for the perception of all colours (A)</p> Signup and view all the answers

Hering's Colour Opponent Theory suggests that which pairs of colours oppose each other?

<p>Blue and Yellow, Red and Green (B)</p> Signup and view all the answers

What defines a person with red-green colour deficiency?

<p>They find it hard to differentiate between red and green hues (D)</p> Signup and view all the answers

Which location is responsible for processing information regarding form and colour through parvocellular neurones?

<p>LGN (B)</p> Signup and view all the answers

What behaviour is associated with colour opponency at the level of retinal ganglion cells?

<p>Simultaneous colour contrast (B)</p> Signup and view all the answers

In cortical processing, what happens in the V1 and V2 areas regarding receptive fields?

<p>They maintain circular colour opponent receptive fields (C)</p> Signup and view all the answers

Which mechanism is not part of the two stages of colour processing described?

<p>Multichromatic channel (C)</p> Signup and view all the answers

What is the key factor leading to colour deficiencies?

<p>Reduced sensitivity to specific wavelengths of light (B)</p> Signup and view all the answers

Flashcards

Lightness

The intensity or brightness of a color, ranging from dark to light.

Saturation

The purity or vividness of a color, ranging from gray to a pure, strong color.

Hue

The actual name of a color, like red, green, or blue. It changes around a circle.

CIE Chromaticity Diagram

A diagram that represents all the colors visible to the human eye. It shows hue and saturation.

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Trichromatic Theory of Color Vision

A theory that explains how we see color using three types of cone cells in the eye: red, green, and blue.

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Duplicity Theory of Vision

The theory that explains how the eye works by describing two main photoreceptor types responsible for vision: rods and cones.

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Dark Adaptation

The process of adjusting your vision from a bright environment to a darker one. It takes longer compared to light adaptation.

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Rods

Photoreceptors responsible for vision in low-light conditions. They are more sensitive to light and primarily operate in scotopic and mesopic conditions.

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Protanomaly

A specific type of color vision deficiency where individuals have decreased sensitivity to red light, making it difficult to distinguish red from green.

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Cones

Photoreceptors responsible for vision in bright light conditions and color perception. They are less sensitive to light and primarily operate in photopic conditions.

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Purkinje Shift

The tendency for our peak luminance sensitivity to shift towards blue colors as we adapt to dim lighting.

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Deuteranomaly

A specific type of color vision deficiency where individuals have decreased sensitivity to green light, making it difficult to distinguish red from green.

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Blue-yellow Colour Deficiency

A color vision deficiency where individuals have difficulty differentiating between blue and green hues, as well as between yellow and red hues.

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Macula Lutea

A natural yellow pigment found in the macula of the eye. It absorbs blue and UV light, protecting the eye just like sunglasses.

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Tritanomaly

A type of color vision deficiency where individuals have reduced sensitivity to blue light.

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Color Vision

The unique ability of the human eye to see colors. It is derived from the combined responses of different types of cone photoreceptors, each sensitive to specific wavelengths.

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Metamers

Colors that appear the same despite having different spectral compositions.

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Monochromacy

A severe form of color vision deficiency where individuals lack most or all color perception, resulting in complete or near-complete color blindness.

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Protan

A type of color vision deficiency where an individual is missing or has an altered sensitivity to the red cone, leading to difficulties distinguishing red from green.

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Principle of Univariance

The principle that states that a single photoreceptor cell can be activated by different combinations of wavelength and intensity. This means that it can't independently determine the color of a stimulus.

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Additive Color Mixing

The process of mixing different wavelengths of light to create new colors. Adding light results in a brighter combination.

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Deutan

A type of color vision deficiency where an individual is missing or has an altered sensitivity to the green cone, leading to difficulties distinguishing red from green.

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Tritan

A type of color vision deficiency where an individual is missing or has an altered sensitivity to the blue cone, leading to difficulties distinguishing blue from green.

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Hering's Opponent Color Theory

The theory that color vision is caused by opposing responses of blue/yellow and red/green.

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S-Cone

This class of cone receptor absorbs maximally at 420nm and is sensitive to short wavelengths, providing blue hues.

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M-Cone

One of the three cone types responsible for color vision. It's most sensitive to medium wavelengths and contributes to green hues.

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L-Cone

This cone class absorbs maximally at 565nm and is sensitive to long wavelengths, contributing to red hues.

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Red-Green Colour Deficiency

A type of colour deficiency where individuals have difficulty distinguishing between red and green hues. Most common type.

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Double Opponent Receptive Field

This refers to the process in which a color opponent cell responds to a specific color in the center of its receptive field, and to the opposite color in the surrounding area.

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Cortical Processing (V1, V2, V4)

Part of the brain responsible for processing visual information including color. It contains cells that respond selectively to colour.

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Parvocellular Neuron

A type of visual neuron in the LGN that carries information about form and colour. It has similar receptive field properties to retinal ganglion cells.

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Study Notes

Colour Vision

  • Photoreceptor Types: There are two main classes of photoreceptors, as shown by the duplicity theory of vision.
  • Light Adaptation: Faster than dark adaptation.
  • Dark Adaptation: The slow recovery of visual sensitivity in low light after exposure to bright light. This process depends on the regeneration of rod pigment.
  • Rod Function: Rods operate primarily in dim light conditions (mesopic and scotopic levels).
  • Visible Light Spectrum: The human eye responds to wavelengths between 360-760 nm , producing different colour sensations.
  • White Light Composition: White light or sunlight is composed of many different wavelengths.
  • Colour Perception: Colour is perceived by the interaction of light wavelengths with the eyes.
  • Additive Colour Mixing: Mixing different wavelengths of light creates new colours.
  • Subtractive Colour Mixing: Mixing pigments subtracts wavelengths of light creating new colours.
  • Spectral Sensitivity: Cones have sensitivity peaks at different wavelengths (long, medium, short).
  • L/M/S cones: Different cone types respond to different wavelengths allowing for colour discrimination. (L:M:S = 8:4:1).

Cone Distribution

  • Cone types: 5-10% of cones in eyes are blue cones.
  • Red/Green Ratio: Ratio of red and green cones is approximately 2:1.
  • Cone distribution in fovea: Mostly densely packed near the centre
  • Randomly mixed: Small patches of cones are clustered randomly.
  • Cone colour experiments: The observer adjusts the amount of mixed wavelengths to match a single wavelength colour.

Colour Matching

  • Metamers: Two objects can appear the same colour even if their spectral power distributions are different.
  • Human visual system: Represents and processes colour using three cones reducing colour inputs to a code of three sensory outputs.
  • Cone absorption spectra: The principle of univariance dictates that a single photoreceptor cannot distinguish between different wavelengths.
  • How to describe colours: Basic colours such as red, yellow, green, and blue, and combinations of these in a circle showing perceptual relationships.

CIE Chromaticity Diagram

  • CIE (International Commission on Illumination): Standardization of colour representation.
  • Chromatic colour representation: 2D representation of hues and saturation (saturation decreases towards white point).
  • Pure spectral colours: Are along the perimeter of the curve.
  • Additive mixture of wavelengths: Straight line connecting the two wavelengths on the diagram.
  • Complementary colours: On opposite ends of the diagram.

Trichromatic Theory

  • Three cone types: S, M, and L cones (short, medium, long wavelength absorption).
  • Responses across cone types: Responsible for perception of a broad range of colours.
  • Cone spectral sensitivity: Relative amount of light per wavelength absorbed by each type of cone.

Hering's Colour Opponent Theory

  • Opponent colour responses: Blue-Yellow and Red-Green (opponent colour mechanisms).
  • Retinal ganglion cells maintain circular opponent receptive fields.
  • V1 and V2:Maintain circular colour opponent receptive fields.
  • V4 (ventral pathway): Colour-selective cells.

Colour Deficiencies

  • Inherited: Common, often genetic or hereditary.
  • Red-Green deficiencies: Most prevalent, difficulty distinguishing between red and green.
  • Protanomaly: Reduced red cone sensitivity.
  • Deuteranomaly: Reduced green cone sensitivity.
  • Tritanomaly: Reduced blue cone sensitivity.
  • Monochromacy: Extreme cases of colour blindness (only one cone type functioning).
  • Colour matching tests: Tools used for assessment of colour vision
  • Ishihara plates: A widely used test that consists of coloured plates for diagnostics.

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OPT 404 - Color Vision PDF

Description

Explore the fascinating world of colour vision through this quiz. Understand the roles of photoreceptors, light adaptation, and how we perceive different wavelengths of light. Test your knowledge on additive and subtractive colour mixing and the visible light spectrum.

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