Lecture 1

Question 1

Cell order from retina to visual cortex

Answer 1

Rods/Cones -> Bipolar cells - > Ganglion cells -> Optic Nerve -> Optic Chiasm -> Lateral Geniculate Nucleus -> Visual Cortex

Question 2

Rhodopsin/Photopsin

Answer 2

This is a protein which converts light into closing of the Na+ channels so that the membrane hyperpolarizes -> neural signal sent to bipolar cell and in turn the ganglion cell

Question 3

Retinal colour blindness

Answer 3

Absence of a particular cone type.
3-8 out of 100 people have this.

Question 4

Macula

Answer 4

Area around the fovea. Has the sharpest vision

Question 5

Macular Degeneration

Answer 5

Symptoms: Blank spots, Distorted central vision, and Acuity loss
Causes: Old age, smoking, diet, genetic
Receptors (pigment epithelium) are lost due to toxic products
No treatment

Question 6

Pigment epithelium

Answer 6

At the back of the retina and these cells prevent the light from scattering. Cats have reflecting PE which means better low light vision but unsharp image.

Question 7

Glaucoma

Answer 7

• Increase pressure inside the eye
• Damage of nerve fibers of the RGC’s: optic nerve
• Loss of peripheral vision first
• Treatment: eyedrops, surgery

Question 8

The need for visual data compression

Answer 8

The brain needs to compress visual data because there are 130M photoreceptors and only 1M nerve fibers

Question 9

Photoreceptors responding to light and dark

Answer 9

When hit with light it hyperpolarizes (closing of Na+ channel).
When hit with dark it depolarizes (opening of Na+ channel).

Question 10

ON and OFF system of bipolar and ganglion cells

Answer 10

Bipolar cells with ON systems have sign inverting synapses which turn hyperpolarization into depolarization and send this signal to an ON ganglion cell. These cells respond to light
Bipolar cells with OFF systems have sign conserving synapses which send the depolarization to the OFF ganglion cells. These cells respond to dark.
Glutamate is used to convert hyperpolarization to depolarization.

Question 11

Horizontal cells

Answer 11

These cells provide negative feedback on the receptors.

Question 12

Ganglion cells and contrast

Answer 12

Ganglion cells respond especially well to contrast and not so much diffuse light. Luminance is discarded.
This causes the perception of luminance to not always be correct. This is demonstrated in visual illusions like with the gray squares and shadows.

Question 13

Rods connecting to bipolar cells

Answer 13

Rods are connected to Rod Bipolar Cells and those are then connected to cone driven Bipolar Cells via Amacrine Cells. This means that Bipolar and RGC’s have receptive fields from cone and rod inputs.

Question 14

Dark adaptation

Answer 14

• Pupil dilation
• Cone to rod transition
• Bleaching of pigment in photoreceptors becomes undone
• Less receptor signal means less negative feedback from horizontal cells.

Question 15

Retinitis Pigmentosa

Answer 15

• Genetic disorder
• Progressive degeneration of receptors: first rods then cones
• Pigment deposits at affected parts of retina, depigmentation at vulnerable sites
• Night blindness -> loss of peripheral vision -> tunnel vision - > full blindness
• No Cure

Question 16

2 types of ganglion cell

Answer 16

1. Midget cell (X-type)
2. Parasol cell (Y-type)

Question 17

Midget cells (X-type)

Answer 17

• Small receptive field
• Single cone center and surround: colour
• Slow sustained responses
• Tuned to high spatial frequencies

Question 18

Parasol cells (Y-type)

Answer 18

• Large receptive field
• Many cones input to center and surround: not colour selective
• Fast transient response
• Tuned to low spatial frequencies

Question 19

Colour coding in the retina

Answer 19

Ganglion cells have a group of cones that are Red vs Green, Green vs Red or Blue vs Yellow

Question 20

High and low spatial frequency

Answer 20

High spatial frequency shows outlines of images very wel and has contrast but not a lot of the overall shape very well.
Low spatial frequency is not very well outlined but you see the overall image but just a vague version of it.

Question 21

Spatial frequency sensitivity

Answer 21

This depends on the contrast and brightness.

Question 22

Spatial frequency sensitivity of RGC’s

Answer 22

Center part of the RGC receptive field is sensitive from low to high SF’s. Surround from low to intermediate SF’s. When combined this gives the characteristic SF tuning of RGC’s.

Question 23

RGC projection to the brain (X and Y)

Answer 23

Midget Cells -> Parvocellular layers of the LGN (M -> P)
Parasol Cells -> Magnocellular layers of the LGN (P -> M)

Question 24

Navon task (hierarchical letter stimuli)

Answer 24

Subjects have to detect either the global target (large letter or shape) , or the local target (small items).
Global targets are detected quicker than local ones. Also congruent stimuli are faster than incongruent.
In addition, global info is faster in the right hemisphere and local info faster in the left.