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PSYCH 367 > Topic 3: Neural Processing in Vision > Flashcards

Topic 3: Neural Processing in Vision Flashcards

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1
Q

Wavelength

A

for light energy, the distance between one peak of a light wave and the next peak

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2
Q

Visible Light

A

the band of electromagnetic energy that activates the visual system and that, therefore, can be perceived

for humans, visible light has wavelengths between 400 and 700 nanometers

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3
Q

Eyes

A

the eyeball and its contents, which include focusing elements, the retina, and supporting structures

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4
Q

Pupil

A

the opening through which light reflected from objects in the environment enters the eye

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5
Q

Cornea

A

the transparent focusing element of the eye that is the first structure through which light passes as it enters the eye

the cornea is the eye’s major focusing element

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6
Q

Lens

A

the transparent focusing element of the eye through which light passes after passing through the cornea and the aqueous humor

the len’s change in shape to focus at different distances is called accommodation

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7
Q

Retina

A

a complex network of cells that covers the inside back of the eye

these cells include the receptors, which generate an electrical signal in response to light, as well as the horizontal, bipolar, amacrine, and ganglion cells

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8
Q

Photoreceptors

A

the receptors for vision

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9
Q

Rods

A

a cylinder-shaped receptor in the retina that is responsible for vision at low levels of illumination

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10
Q

Cones

A

cone-shaped receptors in the retina that are primarily responsible for vision in high levels of illumination and for color vision and detail vision

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11
Q

Outer Segments

A

part of the rod and cone visual receptors that contains light-sensitive visual pigment molecules

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12
Q

Visual Pigments

A

a light-sensitive molecule contained in the rod and cone outer segments

the reaction of this molecule to light results in the generation of an electrical response in the receptors

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13
Q

Optic Nerve

A

bundle of nerve fibers that carry impulses from the retina to the lateral geniculate nucleus and other structures

each optic nerve contains about 1 million ganglion cell fibers

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14
Q

Fovea

A

a small area in the human retina that contains only cone receptors

the fovea is located on the line of sight, so that when a person looks at an object, the center of its image falls on the fovea

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15
Q

Peripheral Retina

A

the area of retina outside the fovea

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16
Q

Macular Degeneration

A

a clinical condition that causes degeneration of the macula, an area of the retina that includes the fovea and a small surrounding area

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17
Q

Retina Pigmentosa

A

a retinal disease that causes a gradual loss of vision, beginning in the peripheral retina

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18
Q

Blind Spot

A

the small area where the optic nerve leaves the back of the eye

there are no visual receptors in this area, so small images falling directly on the blind spot cannot be seen

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19
Q

Accommodation

A

in vision, bringing objects located at different distances into focus by changing the shape of the lens

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20
Q

Refractive Errors

A

errors that can affect the ability of the cornea and/or lens to focus incoming light onto the retina

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21
Q

Presbyopia

A

the inability of the eye to accommodate due to a hardening of the lens and a weakening of the ciliary muscles

it occurs as people get older

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22
Q

Myopia

A

an inability to see distant objects clearly

also called nearsightedness

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23
Q

Refractive Myopia

A

myopia (nearsightedness) in which the cornea and/or the lens bend the light too much

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24
Q

Axial Myopia

A

myopia (nearsightedness) in which the eyeball is too long

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25
Q

Hyperopia

A

a condition causing poor vision in which people can see objects that are far away but do not see near object clearly

also called farsightedness

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26
Q

Isomerization

A

change in the shape of the retinal part of the visual pigment molecule that occurs when the molecule absorbs a quantum of light

isomerization triggers the enzyme cascade that results in transduction from light energy to electrical energy in the retinal receptors

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27
Q

Dark Adaptation

A

visual adaptation that occurs in the dark, during which the sensitivity to light increases

this increase in sensitivity is associated with regeneration of the rod and cone visual pigments

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28
Q

Dark Adaptation Curve

A

the function that traces the time course of the increase in visual sensitivity that occurs during dark adaptation

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29
Q

Light-Adapted Sensitivity

A

the sensitivity of the eye when in the light-adapted state, usually taken as the starting point for the dark adaptation curve because it is the sensitivity of the eye just before the lights are turned off

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30
Q

Dark-Adapted Sensitivity

A

the sensitivity of the eye after it has completely adapted to the dark

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31
Q

Rod Monochromats

A

a person who has a retina in which the only functioning receptors are rods

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32
Q

Rod-Cone Break

A

the point on the dark adaptation curve at which vision shifts from cone vision to rod vision

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33
Q

Visual Pigment Bleaching

A

the change in the color of a visual pigment that occurs when visual pigment molecules are isomerized by exposure to light

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34
Q

Visual Pigment Regeneration

A

occurs after the visual pigment’s two components (opsin and retinal) have become separated due to the action of light

regeneration, which occurs in the dark, involves a rejoining of these two components to reform the visual pigment molecule

the process depends on enzymes located in the pigment epithelium

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35
Q

Detached Retina

A

a condition in which the retina is detached from the back of the eye

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36
Q

Spectral Sensitivity

A

the sensitivity of visual receptors to different parts of the visual spectrum

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37
Q

Spectral Sensitivity Curve

A

the function relating a subject’s sensitivity to light to the wavelength of the light

the spectral sensitivity curves for rod and cone vision indicate that the rods and cones are maximally sensitive at 500 nm and 560 nm, respectively

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38
Q

Monochromatic Light

A

light that contains only a single wavelength

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39
Q

Cone Spectral Sensitivity

A

a plot of visual sensitivity versus wavelength for cone vision, often measured by presenting a small spot of light to the fovea, which contains only cones

can also be measured when the eye is light adapted, so cones are the most sensitive receptors

40
Q

Rod Spectral Sensitivity Curve

A

the curve plotting visual sensitivity versus wavelength for rod vision

this function is typically measured when the eye is dark adapted by a test light presented to the peripheral retina

41
Q

Purkinje Shift

A

the shift from cone spectral sensitivity that takes place during dark adaptation

42
Q

Absorption Spectrum

A

a plot of the amount of light absorbed by a visual pigment versus the wavelength of light

43
Q

Neural Circuits

A

a number of neurons that are connected by synapses

44
Q

Bipolar Cells

A

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

45
Q

Ganglion Cells

A

a neuron in the retina that receives inputs from bipolar and amacrine cells

the axons of the ganglion cells are the nerve fibers that travel out of the eye in the optic nerve

46
Q

Horizontal Cells

A

a neuron that transmits signals laterally across the retina

horizontal cells synapse with receptors and bipolar cells

47
Q

Amacrine Cells

A

a neuron that transmits signals laterally in the retina

amacrine cells synapse with bipolar cells and ganglion cells

48
Q

Neural Convergence

A

synapsing of a number of neurons onto one neuron

49
Q

Visual Acuity

A

the ability to resolve small details

50
Q

Receptive Field

A

a neuron’s receptive field is the area on the receptor surface (the retina for vision; the skin for touch) that, when stimulated, affects the firing of that neuron

51
Q

Center-Surround Receptive Fields

A

a receptive field that has center-surround organization

52
Q

Excitatory Area

A

area of a receptive field that is associated with excitation

stimulation of this area causes an increase in the rate of nerve firing

53
Q

Inhibitory Area

A

area of a receptive field that is associated with inhibition

stimulation of this area causes a decrease in the rate of nerve firing

54
Q

Center-Surround Antagonism

A

the competition between the center and surround regions of a center-surround receptive field, caused by the fact that one is excitatory and the other is inhibitory stimulating center and surround areas simultaneously decreases responding of the neuron, compared to stimulating the excitatory area alone

55
Q

Lateral Inhibition

A

inhibition that is transmitted laterally across a nerve circuit; in the retina, lateral inhibition is transmitted by the horizontal and amacrine cells

56
Q

Edge Enhancement

A

an increase in perceived contrast at borders between regions of the visual field

57
Q

Chevreul Illusion

A

occurs when areas of different lightness are positioned adjacent to one another to create a border

the illusion is the perception of a light band on the light side of the border and a dark band on the dark side of the border, even though these bands do not exist in the intensity distribution

58
Q

Mach Bands

A

light and dark bands perceived at light-dark borders

59
Q

Preferential Looking (PL) Technique

A

a technique used to measure perception in infants

two stimuli are presented, and the infant’s looking behavior is monitored for the amount of time the infant spends viewing the stimulus

60
Q

Visual Evoked Potential

A

an electrical response to visual stimulation recorded by the placement of disk electrodes on the back of the head

this potential reflects the activity of a large population of neurons in the visual cortex

61
Q

How was the Snellen chart used to measure visual acuity?

A

measures foveal acuity only

normal is 20/20 vision (what you can see at 20 feet vs. distance for a normal person to see)

20/200 (or worse) is legally blind

what is the unit of measurement?

62
Q

How do optometrists measure visual acuity?

A

reciprocal of focal length (m) of corrective lens

negative = concave lens (for nearsightedness)
positive = convex lens (for farsightedness)

63
Q

What is visual angle?

A

size of retinal image in degrees

with 20/20 vision, details of 1’ can be resolved (size of a quarter at the distance of a football field)

64
Q

What is hyperacuity?

A

resolution of details of 10” or less of vernier gratings (exceeds resolution of receptors)

cone spacing in fovea = 12” (1 um)
expected resolution = 24” (theoretical limit)

hyperacuity may be due to complex neural processing in the visual cortex

65
Q

How does retinal position affect acuity?

A

fovea has the greatest acuity

high (cone) receptor density
low spatial summation (convergence of a number of receptors to a single neuron)

cortical magnification factor: gives millimeters of cortex per degree of visual angle, as a function of retinal eccentricity

66
Q

What is myopia?

A

image focused in middle of the eyeball (nearsightedness)

67
Q

What is hyperopia?

A

images focused behind retina (farsightedness)

68
Q

What is astigmatism?

A

cornea is not spherical, but asymmetrically curved (like a football), causing multiple focal points

69
Q

What is chromatic aberration?

A

different wavelengths focus at different points

70
Q

What is spherical abberration?

A

light rays focus at different points depending on how far from center they pass through a lens

smaller pupil minimizes this

71
Q

What is diffraction?

A

light waves bend around obstacles in their path or through a slit; affects different wavelengths to different extents

larger pupil minimizes this

optimum pupil trade off size = 2.4 mm

72
Q

What is radiance?

A

radiant power from a light source

unit: lumen = light produced by a standard candle (“candela”)

e.g. 1 lm = 1.46 mW

73
Q

What is illuminance?

A

amount of light falling on a surface

unit: lux = 1 lumen per square metre of area (lm/m^2)

e.g. daylight = 10,000 lux, full moon = 0.1 lux

74
Q

What is luminance?

A

amount of light reflected from a surface

unit: nit = 1 candela per square metre of area (cd/m^2)

e.g. LCD monitor = 260 nits, CRT moniter = 150 units

75
Q

What is reflectance?

A

proportion of light reflected from a surface

unit: percent (%) or “albedo” = (luminance/illuminance) x 100

e.g. white paper = 90%, black paper = 10%

76
Q

What is brightness?

A

perceptual impression of intensity of light source

psychological counterpart to radiance

77
Q

What is lightness?

A

perceptual impression of surface “greyness”

psychological counterpart to reflectance

78
Q

How does dark/light adaptation affect brightness perception?

A

being in a dark room then moving to a bright room seems brighter before you are habituated

79
Q

How does retinal locus affect brightness perception?

A

threshold lower in the periphery (due to greater rod convergence)

80
Q

How does wavelength affect brightness perception?

A

match standard color with comparisons based on brightness; get absorption spectrum

repeat under different illuminations (photopic vs. scotopic)

during dark adaptation, we shift from using cones to rods

result is Purkinje shift: peak sensitivity changes to shorter (bluer) wavelengths

81
Q

How does time and area affect brightness perception?

A

brightness affected by duration and retinal size of stimulus

82
Q

What is the optic nerve?

A

axons of retinal ganglion cells

exits back of the eye where there are no receptors (optic disc), resulting in a blind spot

retina begins processing visual information: ~126 million receptors, but only 1 million nerve fibers

83
Q

What is the receptive field?

A

area on the retina that, in response to a stimulus, influences the firing of a neuron

typical (ganglion cell) receptive field is centre-surround

this formation is due to a pattern of connectivity between many receptors and a single ganglion cell

84
Q

What is lateral inhibition?

A

some cells, when activated (e.g., by the presence of a stimulus), decrease the activity of adjacent cells

due to the release of inhibitory neurotransmitter

85
Q

What is the Chevreul illusion?

A

each band is uniform shade of grey, but seems to darken near a lighter band, and lighten near a darker band

adjacent receptors believed to inhibit neighboring receptors

difference in luminance at border exaggerated by lateral inhibition

86
Q

What is simultaneous contrast?

A

central squares appear different shades

explained by lateral inhibition: receptors activated by larger surrounding square inhibit receptors in smaller central square

87
Q

What is the Benary cross illusion?

A

both triangles should receive equal lateral inhibition, but seem different shades

88
Q

What is White’s illusion?

A

rectangle A should receive little lateral inhibition (and seem lighter), but it seems darker

rectangle B should receive a lot of lateral inhibition (but seem darker), but it seems lighter

explained in terms of “belongingness”: appearance of an areas is influenced by the surroundings to which it seems to belong

suggests higher-order processing instead of retinal mechanism

89
Q

What is spatial frequency?

A

how a stimulus changes over space (cycles per degree of visual angle)

one cycle = one dark bar + one light bar

higher intensity regions produce peaks, lower intensity areas correspond to troughs

90
Q

What is Fourier analysis?

A

simplified scene description in terms of a set of sine waves

result: mathematical expression describing the visual scene in terms of sine waves

better than taking inventory of the activity of all ~126 million receptors

allows us to investigate commonalities in the processing of visual information

91
Q

What is the contrast sensitivity function?

A

describes ability of a system to preserve contrast and spatial frequency information after it has been encoded

92
Q

What is the contrast ratio?

A

based on physical measures of light (L = luminance)

however, apparent contrast is affected by spatial frequency: wide black bars appear darker than narrower bars, wide white bars appear lighter than narrower bars

93
Q

What are the steps of creating a contrast sensitivity function?

A
  1. present observer with a grating of black & white bars of a certain spatial frequency
  2. change contrast between the black and white bars until observer no longer perceives stimulus as lines
  3. change spatial frequency and repeat
94
Q

Is a contrast sensitivity function monolithic or comprised of “channels”?

A
  1. adapt to a spatial frequency of 7.5 cycles/degree
  2. remeasure the contrast sensitivity function

suggests contrast sensitivity function is comprised of a series of spatial frequency channels

95
Q

What did the Maffei & Fiorentini (1973) study demonstrate about contrast sensitivity function?

A

each simple cell responds best to a narrow range of spatial frequencies

adaptation effects are caused by neural fatigue

PSYCH 367 (15 decks)

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