Perception 2

Question 1

Light is…

Answer 1

the main stimulus for vision and contains small pockets of energy known as photons

Question 2

What does wavelength determine and what does intensity determine?

Answer 2

Wavelength determines colour
Intensity determines brightness

Question 3

Light interaction can occur in 3 ways…

Answer 3

-Absorption
-Reflection
-Transmission

Question 4

How is light interpreted?

Answer 4

The convex cornea and lens are used to project an image onto the retina.
Photoreceptors in the retina will then receive light and respond to it

Question 5

Rods are…

Answer 5

-Within the peripheral retina
-Operate in low light conditions
-Can detect single photons

Question 6

Cones are…

Answer 6

-Within the central retina
-Operate in high light conditions
-Require lots of photons

Question 7

Describe the signal pathway from the eye to the brain

Answer 7

Retinal ganglion cells -> Retina -> Optic nerve -> Optic chiasm -> LGN -> Primary visual cortex

Question 8

Name the 3 bottom up processes for brightness perception

Answer 8

-Light/dark adaptation
-Negative afterimages
-Lateral inhibition

Question 9

What happens in light/dark inhibition?

Answer 9

Retina recognises the contrast of light and so plays a massive part in brightness constancy e.g. if you have a piece of paper with black letters on it, whether it’s a sunny day or using indoor lighting, we still see the paper as white (reflects) and the writing as black (absorbs)

If its dark then the intensity needs to be higher, and if it’s lighter then intensity drops

Question 10

What are negative afterimages?

Answer 10

Give the ability to create illusions, and this occurs by changing the sensitivity in areas of the retina which creates different colours

Question 11

What happens in lateral inhibition?

Answer 11

Retinal ganglion cells receive two different types of input; excitatory (+) and inhibitory (-)

Eyes become sensitive to change in light which is important for detecting corners of objects e.g. Hermann grid

We perceive faint grey dots at intersection of white lines because the retinal ganglion cells at this location are inhibited more than the cells responding at other points in the line

Question 12

What happens in the top down process of brightness perception?

Answer 12

The brain uses past knowledge on how light interacts with certain items to help figure out brightness perception and this can create shadows e.g. checker shadow illusion

A 2D object is perceived as a 3D one due to us trying to maintain brightness constancy

Question 13

Why does a lack of light in the world mean a lack of colour?

Answer 13

Only rods are operating (as they only occur in low light conditions) and these only contain one photopigment

Question 14

What is it called when cone receptors contain 3 different photopigments?
Name them

Answer 14

Trichromacy
-S cones (sensitive to short wavelength - blue)
-M cones (sensitive to middle wavelength - green)
-L cones (sensitive to long wavelength - red)

Question 15

What is it called when people have either 0 or 1 functioning cone type?

Answer 15

Monochromacy
Causes full colour blindness

Question 16

What is it called when they are missing a cone type?
Name them

Answer 16

Dichromacy
-Tritanopia (missing S)
-Deuteranopia (missing M)
-Protanopia (missing L)

Question 17

What is called when they have a defect in a cone type?
Name them

Answer 17

Anomalous Trichromacy
-Tritanomaly (defect in S)
-Deuteranomaly (defect in M)
-Protanomaly (defect in L)

Question 18

Describe the bottom up process of colour perception

Answer 18

Opponency is where the retinal ganglion cells receive excitatory and inhibitory input from different cone types which causes very distinct red/green and blue/yellow pathways

This is shown through negative afterimages

Question 19

Describe the top down process of colour perception

Answer 19

Colour constancy created where the perceived colour of certain objects will stay the same even when the light changes e.g. warm/cold tones