Visual system

Question 1

Define decussation?

Answer 1

Criss cross of orientation info from sensory field to opposite side of brain

• left visual field to right cortex
• right visual field to left cortex

Question 2

Is vision partially or fully desuccated? Explain.

Answer 2

Partially.

50% of optic nerve fibres go to opposite side of brain by crossing at the optic chiasm.

Question 3

What is an optic nerve?

Answer 3

Nerve that transports visual info from the eye to the optic chiasm
Has bilateral visual field

Question 4

What is an optic tract?

Answer 4

Nerve that transports visual info from the optic chiasm to the brain
Unilateral visual field

Question 5

Define retinotopic? True/false It is maintained throughout the visual processing hierarchy?

Answer 5

Adjacent points in the visual field that line up with adjacent points in the retina. True

Question 6

Define cortical magnification?

Answer 6

More cortex dedicated to central visual field than periphery - convergence

Question 7

What is the role of the eye in visual processing?

Answer 7

Forms an image
Generates a neural signal
Early neural processing of the signal
Transmits visual signal to brain

Question 8

What is the cornea and what is it’s role in visual processing?

Answer 8

Transparent outer layer of eye

Most refraction of light occurs here

Question 9

What is the lens and what is it’s role in visual processing?

Answer 9

Bouncy elliptical, clear ball behind iris that fine tunes image formation
Adjustable
Stiffens with age

Question 10

What is the iris and pupil and what are they responsible for?

Answer 10

Size of the opening (pupil) regulated by contractile tissue (iris)
Varies light but most importantly focal length

Question 11

What parts of the eye are involved in transduction?

Answer 11

Retina and fovea

Question 12

What is the retina and what is it responsible for?

Answer 12

Layers of neurons for early processing of the signal
Receptors to transduce light signal to neural signal
Retinal ganglion cells final layer - axons to brain

Question 13

What is the fovea and what is it responsible for?

Answer 13

Small specialised high acuity central vision

Solves the backward wiring problem by having less RGCs than rest of retina

Question 14

What are the items responsible for transmission of visual info to brain?

Answer 14

Optic disc and optic nerve

Question 15

What is the optic disc and what is it’s job?

Answer 15

Point on the retina where retinal ganglion cell axons leave to become the optic nerve
Blind spot-no receptors

Question 16

What is the optic nerve and what is it’s job?

Answer 16

Optic tract beyond the optic chiasm
Partial desiccation at the optic chiasm
Neural transmission to brain

Question 17

What are simple cortical cells

Answer 17

Centre-surround cells in layer 4 project to simple cells in layer 3
Detect line segments
Simple cells (and LGN and RGCs) are monocular

Question 18

What type of stimuli do simple cortical cells prefer?

Answer 18

1. Type of edge
   - bars of light in a dark field
   - dark bars in a light field
   - single straight edges between dark and light
2. Orientation
3. Location (retinotopic)

Question 19

What is a scotoma and how does it affect visual perception?

Answer 19

Blind spot in contralateral field of both eyes caused by damage to V1
Often no consciousness awareness due to completion

Question 20

What are receptive fields? What do they reveal about the function of the neuron?

Answer 20

Regions on the retina and the features that excite or inhibit the neuron. Nature of receptive field gives clues about the cell’s function.

Question 21

What are the characteristics of an RF?

Answer 21

Small (high spatial resolution) or large (low spatial resolution), have both excitatory and inhibitory areas

Question 22

Define photopic and scotopic vision

Answer 22

Photopic vision is vision under well-lit conditions. It allows vision of colours and details.
Scotopic vision is vision under dimly lit conditions. It allows vision of light and dark contrast.

Question 23

What is lateral inhibition?

Answer 23

The ability of a neuron to tone down the activity of neighbouring neurons in the lateral direction.

Question 24

What are Mach bands? How does our brain interpret them?

Answer 24

Bands of contrast that are decreasing in intensity. Our brain interprets them using contrast enhancement where perception of edges stronger to detect contrast better.. Firing rate proportional to intensity of light and each neuron decreases activity of its lateral neighbours. Inhibition greater with more intensity and greater inhibition for closest neighbours.