Week 3 - Visual Perception Flashcards

1
Q

How is electromagnetic radiation (EMR) generated

A

EMR is generated when an atom emits a particle called a photon.

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2
Q

Principles of perception

A
  • perception is dynamic, we perceive change
  • we perceive constancies in a a changing environment
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3
Q

For an object to be visible is must emit or reflect_

A

Light

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4
Q

What determines the wavelength of a photon?

A

The energy of the photon.

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5
Q

What does the variation in wavelengths within the visible spectrum determine?

A

Different wavelengths give rise to the perception of different colours

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6
Q

eye movements (saccades)

A
  • constantly moving
  • if an image stays stabilised on the retina it disappears (photoreceptors stop firing) and brain fills in space
  • blind spot at the optic nerve
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7
Q

Accomodation

A

ligaments (ciliary muscles) that attach the lens to the eye control the shape of the lens to accomodate near of far targets.
- stops working once you turn 40 years old so struggle to focus on middle distance

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8
Q

Vergence and stereopsis

A

two eyes converge on the information to produce two different but aligned images of the same target. Helps to tell how far away something is

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9
Q

Physiology of the retina

A
  • densely packed with photoreceptors that point towards the back of the eye (light kills photoreceptors)
  • structure of retina is upside down:
    Ganglion Cells
    Bipolar Cells
    Photoreceptors
    Choroid
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10
Q

Rods (photoreceptor)

A
  • black and white vision
  • low acuity (widely spaced throughout retina, in peripheral field)
  • work well at night (scotopic vision)
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11
Q

Cones (photoreceptor)

A
  • colour vision
  • high acuity (can see fine detail bc densely packed in fovea)
  • work in bright light (photopic vision)
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12
Q

Lateral Inhibition

A

every adjacent unit within the photoreceptor cell or ganglion cell slightly changes the output of the unit next to it

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13
Q

Passage of the visual signal

A

both eyes have a left and right visual field that send information to the left or right side of the brain.
- right visual field is on the left side of each eye and sends info the left side of the brain - vice versa
- Optic chiasm is where the nerves cross

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14
Q

Lateral Geniculate Nucleus (LGN)

A
  • six layers all replicated
  • same properties as ganglion cells
  • ganglion and LGN cells respond to the present of a spot of light on the retina
  • LGN cells receive input from visual cortex
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15
Q

Tectopulvinar System

A
  • optic tract fibres that react to information that are fast moving (periphery)
  • serves several functions:
    1. localisation of objects in space
    2. guidance of eye movements
    3. gross pattern perception
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16
Q

Tectopulvinar System Physiology

A
  • located in thalamic region called tectum
  • cells in superior colliculi have receptive field on the retina and receive input from retinal genglion cells
  • tectopulvinar system reveives back projects from the cortex
  • calls organised in topographic maps
17
Q

Schneider (1969) study

A
  • removed LGN from hamsters and superior colliculi from others
    no LGN = unable to recognise patterns
    no superior colliculi = recognise patterns but not accurately approach them

Focal system: recognition
Ambient system: localisation

Blindsight: damage to focal system can react to visual stimuli but claim they cannot see them

18
Q

The visual cortex

A
  • LGN projects to primary visual cortex and occipital lobe at rear of brain
  • LGN fibres enter layer IV, where the neurons center-surround receptive fields
  • other layers have neurons with more complex behaviour