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What is the pathway that extends from the retina to the primary visual cortex?
What is the pathway that extends from the retina to the primary visual cortex?
What type of ganglion cells are responsible for our perception of colour?
What type of ganglion cells are responsible for our perception of colour?
Which type of ganglion cells project to the two magnocellular layers of the LGN?
Which type of ganglion cells project to the two magnocellular layers of the LGN?
What is the primary function of the magnocellular pathway?
What is the primary function of the magnocellular pathway?
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What is the primary function of the parvocellular pathway?
What is the primary function of the parvocellular pathway?
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What is the primary function of rods in the retina?
What is the primary function of rods in the retina?
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What is the characteristic of magnocellular ganglion cells?
What is the characteristic of magnocellular ganglion cells?
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What is the role of the luminance channel in colour processing?
What is the role of the luminance channel in colour processing?
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What is the function of cones in the retina?
What is the function of cones in the retina?
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What is the function of the geniculostriate pathway?
What is the function of the geniculostriate pathway?
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What type of cells are C-units and L-units?
What type of cells are C-units and L-units?
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What is the characteristic of the C-units?
What is the characteristic of the C-units?
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What is the characteristic of the L-units?
What is the characteristic of the L-units?
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How do rods converge on bipolar cells?
How do rods converge on bipolar cells?
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What is the primary benefit of bipolar cells in the retina?
What is the primary benefit of bipolar cells in the retina?
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What type of bipolar cells are attached to rods?
What type of bipolar cells are attached to rods?
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What is the primary purpose of the experiments conducted by Young and Helmholtz?
What is the primary purpose of the experiments conducted by Young and Helmholtz?
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What is the primary function of dark/light ganglion cells?
What is the primary function of dark/light ganglion cells?
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What is the main idea behind the opponent-process theory?
What is the main idea behind the opponent-process theory?
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What is the difference between dark/light ganglion cells and white/not white cells?
What is the difference between dark/light ganglion cells and white/not white cells?
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What would trigger a dark/light ganglion cell?
What would trigger a dark/light ganglion cell?
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How many different wavelengths are needed to match any other wavelength in the visible spectrum?
How many different wavelengths are needed to match any other wavelength in the visible spectrum?
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What is the benefit of having a single cone in the retina?
What is the benefit of having a single cone in the retina?
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What is the name of the scientist who developed the opponent-process theory?
What is the name of the scientist who developed the opponent-process theory?
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Why do rods distinguish slightly lighter shapes on a darker background better than they distinguish slightly darker shapes on lighter backgrounds?
Why do rods distinguish slightly lighter shapes on a darker background better than they distinguish slightly darker shapes on lighter backgrounds?
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What is the purpose of the test field in the experiments conducted by Young and Helmholtz?
What is the purpose of the test field in the experiments conducted by Young and Helmholtz?
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What is the role of white/not white cells in the retina?
What is the role of white/not white cells in the retina?
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What is the relationship between the trichromatic theory and the opponent-process theory?
What is the relationship between the trichromatic theory and the opponent-process theory?
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What is the result of activating one member of an opposing color pair in the opponent-process theory?
What is the result of activating one member of an opposing color pair in the opponent-process theory?
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What are the three opposing color pairs in the opponent-process theory?
What are the three opposing color pairs in the opponent-process theory?
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What does Newton's colour circle provide in the context of colour matches?
What does Newton's colour circle provide in the context of colour matches?
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What is the purpose of adding the third primary colour in a colour match?
What is the purpose of adding the third primary colour in a colour match?
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What is the name of the theory that explains colour vision and is supported by colour matching and colour mixing studies?
What is the name of the theory that explains colour vision and is supported by colour matching and colour mixing studies?
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What is the result of adding the third primary colour to a colour mixture?
What is the result of adding the third primary colour to a colour mixture?
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What is the purpose of using 'negative' colours in colour matches?
What is the purpose of using 'negative' colours in colour matches?
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What is the alternative name of the trichromatic theory?
What is the alternative name of the trichromatic theory?
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What is the minimum number of colours required to make a colour match?
What is the minimum number of colours required to make a colour match?
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What is the result of using blue and green primaries alone to match a spectral colour of 500 nm?
What is the result of using blue and green primaries alone to match a spectral colour of 500 nm?
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Study Notes
Colour Vision Theories
- The trichromatic theory and the opponent-process theory are two complementary theories that explain processes operating at different levels of the visual system.
- The trichromatic theory states that three different wavelengths (i.e., primaries) are needed to match any other wavelength in the visible spectrum.
- Individuals with normal colour vision need three different wavelengths to match any other wavelength in the visible spectrum.
Opponent-Process Theory
- Developed by Ewald Hering in 1920/1964
- The theory states that cone photoreceptors are linked together to form three opposing colour pairs:
- Blue/yellow
- Red/green
- Black/white
- Activation of one member of the pair inhibits activity in the other.
The Retina's Role in Colour Vision
- The retina contains two types of photoreceptors: rods and cones.
- Rods are more numerous than cones, converge at high rates, and have poor acuity but are suitable for mediating perception in low illuminance (i.e., scotopic) conditions.
- Rods are colour-blind.
- Cones are sensitive to colour information and are responsible for acuity and vision in daylight (i.e., photopic) conditions.
- Cones feed into three neural channels for colour processing, each composed of opponent pairs:
- Red-green
- Yellow-blue
- Black-white
- The first two mediate the perception of hue and form, while the latter is responsible for brightness and darkness (i.e., luminance).
The Geniculostriate Visual Pathways
- The geniculostriate is the primary visual pathway for the processing of form and colour.
- It extends from the retina through the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex (i.e., V1).
- The slow-conducting parvocellular pathway mediates our perception of colour and acuity.
- The fast-conducting magnocellular pathway is responsible for our perception of stimulus change (including motion) and is largely colour-blind.
Chromaticity System
- Newton's colour circle provides a qualitative description of colour matches.
- It can be used to explain why two colours may not be sufficient to make colour matches and also the use of 'negative' colours.
- The addition of a third primary is necessary to desaturate the colour mixture and make the match.
- Negative tristimulus values result when the third primary is added to desaturate the colour mixture.
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