Vision (L7-8) Flashcards

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1
Q

Axons in the optic nerve connect the retina to…

A
  • 90% to the lateral geniculate nucleus in the thalamus then to the primary visual cortex
  • 10% to the pulvinar nucleus and the superior colliculus
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2
Q

Visual perception

A
  • Anterior-posterior organisation
  • The further down in the visual processing stream cells are, they respond to stimuli of increasing complexity and larger receptive fields
  • 2 visual pathways: dorsal and ventral
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3
Q

Area V1

A
  • Primary visual cortex
  • Contains many neurons tuned to bars in different positions of the visual field
  • Important in the ability to detect edges
  • Show outlines with no colour
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4
Q

What is a receptive field?

A
  • The region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron
  • Complex cells have a medium sized RF
  • Hypercomplex cells have a large RF
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5
Q

Damage to V1

A
  • Causes blindsight
  • Patient W: injury to left visual area causes right hemianopia
  • Patient DB: removal of right primary visual cortex causes left visual hemifield blind
  • Patient TN: removal of V1 causes blindness but patient is still able to navigate around objects in their environment
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6
Q

Area V2/3

A
  • V1 connects to V2 which connects to V3
  • Many complex and hypercomplex neurons
  • Visual info is then passed onto V4 and V5
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7
Q

Zeki

A
  • Conducted PET experiments
  • Colour-greyscale contrast is controlled by area V4
  • Motion-static contrast is controlled by area V5
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8
Q

Area V4

A
  • Colour processing
  • Damage causes cerebral achromatopsia
  • Left sided stroke causes patient to lost ability to perceive colours in right visual field
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9
Q

Area V5

A
  • ‘Human middle temple’
  • Detects motion
  • Damage causes cerebral akinetopsia (world appears static)
  • Stevens showed that TMS to V5 impaired ability to identify the global direction of movement
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10
Q

Ungerleider + Mishkin

A
  • Proposed there are 2 streams of visual processing…
    1. Dorsal: where, spatial vision
    2. Ventral: what, visual characteristics of objects
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11
Q

Milner + Goodale

A
  • Proposed the 2 streams were…
    1. Dorsal: how, visually guided action
    2. Ventral: what
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12
Q

Ventral stream

A
  • Important for visual perception and identification of objects
  • fMRI study by Kelly showed words activate the left fusiform gyrus, pictures produce bilateral activity and faces activate the right fusiform gyrus
  • fMRI study by Grill-Spector showed faces activate the fusiform face area, scenes activate the para-hippocampal place area and both activate the lateral occipital cortex
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13
Q

Damage to the lateral occipital cortex

A
  • Causes visual form agnosia
  • Apperceptive agnosia: patient is unable to form a percept to copy the image
  • Associative agnosia: patient is able to form a percept to copy the image but can’t associate semantic knowledge
  • Integrative agnosia: patient is able to form a partial representation but have problems integrating the parts
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14
Q

Damage to the fusiform gyrus

A
  • Causes prosopagnosia
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15
Q

Are faces special?

A
  • Patient WJ: patient with prosopagnosia but no difficulty recognising his sheep
    Y - special brain region (fusiform face area)
    N - in car experts, the FFA is activated by both faces and cars, suggesting it’s activated by expertise (Isobel Gauthier)
    N - Subordinate judgment of faces caused greater activation of FFA than basic judgement (Turk et al.)
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16
Q

Capgras syndrome

A
  • A condition in which sufferers believe someone they know has been replaced by an imposter
  • Damage to link between ventral stream and emotion
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17
Q

Haxy’s model for face processing

A
  • Ventral stream is involved in structure and visual percept
  • Dorsal stream is involved in processing changeable aspects
  • Information is passed forward to determine emotional responses, person knowledge and motor stimulation
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18
Q

Dorsal stream

A
  • Important for visually guided action
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19
Q

Damage to the inferior and superior parietal cortex

A
  • Causes optic ataxia
20
Q

Damage to the inferior parietal lobe

A
  • Causes hemispatial neglect (predominantly left hemisphere)
21
Q

Hemispheric rivalry and communication theory

A
  • Proposed by Kinsbourne
  • Damage to one hemisphere leads to hyper-excitation of the intact hemisphere due to the release of inhibition from the damaged side
  • BUT this does not explain why neglect is almost always due to RH damage
22
Q

Right hemisphere dominance theory

A
  • Proposed by Mesulam
  • Left hemisphere attends to the right hemispace
  • Right hemisphere attends to both the left and right hemispace
  • Damage to the left hemisphere is not as severe as there is compensation by the right hemisphere
23
Q

What is visual acuity?

A
  • The ability to see fine detail

- Assessed using a Snellen chart

24
Q

Sensing light

A
  • Length determines its colour
  • Amplitude determines its brightness
  • Purity (number of wavelengths) determines its saturation
25
Q

Human eye

A
  • Light first passes through the cornea which bends the light wave and sends it through the pupil
  • The iris is a translucent muscle that controls the size of the pupil and hence the amount of light that can enter the eye
  • Muscles inside the eye control the shape of the lens to bend the light and focus it onto the retina by a process called accommodation
26
Q

Myopia

A
  • Nearsightedness

- Caused by images focusing in front of the retina

27
Q

Hyperopia

A
  • Farsightnedness

- Caused by images focusing behind the retina

28
Q

Photoreceptors

A
  • Cones detect colour, operate under daylight conditions and allow us to focus on fine detail
  • Rods become active under low light conditions for night vision (contain same photopigment so can’t distinguish colour)
  • Either excitated or inhibited so signal sent to RGC are based on different levels of receptor activation (lateral inhibition)
29
Q

Phototransduction in the retina

A
  • Fovea contains no rods and lots of cones
  • Inner layer consists of photoreceptor cells
  • Middle later contains bipolar cells that transmit signals to retinal ganglion cells which form the optic nerve and leave the eye through the blind spot to signal to the brain
30
Q

On-centre cells

A

Contain a central excitatory zone surrounded by an inhibitory zone

31
Q

Off-centre cells

A

Contain a central inhibitory zone surrounded by an excitatory zone

32
Q

Trichromatic colour representation

A
  • The pattern of responding across the 3 types of cones provides a unique code for each colour
  • Colour blindness is linked to X chromosome (affects males)
33
Q

Sensory adaptation

A

Our sensitivity to prolonged stimulation declines over time

34
Q

Colour-opponent system

A
  • Pairs of visual neurons work in opposition
  • Red-green cells are excited by red and inhibited by green wavelengths
  • Blue-yellow cells are excited by blue and inhibited by yellow wavelengths
35
Q

What is an illusory conjunction?

A

A perceptual mistake where features from multiple items are incorrectly combined

36
Q

Feature integration theory

A
  • Proposed by Treisment and Schmidt

- Attention binds individual features together to compromise a composite stimulus

37
Q

Synaethesia

A
  • The perceptual experience of one sense that is evoked by another sense
  • Instance of atypical feature binding
  • Parietal lobe becomes activated
38
Q

Perception constant

A

Even as aspects of sensory signals change, perception remains consistent

39
Q

Gestalt perceptual grouping rules

A
  • Govern how features and regions of things fit together…
    1. Simplicity: the simplest interpretation is chosen
    2. Closure: we fill in missing elements of a visual scene
    3. Continuity: edges that have the same orientation are grouped together
    4. Similarity: regions that are similar in colour, lightness, texture or shape are perceived as belonging to the same object
    5. Proximity: objects that are close together are grouped together
    6. Common fate: elements that move together are perceived as parts of a single moving objects
40
Q

Theories of object recognition

A
  • Image-based recognition suggests that an object you’ve seen before is stored as a template to be compared to viewed objects
  • Parts-based object recognition proposes that the brain deconstructs viewed objects into a collection of parts (eg. Biederman’s geons)
41
Q

Theories of face recognition

A
  • Bruce + Young proposed that features, emotional expressions and dynamics of facial movements are involved in face recognition
42
Q

Monocular depth cues

A
  • Provide information about depth when viewed with one eye
  • Familiar size and relative size
  • Linear perspective: parallel lines seem to converge as they recede into the distance
  • Texture gradient: the size of pattern elements grow smaller as the surface receded into the distance
  • Interposition: an object that partly blocks another is closer
  • Relative height: faraway objects are higher
43
Q

Binocular depth cues

A
  • Each eye registers a slightly different view

- The closer the object, the greater the binocular disparity (the difference in retinal images)

44
Q

Motion-based depth cues

A
  • Motion parallax is based on the movement of the head over time
  • Optic flow is the idea that a scene moves outwards from the point to which the observer is moving
45
Q

Apparent motion

A
  • The perception of movement as a result of alternating signals appearing in rapid succession in different locations
  • Basis of animation