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Cognitive Psychology > The Visual Pathway > Flashcards

The Visual Pathway Flashcards

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1
Q

What is light?

A

Light is a wave of electromagnetic energy.

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2
Q

What is a visual field?

A

How much of the outside world the retina can see.

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3
Q

What is distance on the retina measured in?

A

Degrees of visual angle.

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4
Q

What is the fovea?

A

The part of the macula that contains the highest density of photoreceptors and therefore has the highest visual acuity in the retina.

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5
Q

What are the 2 types of photoreceptors?

A

Rods and cones.

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6
Q

There are more rods in the _____ and more cones in the ______.

A

Fovea, periphery.

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7
Q

How many rods do we have per eye?

A

120 million.

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8
Q

____ see in colour and ____ see in monochrome.

A

Cones, rods.

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9
Q

_____ are 1 to 1 with ganglion cells and _____ are many to 1.

A

Rods, cones.

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10
Q

What is the purpose of retinal ganglion cells?

A

They provide action potentials that project to the CNS via the optic nerve.

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11
Q

What is the duplex retina?

A

The idea that we have 2 separate systems that deal with different light levels.
1. Cone driven, light system with high acuity and low sensitivity.
2. Rod driven, dark system with low acuity and high sensitivity. This is also colour-blind.

The pupil will dilate/constrict 1-8mmmm, reducing/increasing the light by 64x.

The photoreceptors increase the amount of photosensitive protein they have, increasing sensitivity by up to 1000x.

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12
Q

How do we carry out single cell recording on retinal ganglion cells?

A

We place a tiny electrode next to the axon of a RGC to record electrical changes in the axon.

We can move the position of a light around until we begin to influence the RGC activity – this area of sensitivity is called the receptive field (RF) of the RGC.

The RF is the region of the visual the cell is responsible for.

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13
Q

What can influence a RGC’s action potential firing pattern?

A

The light in their receptive field.

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14
Q

What is one important thing about a RGC and its firing rate?

A

They have a baseline firing rate, so the firing rate can both increase and decrease from its baseline.

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15
Q

What 2 regions make up a RGC’s receptive field? What do these 2 regions show?

A
  1. Centre region
  2. Surround region

These regions show a centre-surround antagonism.

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16
Q

If a light is turned on in the centre region, the RGC firing rate will _____.
If a light is turned on in the surround region, the firing rate will _____
This is an ______ cell.

A

Increase, decrease, ON-centre.

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17
Q

Where are receptive fields smallest? What do these provide?

A

The fovea. These provide high spatial resolution.

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18
Q

What is the purpose of centre-surround antagonism?

A

It helps identify edges in images.

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19
Q

What do ON and OFF systems allow the visual system to detect?

A

Increment and decrement in light levels.

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20
Q

What is the name of the illusion that portrays centre-surround antagonism?

A

The Hermann Grid.

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21
Q

How can the Hermann Grid be explained?

A

The cell centred on the intersections of the squares will respond less because the surround is balancing out the centre.
Thus, it responds less and the observer will perceive a dark spot at that location.
If you look directly at a spot, smaller receptive fields are involved, which entirely fit within the intersection.

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22
Q

What are the 3 subdivisions of retinal ganglion cells?

A

M-cells
P-cells
K-cells

23
Q

Where do projections of the world switch sides during the visual processing system?

A

The optic chaism.

24
Q

Where does the optic tract project to?

A

The lateral geniculate nucleus.

25
Q

What is the lateral geniculate nucleus?

A

A part of the thalamus and a crucial relay station in the brain.

26
Q

What % of axons from RGCs project to the LGN?

A

80%.

27
Q

How many layers does the lateral geniculate nucleus have?

A

6 layers.

28
Q

The cells in layer 1 and 2 of the LGN are ______ and get input from _____. These are called the ________ layers.

A

Larger, M-cells. Magnocellular.

29
Q

The cells in layer 3 to 6 of the LGN are ______ and get input from _____. These are called the ________ layers.

A

Smaller, P-cells. Parvocellular.

30
Q

What are ipsilateral fibres? What layers do these fibres input to?

A

Fibres that haven’t crossed. These input to layers 2, 3 and 5.

31
Q

What is a retinotopic map?

A

The idea that there is a map of the retina. Each of the 6 LGN layers and their matching regions are stacked on top of each other so the same retinal region is located in the same place within each layer.

32
Q

How do P and M cells process colour?

A

P cells are colour sensitive.

M cells respond to all colours and are not colour sensitive.

33
Q

How do P and M cells process acuity?

A

The best spatial resolution is in P layers.

This is because M layers have the largest LGN receptive fields.

34
Q

How do P and M cells process temporal sensitivity?

A

P cells are slower to respond to rapid change in light sensitivity.

M cells are quicker. They also are much more sensitive to motion.

35
Q

The visual cortex has about _______ cells per hemisphere.

A

100 million.

36
Q

The LGN comes in the visual cortex at which layer?

A

Layer 4. (Magnocellular in upper layer 4, Parvocellular in lower).

37
Q

What are ocular dominance columns?

A

Cells in layer 4 are driven by the input from one eye only.
If a block of cells receives input from the right eye, the cells above and below it will also receive input from the right eye.
But adjacent blocks of cells either side will receive input from the opposite eye.
This creates a pattern of ocular dominance columns that penetrate perpendicular to the surface.

38
Q

What is cortical magnification?

A

The retinotopic map is maintained in the cortex.

However, the distribution of cells associated with each retinal region is distorted: 80% of cortical cells are devoted to the central 10deg of the visual field.

This disproportionate weighting of cortical power is referred to as cortical magnification

39
Q

What are some similarities of cortical cells & RGCs and LGN cells?

A
  1. They maintain the retinotopic map.
  2. They aren’t that sensitive to the illumination level.
  3. They respond best to abrupt changes in luminance.
40
Q

What are some differences of cortical cells & RGCs and LGN cells?

A
  1. Selectivity to orientation
  2. They are sensitive to size in a different way.
  3. They can be binocular.
  4. They are more sensitive to colour.
  5. They are sensitive to direction of motion.
41
Q

Why do cortical cells have a preference of orientations?

A

Cortical receptive fields are organised and shaped differently so that they obtain a maximum response to a line of a specific orientation.

42
Q

How do we create a map of orientation preference for cortical cells?

A

We can use staining to create pinwheels.

43
Q

What are simple cortical cells?

A

Simple cell: Optimum response to an appropriately oriented stimulus and a certain position within the RF. These are phase sensitive.

44
Q

What are complex cortical cells?

A

Complex cell: Optimum response to an appropriately oriented stimulus placed anywhere within the RF. These are phase insensitive.

45
Q

What are hypercomplex cortical cells?

A

Hypercomplex cell: Optimum response depends not only on orientation but also on contour length. Maximum response occurs when the bar length matches the width of the receptive field.This is “end stopping” or “length-width inhibition”.

46
Q

What are binocular cells?

A

Binocular cells have two RFs – Left eye & Right eye.
They are matched in type (e.g. simple), and respond to similar preferred orientations, locations, and directions of motion.
I.e. their response will be maximal when corresponding regions in each eye are stimulated by stimuli of similar size and orientation

47
Q

What are colour sensitive cells concentrated in? Where are these centred?

A

Cortical blobs. Each blob is centred on an ocular dominance column.

48
Q

Within a blob, cells will either have _______ or _______ opponency – these are not mixed in a single blob.

A

red/green, blue/yellow.

49
Q

Where do blobs receive their input from?

A

Lower layer 4 (which gets its input from parvocellular LGN layers).

50
Q

What is direction selectivity?

A

Motion sensitive cells usually respond only to one direction

51
Q

Simple cells respond to ______ motion. Complex cells response to _______ motion.

A

Slow, faster.

52
Q

What is a hypercolumn? What is known as?

A

A set of 18-20 columns cross a complete range of orientations and ocular dominance. This collection of adjacent columns is referred to as a hypercolumn.

This is known as the ice cube model.

53
Q

What is a column?

A

A column consists of cells with the same orientation and ocular dominance preferences.

Cognitive Psychology (19 decks)

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