Center-surround Receptive Fields

Question 1

ON-centre ganglion cells

Answer 1

Excited when light falls in their centre

Inhibited when light falls in the surround

Question 2

OFF-centre ganglion cells

Answer 2

Inhibited when light falls in the centre

Excited when light falls in the surrounding

Question 3

True or False

The diameter size of the light affects the level of excitement of a ganglion cell.

Answer 3

True

If the light covers all the centre part, the ON-center ganglion cells will be very excited compared to just having a small dot of light in the centre.

On the other hand, if the light covers the whole cell, the ON-centre ganglion cells won’t be as excited since there would be light on the surround as well.

Question 4

What is the objective of the centre-surround organisation?

Answer 4

The purpose of the centre-surround organization is to help us perceive edges.

Question 5

Diffuse bipolar cell

Answer 5

Receives input from multiple photoreceptors

Question 6

Midget bipolar cell

Answer 6

Receives input from a single cone.

Question 7

Parvocellular pathway

Answer 7

P cells:

• receive information from midget bipolar cells.

The parvocellular pathway is concerned with visual acuity, colour and shape procession.

• Good Spatial resolution
• Poor Temporal resolution

Question 8

Magnocellular pathway

Answer 8

M ganglion cells:

• Receive information from diffuse bipolar cells

Magnocellular pathway involves motion procession

• Good Temporal resolution
• Poor Spatial resolution

Question 9

Convergence

Answer 9

Information received by cells converges to a single cell.

Notice that an increase in converges causes an increase to light sensitivity and a decrease in visual acuity.

Question 10

Convergence: Consider the image below

Answer 10

Notice that in the image to the left, the convergence prevents the retinal ganglion cell to detect the provenance of the light.

As for the image to the right, the retinal ganglion cell can easily identify the provenance of the light.

Question 11

Acuity

Answer 11

The smallest spatial detail that can be resolved.

Question 12

Name a way to measure acuity

Answer 12

• Vision scientist: Smallest angle of a cycle of the grating
• The smallest the angle, the better your vision
• The limit is determined by the spacing of the photoreceptors on the retina

Question 13

Spatial frequency

Answer 13

Cycles of grating per unit of visual angle (in degrees)

Question 14

Gabor Patches

Identify the spatial frequency (low, medium, high) of each Gabor patch below.

Answer 14

(a) Low spatial frequency
(b) Medium spatial frequency
(c) Hight spatial frequency

Question 15

True or False

Any black and white image can be described in terms of a weighted combination of frequencies with different orientations.

Answer 15

True

Question 16

What happens if we remove the high frequencies of a black and white image?

Answer 16

It becomes blurry!

Question 17

What happens if we remove the low frequencies of a black and white image?

Answer 17

The image becomes brighter