Midterm 2 - Topic 6 Flashcards
1
Q
What is light a form of?
A
Electromagnetic radiation
2
Q
Can humans see most of the electromagnetic spectrum?
A
No, the area that humans can see is quite small
3
Q
How does a boa constrictor see your cat?
A
They have sensory organs sensitive to infrared rays
4
Q
How can light be described in terms of (like sound waves)?
A
Wavelength
Amplitude
5
Q
How can light be described in terms of (unlike sound waves)?
A
Purity
6
Q
Wavelength of light
A
Distance light travels during one cycle
7
Q
Amplitude of light
A
Height of light wave
8
Q
What psychological dimension does amplitude of light correspond to?
A
Intensity/brightness
9
Q
Purity of light
A
Amount of achromatic (colourless) light contained in the stimulus
10
Q
Psychological dimension of wavelength
A
Hue
11
Q
Psychological dimension of purity
A
Saturation
12
Q
Sclera structural description
A
White external membrane
13
Q
Sclera functional description
A
Keeps the light out of the eye except where it should come in
14
Q
Cornea structural description
A
Clear membrane that joins the sclera and bulges out
15
Q
Cornea functional description
A
Involved in the focusing of light on the rear surface of the eyeball
16
Q
Astigmatism
A
Misshaped cornea that results in a blurring of some of the incoming light
17
Q
How is astigmatism corrected?
A
With an external lens
18
Q
Aqueous humour structure
A
Watery liquid similar to the CSF surrounding brain
19
Q
Where does aqueous humour fill?
A
Anterior chamber
20
Q
Aqueous humour life cycle
A
Continually recycled
21
Q
Why may glaucoma result?
A
If the canal through which the humour leaves the anterior chamber is blocked
22
Q
Glaucoma
A
Increase of pressure in the anterior chamber that can produce damage to the nerve cells at the back of the eyeball
23
Q
Prevalence of glaucoma in Canada
Awareness?
A
8.1% of people over the age of 45 in Canada have glaucoma
50% of people with glaucoma were unaware of it (asymptomatic) until diagnosed
24
Q
What must the eye capture? (2 things)
A
Maximal amount of light in dim (scotopic) conditions
Optimal light energy under bright (photopic) conditions
25
What does the iris provide?
Mechanism for adjusting light
26
Reflex of iris name
Explain
Capillary reflex
Ensures amount of light is just right
27
Iris structure
Ring of pigmented muscles
Colour of eyes
28
Pupil location
Hole in the middle of the iris
29
Why does the iris close? What conditions does it correspond with?
To get less light in
Photopic conditions
30
Why does the iris open? What conditions does it correspond with?
To let more light in
Scotopic conditions
31
How might you describe the structure of the lens?
Transparent piece of dried-out jello
32
What does the lens do?
Changes shape to complete the task of bringing light waves into focus on the back of the eye
33
Accommodation
Lens can focus light rays from both nearby and faraway objects
34
Lens thick =
Close (muscles contract)
35
Lens thin =
Far (muscles relax)
36
Rest point
Lens does not need to stretch or contract; object is at the perfect distance
37
Cataract
Lens becomes cloudy as a result of disease or injury
38
Prevalence of cataract in Canada
Asymptomatic prevalence?
Diagnosed in 48.2% of people over the age of 65
45%
39
What is the cure for cataract?
Routine surgery
40
What is the retina structurally?
Layer of photoreceptors and nerve cells at the rear of the eye
41
What is the optic disk structurally?
Region of the retina where the optic nerve leaves the eye
42
What does the optic disk produce and why?
Blind spot, since it has no photoreceptors
43
Fovea
Area that produces the clearest vision
44
What falls on the fovea?
AKA?
Whenever you look at something directly
AKA macula
45
Does the fovea correspond with a thinner or thicker area of neurons?
Thinner
46
2 types of photoreceptors
Cones and rods
47
Under what conditions do rods allow us to see? Meaning?
Scotopic conditions
Black and white only
48
Under what conditions do cones allow us to see? What do they provide?
Photopic conditions
Provide our perception of details and colour
49
What cells bring the info provided by rods and ones to the brain?
Bipolar cells and ganglion cells
50
What forms the optic nerve?
The axons of the ganglion cells
51
What kind of cells allow communication between photoreceptors?
Horizontal cells
52
What kind of cells allow communication between bipolar cells and ganglion cells?
Amacrine cells
53
Why should we care about the structur4es of the eye?
Knowing what can go wrong makes us aware of the importance of regular eye examinations
54
Transduction in vision
Transformation of light into neural impulses
55
Where does transduction in vision occur?
Photoreceptors
56
What accomplish the transduction of light?
The photopigments that are manufactured in the inner segment and stored in the outer segment of the photoreceptors
57
2 components of photopigments
Opsin
Retinal
58
What is the retinal photopigment derived from? What food is this associated with?
Vitamin A
Carrots
59
Does the retinal component of the photopigments vary?
No, it is the same for all photopigments
60
Does the opsin component of the photopigments vary?
Yes, rhodopsin in rods
61
How many types of photopigments do humans have?
4
62
Photopigment and absorption of light
Each photopigment absorbs more light in one portion of the light spectrum than in any other portion
63
What is light first registered by in phototransduction?
Light-sensitive molecules in the photoreceptors
64
What happens when a photon is absorbed by a molecule of rhodopsin?
It changes the chemical state of the photopigment
65
What is the most important chemical change in phototransduction? What is the process called?
That the retinal molecules split
Isomerization
66
What does isomerization set off in phototransduction?
A biochemical chain reaction that leads to an electrical current flowing across the membrane
67
Bleaching in the context of photopigments
Rhodopsin changes colour as it is exposed to increasing amounts of light
68
What happens in phototransduction when the photopigment isomerizes? What does this signal?
The electrical current in the photoreceptor is disrupted
Signals the presence of light
69
What is a single photon of light in a rod enough to do in phototransduction?
To produce a photocurrent
70
Why should we care about transduction in vision?
It makes us aware of nutritional requirements for normal vision (e.g., vitamin A, lutein, iron, etc.)
71
What led to the formation of the duplicity theory?
Findings that rods and cones are actually 2 different systems
72
Kind of vision for cones
Colour
73
Conditions needed for cones
Photopic
74
Kind of vision for rods
Black and white
75
Conditions needed for rods
Scotopic
76
Shape of cones
Fat, pointed
77
Shape of rods
Thin, blunt
78
Number of cones in eye
7 million
79
Number of rods in eye
125 million
80
Distribution of cones throughout eye
Throughout retina, concentrated in fovea
81
Distribution of rods throughout eye
Not in fovea
82
Lighting conditions required for best functioning of cones
Well-lit
83
Lighting conditions required for best functioning of rods
Dimly lit
84
Central vision
Something on fovea
85
Peripheral vision
Anything not on fovea
86
Relative # of receptors for each ganglion cell (convergence) for cones
Few
87
Relative # of receptors for each ganglion cell (convergence) for rods
Many
88
Acuity of cones
Excellent
89
Acuity of rods
Poor
90
Sensitivity of cones
Poor
91
Sensitivity of rods
Excellent
92
Convergence in retina
132 million rods and cones converge to 1 million ganglion cells
93
Which display higher convergence in the retina: cones or rods? Explain.
Higher convergence of rods than cones
Average of 125 rods to one ganglion cell
Average of 7 cones to one ganglion cell
Cones in fovea have 1:1 relation to ganglion cells
94
Convergence and sensitivity relation
Rods are more sensitive to light than cones
Rods take less light to respond
High convergence produces summation of the input of many rods into one ganglion cell --> increases the likelihood of response
But rods cannot distinguish detail (low spatial resolution)
95
Convergence and acuity
1:1 wiring of cones leads to ability to discriminate details
But cones need more light to respond than rods
96
Disc shedding of cones
Evening
97
Disc shedding of rods
Morning
98
What does disc shedding refer to?
The fact that part of the photoreceptor itself regenerates
New discs are formed at the bottom of the photoreceptors and the photoreceptor moves upward
99
What is the end result movement of disc shedding?
The oldest discs at the top of the photoreceptors are cast off
100
Photopigment for cones
3 types
101
Photopigment for rods
Rhodopsin
102
What are the photopigments contained in the rods and cones maximally sensitive to?
Different portions of the light spectrum
103
What are the rods maximally sensitive to?
The part of the spectrum associated with a colour (green)
104
Dark adaptation for cones
Rapid, but high threshold
105
Dark adaptation for rods
Slow, but low threshold
106
Adaptation
Change in sensitivity after exposure to stimulus of a particular intensity
107
Dark adaptation
Increase in sensitivity as the eyes remain in the dark
108
Light adaptation
Decline in sensitivity as the eyes remain in the light
109
How is adaptation measured?
Present an adaptation stimulus (dark)
Present a spot of light (test stimulus)
Measure detection threshold for test stimulus: ascending trials only to minimize light adaptation
110
3 processes promote dark adaptation
Change in pupil size
Dark adapted eyes have a higher concentration of rhodopsin
Some unknown processes at a higher level than the receptor cells
111
What is a receptive field?
The portion of the retina that, when stimulated, produces change in the activity of a given cell
112
Measuring a cell's receptive field
Researcher use animals to place the microelectrode in an exact location in the visual system
113
For ganglion cells, how to measure a cell's receptive field?
The microelectrode is placed within the optic nerve after it leaves the eye
Stimuli (spots of light) of different shapes and sizes are then presented, and the cell's response to these stimuli is recorded
Size, location, shape, and direction of movement of the stimulus may be important
114
2 basic types of ganglion cells receptive fields
On-center
Off-surround
115
Retinotopic
Organization of retinal cells
Cells respond close together respond to similar stimuli
116
Ganglion cells and receptive field illusion
Herman Grid Illusion
117
Herman Grid Illusion and receptive fields
Peripheral vision: Large receptive fields; light in surround inhibits centre and produces dark spots at intersections (several cells that produce response in same ganglion cell)
Foveal vision: Small receptive fields; light and dark areas cancel each other in centre and surround; no dark spots at intersections
118
3 types of ganglion cells
Magnocellular (M)
Parvocellular (P)
Konicellular (K)
119
Parvocellular cells
Most common (80%)
Small cell and small receptive field (high spatial resolution)
Require high contrast differences (low sensitivity)
Conveys color information
120
Magnocellular cells
10% of ganglion cells
Large cell, large receptive field (low spatial resolution)
Low levels of lighting contrast (high sensitivity)
Important to perception of motion
121
Koniocellular cells
>10% of all ganglion cells
Smallest ganglion cell (dust)
Colour-selective - blue centre/yellow surround
Assist in blinking and eye movement
122
What do the visual pathways consist of?
The axons of the ganglion cells form the optic nerve
This is the start of the visual pathways that take the info from the eye to the brain
123
Optic chiasm
Division of the input from each eye occurs there
Input from each hemiretina travels to different area of the brain
Info received on the temporal side of each eye travels to the ipsilateral hemisphere
Information on the nasal side of each eye goes to the contralateral hemisphere
124
What does the superior colliculus contain?
Multisensory cells that respond when visual and auditory stimuli occur together in space
Multisensory cells in the SC enable an organism to detect the location of environmental stimuli
"Where", "magnocellular" or "dorsal" system
125
What is the lateral geniculate nucleus (LGN) involved in?
Involved in more detailed analysis of visual stimuli
"What", "parvocellular", or "ventral" system
126
Structure of LGN
Multilayered, # of layers varies by species
127
What do the first 2 layers of the LGN consist of?
Magnocellular layers
128
What do layers 3, 4, 5, and 6 of the LGN consist of?
Parvocellular layers
129
What does each layer of the retina contain?
A map of the retina
130
What does a retinotopic map preserve?
The topography of the retina
Location information on retina preserved throughout the visual pathways
131
Brodmann's areas
To facilitate communication among researchers, the cerebral cortex is divided in specific zones
132
Which of Brodmann's areas are involved in early visual processing?
Areas 17, 18, and 19
133
Striate cortex
Area 17, the primary visual cortex
134
In the striate cortex, where does the input from the LGN terminate?
In layer IVc
135
What is the arrangement in layer IVc?
Explain pattern.
Retinotopic
Pattern of info in layer IVc has an approximate map-like correspondence to the pattern of info on the retina
136
Neurons in the visual cortex recording
Using the single cell recording technique with cats, Hubel and Wiesel discovered 3 kinds of neurons with different receptive fields and response patterns
137
What 3 kinds of neurons did Hubel and Wiesel discover?
Simple, complex, hypercomplex cells
138
Where are simple cells found?
In layer 4b of area 17, and they receive input from layer 4c
139
What do simple cells respond better to? What do they sometimes show?
Lines and edges in a specific orientation and in a specific region of the visual field
Ocular preference (respond more to stimulation of one eye than the other)
140
Where are complex cells usually found?
In layers 2. 3, 5, and 6 of the cortex
141
What do complex cells respond better to?
Stimuli moving in a specific direction and in a specific orientation
142
Do complex cells have a larger or smaller receptive field than simple cells?
Larger
143
What is the dominant factor for receptive fields?
Orientation
144
Where are hypercomplex cells found?
In areas 18 and 19 of the visual cortex
145
What do hypercomplex cells respond most to?
Moving lines or angles of a specific size
146
What factors impact hypercomplex cells?
Orientation, movement, and size
147
When do end stopped cells produce a larger neural response in the receptive field?
If they have a good fit with the receptive field
148
As we move toward higher levels of visual processing, what happens?
Cells become more selective
149
In higher levels of visual processing, when do ganglion cells & LGN cells respond?
If the centre of the receptive field contrasts with the surrounding area
150
In higher levels of visual processing, what do simple cells require?
Lines in specific orientation
151
In higher levels of visual processing, what do complex cells require?
Moving lines (in specific orientation)
152
In higher levels of visual processing, what do hypercomplex cells require?
Moving lines of a specific size (in specific orientation)
153
Where does support for orientation specificity come from?
The tilt effect
154
Why should we care about vision in the cerebral cortex?
Knowing how vision works in the brain helps us understand the results of brain damage
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