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BioPsych > Chap 5 - Vision > Flashcards

Chap 5 - Vision Flashcards

1
Q

receptors of vision are sensitive to:

A

light

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2
Q

receptors ______ energy into electrochemical patterns so that the brain can perceive sights, sounds, smells.

A

“transduce” (convert)

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3
Q

Law of specific nerve energies

A

states that activity by a particular nerve always conveys the same type of information to the brain

Ex: impulses in one neuron indicate light; impulses in another neuron indicate sound

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4
Q

The eye to the brain

A
  • light enters thru pupil
  • light is focused by lens and cornea onto rear surface of eye (retina)
  • visual receptors send msgs to neurons (bipolar cells)
  • bipolar cells send msgs to ganglion cells
  • axons of ganglion cells join (optic nerve)
  • travels to the brain
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5
Q

Amacrine cells:

A

additional cells that receive info from bipolar cells and send it to other bipolar, ganglion, or amacrine cells

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6
Q

Amacrine cells fx:

A

control the ability of the ganglion cells to respond to shapes, movements, or other specific aspects of visual stimuli

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7
Q

optic nerve

A

consists of the axons of ganglion cells that band together and exit through the back of the eye and travel to the brain

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8
Q

The point at which the optic nerve leaves the back of the eye is called the ________ because it contains no receptors

A

blind spot

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9
Q

The central portion of the retina is the _______ and allows for acute and detailed vision

A

fovea

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10
Q

fovea

A
  • Packed tight with receptors

- Nearly free of ganglion axons and blood vessels

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11
Q

Each receptor in the fovea attaches to a single bipolar cell and a single ganglion cell known as a :

A

midget ganglion cell

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12
Q

Each _____ in the fovea has a direct line to the brain which allows the registering of the exact location of input

A

cone

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13
Q

In the _________ of the retina, a greater number of receptors converge into ganglion and bipolar cells

A

periphery

  • Detailed vision is less in peripheral vision
  • Allows for the greater perception of much fainter light in peripheral vision
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14
Q

The arrangement of visual receptors in the eye is highly adaptive

A

Ex: predatory birds have a greater density of receptors on the top of the eye; rats have a greater density on the bottom of the eye

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15
Q

foveal vision

A
  • receptors - cones
  • convergence of input - each ganglion cell excited by a single cone
  • brightness sensitivity - distinguishes among bright lights; responds poorly to dim light
  • sensitivity to detail - good detail vision b/c each cone’s own ganglion cell sends a message to the brain
  • color vision - good (many cones)
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16
Q

peripheral vision

A
  • receptors - portion of rods increase toward periphery
  • convergence of input - each ganglion cell excited by many receptors
  • brightness sensitivity - responds well to dim light; poor for distinguishing among bright lights
  • sensitivity to detail - poor detail vision b/c many receptors coverage their input onto a given ganglion cell
  • color vision - poor (few cones)
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17
Q

The vertebrate retina consists of two kinds of receptors:

A
  • rods

- cones

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18
Q

rods

A

most abundant in the periphery of the eye and respond to faint light (120 million per retina)

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19
Q

cones

A

most abundant in and around the fovea (6 million per retina)

  • Essential for color vision & more useful in bright light
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20
Q

Though cones are outnumbered, they provide about ______ of the brain’s input.

A

90%

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21
Q

The average number of axons in the optic nerve is ________, but some people may have two or three times as many

A

one million

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22
Q

Photopigments

A

chemicals contained by both rods and cones that release energy when struck by light

  • Consist of 11-cis-retinal bound to proteins called opsins
  • Light energy converts 11-cis-retinal quickly into all-trans-retinal
  • Light is thus absorbed and energy is released that activates second messengers within the cell
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23
Q

color vision

A
  • perception of color is dependent upon the wavelength of the light
  • “Visible” wavelengths are dependent upon the species’ receptors
  • shortest wavelength humans can perceive is 400 nanometers (violet)
  • longest wavelength that humans can perceive is 700 nanometers (red)
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24
Q

Two major interpretations of color vision include the following:

A
  • Trichromatic theory/Young-Helmholtz theory

- Opponent-process theory

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25
Q

Trichromatic theory/Young-Helmholtz theory

A
  • color perception occurs through the relative rates of response by three kinds of cones
  • Short wavelength, medium-wavelength, long-wavelength
  • Each cone responds to a broad range of wavelengths, but some more than others
  • The ratio of activity across the three types of cones determines the color
  • More intense light increases the brightness of the color but does not change the ratio
  • Incomplete theory of color vision
  • Ex: negative color afterimage
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26
Q

opponent-process theory

A
  • suggests we perceive color in terms of paired opposites
  • brain has a mechanism that perceives color on a continuum from red to green and another from yellow to blue
  • possible mechanism for the theory is that bipolar cells are excited by one set of wavelengths and inhibited by another
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27
Q

Both the opponent-process and trichromatic theory have limitations

A
  • Color constancy

- Retinex theory

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28
Q

Color constancy

A

ability to recognize color despite changes in lighting, is not easily explained by these theories

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29
Q

Retinex theory

A

suggests the cortex compares information from various parts of the retina to determine the brightness and color for each area

  • Better explains color and brightness constancy
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30
Q

Color vision deficiency

A

impairment in perceiving color differences

  • Gene responsible is contained on the X chromosome (~8% of men &
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31
Q

Rods and cones of the retina make synaptic contact with ________ and ________.

A
  • horizontal cells

- bipolar cells

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32
Q

Horizontal cells

A

cells in the eye that make inhibitory contact onto bipolar cells

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33
Q

Bipolar cells

A

make synapses onto amacrine cells and ganglion cells

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34
Q

ganglion cell axon form the ______

A

optic nerve

35
Q

The ______ is the place where the two optic nerves leaving the eye meet.

A

optic chiasm

36
Q

Most ganglion cell axons go to the ___________ , a smaller amount to the __________ , and fewer to other areas

A
  • lateral geniculate nucleus

- superior colliculus

37
Q

lateral geniculate nucleus

neural basis of visual perception

A

part of the thalamus specialized for visual perception

  • Destination for most ganglion cell axons
  • Sends axons to other parts of the thalamus and to the visual areas of the occipital cortex
  • Cortex and thalamus feed information back and forth to each other
38
Q

Lateral inhibition

processing in the retina

A

is the reduction of activity in one neuron by activity in neighboring neurons

  • response of cells in the visual system depends upon the net result of excitatory and inhibitory messages it receives
  • Lateral inhibition is the retina’s way responsible of sharpening contrasts to emphasize the borders of objects
39
Q

receptive field

A

refers to the part of the visual field that either excites or inhibits a cell in the visual system of the brain

  • For a receptor, the receptive field is the point in space from which light strikes it
  • For other visual cells, receptive fields are derived from the visual field of cells that either excite or inhibit
    (Ex: ganglion cells converge to form the receptive field of the next level of cells)
40
Q

Ganglion cells of primates generally fall into three categories:

A
  • Parvocellular neurons
  • Magnocellular neurons
  • Koniocellular neurons
41
Q

Parvocellular neurons

A
  • Mostly located in or near the fovea
  • Have smaller cell bodies and small receptive fields
  • Are highly sensitive to detect color and visual detail
42
Q

Magnocellular neurons

A
  • Are distributed evenly throughout the retina
  • Have larger cell bodies and visual fields
  • Are highly sensitive to large overall pattern and moving stimuli
43
Q

Koniocellular neurons

A
  • Have small cell bodies
  • Are found throughout the retina
  • Have several functions, and their axons terminate in many different places
44
Q

Cells of the lateral geniculate have a receptive field similar to those of ganglion cells:

A

An excitatory or inhibitory central portion and a surrounding ring of the opposite effect

45
Q

primary visual cortex (area V1)

A

receives information from the lateral geniculate nucleus and is the area responsible for the first stage of visual processing

46
Q

Some people with damage to V1 show ______: an ability to respond to visual stimuli that they report not seeing

A

blindsight

47
Q

Hubel and Weisel (1959, 1998) distinguished various types of cells in the visual cortex:

A
  • simple cells
  • complex cells
  • end-stopped/hypercomplex cells
48
Q

simple cells

A
  • Fixed excitatory and inhibitory zones
  • The more light that shines in the excitatory zone, the more the cell responds
  • The more in the inhibitory zone, the less the cell responds
  • Bar-shaped or edge-shaped receptive fields with vertical and horizontal orientations outnumbering diagonal ones
49
Q

complex cells

A
  • Located in either V1 or V2
  • Have large receptive field that can not be mapped into fixed excitatory or inhibitory zones
  • Responds to a pattern of light in a particular orientation and most strongly to a moving stimulus
50
Q

end-stopped/hypercomplex cells

A
  • Are similar to complex cells but with a strong inhibitory area at one end of its bar shaped receptive field
  • Respond to a bar-shaped pattern of light anywhere in its large receptive field, provided the bar does not extend beyond a certain point
51
Q

In the visual cortex, cells are grouped together in columns perpendicular to the surface

A

Cells within a given column process similar information

  • Respond either mostly to the right or left eye, or respond to both eyes equally
  • Do not consistently fire at the same time
52
Q

Cells in the visual cortex may be ________ , neurons whose response indicate the presence of a particular feature/ stimuli

A

feature detectors

53
Q

Prolonged exposure to a given visual feature ________ sensitivity to that feature

A

decreases

54
Q

Animal studies have greatly contributed to the understanding of the development of vision

A
  • Early lack of stimulation of ONE eye: leads to synapses in the visual cortex becoming gradually unresponsive to input from that eye
  • Early lack of stimulation of BOTH eyes: cortical responses become sluggish but do not cause blindness
55
Q

Sensitive/critical periods

A

are periods of time during the lifespan when experiences have a particularly strong and enduring effect

  • Critical period ends with the onset of chemicals that inhibit axonal sprouting
  • Changes that occur during critical period require both excitation and inhibition of some neurons
  • Cortical plasticity is greatest in early life, but never ends
56
Q

Stereoscopic depth perception

A

is a method of perceiving distance in which the brain compares slightly different inputs from the two eyes

  • relies on retinal disparity
57
Q

retinal disparity

A

or the discrepancy between what the left and the right eye sees

58
Q

The ability of cortical neurons to adjust their connections to detect retinal disparity is shaped through _________.

A

experience

59
Q

Strabismus

A

is a condition in which the eyes do not point in the same direction

  • Usually develops in childhood
  • Also known as “lazy eye”
60
Q

If two eyes carry unrelated messages, cortical cell strengthens connections with only one eye

A

Development of stereoscopic depth perception is impaired

61
Q

Early exposure to a limited array of patterns leads to nearly all of the visual cortex cells becoming responsive to ______.

A

only that pattern

62
Q

Astigmatism

A

refers to a blurring of vision for lines in one direction caused by an asymmetric curvature of the eyes

  • 70% of infants have astigmatism
63
Q

Study of people born with cataracts but had them removed at age 7 or 12 indicate that vision can be restored gradually, but problems persist:

A
  • Difficulty in recognizing objects
  • Unable to tell that components are part of a whole
  • Best prognosis is for children whose vision problems are corrected early in life
64
Q

the “what” and “where” paths

A
  • ventral stream
  • dorsal stream

The two streams communicate
Each participates in identifying what and where an object is

65
Q

secondary visual cortex (area V2)

A

receives information from area V1, processes information further, and sends it to other areas

Info is transferred between area V1 and V2 in a reciprocal nature

66
Q

ventral stream

A

refers to the path that goes through temporal cortex; the “what” path

  • Specialized for identifying and recognizing objects
67
Q

dorsal stream

A

refers to the visual path in the parietal cortex; the “where” path

  • Helps the motor system to find objects and move towards them
68
Q

Damaging either stream will produce different deficits

A
  • Ventral stream damage: can see where objects are but cannot identify them
  • Dorsal stream damage: can identify objects but not know where they are
69
Q

detailed analysis of shape

A

Receptive fields become larger and more specialized as visual information goes from simple cells to later areas of visual processing

70
Q

inferior temporal cortex

A

contains cells that respond selectively to complex shapes but are insensitive to distinctions that are critical to other cells

  • Cells in this cortex respond to identifiable objects
71
Q

shape constancy

A

is the ability to recognize an object’s shape despite changes in direction or size

  • The inferior temporal neuron’s ability to ignore changes in size and direction contributes to our capacity for shape constancy
  • Damage to the pattern pathways of the cortex can lead to deficits in object recognition
72
Q

Visual agnosia

A

is the inability to recognize objects despite satisfactory vision

  • Caused by damage to the pattern pathway usually in the temporal cortex
73
Q

face recognition

A
  • occurs relatively soon after birth
  • People w/ cataracts removed at 2-6 months develop nearly normal vision but have slight difficulties in distinguishing faces
  • Newborns show strong preference for a right-side-up face and support idea of a built-in face recognition system
  • Facial recognition continues to develop gradually into adolescence
74
Q

Prosopagnosia

A

is the inability to recognize faces

  • Occurs after damage to the fusiform gyrus of the inferior temporal cortex
  • The fusiform gyrus responds much more strongly to faces than anything else
75
Q

color preception

A

depends on both the light reflected on an object and how it compares with objects around it

  • Area V4 may be responsible for color constancy and visual attention
  • Color constancy
76
Q

Color constancy

A

the ability to recognize something as being the same color despite changes in lighting

77
Q

motion perception

A

involves a variety of brain areas in all four lobes of the cerebral cortex

78
Q

middle-temporal cortex (MT/V5)

A

responds to a stimulus moving in a particular direction

79
Q

Cells in the dorsal part of the ________________ respond to expansion, contraction or rotation of a visual stimulus

A

medial superior temporal cortex (MST)

80
Q

MT and MST both receive input from the ________.

A

magnocellular path; color-insensitive

81
Q

motion blindness

A

refers to the inability to determine the direction, speed and whether objects are moving

  • Likely caused by damage in area MT
82
Q

Some people are blind except for the ability to detect which direction something is moving

A

Area MT probably gets some visual input despite significant damage to area V1

83
Q

Several mechanisms prevent confusion or blurring of images during eye movements

A
  • Saccades - decrease in the activity of the visual cortex during quick eye movements
  • Neural activity and blood flow decrease 75 ms before and during eye movements

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