Topic 8 - The Visual System

Question 1

Cornea

Answer 1

Absolute level of refraction (can’t change shape of cornea)

Causes Bending of light energy in order to focus it on certain areas of the retina

Question 2

Lens

Answer 2

Change the amount of refraction of light
(Shape changes to allow for more refraction when you bring object closer)

Shape of lens determines the amount of refraction that occurs

Question 3

Ciliary muscle

Answer 3

Determines shape of the lens

Question 4

Iris

Answer 4

Series of muscles that determines size of pupil

Question 5

Pupil

Answer 5

Window that allows light energy into the eye

Pupil gets bigger in darker room to let more light into eye

Question 6

Retina

Answer 6

Area of eye that converts light energy into APs

Important Functional area of light

Question 7

Fovea

Answer 7

Specialized area of retina

Cornea and lens refract light onto fovea

Fovea is where highest level of visual processing takes place
- highest special acuity/resolution

2 layers (ganglion and bipolar cell layers) are pulled off to the side so that light energy can influence photoreceptors with less distortion (remember distortion of light entering)

Highest concentration of CONES

Lowest ratio of recptors-ganglion cells = smallest receptive field = highest acuity in bright light

Question 8

Optic disk

Answer 8

Output Cells from retina exit here

Question 9

Refraction

Answer 9

Bending of light energy

Question 10

Photoreceptors of the eyes

Answer 10

Rods & cones

Convert light energy into APs

Question 11

3 layers of the retina

Answer 11

1. Photoreceptors (Ross & comes)
2. Bipolar cells
3. Ganglion cells

Question 12

If there is more light energy is there more or less neurotransmitter released?

Answer 12

More light energy = less neurotransmitter release

Less light energy = more neurotransmitter release

Question 13

When is the ON cell depolarizer (excited)?

Answer 13

When there is MORE Light (less neurotransmitter)

Question 14

When is the OFF cell depolarized (excited)?

Answer 14

When there is LESS light (more neurotransmitter)

Question 15

Differences between rods and cones pathway

Answer 15

1. Rod pathway can only activate ON bipolar cells (they then use interneuron called amacrine cell to activate the bipolar cells of the cones pathway)
2. Rods have more convergence to bipolar cells while cones have less convergence to bipolar cells
3. Rods respond better in less light, cones respond better in bring light

Question 16

What does the amacrine cell (interneuron) do?

Answer 16

Excites (depolarizers) the ON cell of the cones pathway

Inhibits the OFF cell of the cones pathway

Question 17

How do you get ⬆️ acuity?

Answer 17

⬇️ ratio of receptors:ganglion cells = ⬇️ receptive field = ⬆️ visual acuity

Question 18

Centre-surround mechanism

Answer 18

“The centre of a visual field responds differently to light than the surrounding (annulus) of a visual field”

Question 19

Receptive field

Answer 19

Area of retina that can be influenced from the firing of a ganglion cell

Question 20

What do horizontal cells do

Answer 20

Enhance the centre-surround mechanism

Question 21

Magnocellular pathway of LGN

Answer 21

provides motion info (important for visual feedback during movement)

More rods (higher sensitivity, don’t like light)

Larger receptive fields bc rods are mainly part of the peripheral retina and have higher ratio of convergence

Question 22

Parvocellular pathway of LGN

Answer 22

Applies meaning to what we’re seeing like identifying objects

More cones (less sensitive bc cones like light)

Smaller receptive fields bs made mainly of cones which is was the fovea is made of and cones have less convergence meaning smaller receptive fields

Question 23

What part of brain does dorsal stream go to

Answer 23

Posterior parietal cortex

Question 24

What part of brain does ventral stream go to

Answer 24

Occipital-temporal cortex

Question 25

How does the dorsal stream represent space

Answer 25

Egocentrically

Object location/size are coded in reference to the body

Absolute coordinates used

Question 26

How does the ventral stream represent space

Answer 26

Allocentrically

Object location/size are coded relative to other objects in the environment (info therefore does not need to be updated as you move closer or further from objects)

Uses relative coordinates for size and location

Question 27

When are tasks immune to size-contrast illusions?

Answer 27

1. When they are performed in ‘real time’ (immediate)

2. When they use absolute coordinates