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NEURO 2470 > Vision > Flashcards

Vision Flashcards

1
Q

Intro facts

A
  • retina: light capturing device
    • 100million photoreceptors
    • only 1 million afferent axons
    • requires convergence
  • binocular: 2 images that must be merged
    • lazy eyes
  • the version of the world we see is not always accurate
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2
Q

Conscious visual perception

A
  1. Retina
  2. LGN (lateral geniculate nucleus) in thalamus
  3. Area 17/V1/Striate Cortex
  4. Many other cortical areas (occipital, temporal, parietal)
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3
Q

Information flow in retina

A
  1. Photoreceptors
  2. Bipolar cells
  3. Ganglion cells
  • horizontal cells between photoreceptors and bipolar
  • amacrine cells between bipolar and ganglion cells
  • horizontal and amacrine for lateral communication (gate keepers)
    • modulate excitement in response to NTs in cleft
  • when photoreceptors become hyperpolarized, bipolar and ganglion become depolarized and vice versa
  • only AP in ganglionic cells… all others use chemical NT
  • calls are translucent so light can pass through
  • melanin in pigment epithelium deflects light
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4
Q

Rods and Cones

A
  • more rods than cones
  • rods: more sensitive to light
    • acramatic
    • scoptic (colourless)
    • low light
    • no rods at fovea
  • cones: colour vision
    • photopic
    • intense/bright light
    • more cones at fovea (only cones at fovea)
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5
Q

Cornea

A

-most refractive power

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6
Q

Lens

A
  • also has refractive power
  • Important for crisp images (9m or closer)
  • ACCOMODATION: additional power provided by changing of lens shape
  • far object require less refraction
  • near objects require more refraction
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7
Q

Visual field

A
  • left visual field imaged on right side of retina

- upper visual field imaged on lower retina

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8
Q

Visual acuity

A
  • ability to distinguish 2 points near eachother
  • poor at distinguishing colour on peripheral retina
  • peripheral retina most sensitive to low light light conditions (due to many rods)
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9
Q

Receptive field

A
  • area of the retina that changes firing rate for specific neuron
  • specified by the pattern of light on retina that elicits neural response
  • input from centre —> ganglion cell = DIRECT
  • input from surround —> ganglion cell = INDRIECT (via amacrine cells)
  • centre vs surround have antagonistic effects
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10
Q

Ganglion cell receptive fields

A
  • ON centre ganglion cells will increase AP fire rate when light hits centre
  • OFF centre will fire fewer AP when light hits centre
    • fire more AP if dark spot covers centre
  • in ON/OFF, response to stimulation of centre is cancelled by response to surround
  • centre/surround organization of receptive fields leads to neural response that emphasizes contrast at light-dark edges
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11
Q

M type ganglion cells

A
  • large cells
  • 5% of cell population
  • large receptive fields
  • conduct AP more rapidly in optic nerve
  • more sensitive to low contrast stimuli
  • respond to stimulation of receptive field centres with transient bursts of APs
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12
Q

P type ganglion cells

A
  • smaller
  • 90% of cell population
  • smaller receptive field (good for discrimination of fine detail)
  • respond with sustained discharge of AP as long as stimulus is on
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13
Q

Retinofugal prjection

A

-eye —> optic nerve —> optic chiasm —> optic tract

  • optic tracts: formed from axons of retinofugal projection
  • binocular visual field: central portion of both visual field viewed by both retinas
  • left visual field viewed by right hemisphere
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14
Q

Targets of optic tract

A
  • most innervate LGN of dorsal thalamus
  • neurons in LGN give rise to axons that project to area 17
    • OPTIC RADIATION
  • legions anywhere in retinofugal projection cause blindness
    • pathway mediates conscious visual perception
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15
Q

Non-thalamic targets

A
  • projections to HYPOTHALAMUS play important tole in synchronizing sleep cycle
  • direct projections to MIDBRAIN control size of pupil/eye movement
  • 10% of ganglion cells project to SUPERIOR COLLICULUS to generate saccadic eye movement (reading a page)
    • RETINOTECTAL PROJECTION = ganglion —> superior colliculus
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16
Q

LGN

A
  • has 6 layers (1=ventral, 6=dorsal)
  • layers are curved
  • receives input from retinal cells from the contralateral visual field
  • output to area 17
  • ipsilateral synapses: 2,3,5
  • contralateral synapses: 1,4,6
  • MAGNOCELLULAR layers:1,2
  • PARVOCELLULAR layers: 3-6
  • KONIOCELLULAR layers: inbetween

-neurons in LGN all MONOCULAR

17
Q

Retinotopy

A
  • organization whereby neighbouring cells in retina feed info to neighbouring places in their target structures
  • 2D surface of retina mapped onto 2D surface of LGN and A17
  • central degrees of visual field are magnified/overprepresented
  • discrete point of light can activate many cells due to overlap of receptive fields
18
Q

Striate cortex

A
  • 6 layers
    • layer IV subdivided in IVA, IVB, and IVC
    • layer IVC subdivided into IVCalpha and IVCbeta
  • spiny stellate cells: layer IVC
  • pyramidal cells: layers III, IVB, V, VI
    • only ones that send axons to other cortical areas
  • magnocellular project to IVCalpha
  • parvocellular project to IVCbeta
  • koniocellular project to I and III

-radial connections maintain retinotopic organization

19
Q

Ocular dominance columns

A
  • Hubel + Weisel (1970)
  • inputs to layer IV laid out in alternating bands
  • layer IVC stellate cells project radially to IVB + III where info from right and left eye begin to mix
20
Q

Outputs from Striate cortex

A
  • layers II, III and IVB —> other cortical areas
  • layer V —> superior colliculus + pons
  • layer VI —> back to LGN
21
Q

Receptive fields of different cells

A
  • retinal/ganglion = monocular, centre/surround
  • Striate cortex = monocular, centre/surround
  • other layers = binocular, orientation selective
22
Q

Orientation column

A
  • preferred orientation remains the same perpendicularly through layers II->VI
  • as electrode passes parallel through layers, optimal orientation shifts
  • complete 180 degree shift requires a transverse of 1mm within layer III
23
Q

Direction selectivity

A
  • response when a bar of light at optimal orientation moves perpendicular to orientation in one direction but not the other
  • subset of orientation selective
24
Q

Simple cells

A
  • binocular
  • orientation selective
  • elongated
  • ON/OFF flanked with opposite ON/OFF
  • constructed from multiple neurons with circular receptive fields
25
Q

Complex cells

A
  • binocular
  • orientation selective
  • elongated
  • ON/OFF responses bu no distinct regions
26
Q

Extra Striate areas

A
  • dorsal stream: motion + visual control of action

- ventral stream: perception of visual world + recognition of object

27
Q

Dorsal stream

A
  • motion and visual control of action
  • V1–>V2–>V3–>MT->MST
  • MT (temporal):
    • large receptive fields
    • direction selective
    • respond to object motion
  • MST (medial superior temporal):
    • linear, radial, circular motion
    • important for navigation, directing eye movement, motion perception
28
Q

Ventral stream

A
  • perception of visual world and recognition of objects
  • V1–>V2–>V3–>V4–>IT
  • V4: large receptive fields
    • orientation selective
    • colour selective (achromatopsia)
  • IT: complex stimuli
    • facial recognition (esp right hemisphere)

NEURO 2470 (6 decks)

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