7 Colour Perception

Question 1

Q: What is color good for?

Answer 1

A: Color serves various purposes in the visual perception of different species:
1. Scene segmentation: Variation in color often signals object boundaries, aiding in the segmentation of scenes.

2. Camouflage: Animals use color markings to disguise themselves, blending into their surroundings for protection.
3. Perceptual organization: Our visual system utilizes color to group elements in a scene, helping us perceive and organize visual information effectively.
4. Evolutionary force: Color perception can be a strong evolutionary force depending on the species, influencing survival and reproduction strategies.
5. Food identification: Color helps in identifying various elements in the environment, such as ripe fruits, correct leaves, and distinguishing between harmful and harmless items, aiding in food identification.

Question 2

Which mammals see the same way as us?

Answer 2

Catarrhine monkeys (old world monkeys + man)
- Platyrrhine monkeys (new world monkeys – only females)

Some tropical fish + birds have 4 types (tetrachromacy)
Pigeons have 5 (pentachromats)

Question 3

Q: What is color?

Answer 3

A: Color is a property of visible light, which forms a narrow band of frequencies in the electromagnetic spectrum. Within this band, different frequencies correspond to different hues, ranging from red (long wavelength) to violet (short wavelength).

Question 4

Q: How do objects obtain their color?

Answer 4

A: Different objects absorb and reflect different wavelengths of light, which gives them their perceived color. The color of an object can also depend on the light source illuminating it.

Question 5

Q: Is color solely determined by wavelength?

Answer 5

A: No, color is more complicated than just wavelength. While the wavelength of the reflected light determines the hue that is seen, perceived color is also influenced by the intensity of reflected light and the saturation of the color (the amount of white light mixed with the hue).

Question 6

Q: What is the electromagnetic spectrum?

Answer 6

A: The electromagnetic spectrum (EMS) encompasses a wide range of wavelengths, with 1 millimeter equaling 10,000,000 nanometers. The visible spectrum, which covers just 400 nanometers, includes the range of colors that are visible to the human eye.

Question 7

Q: What are the properties of light related to color?

Answer 7

A: Light has properties such as wavelength, intensity, and spectral purity.

Question 8

Q: What are the psychological attributes related to color?

Answer 8

A: Psychological attributes of color include hue, brightness, and saturation. Hue refers to the specific color or shade, brightness relates to the intensity of the color, and saturation describes the purity or vividness of the color.

Question 9

What are the 2 theories of colour perception?

Answer 9

trichromatic and opponent process theories.

Question 10

Q: What is the Trichromatic theory of color perception?

Answer 10

A: The Trichromatic theory proposes that there are three types of color receptors (cones) in the retina, each sensitive to different wavelengths of light. These cones are maximally responsive to short (blue), medium (green), and long (red) wavelengths, respectively.

Question 11

Q: How does the Trichromatic theory explain color perception?

Answer 11

A: According to this theory, the combined responses of these three types of cones account for all the colors we perceive. The pigments in the cones determine which wavelengths they respond to best.

Question 12

Q: Do all individuals perceive color in the same way according to the Trichromatic theory?

Answer 12

A: There’s an explanatory gap in understanding whether individuals perceive color in the same way. Variations in color perception can be compared to variations in other sensory perceptions like pain or taste.

Question 13

Q: What is the distribution of cones in the retina?

Answer 13

A: Cones are concentrated in the fovea, which is the central part of the retina responsible for high visual acuity. There are no rods in the center of the fovea.

Question 14

Q: How do rods and cones differ in their sensitivity and distribution?

Answer 14

A: Rods are highly sensitive and are activated in low lighting conditions, while cones require good lighting conditions to be activated. Rods are found throughout the retina except in the fovea, whereas cones are concentrated in the fovea.

Question 15

Q: What supports the Trichromatic theory of color perception?

Answer 15

A: Evidence supporting the Trichromatic theory includes the combination of three primary colors to produce all possible colors, the existence of three forms of dichromatism (color blindness), and the phenomenon of afterimages where the perception of colors is explained by the fatigue or adaptation of specific cone types.

Question 16

What other species have the tapetum laucidum?

Answer 16

dogs, cats, humans

Question 17

Q: What is the Opponent Process theory of color perception?

Answer 17

A: The Opponent Process theory, proposed by Ewald Hering, suggests that there are three pairs of opponent processes in color perception: red-green, yellow-blue, and black-white. According to this theory, these processes are opponent in nature, meaning that the perception of one color suppresses the perception of its opponent.

Question 18

Q: What observation led to the development of the Opponent Process theory?

Answer 18

A: Hering noticed that when people were presented with a large number of color samples and asked to pick those that are pure, they selected red, blue, and green, but also yellow. This observation suggested that there are opponent processes involved in color perception.

Question 19

Q: How does the Opponent Process theory explain color perception?

Answer 19

A: According to this theory, certain color receptors in the retina signal opposing color pairs (red-green, yellow-blue, black-white). For example, a red-green receptor will signal either red or green, but not both simultaneously.

Question 20

Q: What are some pieces of evidence supporting the Opponent Process theory?

Answer 20

A: Evidence supporting the Opponent Process theory includes the non-existence of certain colors, color confusions in color blindness, complementary afterimages, and color context effects. Additionally, phenomena such as lightness constancy, where squares with the same reflected amount of light are perceived as different, support this theory.

Question 21

Q: How do the Trichromatic theory and Opponent Process theory complement each other?

Answer 21

A: Both theories are considered to be correct, but at different levels of visual processing. The Trichromatic theory operates at the level of cones in the retina, while the Opponent Process theory operates at the level of cells in the lateral geniculate nucleus (LGN) and the visual cortex.

Question 22

Q: What is color blindness, and who first described it?

Answer 22

A: Color blindness, also known as color vision deficiency, was first described by John Dalton, who himself suffered from the condition. Despite his own experiences, Dalton’s color blindness was not diagnosed until 200 years later.

Question 23

Q: What are anopias and anomalies in the context of color blindness?

Answer 23

A: Anopias refer to conditions where an individual is insensitive to specific wavelengths (L, M, S) of light due to the absence of a particular type of cone in the retina. There are three types of anopia: protanopia (missing L-cone pigment), deuteranopia (missing M-cone pigment), and tritanopia (missing S-cone pigment). Anomalies, on the other hand, involve a misalignment or deficiency in the L or M cones. The two types of anomalies are protanomaly (L-cone pigment deficiency) and deuteranomaly (M-cone pigment deficiency).

Question 24

Q: How does color blindness support both color vision theories?

Answer 24

A: Color blindness supports both the Trichromatic theory and the Opponent Process theory of color vision. The Trichromatic theory is supported by the fact that different types of color blindness (anopias) correspond to the absence of one of the three cone types. Additionally, the Opponent Process theory is supported by the observation that individuals who have difficulty distinguishing red colors also struggle with distinguishing green colors, indicating an opponent relationship between these colors.

Question 25

Q: Are there individuals with enhanced color vision?

Answer 25

A: Some rare humans possess four types of cone pigments, allowing them to detect variations in hue that are not perceptible to individuals with typical color vision. Additionally, some birds and butterflies have five types of color receptors, although it is impossible to fully understand what these colors look like due to the explanatory gap between human and avian perception.