Vision

Question 1

Characterisitcs of light

Answer 1

wavelength and intensity

Question 2

Intensity

Answer 2

Number of photons hitting ur eyes per second
This change is perceived as a change in brightness

Question 3

What is optic array
What determines the optic array

Answer 3

Is the spatial distribution of light
It is detemiened by the position of sources of light (eg sun) and position of the reflectors of light (eg any visible objects)

Question 4

Pathway from light hitting obejct to perception and recognition of object

Answer 4

Light –> eye/retina –> Optic Chiasm –> LGN –> Striate cortex –> extrastriate cortex –> Perception of object

Question 5

Important function of the visual system

Answer 5

Convert pattern of light on the retina into a perception of a three dimensional world
(eg another function is control of action)

Question 6

Computational approach and key issue of this approach

Answer 6

Perception as information processing
treating image as information where there are areas of high (eg eye) and low (blurred solid background) information
Key question: how and where is information encoded at different levels of visual system

Question 7

Principle of Least commitment (Marr & Barlow)

Answer 7

Dont throw away any information because you might need it later

Question 8

Principle of graceful degradation (Marr & Barlow)

Answer 8

If a system were to break down it should still be useable eg if one eye breaks u still have another one, same with ears

Question 9

Principle of least redundancy (Marr & Barlow)

Answer 9

Encode informrion in the most efficient way possible, because we have limited cpaapcity and dont want to waste energy storing info that is not iportant or necessary

Question 10

Strucutre of visual system in the eye:

Answer 10

Retina -> blood vessels -> Rods and cones activated -> signal goes to bipolar cells -> ganglion cells -> optic nerve -> leaves eye

Question 11

Phototransduction

Answer 11

converting light into electircal signal to
Absorb photons of light –> exposure to light changes the visual pigment molecuels shape which acts as a switch alowing fir chenical reaction

Question 12

Metamers

Answer 12

Different distrituons of light but activate the cones in the same relative amounts

Question 13

Receptive field

Answer 13

Region of retina that when stimulate influences the firing rate of the neuron
A region of space to which a particular sensory neuron responds.

Question 14

Spectral sensitivity

Answer 14

Different photorecptora are sensitve to different wavelenghts (S, M,L)

Question 15

Visual Electrophysiology

Answer 15

Tiny electrodes placed in or close to visual neurons
Visual stimuli presented to animal, and electrical signals/action potentials are recorded (spike)

Question 16

Center-surround structure

Answer 16

found in ganglion cell
if in center then excitatory but if around htr center then inhibitroy to neuron firing
Signal more likely to fire if its in the center bit of the structure
So where there is high information (eg eyes) there will be increased firing rate –> finds intensity differences in image ur looking at
Finds intensity edges- the edge between high info and low info centers
Key- they emphasize edges

Question 17

Color-opponenet ganglion cells

Answer 17

Black-white
Blue-yellow
Red-green
One color will exicte the neuron while the other will be inhibited

Question 18

Lateral Geniculate Nucleus (LGN)

Answer 18

2 LGN (1 in each henmispehre)
Information coming from ipsilateral (same side) and contralateral (opposite side) eye

Question 19

Retinoscoptic organization

Answer 19

Where light is hitting retina
This is mapped out and organized by there light is hitting retina

Question 20

Layers of LGN

Answer 20

6 layers encompassed by:
Parvocellular layers(outermost) - red and green cones
Koniocellular layers - blue/yellow
Magnocellular layers(innermost) - black and white

Question 21

Parallel processing

Answer 21

Fine detail, red-green colour (P pathway)
Blue-yellow colour (K pathway)
Fast temporal changes (M pathway)

Question 22

Striate Cortex aka V1

Answer 22

Stripey (striate)
More refined than LGN but purpose is still debated
We are blind without it
I closest to skull, VI furthest from skull
porbbaly not seat of vision

Question 23

Simple Cells (Hubel & Wiesel, 1981)

Answer 23

In striate cortex
Elongated receptive field (not circular) responsive to bar shape
Orientation tuning - as you rotate bar of light the reponses of neuron changes
But unlike the LGN cells, they have orientation selectivity rather than center-surround visual fields.
Hubel and Wiesel (1959) found that elongated stimuli that looked like bars seemed to be particularly effective stimuli for these cells. Indeed, they found that some cells wanted a dark bar on a light background and others that responded to a white bar on a dark background.

Question 24

Complex cells (Hubel & Wiesel, 1981)

Answer 24

In striate cortex
Complex cells are also neurons in V1 that respond optimally to a stimulus with a particular orientation. But, unlike simple cells, they respond to a variety of stimuli across different locations. For example, a complex cell will respond to a dark bar on a light background and a light bar on a dark background. In contrast, a simple cell only responds to one but not the other.
Complex cells respond best to moving stimuli.

Question 25

End-stopped cells (Hubel & Wiesel, 1981)

Answer 25

In striate cortex

Question 26

Why is there a belief there might be a hierarchal structure in the visual system?

Answer 26

Center surround structure in ganglion and LDN—> tie them together and get simple cell –> tie simple cells together to get complex cells

Question 27

Extrastriate Cortex

Answer 27

Beyond striate cortex/ v1, receptibve fields get bigger and more specialized
As receptoive feield gets bigger, precise retinotopic position becomes less relevant
Lots of other parts of brain reposnidn to visual input

Question 28

Depth perception in V1

Answer 28

Having 2 eyes = axons from both meet at a certain place and our brain takes that into account and this gives us depth perception. Missing one eye means we will lack depth perception