w2Human Visual System 1&2

Question 1

2 roles of the chamber of the eye??

Answer 1

-> exclude light, except that which enters thru the cornea & pupil
-> focus an image, of world onto retinal surface

Question 2

structure of the retina??

Answer 2

structure of the retina is complex, multilayered, contains cell bodies between layers of nerve fibres and dendrites

Question 3

why can’t you see your blood vessels??

Answer 3

Blood vessels are fixed in position with respect to retina, attached and move with it-> stabilised image

Question 4

how many types of photopigment do cones have??

Answer 4

3 types of photopigment (L,M,S)

Question 5

how many types of photopigment do rods have??

Answer 5

1 type of photopigment-> Rhodopsin

Question 6

Cones density wrt fovea??

Answer 6

good acuity -> colour vision, high density in central fovea enabling high acuity and rapid fall in density away from fovea

Question 7

Rods density wrt fovea??

Answer 7

good light sensitivity -> achromatic (no colour vision) absence of rod in fovea -> ‘night blind’, high density of rods in periphery

Question 8

ganglion cells??

Answer 8

-> final output neurons of the vertebrate retina

Question 9

The 2 major types of Ganglion cells in the retina:

Answer 9

Magnocellular (M) cells
Parvocellular (P) cells

Question 10

Magnocellular (M) cells:

Answer 10

receive inputs from many photoreceptors
respond faster and respond to transient/moving stimuli
poor spatial resolution since they combine inputs from many photoreceptors

Question 11

Parvocellular (P) cells:

Answer 11

receive inputs from fewer cones
have high spatial resolution
play a key role in colour vision

Question 12

Why can’t you see the shadow cast on the photoreceptors of your own blood vessels
in normal everyday vision?

Answer 12

the blood vessels are fixed in position with respect to your retina. as you move your eye, since the blood vessels are attached to
your retina, they move about with it, forming a fixed relationship. The pattern of retinal blood vessels does not change as you move your eyes. a stabilized image. eye is insensitive to stabilized images.
Under stabilized viewing conditions, the image of the world that is projected onto your retina does not make it to your conscious awareness. After a few seconds of stabilization, the entire scene seems to fade and disappear. The stabilized scene of the world disappears just like the shadows of your blood vessels disappear