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Sensation and Perception > The First Steps in Vision > Flashcards

The First Steps in Vision Flashcards

Chapter 2 - PP

1
Q

Your field of view is:

A

The portion of the world that you can see without moving your eyes

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2
Q

Human field of view is:

A

About 140 degrees vertically (60 degrees up and 80 degrees down) and about 190 degrees horizontally

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3
Q

Of the 190 degrees that the human field of view can see horizontally, about 110 degrees:

A

Is visible to both eyes simultaneously, enabling high resolution dept perception, which requires both eyes

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4
Q

Field of view:

A

The portion of the surrounding space you can see when your eyes are in a given position in their sockets

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5
Q

Eyes in front of the head enables:

A

High debt perception

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6
Q

Eyes on the sides of the head:

A

More extensive field of view, but only a narrow range in front where high-resolution dept perception is possible

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7
Q

Acuity:

A

A measure of how clearly fine detail is seen

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8
Q

We see things much more clearly when:

A

Our eyes are pointed at them

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9
Q

Extraocular muscles:

A

Three pairs of muscles around each eye that enable us to move our eyes very rapidly and accurately and keep the eyes always pointed in that same direction

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10
Q

What are the three pairs of extraocular muscles that move the eyes?

A

a) Superior rectus + inferior rectus
b) Medial rectus + lateral rectus
c) Inferior oblique + superior oblique

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11
Q

The superior rectus and inferior rectus move the eye:

A

Up (elevation) and down (depression)

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12
Q

The medial rectus and lateral rectus:

A

Move the eye toward the side of the nose (adduction) and away from the nose (abduction)

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13
Q

The superior and inferior oblique muscles:

A

Rotate the eye clockwise (intorsion) and counter clockwise (extorsion)

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14
Q

Any given eye movement;

A

Is the result of an exquisitely balanced interaction of these three pairs of muscle

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15
Q

The __ and __ accounts for about 80% of the focusing of the eye

A

Cornea and aqueous fluid

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16
Q

The iris controls:

A

The amount of light entering the eye

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17
Q

In bright light, the iris __ which __ the pupil

A

In bright light, the iris CONTRACTS, which CONSTRICTS the pupil

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18
Q

In medium light, the iris contracts __ which __ the pupil

A

In medium light, the iris contracts less, which dilates the pupil

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19
Q

In dim light, the iris is fully __ and the pupil is fully __

A

In dim light, the iris is fully relaxed, and the pupil is delighted

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20
Q

Optic axis:

A

An imaginary diameter line from the front to the back of the eye, passing through the center of the lens

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21
Q

Sclera:

A

The outer membrane of the eye:
A tough protective membrane covering whose visible portion portion is the white of the eye

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22
Q

Choroid:

A

The middle membrane of the eye, lining the interior of the sclera and containing most of the blood vessels that supply the inside of the eye with oxygen and nutrients

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23
Q

Retina:

A

The inner membrane of the eye, made up of neurons, including the photoreceptors that convert the light entering the eye into neural signals

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24
Q

Cornea:

A

A transparent membrane at the front of the eye: light enters the eye by first passing through the cornea, which sharply refracts the light

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25
Q

Iris:

A

The coloured part of the eye - a small circular muscle with an opening in the middle (the pupil) through which light enters the eye

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26
Q

What accounts for about 20% of the focusing of the eye?

A

The lens, which adjusts shape for object distance

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27
Q

Accomodation results when:

A

Ciliary muscles are tightened which causes the lens to thicken, this bends the light rays (via refraction_
Light passes through the lens more sharply and focus near objects on retina

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28
Q

pupillary reflex:

A

The automatic process by which the iris contracts and relaxes to control the size of the pupil, in response to the relative intensity of light entering the eye

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29
Q

Anterior chamber:

A

The space between the cornea and the iris, filled with aqueous humour

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30
Q

posterior chamber:

A

The space between the iris and the lens, filled with aqueous humor

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31
Q

Aqueous humour:

A

A clear, thin fluid filling the anterior and posterior chambers of the eye

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32
Q

Vitreous chamber:

A

The main interior portion of they eye, filled with vitreous humour

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33
Q

Vitreous humor:

A

A clear, somewhat gel-like fluid filling the vitreous chamber of the eye

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34
Q

Intraocular pressure

A

The pressure of the fluids in the three chambers of the eye

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35
Q

Lens:

A

A transparent structure near the front of the eye that refracts the light passing through the pupil so that the light focuses properly on the retina

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36
Q

Focal length:

A

The distance from a lens at which the image of an object is in fous when the object is far away from the lens (at “optical infinity”)

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37
Q

diopters:

A

Units to express the power of a lens; diopters = 1 / (focal length)

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38
Q

emmetropia:

A

The happy condition of no refractive error

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39
Q

Zonule Fibers:

A

Fibers that connect the lens to the choroid: they pull on the lens to change its shape

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40
Q

Ciliary muscles:

A

Tiny muscles attached to the choroid; they relax and contract to control how the choroid pulls on the zonule fibers to change on the shape of the lens

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41
Q

Accomodation:

A

Adjustment of the shape of the lens so light from objects at different distances focuses correctly on the retina

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42
Q

Accomodation for light from distant object:

A

Zonule fibers very taut
Ciliary muscle relaxed
Thinner lens

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43
Q

Accomodation for light from a closer object:

A

Zonule fibers less taut
ciliary muscle contracted
thicker lens

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44
Q

The distance of the near point increases with:

A

Increasing age

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44
Q

Define the near point:

A

The near point occurs when the lens can no longer adjust for close objects without strain (at about 10 inches or 25 cm)

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45
Q

When the near point becomes further than a comfortable reading distance:

A

Corrective lenses (reading glasses) become necessary

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46
Q

Myopia:

A

When light entering the eye is focused in front of the retina and distant objects cannot be seen sharply: nearsightedness

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47
Q

Hyperopia:

A

When light entering the eye is focused behind the retina; farsightedness

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48
Q

Presbyopia:

A

Distance of nearpoint increases due to hardening of lens and weakening of ciliary muscles
Causes image to be focused behind the eye; farsightedness

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49
Q

Astigmatism:

A

A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye: usually the cornea

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50
Q

Using the ophthalmoscope, we can view the back of the patient’s eye called the:

A

fundus

51
Q

Photoreceptors:

A

Cells in the retina that initially transduce light energy into neural energy

52
Q

Rods:

A

Photoreceptors that are specialized for night vision

Respond well in low luminance conditions

Do not process color

53
Q

Cones:

A

Photoreceptors that are specialized for daylight vision, fine visual acuity and color

Respond best in high luminance conditions

54
Q

Photopigment in S-cones is most sensitive to:

A

short-wavelength light
peak sensitivity at 443nm

55
Q

photopigments in m cones and L cones both have some sensitvity :

A

across the entire spectrum of visible light

56
Q

Sensitivity of M- cones is greater toward:

A

The middle wavelengths
peak 543 nm

57
Q

Sensitivity of L-cones:

A

greater toward the longer wavelengths
peak 574

58
Q

Sensitivity of rods:

A

The photopigment in rods is most sensitive to light with a wavelength of 500 nm

59
Q

Receptors have outer segments, which contain:

A

Visual pigment molecules:
Opsin- a large protein
Retinal - a light sensitive molecule

60
Q

Opsin

A

A large protein

61
Q

Retinal

A

A light sensitive molecule

62
Q

Visual pigment molecules cross the disk membrane:

A

7 times

63
Q

Retinal is attached to opsin and __

A

reacts to the light

64
Q

Retinal is responsible for

A

visual transduction

65
Q

Visual transduction occurs when

A

the retinal absorbs one photon of light

66
Q

When retinal changes its shape, it is called,

A

isomerization

67
Q

The distribution of rods and cones is

A

not constant over the retina

68
Q
A
69
Q

number in normal retina of rods vs cones

A

120 million rods, 5 million cones

70
Q

unlike rods, cones can

A

process color!

71
Q

We have poor __ in our periphery

A

color vision

72
Q

There is a high density of cones:

A

in the center and around the edge of the fovea

73
Q

At the optic disk there are

A

No rods or cones

74
Q

Vision scientists

A

measure the size of visual stimuli by how
large an image appears on the retina rather than by how
large the object is.

75
Q

The visual angle of an object is a function of:

A

both its actual size and
distance from the observer

76
Q

One of the most remarkable things about the human visual system is

A

the
incredible range of luminance levels we can adjust to

77
Q

Two mechanisms for dark and light adaptation:

A
  • Pupil dilation
  • Photoreceptors and their replacement
78
Q

Neural circuitry of the retina accounts for:

A

why we are not bothered by variations in
overall light levels.

79
Q

The amount of photopigment available in photoreceptors:

A

Changes over time

80
Q

The more light entering the retina,

A

the faster the photopigments are used up, and the fewer
photopigments there are to process more light

81
Q

The less light entering the retina,

A

the more slowly photopigments are used up, and the more
photopigments there are to process what little light is there

82
Q

The ganglion cell layer consists of:

A

retinal ganglion cells

83
Q

The inner nuclear layer consists of:

A

Bipolar, horizontal and amacrine cells

84
Q

The outer nuclear layer consists of:

A

rods and cones

85
Q

horizontal cells:

A

Specialized retinal cells that run perpendicular to the photoreceptors and
make contact with photoreceptors and bipolar cells
- Responsible for lateral inhibition

86
Q

amacrine cells:

A

These cells synapse horizontally between bipolar cells and retinal ganglion
cells
- Have been implicated in contrast enhancement and temporal sensitivity
(detecting light patterns that change over time)

87
Q

What cells are involved in the retina’s horizontal pathway?

A

horizontal cells and amacrine cells

88
Q

What cells are involved in the retina’s VERTICAL pathway?

A

bipolar cell (diffuse bipolar cell + midget bipolar cell)
P ganglion cells
M ganglion cells

89
Q

P ganglion cells: Connect to

A

parvocellular pathway

90
Q

P ganglion cells receive input from

A

midget bipolar cells

91
Q

Parvocellular (“small cell”) pathway is involved in

A

fine visual acuity, colour, and shape
processing. Poor temporal resolution, but good spatial resolution.

92
Q

M ganglion cells: Connect to the

A

magnocellular pathway

93
Q

M ganglion cells receive input from:

A

Diffuse bipolar cells

94
Q

Magnocellular (“large cell”) pathway is involved in:

A

motion processing. Excellent
temporal resolution, but poor spatial resolution

95
Q

Convergence in the Retina:

A

126 million photoreceptors converge to 1 million ganglion cells.

96
Q

Higher convergence of __ than __ in the retina

A

rods than cones
Average of 50 rods to one bipolar cell.
* Average of 6 cones to one diffuse bipolar cell.
* Cones in fovea have 1 to 1 relation to midget bipolar cells.

97
Q

Nuclear layers:

A

The three main layers of the retina, including the outer nuclear layer, inner nuclear layer and ganglion cell layer

98
Q

Photoreceptors:

A

-Transduce light into neural signals
-Send signals to bipolar cells
-Send signals to and receive signals from horizontal cells

99
Q

Rods:

A

Provide black and white vision in dim light

100
Q

Cones:

A

Provide high-acuity color vision in bright light

101
Q

s-cones

A

most sensitive to shorter wavelengths

102
Q

m cones

A

most sensitive to medium wavelengths

103
Q

L-cones

A

most sensitive to longer wavelengths

104
Q

Horizontal cells

A

Receive signals from and send signals to photoreceptors and other horizontal cells

105
Q

Bipolar cells:

A

-Receive signals from photoreceptors
-Send signals to amacrine cells and retinal ganglion cells

106
Q

Amacrine cells:

A

-Receive signals from and send signals to bipolar cells and other amacrine cells
-Send signals from bipolar cells and amacrine cells
-send action potentials to the brain via the optic nerve

107
Q

The axons of RGC’s exit the eye at:

A

the optic disk, forming a bundle called the optic nerve

108
Q

Photopigment regeneration:

A

The process whereby photopigment molecules change back into the 11-cis shape after photoisomerization.

108
Q

126 million photoreceptors converge to

A

1 million ganglion cells

109
Q

50 _ to 1 bipolar cell

A

50 rods to one bipolar cell

110
Q

6 cones to

A

one diffuse bipolar cell

111
Q

cones in fovea have a __ relationship to midget bipolar cells

A

1:1

112
Q

luminance contrast:

A

A difference in intensity of illumination at adjacent retinal locations

113
Q

what are the two types of retinal ganglion cells?

A

Parasol RCGs and Midget RCGs

114
Q

Midget RCG’s have:

A

Relatively small receptive fields

115
Q

Parasol RCG’s have:

A

Relatively large RCG’s

116
Q

ON-center receptive fields:

A

Excited by light falling on centre, inhibited by light falling surround

117
Q

OFF-center receptive fields:

A

Inhibited by light falling on centre, excited by light falling on surround

118
Q

Retinal ganglion cells are most sensitive to

A

differences in the intensity of light between center and surround and are relatively unaffected by the average intensity

119
Q

Luminance variations tend to be

A

smooth within objects and sharp between objects

120
Q

Center-surround receptive fields help to

A

emphasize object boundaries

121
Q

lateral inhibition:

A

Inhibitory neural signals transmitted by horizontal cells in retinal circuits

122
Q

P ganglion cells (Parvocellular cells):

A

Small receptive fields, high acuity, work best in high luminance
situations, sustained firing
Provide information mainly about the contrast in the retinal image

123
Q

M ganglion cells:

A

Large receptive fields, low acuity, work best in low luminance
situations, burst firing
- Provide information about how an image changes over time

Sensation and Perception (6 decks)

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