Lecture 17 Vision II Flashcards
What light properties are used to create colour?
How is colour perception formed in the brain?
The intensity of the wavelength, the type of wavelength
Retina processes the two properties. Brain recombines this information into colour perception
How are we able to see colours of an object
Objects reflect & absorb some colours (wavelengths). The colours we see are reflected wavelengths.
The similarities & differences between rod & cone photoreceptors
Similarities
outer & inner segment, synaptic terminal, lots of mitochondria in inner segment (lots of ATP), energetically active tissue, release neurotransmitter
Differences [rod, cone]
Type: 1, 3 Location: periphery, fovea
Vision type: black & white , colour Number: 20X , 1x
Sensitivity: 1000x (1 light photo - activate), 1x (10s - 100s photons - activate )
Recovery time: slow , fast (rapid adapt to illumination change)
Correct this paragraph
Most vertebrae eyes are cone dominant. In humans, the fovea has a mixture of cone and rod cells so it is not involved in acute vision. So, the fovea is no different to the retina
Correction
Most vertebrae eyes are rod dominant.
In human, the retina - mainly rod cells
Fovea - only cone cells, mediates acute vision
Scotopic vision
- Low light/dim conditions
- Only rod cells function - very sensitive to light
- Cone - no light to respond to
- No colour seen
Phototopic vision
- Daylight conditions
- Cones only function - less sensitive to light, adaptable to background light, vision in brighter light
- Rod - bleach out quickly (bright light)
- 3 cone types - give wide range of bright light colour perception
Mesopic vision (between dim & day light)
- Moderately low light levels (right after sunset)
- Rods & cones function
- Cones - enough light to proved colour vision
Colour information processing is carried out by…
What are their features compared to M cells:
P cells (parvocellular cells)
- smaller cell bodies and dendritic fields (midget cells)
- Sustained fashion response
- slower conduction velocities
- Sensitive - light wavelength differences -> convey colour information
Visual pathway for colour
Location in cortex
Outer layers of lateral genicular nucleus
Third distinct LGN anatomical pathway
Optic nerve (monocular information) -> optic chiasm (nasal fibres crossover) -> LGN thalamus -> Optic radiation -> V1
Ventral pathway to temporal lobe (optic radiation -> V1 -> V2 -> V4 -> Temporal lobe [object processing: colour, texture, shape, size])
4 layers (P3 -P6) - transmitted necessary information regarding colour perception (especially red & green) to V1
Koniocellular pathway: neurons that reside between LCN layers - ? Involved in relay info from S M L cones
What are the three theories of colour vision
What does trichromatic and colour opponency theory suggest?
Trichromatic theory
Opponent colour theory
Stage theory
Trichromatic theory: indicates how retina allow visual system to detect colour with three cone types
Colour opponency theory: considers mechanisms that take and process information from cones
What is the trichromatic theory?
What are the 3 types of cone photoreceptors and their features?
All colours can be perceived by a combination of three colours
L-cone - sensitive to long wavelength light -> RED
M-cone - sensitive to medium wavelength light -> GREEN
S-cone - sensitive to short wavelength light -> BLUE a
Trichromatic colour theory
Explain the spectrum of colour absorption and how this allows colour to be perceived by the brain
What is the downside of this theory
Each cone overlaps another -> same wavelength trigger different cone response combinations
Difference in signal receive from three cone types -> brain perceive continuous range of colours
Some colour perception phenomenon cannot be explained by this theory
What is the colour opponent theory
Some colours can be perceived in ordinary perception simultaneously (purple [red &blue], orange [red&yellow]) while others do not exist (red & green, blue & yellow)
do not relate to paint, this is single visual pigment
- What are the three opponent channels
- What is their function
- Information processing in Red-green opponent channel, Blue-yellow opponent channel & black-white opponent channel
- Red-green, blue-yellow, black and white (brightness, luminosity/achromatic channel)
- A member of the colour pair suppress the other colour. P cell receptive field: center activated by one colour, surround activated by another.
- RG: process info -> firing difference - L cone (+ S cone input) & M cone
BY: process info -> firing difference - S cone & (combine L & M signal). [blue light present: S cone activated, B+Y- cell excitatory input, blue colour perceived. ]
BW: conduct light intensity infor
Explain colour afterimage
Optical illusion - image continuing to appear even after exposure to original image stopped
Prolonged viewing of coloured patch - afterimage with complementary colour.
