EYE

Question 1

How did the evolution of the eye from 1-dimensional photo-receptors through to the cone shape improve vision

Answer 1

• 1-dimensional photoreceptive cells can only tell if the light is coming from a fixed direction
• 2-dimensional cells can tell if the light is coming from a specific angle according to their activations ( if they are arranged in a line)
• The cone shape improved by narrowing the range of angles of incoming photons, which reacted with a specific cell, better directional data; however, the images are low resolution. This later got better via the lense and combinations of cone and pinhole architectures

Question 2

What is the difference between the cone shape and the pinhole

Answer 2

Cone Shape:
-good directional data
-bright images
-poor resolution

Pin Hole:
-dim images
-sharp
-less data preserved

Question 3

How does a lense work

Answer 3

-Combines pinhole accuracy with brightness and spatial data of image. Light rays spread out and hit lense which then causes the light rays to concentrate as they hit their target
-This has the consequence of images being inverted

Question 4

What is the composition of the eye

Answer 4

Rods: (far more than cones)
-sensitive photosensors
-responds to single photon
-poor spatial resolution as their nerves converge with the same neuron as the retina
-don’t process colour
Cones: (much fewer)
-active only at higher light levels
-signal is processed by several neurons
-higher resolution
-process colour

Question 5

What are the types of Ganglion cells

Answer 5

On centre:
-lots of firing if light hit’s centre but doesn’t hit outside
-medium firing if both outside and inside is hit by photons
-no firing if just outside is activated
Off Centre:
-fires rapidly if outside is activated and inside is not
-fires meh if both activated
-doesnt fire if only inside is activated

Question 6

How can on-centre cells detect contrast

Answer 6

If say left side is brighter than the right side. The centre of the cell will be illuminated as will the outside on the left, however the outside on the right may not be activated causing the outside of the cell to be less illuminated overall than the centre. This would cause the on cell to fire rapidly

Question 7

What are the main two colour theories

Answer 7

Trichromatic
Mixing colour theory

Question 8

What is the trichromatic colour theory

Answer 8

We have 3 colour cones, Red, Green, Blue. Each ganglion cell is activated proportionally to the wavelengths intensity of the corresponding colour:

Explains:
-colour blindness
-how we discriminate between wavelengths
-how many wavelengths could match to single colour

Does not explain:
-why some colour blend but others don’t

Question 9

what is the mixing colour theory

Answer 9

2different types of cones which correspond to two colour that oppose each other. for example if a blue/yellow ganglion will increase activation for blue wave lengths it will inhibit the activation of yellow ones

This explains why some colour mix and others don’t

proposes Blue/Yellow ganglion and Red/Green Ganglion

Question 10

Is either of the colour theories accepted as the one true theory of colour perception?

Answer 10

Nah, probably a mixture of both