Human Vision

Question 1

What is a photopigment?

Answer 1

A molecule in which light triggers a physical or chemical change

Question 2

What does a single photocell allow you to see?

Answer 2

Light in one dimension

Question 3

What do you need in order to see in 2 dimensions?

Answer 3

Multiple photocells stacked together

Question 4

How can you arrange photocells to be able to determine the direction the image is coming from?

Answer 4

In an arc

Question 5

What’s the main issue with using many photocells to see?

Answer 5

Possible for light to hit all photocells, making it difficult to determine where the image is coming from

Question 6

How can a pinhole aperture be used to improve vision?

Answer 6

Focuses the light from an image on a few photocells, making it easier to determine where the direction the image is coming from.

Question 7

What is the problem caused by a pinhole aperture?

Answer 7

A large amount of light is blocked from entering the eye, which leads to dim images

Question 8

How can a lens be used to improve vision?

Answer 8

Can be used to focus a large amount of light into a point, to make images brighter

Question 9

What is the difference between rods and cones?

Answer 9

Rods are extremely sensitive to light, cones only active at higher light levels
Many more rods than cones
Cones have much better spatial resolution than rods

Question 10

What are the two types of ganglion cells and what is the difference between them?

Answer 10

on-center and off-center cells
On-center cells fire when the center of the cell is stimulated, and do not when the outside is stimulated. If both are stimualted, it gives a weak response. Off-center is the other way around.

Question 11

Why does the human eye have a blind spot?

Answer 11

Where the optic nerve is connected to the eye there are no photoreceptors

Question 12

How do on/off cells allow you to see edges?

Answer 12

When a line of ganglion cells are in the middle of a change in the contrast of light, the on-center and off-center cells will react differently, so you know there is an edge. While when all the cells are being hit with the same amount of light, both types of cell act the same, so there must be no edge.

Question 13

What is trichromatic coding theory?

Answer 13

1802 theory proposing that the eye contains 3 types of cones to see red, green and blue. Equal amounts of red and green cones, but only 8% are blue cones.

Question 14

What does trichromatic coding theory explain?

Answer 14

How we can discriminate against wavelengths with 2nm in difference
How we can match a range of wavelengths to the same colour
Some types of colour blindness

Question 15

What does trichromatic coding theory not account for?

Answer 15

Why only some colours blend
Why yellow is a primary colour

Question 16

What is opponent colours theory?

Answer 16

Proposed in 1930s where colours may be represented in visual system as opponent colours. Neurons respond to pairs of primary colours, red-green and yellow-blue. You can get red-center ganglion cells and green-center ganglions cells. Same with yellow-blue.