Chap 5 - Vision Flashcards
1
Q
receptors of vision are sensitive to:
A
light
2
Q
receptors ______ energy into electrochemical patterns so that the brain can perceive sights, sounds, smells.
A
“transduce” (convert)
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
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
5
Q
Amacrine cells:
A
additional cells that receive info from bipolar cells and send it to other bipolar, ganglion, or amacrine cells
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
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
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
9
Q
The central portion of the retina is the _______ and allows for acute and detailed vision
A
fovea
10
Q
fovea
A
- Packed tight with receptors
- Nearly free of ganglion axons and blood vessels
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
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
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
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
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)
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)
17
Q
The vertebrate retina consists of two kinds of receptors:
A
- rods
- cones
18
Q
rods
A
most abundant in the periphery of the eye and respond to faint light (120 million per retina)
19
Q
cones
A
most abundant in and around the fovea (6 million per retina)
- Essential for color vision & more useful in bright light
20
Q
Though cones are outnumbered, they provide about ______ of the brain’s input.
A
90%
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
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
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)
24
Q
Two major interpretations of color vision include the following:
A
- Trichromatic theory/Young-Helmholtz theory
- Opponent-process theory
25
Trichromatic theory/Young-Helmholtz theory
- 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
26
opponent-process theory
- 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
27
Both the opponent-process and trichromatic theory have limitations
- Color constancy
| - Retinex theory
28
Color constancy
ability to recognize color despite changes in lighting, is not easily explained by these theories
29
Retinex theory
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
30
Color vision deficiency
impairment in perceiving color differences
- Gene responsible is contained on the X chromosome (~8% of men &
31
Rods and cones of the retina make synaptic contact with ________ and ________.
- horizontal cells
| - bipolar cells
32
Horizontal cells
cells in the eye that make inhibitory contact onto bipolar cells
33
Bipolar cells
make synapses onto amacrine cells and ganglion cells
34
ganglion cell axon form the ______
optic nerve
35
The ______ is the place where the two optic nerves leaving the eye meet.
optic chiasm
36
Most ganglion cell axons go to the ___________ , a smaller amount to the __________ , and fewer to other areas
- lateral geniculate nucleus
| - superior colliculus
37
lateral geniculate nucleus
| neural basis of visual perception
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
Lateral inhibition
| processing in the retina
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
receptive field
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
Ganglion cells of primates generally fall into three categories:
- Parvocellular neurons
- Magnocellular neurons
- Koniocellular neurons
41
Parvocellular neurons
- 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
Magnocellular neurons
- Are distributed evenly throughout the retina
- Have larger cell bodies and visual fields
- Are highly sensitive to large overall pattern and moving stimuli
43
Koniocellular neurons
- Have small cell bodies
- Are found throughout the retina
- Have several functions, and their axons terminate in many different places
44
Cells of the lateral geniculate have a receptive field similar to those of ganglion cells:
An excitatory or inhibitory central portion and a surrounding ring of the opposite effect
45
primary visual cortex (area V1)
receives information from the lateral geniculate nucleus and is the area responsible for the first stage of visual processing
46
Some people with damage to V1 show ______: an ability to respond to visual stimuli that they report not seeing
blindsight
47
Hubel and Weisel (1959, 1998) distinguished various types of cells in the visual cortex:
- simple cells
- complex cells
- end-stopped/hypercomplex cells
48
simple cells
- 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
complex cells
- 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
end-stopped/hypercomplex cells
- 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
In the visual cortex, cells are grouped together in columns perpendicular to the surface
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
Cells in the visual cortex may be ________ , neurons whose response indicate the presence of a particular feature/ stimuli
feature detectors
53
Prolonged exposure to a given visual feature ________ sensitivity to that feature
decreases
54
Animal studies have greatly contributed to the understanding of the development of vision
- 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
Sensitive/critical periods
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
Stereoscopic depth perception
is a method of perceiving distance in which the brain compares slightly different inputs from the two eyes
- relies on retinal disparity
57
retinal disparity
or the discrepancy between what the left and the right eye sees
58
The ability of cortical neurons to adjust their connections to detect retinal disparity is shaped through _________.
experience
59
Strabismus
is a condition in which the eyes do not point in the same direction
- Usually develops in childhood
- Also known as “lazy eye”
60
If two eyes carry unrelated messages, cortical cell strengthens connections with only one eye
Development of stereoscopic depth perception is impaired
61
Early exposure to a limited array of patterns leads to nearly all of the visual cortex cells becoming responsive to ______.
only that pattern
62
Astigmatism
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
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:
- 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
the "what" and "where" paths
- ventral stream
- dorsal stream
The two streams communicate
Each participates in identifying what and where an object is
65
secondary visual cortex (area V2)
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
ventral stream
refers to the path that goes through temporal cortex; the “what” path
- Specialized for identifying and recognizing objects
67
dorsal stream
refers to the visual path in the parietal cortex; the “where” path
- Helps the motor system to find objects and move towards them
68
Damaging either stream will produce different deficits
- 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
detailed analysis of shape
Receptive fields become larger and more specialized as visual information goes from simple cells to later areas of visual processing
70
inferior temporal cortex
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
shape constancy
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
Visual agnosia
is the inability to recognize objects despite satisfactory vision
- Caused by damage to the pattern pathway usually in the temporal cortex
73
face recognition
- 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
Prosopagnosia
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
color preception
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
Color constancy
the ability to recognize something as being the same color despite changes in lighting
77
motion perception
involves a variety of brain areas in all four lobes of the cerebral cortex
78
middle-temporal cortex (MT/V5)
responds to a stimulus moving in a particular direction
79
Cells in the dorsal part of the ________________ respond to expansion, contraction or rotation of a visual stimulus
medial superior temporal cortex (MST)
80
MT and MST both receive input from the ________.
magnocellular path; color-insensitive
81
motion blindness
refers to the inability to determine the direction, speed and whether objects are moving
- Likely caused by damage in area MT
82
Some people are blind except for the ability to detect which direction something is moving
Area MT probably gets some visual input despite significant damage to area V1
83
Several mechanisms prevent confusion or blurring of images during eye movements
- 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
