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PSYC 212 > Chapter 3: The Eye and the Retina > Flashcards

Chapter 3: The Eye and the Retina Flashcards

1
Q

bionic eye

A

an array of electrodes implanted in the back of the eye that, through a camera mounted on eyeglasses, sends signals to the visual system about one’s surroundings

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2
Q

electromagnetic spectrum

A

a continuum of electromagnetic energy that is produced by electrical charges and is radiated as waves

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3
Q

wavelength

A

the distance between the peaks of the electromagnetic waves

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4
Q

visible light

A

the energy within the electromagnetic spectrum that humans can perceive (400-700 nm)

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5
Q

short wavelengths

A

blue

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6
Q

middle wavelengths

A

green

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7
Q

long wavelengths

A

yellow, orange, and red

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8
Q

pupil

A

where light enters the eye

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9
Q

cornea & lens function

A

focus the light to form sharp images

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10
Q

cornea vs. lens

A

The cornea is fixed and can’t adjust its focus, but the lens can change its shape to focus on objects located at different distances

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11
Q

retina

A

the network of neurons that covers the back of the eye and that contains photoreceptors

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12
Q

photoreceptors

A

receptors for vision

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13
Q

how did rods and cones receive their name

A

from the shape of their outer segments

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14
Q

outer segments

A

the part of photoreceptors that contain visual pigments

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15
Q

visual pigments

A

light-sensitive chemicals that react to light and trigger electrical signals

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16
Q

optic nerve

A

conducts signals toward the brain

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17
Q

what type of photoreceptors is in the fovea?

A

cones

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18
Q

what type of photoreceptors is in the periphery?

A

both rods & cones but mostly rods

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19
Q

how many rods and cones are there

A

120 million rods and 6 million cones

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20
Q

blind spot

A

the area of the retina where the optic nerve leaves the brain and there are no photoreceptors

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21
Q

how does the brain fill in the blind spot

A

by creating a perception that matches the surrounding pattern

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22
Q

macular degeneration

A

the destruction of the fovea and a small area that surrounds it. Results in a blind region in central vision

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23
Q

Retinitis pigmentosa

A

degeneration of the retina that is passed from one generation to the next. First attacks the peripheral rod receptors and results in poor peripheral visual field vision. In some cases, the foveal receptors are also attacked, resulting in complete blindness

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24
Q

accomodation

A

The change in the lens’ shape that occurs when the ciliary muscles at the front of the eye tighten and increase the curvature of the lens so that it gets thicker

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25
Q

refractive errors

A

errors that affect the ability of the cornea and/or lens to focus the visual input onto the retina

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26
Q

presbyopia

A

the age-related loss of the ability to accommodate, resulting in hyperopia

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27
Q

myopia

A

(nearsightedness): the inability to see distant objects clearly

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28
Q

refractive myopia

A

the cornea and/or lens bends the light too much

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29
Q

axial myopia

A

the eyeball is too long

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30
Q

hyperopia

A

(farsightedness): the inability to see nearby objects because the focus point for parallel rays of light is located behind the retina, usually because the eyeball is too short

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31
Q

2 parts of visual pigments

A

opsin (long protein) & retinal (small light-sensitive component)

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32
Q

steps of visual transduction

A
  1. The visual pigment molecule absorbs the light
  2. The retinal within that molecule changes its shape and becomes straight (isomerization)
  3. This creates a chemical chain reaction that activates thousands of charged molecules to create electrical signals in receptors
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33
Q

dark adaptation

A

increasing sensitivity in the dark with time

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34
Q

how is dark adaption measured?

A

with the dark adaptation curve

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35
Q

steps for measuring the dark adaptation curve

A
  1. Have the participant look at a small fixation point while paying attention to a flashing test light that is off to the side (fixation point falls on the fovea & test light falls on the periphery)
  2. Have the participant turn a knob that adjusts the intensity of the flashing light until it can just barely be seen. This establishes the light-adapted sensitivity
  3. Extinguish the light so the participant is in the dark
  4. Have the participant continue adjusting the intensity of the light so that they can just barely see it, tracking the increase in sensitivity that occurs in the dark
  5. As the participant becomes more sensitive to the light, they must decrease the light’s intensity to keep it just barely visible, resulting in the dark adaptation curve
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36
Q

2 phases of increased sensitivity in the dark adaptation curve

A
  • Increases rapidly for the first 3-4 minutes then levels off
  • It begins increasing again at around 7-10 minutes and then continues to do so until 20-30 mins
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37
Q

dark-adapted sensitivty

A

the sensitivity at the end of dark adaptation

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38
Q

dark vs. light-adapted sensitivity

A

dark adapted-sensitivity is 100,000 times greater

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39
Q

measuring the dark adaptation of cones only

A

have the participant look only at the test image so the image falls on the fovea and by making the image small enough so that the entire image falls on the fovea

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40
Q

measuring the dark adaptation of rods only

A

measure the dark adaptation of a person who has no cones

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41
Q

rod monochromats

A

people who have no cones due to a rare genetic defect

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42
Q

dark adaptation of rods vs. cones

A

As soon as the light is extinguished, the sensitivity of both rods and cones begins increasing. However, because cones are more sensitive than rods at the beginning of dark adaptation, we see them right after the lights are turned off. After 3-5 mins in the dark, cones reach their maximum sensitivity and level off, but rods are still adapting and by about 7 mins they catch up and become more sensitive than the cones.

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43
Q

rod-cone break

A

where the cones can no longer get more sensitive. Occurs around 5-6 minutes

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44
Q

visual pigment bleaching

A

when the visual pigment becomes lighter in colour as a result of the change in shape and separation from the opsin

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45
Q

visual pigment regeneration

A

the process of reforming the visual pigment (returning it to its bent shape and reattaching it to the opsin)

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46
Q

pigment epithelium

A

a layer that contains enzymes necessary for pigment regeneration

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47
Q

pigment regeneration in the light vs. dark

A
  • In the light, some pigments are isomerizing and bleaching and others are regenerating
  • In the dark, there is no more isomerization or bleaching, so eventually, there are only intact visual pigment molecules
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48
Q

William Rushton concluded that…

A

1) Our sensitivity to light depends on the concentration of visual pigment
2) The speed at which our sensitivity increases in the dark depends on the regeneration of the visual pigment

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49
Q

how long does it take cone vs. rod pigment to regenerate

A

cone pigment took 6 mins to regenerate, whereas rod pigment took more than 30 mins.

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50
Q

detached retina

A

when a person’s retina becomes detached from the pigment epithelium

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51
Q

spectral sensitivity

A

The eye’s sensitivity to light as a function of the light’s wavelength

52
Q

monochromatic light

A

light of a single wavelength

53
Q

measuring a spectral sensitivity curve

A
  1. Present the participant with one wavelength at a time and measure their sensitivity to each wavelength
  2. Determine the person’s threshold for seeing monochromatic lights across the threshold
  3. The threshold is higher at short and long wavelengths and lower in the middle of the spectrum
  4. Using the equation sensitivity= 1/threshold, convert the threshold curve into the spectral sensitivity curve
54
Q

measuring the cone spectral sensitivity curve

A

have the participant look directly at a test light so it stimulates only the cones in the fovea

55
Q

measuring the rod sensitivity curve

A

measure sensitivity after the eye is dark-adapted

56
Q

what frequency of wavelength are rods most sensitive to

A

short wavelengths (500 nm)

57
Q

what frequency of wavelength are cones most sensitive to

A

medium wavelengths (560 nm)

58
Q

Purkinje shift

A

enhanced perception of short wavelengths during dark adaption

59
Q

absorption spectra

A

A plot of the amount of light absorbed vs. the wavelength of the light

60
Q

when does the short-wavelength pigment best absorb light?

A

419 nm

61
Q

when does the medium-wavelength pigment best absorb light?

A

531 nm

62
Q

when does the long-wavelength pigment best absorb light?

A

558 nm

63
Q

neural circuits

A

interconnected groups of neurons within the retina

64
Q

bipolar cells

A

a retinal neuron that receives inputs from visual receptors and sends signals to the retinal ganglion cells

65
Q

ganglion cells

A

a retinal neuron that receives inputs from bipolar and amacrine cells. Their axons are the nerve fibres that travel out of the eye in the optic nerve

66
Q

horizontal cells

A

a neuron that transmitted signals laterally in the retina. They synapse with receptors and bipolar cells

67
Q

amacrine cells

A

a neuron that transmitted signals laterally in the retina. They synapse with bipolar cells and ganglion cells

68
Q

when does neural convergence occur?

A

when many neurons synapse onto a single neuron

69
Q

how many photoreceptors do ganglion cells receive signals from?

A

126

70
Q

what type of photoreceptor has greater convergence

A

rods

71
Q

rods are ____ sensitive than cones & why

A

more because they converge onto fewer ganglion cells

72
Q

rods have ___ acuity than cones & why

A

worse because they converge onto fewer ganglion cells

73
Q

visual acuity

A

the ability to see details

74
Q

receptive field

A

the retinal region over which a cell in the visual system can be influenced by light

75
Q

who discovered receptive fields

A

Hartline

76
Q

centre-surround receptive fields

A

receptive fields that are arranged like concentric circles, where the centre of the field responds differently to the surround

77
Q

who discovered centre-surround receptive fields?

A

Kuffler

78
Q

excitatory area

A

the area of the receptive field, where presenting a spot of light increases firing

79
Q

inhibitory area

A

the area of the receptive field, where presenting a spot of light decreases firing

80
Q

centre-surround antagonism

A

the competition between the centre and surround regions of a centre-surround receptive field caused by the fact that one is inhibitory and the other is excitatory. Stimulating centre and surround areas simultaneously decreases responding of the neuron compared to stimulating the excitatory area alone because the size of spot of light in the centre begins increasing and stimulating the inhibitory surround

81
Q

lateral inhibition

A

inhibition that is transmitted across the retina by the horizontal and amacrine cells

82
Q

Hartline et al’s 1961 limulus experiment

A

found that the illumination of receptor A caused a large response but the activation of A & B together inhibited firing, particularly as the intensity of B was increased due to centre-surroud antagonism

83
Q

edge enhancement

A

an increase in perceived contrast at borders between regions of the visual field caused by centre-surround cells

84
Q

stimuli that are part of the inhibitory surround have ___ edges

A

darker

85
Q

Chevreuil illusion

A

perceived light and dark bands that appear at borders, which are not present in the actual physical stimuli

86
Q

Mach bands

A

The borders between bands appear slightly lighter than the band itself

87
Q

how are the Chevreuil & Mach illusions explained

A

Both can be explained by center-surround receptive fields and lateral inhibition; greater areas of high illumination result in more inhibition, which decreases neural responding

88
Q

preferential looking

A

A technique used to determine infant’s visual acuity

89
Q

how does preferential looking work?

A

Two stimuli are presented and if the infant looks at one more than the other, the experimenter can conclude that they can tell the difference between them. This works because infants have spontaneous looking preferences–they prefer to look at certain types of stimuli

90
Q

visual evoked potential

A

an electrical response generated by disc electrodes placed on the infant’s head over the visual part of the brain if the stimulus is large enough to be detected by the visual system

91
Q

which method of measuring an infant’s visual acuity usually indicates better acuity

A

preferential looking

92
Q

visual acuity during development

A

Visual acuity is poor at birth, but drastically increases during the first 6-9 months of life, followed by a levelling-off period where full adult acuity is reached just after 1 year of age

93
Q

why do infants have poorer visual acuity?

A

Infant cones have fat inner segments and small outer segments, resulting in them containing less visual pigment and being spaced further apart. This can be traced to the infant’s visual area of the brain being poorly developed at birth and the subsequent increase in neurons and synapses to the cortex during the first 6-9 months

94
Q

nature, 2010 study

A

discovered protein ion channels in snakes, activated by heat from the bodies of their prey, that allows them to see like an infrared camera

95
Q

femi gamma-ray space telescope

A

Can detect high energy, short wavelength gamma rays

96
Q

when does the pupil constrict/dilate

A

The pupil constricts when exposed to light and dilates in the dark

97
Q

rods vs. cones

A

Rods: more sensitive to light, can be used in low-light conditions, can’t perceive colour, low visual acuity, located in the periphery
Cones: less sensitive to light, used for photopic (daytime) vision, perceive colour, high visual acuity, highly concentrated in the fovea

98
Q

fovea

A

centre of the retina where cones are located

99
Q

periphery

A

outside of the retina where both rods and cones are located, but mostly rods

100
Q

when does accommodation occur?

A

for nearby objects

101
Q

where is light focused for faraway objects?

A

on the retina

102
Q

where is light focused for close objects?

A

behind the retina, so the eye has to accommodate

103
Q

where is light focused in the myopic eye

A

in front of the retina, so corrective lenses are needed to focus the eye properly

104
Q

astigmatism

A

a misshapen lens that can cause myopia or hyperopia

105
Q

how long does it take to become fully adapted to low-light conditions?

A

20 mins

106
Q

sensitivity

A

the minimum amount of energy necessary to just barely see the light

107
Q

light-adapted sensitivty

A

sensitivity in the light

108
Q

dark-adaptation curve

A

A function relating sensitivity to light to time in the dark

109
Q

sensitivity during dark adaptation _____

A

increases

110
Q

pigment absorption spectra

A

the level of absorption of the wavelength. ex. there are 3 different kinds of cones, each one of which is best at absorbing light from a specific wavelength

111
Q

main properties of receptive fields

A
  1. Receptive fields overlap
  2. The input that a Ganglion cell receives comes from many photoreceptors
  3. Receptive fields differ in size across the retina
112
Q

what area of the retina has larger receptive fields

A

the periphery

113
Q

what area of the retina has smaller receptive fields

A

the fovea

114
Q

two-point discrimination test

A

put two points close together and ask the participant if they feel one or two. Then try the same task in different locations (ex. Shoulders, fingertips)

115
Q

hartline’s discovery

A

Hartline isolated a single ganglion cell axon in the opened eyecup of a frog. Illuminated different areas of the retina and found that the cell he was recording from responded only when a small area of the retina was illuminated. He called the area of the receptive field of that RGC. The receptive field covered a much greater area than a single photoreceptor

116
Q

kuffler’s discovery

A

Stephen Kuffler (1953) measured ganglion cell receptive fields in the cat and reported a property of these receptive fields that Hartline hadn’t observed in the frog. Ganglion cells have centre-surround receptive fields that are arranged like concentric circles in a centre-surround organization

117
Q

excitatory centre inhibitory surround cell

A

shining light in the centre increases firing and shining light in the surround decreases firing

118
Q

RCG’s rate of firing depends on____

A

the amount of light in the surround or periphery

119
Q

the Hermann grid

A

Perceived circles appear at borders, which are not present in the actual stimulus

120
Q

looking at an intersection in the Hermann illusion

A

If you’re looking at an intersection, the fovea is looking at it. The receptive fields are small in the fovea, meaning that the entire ON-OFF part is illuminated by light. So, you don’t see a dark spot in the middle

121
Q

how is the Mach Bands illusion explained?

A

The receptive field at the border has less inhibition because part of it is in the darker area and isn’t inhibiting the centre, so it appears lighter. The receptive field at the next border has more inhibition because part of it is in the lighter area and is inhibiting the centre, so it appears darker

122
Q

why is the Mach bands illusion helpful?

A

it helps the brain to differentiate between similar shades

123
Q

the Mach bands illusion is useful in what profession?

A

Radiologists learn about this illusion because sometimes, X-rays will show a thin, well-defined, black line around one or both lateral margins of the heart. This results from the overlap of superimposed normal structures

124
Q

looking at a square in the Hermann illusion

A

If you’re looking right at the square, you see a dark spot because the periphery’s receptive fields are large and are being inhibited on four sides, so the neurons fire at a rate lower than their spontaneous firing rate

125
Q

when does the firing rate decrease below the spontaneous firing rate for an on-centre/off-surround cell?

A

when it’s firing in the periphery

126
Q

when does the firing rate increase above the spontaneous firing rate for an on-centre/off-surround cell?

A

when it’s firing in the fovea

127
Q

function of lateral inhibition

A

Allows one to perceive contrast

PSYC 212 (11 decks)

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