Week 2 Lecture 5: Colour Vision

Question 1

What does colour depend on?

Answer 1

wavelengths of light

Question 2

What is a wavelength?

Answer 2

the distance between one wave peak and the next

Question 3

What is the range of the wavelengths humans can see?

Answer 3

400 to 700 nm

Question 4

What different wavelengths correspond to?

Answer 4

different colours

Question 5

Why did evolution give us eyes that see 400-700 nm?

Answer 5

The power in sunlight peaks at these wavelengths and the atmosphere is most transparent to these wavelengths

Question 6

What are 3 cones that most humans sense colour with?

Answer 6

Red (63%), green (31%) and blue (6%)

Question 7

What are orgnanisms that sense colour with three types if cones called?

Answer 7

Trichromats

Question 8

What light (wavelength) does red and green cone pigments prefer?

Answer 8

Yellow and yellow-green light

Question 9

What light (wavelength) does blue cone pigments prefer?

Answer 9

Blue light

Question 10

What light (wavelength) does rhodopsin prefer?

Answer 10

Blue-green light

Question 11

What light (wavelength) does melanopsin prefer?

Answer 11

Blue light

Question 12

How does the brain infer colour?

Answer 12

By comparing the data from the three types of cone e.g. yellow light affects red and green cones but blue cones so if red and green cone are hyperpolarized, the brain perceives yellow

Question 13

Can the brain infer the wrong colour?

Answer 13

Yes, e.g. a red and green light can produce the same cone activities a yellow light would so the brain perceives yellow either way

Question 14

How do we perceive colour?

Answer 14

By mixing the primary colours of light (red, green, blue), we can produce any colour perception which corresponds to a pattern of activity in the 3 types of cones

Question 15

What are spectral colours?

Answer 15

The colours of the rainbow, colours that can be evoked by the light of a single wavelength

Question 16

What are extraspectral colours?

Answer 16

Colours like purple and white, colours that are evoked by a mix of wavelengths

Question 17

What are ganglion cell colour signals?

Answer 17

Combinations of cone signals

Question 18

What are ganglion cells excited by red and green light called?

Answer 18

Yellow channels (R + G)

Question 19

What are ganglion cells excited by red light and inhibited by green light (or vice versa) called?

Answer 19

Red-green opponent channels (R - G / G - R)

Question 20

What are ganglion cell excited by blue light and inhibited by red and green light (or vice versa) called?

Answer 20

Blue-yellow opponent channels

Question 21

What opponent channels thought to explain?

Answer 21

Afterimages

Question 22

What is most common variant of colour blindness?

Answer 22

Red-green colour blindness or Daltonism

Question 23

What is the inheritance pattern of red-green colour blindness

Answer 23

Colourblind fathers have colour-normal daughters who have colour blind sons

Question 24

What chromosome is gene for red and green visual pigments located?

Answer 24

The X-chromosone

Question 25

How does mutations at the loci for red and green visual pigments affect women?

Answer 25

If one X-chromosone codes for faulty pigment then the other X-chromosone compensates. If the two X-chromosones code for different functional pigments, the woman may be tetrachromat

Question 26

What is reflectance?

Answer 26

The intrinsic colour of a surface or the tendency of a surface to reflect certain wavelength and absorb others

Question 27

Why is reflectance important?

Answer 27

It carries information about an object e.g. reflectance of a banana tells you its ripeness

Question 28

What does the light sent to our eyes depend on?

Answer 28

Reflectance and illumination

Question 29

What is colour constancy?

Answer 29

Our ability to infer the reflectance of an object by comparing parts of the image

Question 30

What can colour constancy affect?

Answer 30

Our perception of brightness, hue and saturation