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PSY219 > 6: The Visual System > Flashcards

6: The Visual System Flashcards

1
Q

Light…

A

Sometimes described as electromagnetic waves or photon-particles.

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2
Q

Infrared light waves…

A

Humans cannot see them because they are too long.

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3
Q

Intensity/brightness…

A

= Wavelength/colour.

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4
Q

What length wave is bright red?

A

= 700nm wave.

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5
Q

High illumination…

A

+ acuity, - sensitivity.

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6
Q

Low illumination…

A
  • acuity, + sensitivity.
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7
Q

What is the role of ciliary muscles?

A

Hold lens in place with ligaments.

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8
Q

Accommodation…

A

Changes in focus made my lenses.

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9
Q

Prey have eyes on the sides of their heads because…

A

It allows for a wider visual field to spot approaching predators.

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10
Q

Predators have eyes side-by-side because…

A

It allows for better accuracy, such as better depth perception for determining the distance of their prey.

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11
Q

Binocular disparity…

A

Difference in position of an image on eye retinas due to eyes not being in exact same position.

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12
Q

Retina has 5 layers of neurons (Re, Ho, Bi,Am,ReG)…

A

(Back-front) Retina receptors, horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells.

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13
Q

Blind spot…

A

The gap in the receptor layer that affects exiting ganglion cells due to the retina being back-to-front.

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14
Q

Fovea helps…

A

Minimise distortion of light due to retina being back-to-front.

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15
Q

Completion…

A

Helps compensate for blind spot.

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16
Q

Surface interpolation…

A

A type of completion process that helps complete the appearance of a large surface by using information such as edges and contrast.

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17
Q

Nocturnal creatures…

A

Have rod-only retinas (rod-type of receptor).

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18
Q

Daytime creatures…

A

Have cone-only retinas (cone-type of receptor).

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19
Q

Duplexity Theory…

A

Vision is influenced by rods and cones.

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20
Q

Photopic (cone) vision…

A

Used in good lighting, high acuity provided.

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21
Q

Scotopic (rod) vision…

A

Used in poor lighting, high sensitivity provided.

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22
Q

Fovea only contains…

A

Cones, hence superior acuity.

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23
Q

Spectral sensitivity curve (SSC)…

A

A graph displaying relative brightness of lights at different wavelengths.

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24
Q

Photopic SSC…

A

Relative brightness of light shone on fovea.

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25
Q

Scotopic SSC…

A

Relative brightness of light shone on retina.

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26
Q

Purkinje effect…

A

When the relative brightness of objects changes due to changes in scotopic and photopic spectral sensitivity.

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27
Q

Summation…

A

A process whereby our eyes build on the last ‘scan’ it makes of the seen environment, enabling us to have a continual perception of our environment.

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28
Q

Pigment…

A

Any substance that absorb light; in this case, rhodopsin, a red pigment.

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29
Q

Light effects on rhodopsin…

A

It becomes bleached when it absorbs too much bright light, and regains colour in darkness.

30
Q

Rhodopsin is…

A

A G-protein that responds to light, not neurotransmitters.

31
Q

Retina-Geniculate-Striate pathways…

A

Conduct signals from the retinas to the primary visual cortex via the lateral geniculate nuclei in the thalamus. Its system is retinotopic.

32
Q

25% of the primary visual cortex…

A

Is for the analysis of fovea input.

33
Q

Parvocellular layers…

A

A channel of communication via RGS pathways. Cones provide most input to these.

34
Q

Magnocellular layers…

A

A channel of communication via RGS pathways.

Rods provide most input to these.

35
Q

Edges…

A

The most important piece of information in any visual display, as it establishes object separation and their positions.

36
Q

Mach Bands…

A

A.K.A the Chevreul illusion. Stripes used to emphasises differences of a colour along a spectrum.

37
Q

Lateral inhibition…

A

+ intense light = + ommatidium axon firings = + lateral inhibition
Inhibition of rate of firing of surrounding cells.

38
Q

Receptive field…

A

The area of a visual field of a neuron in which a visual stimulus can influence the firing rate.

39
Q

Fovea receptive fields…

A

Are smaller than in periphery visual components of eye. Supports idea of small area-high acuity.

40
Q

Neurons are monocular…

A

Meaning their receptive field only accounts for one eye.

41
Q

On-centre cells…

A

Illumination on central region = excitatory.

Illumination on peripheral region = inhibitory.

42
Q

Off-centre cells…

A

Illumination on central region = inhibitory.

Illumination on peripheral region = excitatory.

43
Q

Simple cells…

A

On-off response, receptive fields are rectangular shaped, so respond best to bar-shaped features.

44
Q

Complex cells…

A

On-off response, except its ‘on’ and ‘off’ regions aren’t static, enabling continuous response to a stimulus. Good for recognising moving objects.

45
Q

Organisation of cells…

A

Determines its preference for the orientation of features, e.g. | / - \ | , horizontal or columnar organisation.

46
Q

Plasticity…

A

Is a key function in the visual cortex, and contradicts the key assumption that receptive fields are static properties of neurons.

47
Q

Black…

A

Absence of light.

48
Q

White…

A

Intense and equal mixture of a wide range of wavelengths (colours).

49
Q

‘Component’ or ‘Trichromatic’ theory…

A

Young (1802)

  • 3 types of colour receptors, and stimulus is perceived in varying ratio by these receptors.
  • Can be any 3 wavelengths provided that the colours are mutually exclusive.
  • Supported by findings that there are 3 types of cones that are mutually exclusive.
50
Q

‘Opponent Process’ theory…

A

Hering (1878)

  • 2 cell classes for colour coding, and another class for brightness coding.
  • Each class has 2 complementary colour perceptions (red-green, blue-yellow, and black-white for brightness).
  • Supported by idea that there is no such thing as ‘reddish-green’ or ‘bluish-yellow’.
51
Q

Dichromats…

A

Most mammals are this, lacking perception of red hues.

52
Q

Quadromats…

A

Some birds and reptiles are this. Can detect ultraviolet light.

53
Q

Colour constancy…

A
  • Tendency to perceive an object as same colour in spite of the major variations occuring in the wavelengths said object reflects.
  • Trichromatic and Opponent Process theories cannot explain this.
54
Q

Colour constancy remains providing that…

A

The illumination contains a mixture of short, medium, and long wavelenghts, and that the object is perceived as part of the visual scene.

55
Q

‘Retinex’ theory…

A

Land (1977)
Object colour is dictated by its reflectance, which is the ratio of different wavelengths of light reflected by its surface.

56
Q

Dual-opponent colour cells…

A

Fire ‘on’ when red is on periphery and green is on centre, and ‘off’ for the reverse.

57
Q

‘Blobs’…

A

Peglike, cytochrome, oxidase-rich, dual-opponent colour columns. This supports discovery that visual cortex organisation is largely columnar.

58
Q

Visual cortex is divided into 3 parts…

A

1: Primary visual cortex (V1) <— Secondary visual cortex information.
- The further away from V1 neurons are, the larger their receptive fields are, and the more complex and specific the stimuli they respond to.

59
Q

V1’s location…

A

Hidden in posterior of the occipital lobes, surrounded by the prestriate cortex.

60
Q

Scotoma…

A
  • An area of blindness induced by V1 damage.
  • Tested for using the ‘perimetry test’, which creates a visual map for each eye, which is indicative of areas of damage.
61
Q

Hemianopsic…

A

A scotoma in half of one’s visual field.

62
Q

Blindsight…

A

When patients with scotomas can still respond to visual stimuli that pops up in scotomas, even though they don’t have any conscious awareness of it.

63
Q

Perception of motion…

A

Is hardiest visual ability when visual damage occurs. Probably because it is one of our most basic perceptual abilities.

64
Q

First theory for blindsight…

A

Remaining cells of striate cortex are still alive,and there is a sufficient amount of them to continue carrying out visual abilities without conscious awareness.

65
Q

Second theory for blindsight…

A

Visual pathways between secondary visual cortex and visual structure that don’t go through V1 are still able to carry out visual abilities as they don’t need cognitive awareness.

66
Q

Visual pathways are mainly part of two streams…

A
  • Dorsal stream
  • Ventral stream
  • Same as sensorimotor system!
67
Q

Dorsal stream…

A

V1 —> dorsal prestriate cortex —> posterior parietal cortex. This responds to spatial stimuli.

68
Q

Ventral stream…

A

V1 —> ventral prestriate cortex —> inferotemporal cortex. This responds to colour, shape, size etc. of stimuli.

69
Q

‘Where-vs-What’ theory…

A

Organises roles of the 2 streams as:

  • Dorsal - where?
  • Ventral - what?
70
Q

‘Control of Behaviour-vs-Conscious Perception’ theory…

A

Organises roles of the 2 streams as:

  • Dorsal - control of behaviour
  • Ventral - conscious perception
71
Q

Prosopagnosia…

A
  • Visual agnosia for faces.
  • Damage to an area of secondary visual cortex that is responsible for face recognition.
  • Can detect faces, but cannot recognise.
  • Not just specific to face recognition, but recognition of objects, i.e whose chair/dog/house/car?
72
Q

Akinetopsia…

A
  • Inability to see movement in smooth progression.
  • Nefazodone (drugs) can induce temporary akinetopsia.
  • Damage to middle temporal area of cortex (MT).
  • MT function is likely the perception of motion.

PSY219 (11 decks)

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