Chapter 9 Flashcards
What is cerebral achromatopsia?
Colour blindness caused by a cortical injury
How does most colour deficiency occur?
At birth because of genetic absence of one or more types of cone receptors
What did Thortstenson find?
That colour can be a cue to emotions signaled by facial expressions
What wavelengths appear violet?
400 to 450 nm
What wavelengths appear blue?
450 to 490 nm
What wavelengths appear green?
500 to 575 nm
What wavelengths appear yellow?
575 to 590 nm
What wavelengths appear orange?
590 to 620 nm
What wavelengths appear red?
620 to 700 nm
What are chromatic colours?
Blues, greens, reds
Occur when some wavelengths are reflected more than others
What is selective reflection?
When some wavelengths are reflected more than others
What are achromatic colours?
Whites, grays, blacks
Occur when light is reflected equally across the spectrum
What is a reflectance curve?
Plots the percentage of light reflected form objects in the visible spectrum
What is selective transmission?
In terms of things that are transparent, only some wavelengths pass through the object or substance
What are transmission curves?
Plots of the percentage of light transmitted at each wavelength
They look similar to reflectance curves but with percent transmission plotted on the vertical axis
What happens when two paints are 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
What are nonspectral colours?
Those that do not appear in the spectrum because they are mixtures of other colours
What happens when hues because desaturated?
They can take on a faded or washed-out appearance
What did Newton argue about the colour spectrum?
That each component of the colour spectrum must stimulate the retina differently in order for us to perceive colour
What is the trichromacy of colour vision?
Colour vision depends on the activity of three different receptor mechanisms
What is the colour matching experiment?
The participant is shown a reference colour that is created by shining a single wavelength of light on a reference field
The participant then matches the reference colour by mixing different wavelengths of light in a comparison field
What are the findings from the colour matching experiment?
Any reference colour could be matched provided that observers were able to adjust the proportions of 3 wavelengths in the comparison field
What is microspectrophotometry?
Technique used to discover the three types of cones
Directed a narrow beam of light into a single cone receptor
What is adaptive optical imaging?
Made it possible to look into a person’s eye and take pictures that show how the cones are arranged in the retina
What do aberrations on the cornea and lens do?
Distort light on its way to the retina
What is a cone mosaic?
Shows foveal cones
What is metamerism?
Occurs when two physically different stimuli are perceptually identical
What is monochromatism?
Hereditary colour blindness
No functioning cones
What is the principle of univariance?
States that once a photon of light is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost
What is a unilateral dichromat?
A person with trichromatic vision in one eye and dichromatic vision in the other
What is protanopia?
Sex-linked
Missing long-wavelength pigment
What is the point when a protanope reaches grey?
The neutral point (492 nm)
What is deuteranopia?
Sex-linked
Missing medium-wavelength pigment
Neutral point = 498 nm
What is tritanopia?
Missing short-wavelength pigment
Neutral point = 570 nm
What is anomalous trichromatism?
Mix wavelengths in different proportions they they are not as good at discriminating between wavelengths that are close together
What is opponent process theory?
There are two pairs of chromatic colours
-red-green
-blue-yellow
What are the 4 primary colours according to Hering?
Red, yellow, green, blue
What is hue scaling?
A procedure in which participants were given colours from around the hue circle and told to indicate proportions of red, yellow, blue, and green they perceived in each colour
What is another term for primary colours?
Unique hues
Why was opponent-process theory widely accepted?
Its main competition, trichromatic theory, was championed by Helmholtz who had prestige in the scientific community
Hering’s phenomenological evidence could not compete with Maxwell’s quantitative colour mixing data
There was no neural mechanism known at that time that could respond in opposite ways
What is the purpose of hue cancellation experiments?
To provide quantitative measurements of the strengths of B-Y and R-G components of the opponent mechanism
What is the hue cancellation experiment?
Adding wavelengths of light until the colour is cancelled out
What are opponent neurons?
Respond with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
Physiological evidence for opponent-process theory
How do we know that color and form are processed independently?
Due to double dissociation studies
What is colour constancy?
We perceive colours of objects as being relatively constant even under changing illumination
What is chromatic adaptation?
The eye’s sensitivity is affected by the colour of the illumination of the overall scene after prolonged exposure to chromatic colour
What is partial colour constancy?
The perception of the object is shifted after adaptation, but not as much as when there was no adaptation
What is memory colour?
The effect of perception on prior knowledge of the typical colours of objects
-Grey-scale coloured fruits had a slight tinge toward the colour they are in real life
-perceive them to be more saturated than unfamiliar objects with the same wavelength
When does size constancy work best?
When an object is surrounded by objects of many different colours, a situation that occurs often when viewing objects in the environment
When objects are viewed with two eyes
When looking at a 3D scene
What are some explanations for the dress phenomenon?
Different illuminations make the dress be perceived differently
Experiences with illumination may affect the assumptions they are making about how the dress is illuminated
What is lightness constancy?
We see whites, grays, and blacks as staying about the same shade under different illuminations
What does the intensity of light hitting the eye depend on?
The illumination, the total amount of light that is striking the object’s surface
The object’s reflectance, the proportion of this light that the object reflects into our eyes
What is our perception of an object’s lightness related to?
The percentage of light reflected from the object (constant), not the amount of light that is reflected from the object
What is the ratio principle?
As long as the ratio of reflectance of the object to the reflect of the surrounding objects remains the same, the perceived lightness will remain the same
What is a reflectance edge?
An edge where the reflectance of two surfaces changes
What is an illumination edge?
An edge where the lighting changes
