Visible light consist of ____ ____ within the range from less than 400 nm to more than 700 nm.
We perceive the shortest visible wavelength as ____.
Progressively longer wavelengths are perceived as ____, ____, ____, ____, and ____.
blue, green, yellow, orange, and red
We call these ____ "light" only because the receptors in our eyes are turned to detect them.
____ ____ (shorter wavelengths) are not seen by humans, however, many species of birds, fish, and insects have visual receptors sensitive to shorter wavelengths.
Thomas Young proposed that we perceive colour by ____ the responses across a few types of receptors, each of which was sensitive to a different range of wavelengths.
This theory of receptor comparison, later modified by Hermann Helmholtz, is known as the ____ ____ of colour vision, or the Young-Helmholtz theory.
According to this trichromatic theory, we perceive ____ through the relative rates of response by three kinds of cones, each one maximally sensitive to a different set of wavelengths. (Trichromatic means three colours)
Helmholtz found that people could match any colour by mixing appropriate amounts of just three wavelengths. Therefore, he concluded that three kinds of receptors – we now call them cones – are sufficient to account for human ____ ____.
According to the trichromatic theory, we discriminate among wavelengths by the ____ of ____ across the three types of cones.
ratio of activity
Cones is come in ____ wavelength types: short-wavelength, medium-wavelength, and long-wavelength.
Given the desirability of seeing all colours in all locations, we might suppose that the three kinds of cones would be evenly abundant and evenly distributed. In fact, they are not. ____ and ____ wavelength cones are far more abundant than short wavelength cones.
Long and medium
Although the ____ wavelength cones are about evenly distributed across the retina, the other two kinds are distributed haphazardly, with big differences among individuals.
In the retinas periphery, cones are so scarce that you have no useful ____ ____.
The ____ ____ is the part of the world that you see.
The trichromatic theory is ____ as a theory for colour vision. It cannot account for negative colour after images.
Edward Herring, a 19th century physiologist, proposed the ____ ____ ____.
opponent process theory
The opponent process theory is, the brain has a mechanism that perceives colour on a continuum from ___ to ___, another from ___ to ___, and another from ___ to ___.
red to green, yellow to blue, white to black
If light stimulates a cell long enough, the cell becomes fatigued. If we now remove the light, the cell responds less than its baseline level, and therefore produces an experience of an opposite colour. This is a special kind of coding, in which an increase in response produces one ____, and a decrease produces a different ____.
However, after-images depend on the whole context, not just the light on individual receptors. The ____ ____ must be responsible, not the bipolar or ganglion cells.
The trichromatic theory and the opponent-process theory cannot easily explain ____ ____, the ability to recognise colours despite changes in lighting.
Our perception of the ____ of an object requires comparing it with other objects.
To account for colour and brightness constancy, Edwin Land proposed the ____ ____ (a combination of the words retina and cortex): the cortex compares information from various parts of the retina to determine the brightness and colour for each area.
Whenever we see anything, we make an ____. That is, visual perception requires a reasoning process, not just retinal stimulation.
____ ____ ____ is also know as colourblindness.
Colour vision deficiency
Before colour vision deficiency was discovered in the 1600s, people assumed that vision ____ the objects we see. They assumed that everyone saw objects the same way.
Investigators discovered that it is possible to have otherwise satisfactory vision without seeing colour. That is, colour depends on what our ____ do with incoming light, it is not a property of the light itself.
In red-green colour deficiency, the most common form of colour deficiency, people have trouble distinguishing red from green because the long- and medium-wavelength cones have the same ____ instead of different ones.
The gene causing red-green colour deficiency is on the ____. About 8% of men are red-green colourblind compared with less than 1% of women.