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Flashcards in Vision (Lecture 5) Deck (63):
1

vision pathway

light enters through the pupil and reaches the retina, the cornea refracts light onto the fovea (center of the retina with highest acuity)

2

equivalent of light

waves of photons

3

Photons

-emitted with different energies resulting in different wavelength and different quantities resulting in different amplitudes of waves

4

Visible Light Spectrum

-we only see (380-760nm)
-we perceive different wavelengths as different colors which is a creative process of the brain

5

light enters they eye through....

the pupil

6

lens

attached to ciliary muscles, important for contraction and reflection of light to the back of the eye

7

cornea

-refracts the light onto the fovea

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ciliary muscle

-contort lens to focus on fovea
-far objects ---> relax ciliary muscles
-close objects ---> contract cilary muscles --> fat lens
-this is ACCOMMODATION

9

fovea

-center of the retina with highest acuity (ability to see details)
-focuses objects in center of visual field
-CONES ONLY
-thinning of ganglion cell layer reduces distortion

10

emmetropia

PERFECT??

11

hyperopia

images appear behind the retina, farsightedness

12

hyperopia correction

-convex lens

13

myopia

images appear before the retina, nearsightedness

14

myopia correction

-convave lens

15

convergence

-eyes must turn slightly inward when objects are close

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binocular disparity

difference between the images on the two retinas = 3D vision

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RETINA

thin strip of tissue (contains the fovea) along the back of the eye where light is converted to neural signals that can be sent to the brain through the optic nerve (blind spot)

18

blind spot

areas of no photoreceptors in the retina
-located at the optic disk
-completion

19

optic disk

-where axons of retinal ganglion cells gather together and leave the eyeball (optic nerve)

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ganglion cells

-primary visual neurons

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optic nerve

projects to brain

22

horizontal, bipolar, and Amacrine cells

-process info from rods and cones

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photoreceptors

-rods and cones
-detect light
-contain light sensing photopigments in discs within their outer segments
middle (cell body), and synaptic ending-makes contact with bipolar cells

24

lateral communication

the synaptic points
(amacrine cell between ganglion and bipolar)
(horizontal cell between photoreceptors and bipolar)

25

ganglion cell axons

-project to forebrain

26

rods

-scotopic (nighttime vision)
-high-sensitivity to light because more photopigment (larger outer segment) allowing for low-acuity vision in dim light, but lacks detail and color information
-only one type
-in bright daylight rods are saturated and the cell can not be further hyper polarized

27

cones

-photopic (daytime) vision
-high acuity color information in good lighting
-different opsin proteins that are differentially activated by specific wavelengths of light

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rods ratio

-many:1 ratio with retinal ganglion cells

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Why do rods and cones differ in sensitivity and acuity?

1. differences in amount of light sensing photopigments
2. convergence

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cones ratio

-1:1 ratio with retinal ganglion cells

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less of a light signal (dim/fewer photons)=

-greater change of exciting a rod-fed ganglion cell = greater sensitivity
-ganglion cell carries less information about where photons were revieced = less acuity

32

visual transduction

conversion of light to neural signals by photoreceptors

33

in dark the cell is depolarized and releases....

glutamate

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light causes cell to hyper polarize glutamate....

-rate of release is reduced

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lack of light (pathway)

1. second messenger (cGMP) na+ channels open
2. cell is depolarized
3. glutamate is being released

36

optic nerve

-formed by asons of ganglion cells

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optic chiasm

-the part of the brain where the optic nerves partially cross (located at the bottom of the brain below the hypothalamus)
-where part of image crosses over to opposite side

38

optic tract

continuation of the optic nerve and runs from the optic chiasm to the lateral geniculate nucleus

39

visual fields

-travel to contralateral(opposite) cortex
-fields are not defined by the eyes; cortex recieves info from ipsilateral (same side) and contralateral (opposite side) eye

40

retina-geniculate-striate system

-90% of axons of retinal ganglion cells
information received at adjacent portions of the retina remains adjacent = retinotopic

41

lateral geniculate body/nucleus (thalamus/LGN)

-thalamic relay center nucleus that deals with visual information
-asons from retinal ganglion cells synapse on other neurons here

42

P(parvocelluar) layers

-small cell bodies
-color and fine details
-stationary objects
-input from cones

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M(magnocellular) layers

-large cell bodies
-detect movement
-primary input from rods

44

do retinal cell project anywhere else?

-some axons from the optic nerve go out of main pathway and relay into the hypothalmus(important fro sleep/wake cycle) and superior colliculus (orientation reflex)

45

primary visual cortex (occipital lobe)

-V1
-brodmann's Area 17
-Striate Cortex
-axons from LGN (M?P cells) terminate in layer 4 of V1
-info arriving in layer 4 remains segregated(i.e. is either from one eye or the other) until it travels to other cortical layers for further processing
-most neurons in V1 are either simple or complex

46

Hubel and Wiesel (1979)

-mapped receptive fields of retinal ganglion cell, LGN cells, and layer 4 V1 cells

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receptive field

-area in visual field within which it is possible for a visual stimulus to influence that neurons firing

48

receptive field of foveal areas vs periphery

foveal areas are smaller than those in periphery (due to convergence)

49

neurons receptive fields

-circular in shape
-neurons are monocular
-many neurons at each level had receptive fields with excitatory and inhibitory area

50

center-surrounded receptive fields

-bipolar and retinal ganglion cells and neurons in V1 layer 4

51

on-center (off-surround)

-cells fire more when light is in center of receptive field
-firing it inhibited when light is shone in surrounding receptive field

52

off-center (on-surround)

-cells fire more when light is shone in surround
-firing is inhibited when light is shone in center of receptive field

53

lateral inhibition

-capacity of excited neuron to reduce the activity of its neighbors
-used in vision to sharpen signals to the brain, it increases the contrast and sharpness in visual response

54

simple visual cortex receptive fields

-rectangular
-on and off regions (like cells in layer IV)
-orientation and location sensitive
all are monocular

55

complex visual cortex receptive fields

-rectangular
-do not have static on and off regions
not location sensitive
-motion sensitive
-many are binocular
larger receptive fields

56

secondary visual cortex

-association cortex

57

dorsal steam

-"how" pathway
-processing objects spatial location
-specialized for motion
-"where" stimuli are for the "control of behavior"

58

ventral steam

-specialized for attributes
-"what" stimuli are for "conscious perception"

59

posterior parietal cortex (dorsal stream)

-cells selective for linear motion, radial motion, or circular motion
-brain lesion in this area-->

60

inferior temporal lobe (ventral steam)

-cells are orientation selective and color selective
-important for shape and color perception
-what would happen if you sustain a brain lesion in this area???

61

fusiform face area

-specialized face recognition circuit
-shows enhanced activation in fMRI when subjects shown faces as opposed to other shapes

62

prosopagnosia

-damage to fusion face areas
-damage to other object recognition areas but no FFA results in recognition of face and not other objects

63

retinotropic

mapping of visual information from retina to neurons within the visual system