Topic 7: Colour Perception Flashcards
How is the perception of colours created?
Created by nervous system activity when light that has no colour is reflected into your eyes and activates three types of retinal cone photopigment
What are the three main functions colour perception serves?
Can help us identify things
Can help us classify things
Can help inform our actions
Brain injury resulting in an inability to name colours
Colour anomia
Colours of the visible spectrum are associated with…
different wavelengths of light
How are object colours determined?
Determined by the specific wavelengths of light that are reflected from, or transmitted through, that object
Colours with hue
Chromatic colours
Occurs when some wavelengths are reflected from an object more so than others
Selective reflection
Colours without hue
Achromatic colours
% of light reflected from an object vs. wavelength
Reflectance curves
What do reflectance curves tell us about colour perception?
Reflect a range, but each selectively reflects more light in one part of the spectrum over the others = colour perception of that object
Occurs when only some wavelengths pass through transparent objects while others do not.
Selective transmission
Creation of colours that occurs when coloured paints/pigments are mixed together
Subtractive colour mixing
Explain subtractive colour mixing
Paints absorb the same wavelengths they absorbed when they were alone, so the only wavelengths reflected are those that are reflected by all paints
Creation of colours that occurs when lights of different colours are superimposed
Additive colour mixing
Explain additive colour mixing
When coloured lights are superimposed all the light that is reflected from the surface by each light alone is also reflected when lights are combined.
Colours that appear in the visible spectrum
Spectral colours
Colours that do not appear in the visible spectrum
Nonspectral colours
What is the major limitation in describing colour?
Language: Difficulties describing differences between colours
Three perceptual dimensions of colour which together create and allow us to describe the large number of colours we can perceive…
Hue
Saturation
Value
Perception of chromatic colours, or variations of these colours
Hue
Amount of “whiteness” added to a colour
Saturation
“Light-dark dimension” of a colour
Value
Idea that our perception of colour is determined by the activity in three different cone photopigments that have different sensitivities
Trichromacy of colour vision
Evidence that it is a function of three distinct pigments comes from…
Colour matching experiments
According to the trichromacy of colour vision theory, light of a particular wavelength stimulates…
Each of the 3 photopigments, but to different degrees
What are the relative wavelengths of short, medium, and long waves as they relate to photopigments?
(S) - Short-wavelength pigment = ~419 nm
(M) - Medium-wavelength pigment = ~ 531 nm
(L) - Long-wavelength pigment = ~ 558 nm
Rare form of colour blindness – “complete colour blindness”
Monochromacy
What produces monochromacy?
bsence of cone receptors results in the perception of only shades of lightness (white, grey, black), with no chromatic colour present
Colour vision with two pigments
Dichromacy
Considering the difficulties in determining what exactly a dichromat perceives, what do we rely on?
Those with unilateral dichromacy
What are the three types of dichromacies?
Protanopia: Missing long-wavelength photopigment
Deuteranopia: Missing medium-wavelength photopigment
Tritanopia: Missing short-wavelength photopigment
What did Hering (1878) claim with regards to colour perception?
Our perception of colour is determined by the activity of two opponent mechanisms: a blue-yellow mechanism and a red-green mechanism
What is the modern evidence to support Hering’s opponent-process theory of colour vision?
Presence of opponent neurons in the visual cortex
Excitatory response to wavelengths in one part of the colour spectrum; inhibitory response to wavelengths in the other part
Our perception of an object’s colour remains relatively constant when the amount of illumination is changed
Colour constancy
Our perception of an object’s lightness remains relatively constant under different intensities of illumination
Lightness constancy
Why is colour constancy helpful?
Helps with object recognition/identification regardless of illumination
Why does lightness constancy occur?
Occurs because the relative proportion of light being reflected into the eye stays the same regardless of illumination
