Perceiving colour Flashcards
(35 cards)
What is colour good for?
The detection and segmentation of objects, ripeness of fruit and veg.
What is it in the environment that allows us to perceive change in colour?
The dependance on the amount of visible light waves, the more light reflected off an object the colour will change.
How do we perceived different wavelengths?
Short-Blue Medium- Green Long- Red Long and medium together- Yellow Long medium and short together-White.
What is the process of transduction?
When a photon strikes a photopigment, it splits it into two molecules (isomerization).
The splitting starts a chemical reaction that causes the photoreceptor to send an electrical signal to the bipolar cell. i.e. transduction took place.
The bipolar cell conveys this electrical signal to the ganglion cell that sends it up the optic nerve towards the brain.
Which two element make up a photopigment?
Opsin and retinal.
How are different spectral sensitivities created?
Due to the absorption spectra of the individual visual pigments.
At what spectra do rod pigments absorb best at?
500nm
At what spectra do cone pigment absorb best at?
Short (s)- 420nm
Middle (m)-530nm
Long (L)- 560nm
How much light can 480 and 600 wavelengths absorb?
480=10%
600= 5%
What is the principle and univariance?
The idea that wavelength and light are interchangeable due to the only and main function always being isomerization in the same type of photoreceptor, i.e. single class of photoreceptors.
What does the principle of univariance show about rod cells?
They cannot signal colour as they only have a single type of photo pigment therefore no matter the wavelength of light intensity they are still interchangeable.
Why can cone cells produce colour but rods cant?
Because cone cells have 3 different photo pigments and spectral sensitivities, S,M and L.
What colours so S M and L sensitivities produce in cone cells?
S- Blue spectrum
M- Green and neutral spectrum
L- Red spectrum
How do cone cells produce all of the colour wheel out of the 3 pigments?
Because multiple wavelengths can be transmitted at once causing colours such as yellow to be visible.
Why does one specific colour become the most visible?
Because the colour that becomes visible directly correlates to the pigment that is the most active.
What is the Trichromatic theory of colour vision?
Thomas Young and Herman von Helmholtz theory in 19th century. Derived from psychophysical experiments of colour matching in human subjects.
What is the colour matching experiment?
Participant had dials in which the wavelengths of the photo pigment can be controlled producing, S M and L waves. Participants had to use the waves to match the colour presented by the observer.
What were the findings of the colour matching experiment?
Subjects with normal vision could not match all test wavelengths unless they had more than 2 wavelengths (at least 3). Concluded that colour vision is trichromatic, required three colour mechanisms.
What did Ewald Hering do in the 1800’s?
Observed that when colours that are perceptually similar are arranged in a circle they can fall into four distinct groups. Red, Green, Blue or Yellow.
What are the two perceptual opponent channels suggested by Hering?
Blue- Yellow, Red-Green
Why are the Opponent-Process and Trichromatic theory not mutually exclusive?
Because neither psychologist had knowledge of the rod and cone cells, and the three photopigments. Neither theory is wrong they just do not explain the same aspect of colour theory.
Which elements of colour vision do the Trichromatic theory and the Opponent-Process theory explain?
Trichromatic theory- explains the responses of the cones in the retina.
Opponent-process theory explains the neural responses of cells connected to the cones further up the visual system.
What is additive colour mixing?
When mixing light of different wavelengths superimposing blue and yellow lights lead to white as all three S,M and L wavelengths are interacting.
What is subtractive colour mixing?
When mixing paints or different pigments, additional pigments reflect fewer wavelengths therefore mixing blue and yellow leads to green rather than red. Mixing all three colours would lead to dark colours or black.
