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perception > Problem 2 - DONE > Flashcards

Problem 2 - DONE Flashcards

the retina

1
Q

human eye

cornea

A
  • first tissue that light will encounter; transparent ‘window’ into the eyeball
    made of highly ordered arrangement of fibres, contains no blood vessels or blood
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2
Q

human eye

aqueous humour

A
  • watery fluid in the anterior chamber of the eye
  • -> fluid derived from blood; removing waste, supplying oxygen and nutrients to cornea and lens
  • anterior chamber = space immediate behind the cornea
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3
Q

human eye

lens

A
  • lens inside the eye that enables the changing of focus

- -> no blood supply —> can be completely transparent; shape is controlled by ciliary muscle

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4
Q

human eye

pupil

A
  • dark, circular opening at the centre of the iris in the eye, where light enters the eye
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5
Q

human eye

iris

A
  • coloured part of the eye, consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil
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6
Q

human eye

viterous humour

A
  • transparent fluid that fills the vitreous chamber in posterior part of the eye
  • -> gel-like and viscous
  • vitreous chamber = transparent fluid that fills the vitreous chamber in posterior part of the eye
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7
Q

human eye

retina

A
  • light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve
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8
Q

lens - accommodation

A
  • change in the lens’s shape that occurs when the ciliary muscles at the front of the eye tighten + increase the curvature of the lens so that it gets thicker
  • ciliary muscles –> increase focusing power of lens by increasing its curvature
  • near point –> distance at which lens can no longer accommodate to bring closer objects into focus
  • far point –> distance at which light becomes focused on the retina
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9
Q

retina

fundus

A
  • back layer of retina
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10
Q

retina

optic disk

A
  • point where the arteries and veins that fedd the retina enter the eye + where the axons of ganglion cells leave the eye via the optic nerve
  • contains no photoreceptors = blind spot
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11
Q

retina

photoreceptors

A
  • light-sensitive receptor in the last layer of retina
  • -> rods and cones
  • -> third type (melanopsin)
  • help transducting light energy to neural energy
  • graded potential –> how information is passed to bipolar cells
  • structure
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12
Q

photoreceptors

rods

A
  • periphery, NOT fovea
  • very light-sensitive photoreceptor
  • only activated by a single photon
  • depolarised at night –> specialised for night vision (releases inhibitory neurotransmitter at night)
  • high convergence, low acuity, high light sensitivity
  • slow regeneration of pigments; slow response
  • contain photopigment –> rhodopsin
  • only one type of rods: no colour perception (all same type of photopigment)
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13
Q

photoreceptors

cones

A
  • mostly present in fovea –> the farther from it, the lower is their density
  • specialised for daylight and vision (because of low sensitivity but high acuity)
  • to be activated, they need light
  • receptive fields are bigger
  • little convergence, high acuity, low light sensitivity
  • fast response
    three types:
    –> three photopigments (blue, green, red)
    –> S-cones, M-cones, L-cones
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14
Q

horizontal cells and amacrine cells

A
  • lateral pathway in retina

- run perpendicular to photoreceptors in inner layer of retina

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15
Q

horizontal cells

A

= specialised retinal cell that contacts both photoreceptor and bipolar cells

  • makes contact between near photoreceptors
  • first layer after photoreceptors
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16
Q

amacrine cells

A

= retinal cell found in the inner synaptic layer that makes synaptic contacts with bipolar cells, ganglion cells, and other amacrine cells

  • receive input from bipolar cells + other amacrine cells
  • send signals to bipolar, amacrine, retinal ganglion cells
17
Q

lateral inhibition

A

= antagonistic neural interaction between adjacent regions of retina

  • important role in visual perception + several illusions
  • perceiving contrast
18
Q

bipolar cells

A

= retinal cell

  • -> synapses with rods/cones (not both) + horizontal cells –> passes signals on to ganglion cells
  • intermediaries: pools information –> passes information on to a ganglion cell => convergence
  • wiring of bipolar cell type: determines information that is passed on
  • -> diffuse bipolar cells
  • -> midget bipolar cells
  • each foveal cone contacts two bipolar cells
  • -> ON bipolar cells
  • -> OFF bipolar cells
19
Q

diffuse bipolar cells

A

= bipolar retinal cell whose processes are spread out to receive input from multiple cones

  • most rods communicate through these
  • convergence
20
Q

midget bipolar cells

A

= small bipolar cell in the central retina that receives input from a single cone

  • in the fovea
  • one-to-one pathway: receive input from single cone –> to single ganglion cell
21
Q

ganglion cells

A

= retinal cell in the final layer of retina

  • receives input from bipolar and amacrine cells –> process information –> send messages off to the brain through optic nerve
  • -> P ganglion cell
  • -> M ganglion cell
  • -> koniocellular cell
22
Q

receptive fields

A
  • receptive field = region in the visual field where light changes will influence the activity of the receptor
    –> light change will change the activity of the receptor
    –> each cell in retina has its own receptive field
    examples:
  • retina:
    –> receptive field is determined by location where in the visual surrounding the stimulus has to be placed in order to change the firing rate of the cell
  • simple cortical cells:
    –> receptive field is determined by the orientation of a certain line at a certain location in the visual field
23
Q

antagonistic centre-surround receptive fields

overview lecture

A

=> effect of light absorption of photoreceptors in SURROUND always turns around effect of light absorption in the CENTRE

  • light absorption in CENTRE: hyper polarisation
  • light absorption in SURROUND: depolarisation
  • -> gets inhibited less by horizontal cells
  • -> perform best when light optimally fills CENTRE
  • -> perform less and less good when light hits SURROUND (worst when fills CENTRE + SURROUND)
24
Q

neural convergence

A

= convergence = when a number of neurones synapse onto a single neurone

  • about 120 rods send their signals to a single ganglion cell
  • only about 6 cones send signals to a single ganglion cell
  • -> explains elongated forms of receptive field in simple cells (circular LGN receptive fields converge to rectangular/oriented receptive fields in simple cells)
25
Q

lateral inhibition - match band

overview lecture

A
  • white area = light, very active
  • area with white and a little black/grey = little more inhibited
  • area with black and a little white = more inhibited
  • black area = activity is low; not inhibited so much but already not so active
26
Q

lateral inhibition - Hermann grid

overview lecture

A
  • explained by receptive field
    = the more light hits the surround —> the more inhibition
  • more inhibition in crossings —> greyish points in crossings
27
Q

photoreceptors

third type

A
  • lives among ganglion cells
  • involved in adjusting our biological rhythms –> match day and night of external world
  • sensitive to ambient light level
  • contain melanopsin
  • send signals to suprachiasmatic nuclei
28
Q

visual sensitivity

A

= ability to respond to transmitted signals

29
Q

visual acuity

A

= measure of the finest detail that can be resolved by the eyes
- falls off rapidly with eccentricity

30
Q

P ganglion cell

A

= small ganglion cell (70%)

  • input: excitatory, from single midget bipolar cells in the central retinal
  • output: parvocellular layer of the lateral geniculate nucleus
  • -> information about contrast in retinal image
  • smaller receptive fields –> do not converge, connected to one photoreceptor
  • finer resolution: greater acuity (if enough light given)
  • temporal response: sustained firing when light shines on excitatory regions
31
Q

M ganglion cell

A

= umbrella-like ganglion cell –> dendrites spread out more (8-10%)

  • input: excitatory, from diffuse bipolar cells
  • output: magnocellular layer of the lateral geniculate nucleus
  • -> information about how image changes over time
  • bigger receptive fields –> convergence
  • more sensitive (under low-light conditions)
  • temporal response: brief bursts of impulses when the spot of the receptive field is turned on –> quick return to spontaneous state
32
Q

koniocellular cell

A

= neurone located between magnocellular and parvocellular layers of the lateral geniculate nucleus (= koniocellular layer)
- 10% of ganglion cells

33
Q

photoreceptors

structure

A
  • outer segment = contains photopigment molecules and is adjacent to pigment epithelium
  • inner segment = between outer segment and cell nucleus
  • -> filled with mitochondria, produces visual pigment molecules
  • synaptic terminal = where axons terminate for transmission of information by release of chemical transmitters
  • -> contains connections from neurones to which photoreceptors communicate (horizontal and bipolar cells)
34
Q

convergence - why rods better sensitivity?

A
  • rod ganglion cell receives 2 units of excitation from each of its 5 receptors = 10 units of excitation –> ganglion cell fires (light is perceived)
  • cones’ ganglion cells are each receiving 2 units of excitation –> ganglion cell DOESN’T fire
35
Q

convergence - why cones better acuity?

A
  • present light that stimulates two neighbouring cones –> two separate ganglion cells fire –> gives information of spatial separation
  • present light that stimulates two neighbouring rods –> ganglion cell fires despite of separation –> no information about spatial separation
36
Q

accommodation and dark adaptation

lecture

A
  • accommodation = process of changing the refraction of your lens
  • -> for different distances you can hold your object in focus in the retina
  • dark adaptation
  • -> adaptation of pupil to capture as much light as possible
  • constriction (small pupil) –> dilation (large pupil)
37
Q

transduction

lecture

A

= transformation of physical energy into a neuronal signal

  • isomerisation = activation of photopigment
  • -> light changes the shape of retinal –> detachment of retinal from opsin
  • less light –> depolarisation –> more neurotransmitter (more activity)
  • more light –> hyper-polarisation –> less neurotransmitter
  • graded signal, no spikes
  • visual pigment bleaching = when a lot of retinal detach from opsin
38
Q

each receptor has a receptive field

lecture

A
  • centre = each receptor gives input to a bipolar cell & ganglion cell > each ganglion cell knows precisely where input is coming from = high visual acuity in centre of visual field
  • periphery = many receptors are pooled together to activate bipolar cells; bipolar cells are pooled together to activate ganglion cells; pooling > ganglion cells of higher sensitivity, but lack knowledge about where input comes from = lower visual acuity in periphery
39
Q

orientation tuning curve

lecture

A
  • response as a function of orientation
  • biggest response for preferred orientation
  • deviate from preferred orientation –> response becomes less

perception (9 decks)

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