Light, Eye, Brain - Terminology

Question 1

Accommodation

Answer 1

The lens can be stretched to allow focusing of far objects

Question 2

Acuity

Answer 2

Acuity is precision.

Question 3

Astigmatism

Answer 3

• Eyes are rugby ball shaped instead of soccer-ball-shaped
• Different focal lengths for different orientations
  E.g. ok for verticle lines but myopic for horizontal lines.

Question 4

Blind spot

Answer 4

Where the optic nerve/ disc leaves the eye. There are no photoreceptors here. Hence, blind spot.

Question 5

Contrast

Answer 5

Relative luminance is constant, regardless of absolute luminance.
E.g. White paper vs. Black paper
A numerical value between 1 and 0. Zero is all grey. One shows a significant difference.
Contrast = (Lmax - Lmin) / (Lmin + Lmax)

Question 6

Cornea

Answer 6

The transparent “window” into the eyeball. A lot of focusing is done by the cornea. Estimates say up to about 2/3rds.

Question 7

Contrast

Answer 7

A measure of the difference between the highest and lowest luminance emitted or reflected from a surface
E.g. White paper vs. Black paper
A numerical value between 1 and 0. Zero is all grey. One shows a significant difference.
Contrast = (Lmin - Lmax) / (Lmin + Lmax)

Question 8

Lens

Answer 8

Clear structure. Enables changing focus using ciliary muscles (stretches and squishes to focus light).

Question 9

Photons

Answer 9

Particles of light.

Question 10

Emmetropia

Answer 10

Appropriate focus. The normal refractive condition of the eye.

Question 11

Extrastriate Cortex

Answer 11

Extrastriate cortical visual areas. 
V1 - 
V2 - 
V3 - 
V4 - 
V5/MT - 
These areas have been associated with processing certain stimuli/ are specialised however they all do a variety of processes. 
The deeper the area, the more advanced the specialisation (generally).

Question 12

Focus

Answer 12

Focussing is recombining rays from various directions to form a single point on the imaging surface.

Question 13

Fovea

Answer 13

Fovea or Macula
A central part of the retina with the best resolution.
The part where photoreceptors are most denesly packed.
No blood vessels - they would obscure vision.

Question 14

Ganglion Cells

Answer 14

Recieve electrical impulse from rods and cones.
Have long axons that exit the eyeball via a bundle called the optic nerve.
All of the ganglion cell body is in the eyeball itself.

Question 15

Hyperopia/ Hypermetropia

Answer 15

• Far or long sightedness
• Focal length is too long
• Need convex corrective lenses

Question 16

Lateral Geniculate Nucleus (LGN)

Answer 16

Ganglion cell axons terminate in the Lateral Geniculate Nucleus (LGN).

Question 17

Rods

Answer 17

High sensitivity (low threshold)
Night vision
Pass electrical impulses to ganglion cells

Question 18

Cones

Answer 18

Low sensitivity (high threshold)
Daytime / colour
Pass electrical impulses to ganglion cells

Question 19

Macula

Answer 19

Macula or fovea.

A central part of the retina with the best resolution.

Question 20

Optic disc

Answer 20

Optic disc or optic nerve.
Where the ganglion cell axons leave the eye.
There are no receptors here.
Blind spot.

Question 21

Receptive field

Answer 21

The area in which one ganglion cell receives input from many photoreceptors.
Receptive fields for foveal vision are smaller and more densely packed.
Receptive fields for periphery are larger and less dense.

Question 22

Optic chiasm

Answer 22

Ganglion cell axons cross at the optic chiasm.

Question 23

Partial decussation

Answer 23

Left visual field goes to right LGN.
Right visual field goes to left LGN.
Visual stimulus that lands on the nasal side of the eye will cross to the other side.

Question 24

Retinotopic

Answer 24

Cells next to each other in the brain have retinal receptive fields next to each other in your eye.
The organisation of cells in the brain relates to the organisation of cells in your eye.

Question 25

Striate Cortex

Answer 25

The striate cortex or the primary visual cortex is located in the occipital lobe. LGN projects to it via optic radiations.

Question 26

Refraction

Answer 26

The change in direction of a light ray, as it passes through one transmitting media to another, caused by a change in the velocity of propagation.
E.g. Air vs. Water

Question 27

Interference Pattern

Answer 27

The pattern that is formed when two sets of waves overlap. Producing mutual reinforcement and some locations and cancellation at others.

Question 28

Focal length

Answer 28

The distance from the centre of a lens to its focus.

Question 29

Luminance

Answer 29

A photometric measure of energy emitted or reflected from a light source. Measured in candelas.

Question 30

Reflectance

Answer 30

The proportion of incident light reflected from a surface.