Sensory Six - Vision part two Flashcards
How is colour in light percieved?
using intensity and wavelength
How is intensity and wavelength processed?
Firstly they are done separately by the retina, then both are integrated in the brain to give color perception
What gives rise to colour of an object?
The object reflects some colours and those are sensed leading to the perception of the object being those colours.
What is the colour management system?
A system that is used as convention to ensure monitors, printers all have the same colour schemes
What is the first component of colour perception?
Light detection by the photoreceptors
What are the three classes of cones called?
Trivariant
What are the three cones called?
S cone = short wave length (blue)
M cone = med wave length (green)
L cone = Long wavelength (red)
What do rods detect?
They are our night vision
Low threshold to light
Do not detect colour
= Intensity only, contrast
What do cones detect?
Day vision
Intensity and Wavelength = Colour vision
Higher threshold to light
As we have three classes of cone how else is colour specified?
Can be specified in terms of their: Hue, tone and saturation
What is the munsell colour system?
A classification based on
Hue : Dominant wavelenght
Value : Reflectance and luminosity
Chroma : Saturation of the signal
i.e colours of equal hue, value and chroma on opposite sides of the circle are complimentary
when mixed they add
Whats the first theory of colour vision?
The trichromatic theory
= Combination of three channels explain the colour discrimination functions of the eye
What is unique about each cone?
A range of wavelengths activate each cone to varying degrees (each have a maximum too) this following from the the trichromatic theory could explain how colours mix and form different ones…
What is the second theory of colour?
Opponent theory colour:
- Three channels, each with an antagonist
i. e Red-green, blue-yellow and black-white
Hue cancellation paradigms suggest that there is only every pure colours and never greenish-red. either red or green
What is the third theory of vision?
Stage theory (modern theory)
- Incorporates both previous theories but is based on a two stage model
Stage One: Receptor stage, three colour receptors
Stage Two: Neural processing stage, where colour opponency occurs at a post receptoral level, and occurs in the horizontal cells of the retina and continues in the brain.
What is meant by colour opponency?
i.e Red and green cancel each other (varying degrees based on intensity etc…) and this is processed by the P cells (retina) before the Parvocellular cells in the LGN
or
I.e Red and green summat, blue is subtracted, then processed by small-bistratified ganglion cells in the retina then Koniocellular neurons in the LGN
So according to theory three how is light perceived?
- Activation of L,M,S cone pigments.
- Opponency pathways that allows us to sort colour information for black/white, yellow/blue and red/green
- Brain combines the information received from the retina to give rise to perception of different wavelengths of light.
What are people with normal colour vision called?
Trichromats
What is colour blindness called?
Dichromacy
X linked, so more common in males
People who are less sensitive to red are called?
Protanopia
People who are less sensitive to green are called?
Deuteranopia
People who see no colour are called?
Monochromats
What is the farnsworth panel d15?
A method of detecting colour blindness where subjects are asked to order colours in similarity from a pilot cap colour
What are the ventral and dorsal streams also called?
Dorsal = where Ventral = What
What is the ishahara test?
Reading the numbers in the colours
How does the colour afterimage occur?
Adaptation, prolonged viewing of a stimulus, cells tire and stop firing.
