week 8 Flashcards
is there colour perception ?
There is no real colour there is only perception
What is the definition of for colour perception?
colour perception is the product of network activity
What are the properties of light?
light is a psychophysical property
light is a reflection
only 400 - 700 nm is visible on the spectrum
how is visible light processed ?
visible light causes activity on the receptors
What are the basic principles of colour perception?
Detection
Discrimination
Appearance
Definition of Detection Colour perception?
Wavelength of light must be dated in the first place
Definition of Discrimination of colour perception?
Must be able to tell the difference between one wavelength and another
Definition of Appearance of colour perception?
Assign perceived colours to light surface
have the preceded colours be stable overtime
regardless of lighting conditions
What are the two types of colour detection?
Photopic
Scotopic
What is Photopic colour detection?
Light intensities that are bright enough to stimulate the cone receptors and saturate the rod receptors
eg. sunlight
What is Scotopic Colour detection?
Light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors
eg. moonlight
What are three types of photopic vision?
S-cones = short ƒ M-cones = medium ƒ L-cones = Large ƒ
What is the peak sensitivity and colour corresponding of the L-cone?
565 nm
yellow
What is the problem of univariance?
an infinite set of different wavelength - intensity combinations can elicit exactly the same response demo a single type of photoreceptor
one type of photoreceptor cannot make colour discrimination based on wavelength
What are the properties of scotopic vision?
- Rods sensitive to scotopic light levels
- all rods contain photopigments
- All rods have the same sensitivity
- rods suffer from invariance and cannot sense difference in colour
- only rods are active under scotopic conditions
What is the minimum about of colour intensity required for the cones to be active?
colour vision needs more than one tenth of a wavelength
What is the basis of colour vision?
The three cones that distinguish between lights of different wavelength
What is the theory of trichromatic?
colour of any light is defined in out visual system by the relationships of three numbers, the outputs of three receptors types now to be the three cones
What is the trichromatic theory known as?
Young-Helmholtz
What does metamers mean?
- Different mixtures of wavelength that look identical.
- two stimuli perceived as identical spite physical differences
What are the two different colour cone responses?
LGN
Cone-opponent cell
What does the LGN says do ?
Visual pathway stops at LGN beofre visual cortex
LGN has receptive fields with center- surround organization.
what are the three Detection of discrimination?
- Output is important even if the phsically wavelength are different
- Retina and LGN contain cells repackage into cone-opponent differnt signials
- Brain disciminates between 2 million colours
What doe Cone-opponent cells ?
A neuirn whose output is based on a difference between sets of cones.
What is colour appearance?
A 3D space that descirbes all colour
What is the Equivalent of the RGB colour space?
similar to the long, medium short wavelength
What is the HSB stand for?\
Hue
Situation
brightness
what is hue ?
the chromatic aspect (colour)
What is saturation?
The chromatic strength of hue (intensity)
What is the brightness??
The distance from the black in colour space
What is the opponent colour theory?
Thery that perception of colour is based on the output of three mechanise (opponency between two colour)
red-green
blue-yellow
black-white
The relationship between the LGN and cone in regards to colour opponent?
LGN are exited by L-cone onset in centre which is inhibited by the M-cone onsets in surround
Eg. Red verse green
S-cone onset in centre, inhibited by (L+M)-cone onset in their surround
eg. Blue verse yellow
What is an after-image?
A visual seen after a stimulus has been removed
what is a negative afterimage?
An afterimage whose polarity is the opposite if the original stimuli (seeing opposite colour
What is the process of opponent colours?
Step 1: detection (s,m, L cones)
step 2: discrimination
Step 3: Appearance
Does everyone see colour the same way?
Yes: some variations due to age
No: About 8% of male population, 0.5% of female.
What are the three types of colour blindness due to lacking cones?
Protanope: Absence of L-cone
Deuteranope: Absence of M-cones
Tritanope: Absence of S-cones
What are the three types of colour blindness due to colour difference?
Colour-anomalous: two cones so similar can’t tell the difference.
Cone monochromat: having only one cone type
Rod monochromat: having no cones only
What is colour contrast?
Colour perception effect in which the colour of one region indices the opponent colour in the neighbouring region
what is colour assimilation?
Colour perception effect in which two colours bleed into each other, each taking up qualities of the other.
What is colour constancy?
The tendency of a surface to appear the same colour under a fairly wide range of illuminations.
-visual system must take note of the lighting source
Which two colours are furtherest apart in wavelength
Blue and red
According to the opponent colour theory, the perception of colour is based on the output of ____ cones, each of them an opponency between ____ colors.
three; two
If a video game labels friendly characters as green and enemy characters as red, who might have a hard time seeing the difference
between friendly and enemy characters?
Both deuteranopes and protonopes
In tie case of a negative afterimage, a yellow stimulus would produce a ____ afterimage.
Blue
