Exam Questions Flashcards
A cardinal colour space was defined on the basis of
Note: Include 3 properties
Cardinal colour space consists of two chromatic axes (colour) and one achromatic axis (luminance)
- Psychophysically orthogonal
- ‘Excitation’ stage of processing
- The axes should not be termed red-green and blue-yellow or any other colour-name as they correspond to cone excitation
- BY: S-(L+M)
- RG: L-M
- Luminance: (L+M)+S
Orthogonality in the vector representation of signal-coding confers which of the following properties upon that stage of the system?
Cardinal Colour Space
- Threshold is only raised by adapting to a stimulus along the same axis; threshold is unaffected by adapting to other two axes
- Three independent detection mechanisms mediate the transmission of spatio-chromatic information from retina to cortex
The physiological basis for cardinal colour sensitivity is found in
LGN (P Cells)
First candidates were Retinal ganglion cells
The problem with colour vision is
2 things
- Simplest visual task involving coloured stimuli cannot be explained by what we currently know about the visual system, let alone the more complex observations we make all the time
- Excitation (neural properties) and sensation (what we experience) do not align because the cardinal axis and unique hue axis do not align
The term “opponency” refers to..
- When the bipolar cells wire up to retinal ganglion cells they wire up in an opponent mechanism which contributes to the colour after image we perceive. Red-Green and Blue-Yellow
- Receptors act in opposite ways to wavelengths associated with 2 pairs of colours
- Accounts for the perception of four primary colours and afterimages (the colours perceived after the complementary colours are removed)
- Adapation by Cardinal Neurons?
What is red?
- Subjective
- Uniquely definable in terms of wavelength of photon and something that is impossible to describe what the sensation is
- Can’t describe red without using the word ‘colour’ to someone who hasn’t seen red
- L Wave Length
Neurones in the LGN cannot be the physiological substrate for the cardinal axes because..
LGN neurones have cardinal colour signatures but don’t adapt
Cardinal behaviour (independent adaptability) can only be explained on the basis of a combination of LGN and cortical properties
Neurones in primary visual cortex (V1) cannot be the physiological substrate for the cardinal axes because..
V1 neurones do not have cardinal signatures but do adapt
Cardinal behaviour (independent adaptability) can only be explained on the basis of a combination of LGN and cortical properties
The fundamental crux of the argument between Hering and Helmholtz was..
Helmholtz
- Helmholtz suggested there were three receptors, sensitive each to red, green, and blue wavelength
Hering
- 4 receptors, sensitive each to red, green, blue, and yellow wavelengths, with these wired in pairs of red-green and blue-yellow
- First stage of colour vision could be a trichromatic stage and then an opponent stage
- Note: It is not mutually exclusive
The relationship between our experience and the ensemble of neural responses mediating that experience
Ensemble of neural responses are generally distributed and do not predict our experience (Perception and sensation do not always correlate)
The cardinal space are not the mechanisms that mediate our primary sense of colour
TheDress is an example of…
- Colour is context-dependent
- Each system (person) viewing the photo is unique, from the photoreceptor mosaic onward, and everyone does see their own version of the world
- Different sensation and perception
Colour constancy confers what benefits upon the organism
Color constancy is an example of subjectivism and a feature of the human colour perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions.
Colour categorisation is unique to each person, but colour discrimination remains relatively constant between people, which enables organisms to agree on colour differences despite seeing ostensibly different categorisations
In the context of the ‘local’ versus ‘distributed’ processing debate
Local processing
- Cardinal neurones would be in the retina and the LGN.
- They would be adapting nicely and they would be clustered along the axis and you would call that pinkish colour the red, greenish colour green, but we don’t.
Completely distributed
- Difficult to define fine motion. Having a distributed visual system in space and time would not be good for the detection of motion.
- No single neuron or group of neurons with a specific role of mediating a specific sensation or experience.
The Jennifer Aniston neurone is….
- Grandmother cells that respond selectively to a stimulus such as Jennier Aniston and Halle Berry
- Hypothetical neuron that represents a complex but specific concept or object
- An extreme version of the idea of local processing (single neuron level)
A cardinal colour is….
A cardinal colour is in relation to categorised vs. discriminated colours
No common category structure in colour until we tell people to learn colour.
