Vision: from retina to cortex

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what is the ‘problem’ with vision?

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1

what is the ‘problem’ with vision?

there is an inherent ambiguity in the visual signals our eyes receive

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2

what is the pupil?

where light enters the eye

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3

what is the iris?

adjustable aperture, constricts in bright light to make pupil smaller

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4

what does the cornea and lens do?

focuses light on retina

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5

what is accommodation?

when ciliary muscles change shape of lens to bring objects into focus at different distances

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6

what are photoreceptors?

cells with light sensitive photopigments in outer segments

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7

what are rods?

  • contain rhodopsin

  • respond in dim light

  • none in the fovea

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8

what are cones?

  • three types with photopigments sensitive to different wavebands (long, medium, short)

  • daytime vision

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9

what are the large parasol ganglion cells?

  • connects to the magnocellular system

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10

what are the small midget ganglion cells?

  • connects to the parvocellular system

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11

what are receptive fields?

the part of the retina from which the ganglion cells receive input

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12

how does lateral inhibition affect the action potential of retinal ganglion cells?

  • centre-surround relationship (on-centre, off-surround)

  • light in the centre of the cell increases activity

  • light surrounding the cell decreases activity

<ul><li><p>centre-surround relationship (on-centre, off-surround)</p></li><li><p>light in the centre of the cell increases activity</p></li><li><p>light surrounding the cell decreases activity</p></li></ul>
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13

features of retinal ganglion processing

  • poor at spotting change

  • good at picking out sharp edges

  • filters the input for useful info

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14

what is the lateral geniculate nucleus?

  • contains pathways and cells that are responsive to vision??

  • in the thalamus

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15

what do (parasol) magnocellular cells respond to?

movement and flicker

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16

what do (midget) parvocellular cells respond to?

colour and detail

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17

where are the koniocellular cells located?

in between the layers of the lateral geniculate nucleus

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18

what do the koniocellular cells respond to?

blue-yellow colour??

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19

what percentage of the cortex is dedicated to vision?

greater than 50%

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20

other names for the primary visual cortex

  • V1

  • striate cortex

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21

what are the cells in V1 sensitive to? (Hubel and Wiesel)

lines and specific orientations of lines

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22

what does v1 contain?

a retinotopic map (not all parts of the visual system has this)

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23

what are the streams of processing?

  • dorsal

  • ventral

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24

what does the dorsal stream do?

  • ‘where’ pathway

  • focuses on where things are in space

  • movement

  • runs along the top of the brain

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25

what does the ventral stream do?

  • ‘what’ pathway

  • focuses on object identification and recognition

  • runs along the bottom of the brain

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26

what is a retinotopic map?

a representation of each point in the visual field arranged so that neighbouring parts of the retina are represented by neighbouring parts of V1

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27

how do centre-surround receptive fields and v1 simple cells relate to each other?

if you take the outputs from the receptive fields and organise them in a specific way you can get a rectangular receptive field which is responsive to a certain orientation of line but not others

<p>if you take the outputs from the receptive fields and organise them in a specific way you can get a rectangular receptive field which is responsive to a certain orientation of line but not others</p>
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