5. Spatial Vision

Question 1

What is spatial vision

Answer 1

Ability to resolve detail and process lines and edges

Question 2

What do V1 simple cells respond to

Answer 2

oriented bars and edges (lines)

Question 3

Why is there a bell shaped distribution for orientation tuned neurons

Answer 3

Neurons have a preferred orientation they fire to, but will also fire (less) to other similar orientations

Question 4

What happens if you see a line stimulus which doesnt perfectly match and neurons preferred orientation?

Answer 4

There will be a distribution of responses and the visual system will use the peak to perceive an angle somewhere in between

Question 5

What is adaptation in response to a stimulus?

Answer 5

The cell will start to respond less following long periods of being active

Question 6

Explain the tilt after effect if the test stimulus are vertical lines and the adaptation stimulus is diagonal lines to the left

Answer 6

• before adaptation, cell 3 that prefers vertical lines is responding most to the test. 2 and 4 are slightly active.
• during adaptation, 2 is responding most but after a while will adapt and respond less
• when test presented again, there will be less response from 2 and 3, but 4 will respond larger relative to the others
• will percieve tilted lines in the opposite direction

Question 7

Explain the tilt after effect if the test stimulus are vertical lines and the adaptation stimulus is diagonal lines to the left

Answer 7

• before adaptation, cell 3 that prefers vertical lines is responding most to the test. 2 and 4 are slightly active.
• during adaptation, 2 is responding most but after a while will adapt and respond less
• when test presented again, there will be less response from 2 and 3, but 4 will respond larger relative to the others
• will percieve tilted lines in the opposite direction

Question 8

What influences the size of the tilt after-effect

Answer 8

the difference between the adaptation stimulus and the test stimulus

Question 9

You will get a smaller tilt after-effect if there is a _ difference between test and adaptation (bigger or smaller)

Answer 9

bigger

Question 10

If you make the adaptation and test stimuli more similar, you get a _ tilt after-effect (larger, smaller)

Answer 10

Larger

Question 11

What is the peak degree difference between stimuli for a strong tilt-aftereffect

Answer 11

10-20 degree difference

Question 12

The tilt after effect provides evidence for:

Answer 12

orientation tuned cells in the human V1

Question 13

Explanation of the size after-effect if the test lines are intermediate thickness (Cell 3), and adapt stimulus are fat lines (cell 4)

Answer 13

The test stimulus will activate cell 3 most, and 2 and 4 slightly. Then when a fatter adapt stimulus presented, cell 4 would be most active, and 3 and 5 slightly active. Eventually cell 4 would adapt
When test stimulus presented again, cells 2 and 3 would respond more strongly relative to cell 4, making the lines appear thinner.

Question 14

Size after-effect provides evidence for:

Answer 14

size tuned cells in V1

Question 15

‘Fat’ bars have a __ spatial frequency (high or low)

Answer 15

Low - less fit in given space on retina

Question 16

‘Slim’ bars have a __ spatial frequency

Answer 16

High

Question 17

Spatial frequency is:

Answer 17

the number of bars per unit distance

Question 18

What is used to define the size of bars on the retina

Answer 18

Spatial frequency

Question 19

High spatial frequency in natural images corresponds to:

Answer 19

Finer details of the image ie contours of a face

Question 20

High contrast

Answer 20

there is a large difference between light and dark areas

Question 21

Low contrast

Answer 21

there is a low difference in light/dark regions

Question 22

How does contrast sensitivity affect spatial frequency?

Answer 22

Can see a larger range of SFs at higher contrast (bell shaped distribution)

Question 23

We have the lowest sensitivity to these types of spatial frequency (high, low, intermediate)?

Answer 23

High and low - need higher contrast to see

Question 24

We are most sensitive to this spatial frequency (high, low, intermediate)

Answer 24

Intermediate - can see at lower contrasts

Question 25

Why is it harder to recognise faces from far away?

Answer 25

The fine details have a much higher spatial frequency that becomes invisible to us as there aren’t cells with small enough RFs

Question 26

Collections of neurons tuned to the same SFs are known as:

Answer 26

Spatial frequency channels

Question 27

In V1, cells with smaller receptive fields are correspond to which part of the retina:

Answer 27

The fovea

Question 28

Why do V1 cells corresponding to the fovea have smaller RFs?

Answer 28

To enable us to see finer detail (higher SFs)

Question 29

Size constancy

Answer 29

we perceive an objects real size in the world regardless of distance and the size on the retina

Question 30

if you adapt neurons to a line that is 10 degrees anticlockwise to vertical, and then see a vertical line, how will it appear?

Answer 30

will appear to be less than 10 degrees clockwise from vertical