psych of perception chapter 9 Flashcards
saturation
changing the intensity to make colours brighter or dimmer, or by adding white to change a colour’s saturation
reflectance curves
plots of the percentage of light reflected versus wavelength - for a number of objects
chromatic colours / hues
when some wavelengths are reflected more than other - as for the colored paints and the tomato
selective reflection
this property of reflecting some wavelengths more than others, which is a characteristic of chromatic colours, is called selective reflection
achromatic colours
when light reflection is similar across the full spectrum - that is, contains no hue - as in white, black, and all the grays between these two extremes, we call these colors achromatic colors
selective transimmission
in the case of things that are transparent, such as liquids, plastics, and glass, chromatic colour is created by selective transmission, meaning that only some wavelengths pass through the object or substance
additive color mixture
mixing lights involves adding up the wavelengths of each light in the mixture, mixing lights is called additive color mixture
what happens when coloured lights are superimposed?
all of the light that is reflected from the surface by each light when alone is also reflected when the lights are superimposed
what happens when coloured paints are mixed?
when mixed, both paints still absorb the same wavelengths they absorbed when alone, so the only wavelengths reflected are those that are reflected by both paints in common
subtractive colour mixture
each blob of paint absorbs wavelengths and these wavelengths are still absorbed by the mixture, mixing paints is called subtractive color mixture. The blue and yellow blobs subtract all of the wavelengths except some that are associated with green.
mixing lights vs mixing colours
Mixing lights causes more wavelengths to be reflected (each light adds wavelengths to the mixture); mixing paints causes fewer wavelengths to be reflected (each paint subtracts wavelengths from the mixture)
trichromatic theory of colour vision
states that colour vision depends on the activity of three different receptor mechanisms
this theory relies only on the retinal level
color-matching experiments
observers adjusted the amounts of three different wavelengths of light mixed together in a “comparison field” until the colour of this mixture matched the colour of a single wavelength in a “test field.”
Young-Helmholtz theory of color vision
idea of the theory is that colour vision depends on three receptor mechanisms, each with different spectral sensitivities
- according to this theory, light of a particular wavelength stimulates the three receptor mechanisms to different degrees, and the pattern of activity in the three mechanisms results in the perception of a colour
cone pigments
all visual pigments are made up of a large protein component called opsin and a small light-sensitive component called retinal. Differences in the structure of the long opsin part of the pigments are responsible for the three different absorption spectra
matamerism
two physically different stimuli are perceptually identical
metamers
two identical fields in a colour-matching experiment are called metamers
trichromats
people with three visual pigments
colour deficiency
most problems with colour vision involve only a partial loss of colour perception, called colour deficiency, and are associated with problems with the receptors in the retina
Isihihara plates
colour vision test (colour vision plates) for detection of red-green colour deficiencies
monochromat
monochromat can match any wavelength in the spectrum by adjusting the intensity of any other wavelength. Thus, a monochromat needs only one wavelength to match any colour in the spectrum and sees only in shades of grey
dichromat
dichromat needs only two wavelengths to match all other wavelengths in the spectrum
anomalous trichromat
anomalous trichromat needs three wavelengths to match any wavelength, just as a normal trichromat does. However, the anomalous trichromat mixes these wavelengths in different proportions from a trichromat, and an anomalous trichromat is not as good as a trichromat at discriminating between wavelengths that are close together
unilateral dichromat
person with trichromatic vision in one eye and dichromatic vision in the other
colour-blind
monochromats see everything in shades of lightness (white, grey, and black) and can therefore be called colour-blind (as opposed to dichromats, who see some chromatic colours and therefore should be called colour deficient)
simultaneous colour contrast
background of object can affect colour perception
principle of univariance
absorption of a photon causes the same effect no matter what the wavelength
whatever colours you are perceiving it is coming from the number of photons
monochromat
just one type of pigment (total colour blind)
can see brightness of shades of grey
dichromat
two types of pigment (partially colour blind, weak colour perception)
can see chromatic colours, but cannot distinguish among all colours
trichromat
three types of pigment (normal colour vision)
can discriminate among more wavelengths across spectrum
opponent-process theory of colour vision
this theory states that colour vision is caused by opposing responses generated by blue and yellow and by red and green
behavioural evidence for opponent-process theory of colour vision
- colour afterimages and simultaneous colour contrast show the opposing pairings
- types of colour blindness are red/green and blue/yellow
colour constancy
perception of colours as relatively constant despite changing light sources
chromatic adaptation occurs when
occurs when prolonged exposure to chromatic colour leads to receptors:
* “Adapting” when the stimulus colour selectively bleaches a specific cone pigment
* Decreasing in sensitivity to the colour
perception of lightness
- is not related to the AMOUNT of light reflected by the object
- is related to the PERCENTAGE of light reflected by an object
RATIO
reflectance edges
edges where the amount of light reflected changes between two surfaces
illumination edges
edges where lighting of two surfaces changes
