Chapter 6 Vision Flashcards
1
Q
Astigmatism
A
a decreased responsiveness to one kind of line or another, caused by an asymmetric curvature of the eyes
2
Q
Binocular input
A
stimulation from both eyes
3
Q
Bipolar cell
A
type of neuron in the retina that receives input directly from the receptors
4
Q
Blind spot
A
area at the back of the retina where the optic nerve exits; it is devoid of receptors
5
Q
Blindsight
A
the ability to respond in limited ways to visual information without perceiving it consciously
6
Q
Colour Constancy
A
the ability to recognize colors despite changes in lighting
7
Q
Colour vision deficiency
A
inability to perceive color differences
8
Q
Complex cell
A
type of visual cortex cell located in areas V1 and V2 that responds to a pattern of light in a particular orientation anywhere within its large receptive field
9
Q
Cones
A
type of retinal receptor that contributes to color perception
10
Q
Dorsal stream
A
visual path in the parietal cortex that helps the motor system locate objects; the “where” path
11
Q
End-stopped (hypercomplex) cell
A
type of visual cortex cell that resembles complex cells; responds best to stimuli of a precisely limited type, anywhere in a large receptive field, with a strong inhibitory field at one end of its field
12
Q
Feature detectors
A
neurons whose responses indicate the presence of a particular feature
13
Q
Fovea
A
a tiny area of the retina specialized for acute, detailed vision
14
Q
Ganglion cell
A
type of neuron in the retina that receives input from the bipolar cells
15
Q
Horizontal cell
A
type of cell that receives input from receptors and delivers inhibitory input to bipolar cells
16
Q
Inferior temporal cortex
A
portion of the cortex where neurons are highly sensitive to complex aspects of the shape of visual stimuli within very large receptive fields
17
Q
Koniocellular neurons
A
small ganglion cells that occur throughout the retina
some of these are colour sensitive and have various responses to stimuli.
18
Q
Lateral geniculate nucleus
A
thalamic nucleus that receives incoming visual information
19
Q
Lateral inhibition
A
the reduction of activity in one neuron by activity in neighboring neuron
20
Q
Law of specific nerve energies
A
statement that whatever excites a particular nerve always sends the same kind of information to the brain
21
Q
Magnocellular neurons
A
large cell bodies with large receptive fields that are distributed evenly throughout the retina
specialized for depth, movement and overall patterns.
22
Q
Middle temporal cortex (MT or V5)
A
area of the brain that detects moving objects
23
Q
Midget ganglion cell
A
ganglion cells in the fovea of humans and other primates
24
Q
Motion blindness
A
an impaired ability to perceive movement
25
Negative Colour after imaging
result of staring at a colored object for a prolonged length of time and then looking at a white surface, the image is seen as a negative image, with a replacement of red with green, green with red, yellow and blue with each other, and black and white with each other
26
Opponent-process theory
idea that we perceive color in terms of opposites.
visual system neurons beyond the receptors themselves respond with an increase in activity to indicate one colour of light and a decrease to indicate the opposite colour.
The three pairs of opposites are red-green, yellow-blue, and white black.
27
Optic Nerve
ganglion cell axons that exit through the back of the eye and continue to the brain
28
Parvocellular Neurons
small cell bodies with small receptive fields in or near the fovea
specialized for perception of colour and fine details.
29
Photopigments
chemicals contained in rods and cones that release energy when struck by light
30
Primary Visual Cortex
area of the cortex responsible for the first stage of visual processing
31
Prospagnosia
the inability to recognize faces due to damage of several brain areas
32
Pupil
an opening in the center of the iris where light enters
33
Receptive field
the area in visual space that excites or inhibits any neuron
34
retina
the rear surface of the eye, which is lined with visual receptors
35
retinal disparity
the discrepancy between what the left and right eyes see
36
Retinex Theory
concept that the cortex compares information from various parts of the retina to determine the brightness and color for each area
37
Rods
type of retinal receptor that detects brightness of light
38
saccades
Saccades
| voluntary eye movements
39
Secondary visual Cortex v2
area of the brain that processes information from the primary visual cortex and transmits it to additional areas
40
Sensitive period
time early in development when experiences have a particularly strong and enduring influence
41
Simple cell
type of visual cortex cell that has a receptive field with fixed excitatory and inhibitory zones
42
Strabismus (or strabismic amblyopia or lazy eye)
a condition in which the eyes do not point in the same direction
43
Superior colliculus
swelling on either side of the tectum; important to visual processing
44
Trichromatic theory (Young-Helmholtz Theory)
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Trichromatic theory (Young-Helmholtz theory)
theory that color is perceived through the relative rates of response by three kinds of cones, each one maximally sensitive to a different set of wavelengths
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45
Ventral stream
visual paths in the temporal cortex that are specialized for identifying and recognizing objects; the “what” path
46
Visual agnosia
an inability to recognize objects despite otherwise satisfactory vision
47
Visual Field
area of the world that an individual can see at any time
48
Distinguish between reception, transduction, and coding
Reception-eye gets the signal anything that exits the receptors and is perceived as light.
Transduction: light is converted to energy signals
coding: brain codes visual information according to which neurons respond, their amount of response, and the timing of their responses.
49
What is the fovea? How did it get its name?
fovea means pit
| a tiny area specialized for acute detailed vision
50
How have many bird species solved the problem of getting detained information from different directions?
more receptors at bottom of eye or one area of eye so they can see more of where they want to see
51
Trace the path of visual information from a receptor to the optic nerve. What is the blind spot
receptors at the back of the ey to bipolar cells (close to centre of the eye) => ganglion cells
-ganglion cells axons join together and travel back to the brain
-also additional cells called amacrine cells get information from bipolar cells and send to other bipolar amacrine and ganglion cells enabling them to respond to specifically to shapes and movement etc
-ganglion cells form the optic nerve
Blind spot is where the optic nerve leaves the back of the eye.
52
Compare foveal and peripheral vision with regard to acuity, sensitivity to dim light and colour vision.
foveal has good acuity (good detail vision) whereas peripheral vision has poor acuity
Sensitivity to light: foveal distinguishes among bright-poor in dim and peripheral vision responds well to dim
Colour vision: good for foveal and poor for peripheral
Note: rods are abundant in periphery and cones are abundant near fovea for colour vision
53
What is the specific role of light in the initiation of a response in a receptor what is photopigment?
Photopigment-chemicals that release energy when struck by light.
54
What is the relationship of 11-cis-retinal to all-trans-retinal?
light converts 11-cis-retina (a derivative of Vit A) to all-trans-retinal , thus releasing energy that activates second messengers within the cell.
55
What is an opsin?
opsin is a protein that 11-cis-retinal binds to
| function: it modified stye photopigments sensitivity to different wave lengths of light.
56
Why does the presence of cones in the retina of a given species not guarantee colour vision? Why does colour vision necessarily depend on the pattern of responses of a number of different neurons?
depends how many cones they have
57
How did Young and Helmholtz propose to account for colour vision? On what kind of data was their theory based?
aka Trichromatic Theory
Perceive colour thru the relative rates of responses by 3 kinds of cones, each one maximally sensitive to a different set of wavelengths
Helmholtz-found that people could match any colour by mixing appropriate amounts of just three wavelengths therefore three kinds of cones (receptors) are sufficient for colour vision.
58
What kind of theory did Hering Propose? What observations supported his theory?
Opponent Process theory
-we perceive colour in terms of opposites
-brain has mechanism to perceive colour from red-green
another yellow to blue
another white to black.
59
What is the current relationship between the Trichromatic Theory and the Opponent Process theory
Trichromatic theory and opponent process theory both cannot explain colour constancy which is the ability to recognize colours despite changes in lighting.
60
What visual ability does the retinex theory explain?
Colour constancy-ability to recognize colour despite changes in lighting
cortex compares the responses from different parts of the retina to determine brightness and colour
61
What is the genetic basis for the most common form of colour vision deficiency? Why do more males than females have this form of colour deficiency/
some people lack one/two cones or some have three cones but one is abnormal
-gene that causes the most common deficiency in on X chromosome (red-green colour blindness-their long and medium wavelengths cones have same photopigments)
62
Diagram of relationships among the rods and cones, the bipolar and horizontal cells, and the ganglions and amacrine cells
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Rod and cones
Horizontal H
Bipolar B
Amacrine A
Ganglion G
```
R R R R R R R R R R
B B B B H B B
A A
G G G G
63
Axons of which kind of cell form the optic nerve? What is the name of the site where the right and left optic nerves meet?
Ganglions cell axons for the optic nerve
Optic chasm is where the optic nerve from L and R eye meet
-Humans half of the axons cross to the otherside
- In species with eyes on side of head -almost all axons cross over to the other side of the head.
64
Where do most axons in the optic nerve synapse? where do some other optic here axons synapse?
Most aons in the optic nerve go tot the lateral geniculate nucleus (part of the thalamus)
-others go to the superior colliculus and other areas including parts of the hypothalamus that controls the waking-sleeping schedule.
65
What is the destination of axons from the lateral geniculate nucleus?
Lateral geniculate nucleus sends axons to other parts of the thalamus and occipital cortex
-cortex returns many axons tot he thalamus, so they constantly feed information back and forth.
66
What is the definition of the receptive field of a neuron in the visual system?
area in visual space that excites/inhibits the cell
| -simply the point in space tom which light strikes the cell
67
What is lateral inhibition? How does enhanced contrast?
- the retina's way of sharpening contrasts to emphasize the borders of objects
- reduction of activity in one neuron by activity in neighbouring neurons
- it heightens contrast because when light falls on a surface, the bipods just inside the border are most excited and those outside the border respond the least.
68
How is lateral inhibition accomplished in the vertebrate retina?
e.g. light exits receptors 6-10
-bipolar cells 6-10 all receive the same excitation
Bipolar cells 7,8,9 are inhibited by input on both sides, but bipolar cells 6 and 10 are inhibited by one side not the other.
-5 and 11 get no excitation
69
If several bipolar cells provide input to a certain ganglion cell, what can be said about location of their receptive fields relative to that of the ganglion cell?
receptive field-which is the area in visual space that exits/inhibits it.
-they are in the same receptive field as the ganglion
70
What is a feature detector?
Neurons whose responses indicate the presence of a particular feature
71
What evidence suggests that neurons in areas V1 and V2 are feature detectors?
Primary visual cortex in he occipital cortex is known as area VI (also known as striated cortex because of its striped appearance
-people with damage to area VI-report no conscious vision no visual imagery and no visual images in their dreaming
72
What is the evidence for spatial frequency detectors? What is the spatial frequency detectors? What is the problem with the view that the neurons in V1 and V2 are primarily spatial frequency detectors
Prolonged exposure to a given visual feature decreases sensitivity to that feature.
73
What is blindsight? what are two potential explanations for this?
- people with damage to V1 are have this phenomenon where they have the ability to respond in limited ways to visual information without perceiving it consciously
explanations: 1. many cases ; small islands of healthy tissue remain within an otherwise damaged visual functions
2. the thalamus sees visual input to several other areas besides VI, including parts of the temporal cortex. After VI damage connections to other areas strengthen to produce an experience
74
What is the effect of depriving only one eye of pattern vision during the critical period?
The deprived eye-the kitten doesn't respond to it when it is uncovered
B/C synapses in the visual cortex gradually become unresponsive to input from the deprived eye
75
What happens if both eyes are kept shut early in life?
-if neither eye is open box axons out compete for any other for at least 3 weeks the kittens eyes remain responsive but if no stimuli linger than the cortical responses start to become sluggish and lose their well defined fields.
76
What is a sensitive or critical period?
Sensitive period-when experiences have a particularly strong and enduring influence
-the sensitive period ends with the onset of certain chemicals that stabilize synapses and inhibit axonal sprouting
77
Define retinal disparity. How does this brain use this information to produce stereoscopic depth perception?
- Is the discrepancy between what the left and right eye sees
- experience fine tunes binocular vision.
78
What is strabismus? Does surgical correction is adulthood improve depth perception in people with this disorder?
Lazy eye
- put a patch over good eye to force the lazy eye to work
- helps if caught early
- now asking kids to concentrate on video games that require attention to both eyes
79
What is the effect of supplying excess neurotrophins during the time when one yes is closed?
?? the weaker the eye gets weaker??
80
What happens to the response characteristics of visual cortical cells in a kitten exposed to only horizontal lines early in life?
- kitten only responds to horizontal stimuli
| - and not as sensitive to vertical
81
What is astigmatism? what happens if a child has severe,, uncorrected astigmatism during the first few years of life?
astigmatism-a blurring of vision for lines in one direction
| it is caused by an asymmetric curvature of the eyes.
82
What is a receptor potential?
6.1
| a transmembrane potential difference produced by activation of a sensory receptor (from the web)
83
State the law of specific nerve energies. Who formulated it?
Johannes Muller described it.
Whatever excites a particular nerve establishes a special kind of energy unique to that nerve.
I.e. the brain somehow interprets the action potentials from the auditory nerve as sounds, those from the olfactory nerve as odors
84
visual coding
sensory information is coded so that the brain can process it. The coded information bears no physical resemblance to the stimuli it describes.
85
The axons from the retinal loop around to form the __ ___, which exits from the eye at a point called the ___ ___.
optic nerve
| blind spot
86
Visual ___ is greatest at the fovea, the central area of the retina. Because so many receptors in the periphery converge their messages to their ___ ___, our peripheral vision is highly sensitive to faint light but poorly sensitive to detail
Acuity
| bipolar cells
87
Two kinds of receptors in the retina
rods and cones
Rods are more sensitive to faint light.
Cones are more numerous in the fovea and better in bright light.
88
Light stimulates the receptors by triggering a molecular change in what?
11-cis-retinal
| This then causes a release in energy thereby activating second messengers within the cells.
89
Describe receptive fields of simple cells
Each neuron in a visual system has a receptive field, an area of the visual field to which it is connected. Light in the receptive field excites or inhibits the neuron depending on the light's location wavelength, movement, and other properties.
A simple cell has a receptive field with fixed excitatory and inhibitory zones.
90
Describe the characteristics of parvocellular ganglion cells.
Parvocellular ganglion cells are specialized for perception of colour and fine details
(in contrast to magnocellular system--which is specialized for perception of depth, movement and overall patterns.)
91
Describe the characteristics of the magnocellular system
specialized cells for the perception of depth , movement and overall patterns.
(as opposed to parvocellular for perception of colour and fine details.)
92
What happens to the parvocellular and magnocellular pathways in the cortex?
the axons from the ganglion cells form the optic nerve, which proceeds to the optic chasm, where half of the kaons cross to the opposite hemisphere.
most of the axons go to the lateral geniculate nucleus of the thalamus. cells of the lateral geniculate have receptive fields that resemble those of the ganglion cells -an excitatory or inhibitory central portion and a surrounding ring with the opposite effect.
After the info reaches the cerebral cortex the receptive fields become more complicated.
93
For what accomplishment did David Hubel and Torsten Wiesel share the nobel Prize?
Research with receptive fields like cells in retinals and lateral geniculate. They pioneered the use of micro electrode recording to study the properties of individual neurons in the cerebral cortex.
94
What is the major difference between responses of simple and complex visual cortical cells?
simple visual cortical cells which have fixed excitatory and inhibitory fields, and complex cells which respond to a light pattern of a particular shape regardless of its exact location.
95
Describe the receptive field of an end-stopped or hypercomplex cell.
end stopped or hypercomplex cells resemble complex cells with one exception: an end-stopped cell has a strong inhibitory area at one end of its bar-shaped receptive field. The cell responds to a bar s-shaped pattern of light anywhere in its broad receptive field, provided the bar does not extend beyond a certain point.
96
What can be said about the receptive fields of neurons in a column in the visual cortex?
Cells having similar properties are groupie together in the visual cortex in columns perpendicular to the surface.
97
Which areas, beyond V1, are important for shape analysis? What are their major contributions?
6.2
| primary visual cortex and other brain areas.
98
What is a feature detector
neurons whose responses indicate the presence of a particular feature.
99
What is visual agnosia?
Inability to recognize objects despite otherwise satisfactory vision
100
What is prosopagnosia?
Inability to recognize the faces
101
Which area in the inferior temporal lobe increases its activity when People with intact brains recognize faces?
6.3
| the inferior temporal cortex responds to identifiable objects.
102
what appears to be the special function of the area V4?
Really important for colour.
| and colour constancy
103
What two areas of the cortex are specialized for motion perception?
area MT (middle temporal cortex) aka area V5
and adjacent area MST (medial superior temporal cortex)
both these areas must receive information from the magnocellular cortex which is responsible for patterns and movement in a large field.
104
Describe the response characteristics of some cells in the area MT.
most cells in area MT respond selectively when something moves at a particular speed and in a particular direction.
They detect acceleration or deceleration as well as the absolute speed and they respond to motion in all there dimensions.
105
Describe the preferred stimuli for many cells in the dorsal part of area MST
they respond best to more complex stimuli such as expansion, contraction, or rotation of a large visual scene.
106
What is the role of the cells in the VENTRAL part of the MST
where cells respond to an object that moves relative to its background.
107
Why don't we see a blur when we move our eyes?
6.3
When we move our eyes the MST cells are silent hence we do not see a blur so therefore the MST cells help you distinguish between eye movement and an object moving against a background
108
Describe the symptoms of motion blindness. Damage to what are might cause motion blindness?
Damage to the MT and MST areas .
MT=middle temporal cortex and MST is the medial superior temporal cortex.
These people have the ability to see objects but can't tell if they are moving or not and in which direction and how fast.
109
What cortical area may be important for shifting visual attention? How does activity in the visual cortex change when attention is shifted?
6.3
saccades is voluntary eye movement and the brain monitors that motion. An area particularly impt is the MT or the middle temporal cortex where blood flow is suppressed. actually blood flow is suppressed to much of the visual cortex but more so in this area.
110
what is the ventral stream of the cortex important for?
shape perception
111
What is the dorsal stream of the cortex important for
localizing visual perceptions and integrating them with action.
112
What happens to people who have damage to the inferior temporal cortex
```
function of inferior temporal cortex is to detect objects and recognize them despite changes in position, size etc.
After damage people get agnosia--difficulty in recognizing the objects they see
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113
What is specialized to recognize faces.
a circuit including the fusiform gyrus of the temporal cortex
