Visual Cortex Flashcards
1
Q
If light falling on a region of the retina causes a decrease in the response of a ganglion cell – what type of region is this?
A
Inhibitory region
2
Q
If a spot of light falls outside the receptive field of a ganglion cell what firing rate will be produced?
A
Baseline firing rate
3
Q
Why do receptive fields increase in size with eccentricity (distance from the fovea)?
A
More rods are in the periphery and rods have more neural convergence
4
Q
What kind of stimuli are ganglion cells good at detecting?
A
Change in the pattern of light
Spots of light or edges of light and dark
5
Q
Define a receptive field
A
A region of the retina which, when stimulated by light, affects the firing rate of the cell
6
Q
A region of the retina which, when stimulated by light, affects the firing rate of the cell
This is known as…?
A
Receptive field
7
Q
Ganglion cell receptive fields have ……….. organisation
A
Centre-surround organisation
8
Q
Ganglion cell receptive fields have centre-surround organisation. What are they?
A
1) ON-centre, OFF-surround
2) OFF-centre, ON-surround
9
Q
What do retinal ganglion cells detect?
A
Spots of light and edges between areas of light and dark falling within the receptive field
10
Q
Ganglion cell fibres leave the retina along the…?
A
Optic nerve
11
Q
Detects spots of light and edges between areas of light and dark falling within the receptive field
Which cell does this?
A
Retinal ganglion cell
12
Q
How is the optic nerve formed?
A
Ganglions have really long axons
The axons bundle together to form the optic nerve
The information then leaves the eye and travels up toward the brain
13
Q
Define optic chiasm
A
Cross over point
14
Q
What is the purpose of the optic chiasm?
A
Allows visual information to be represented as where in the world is the information coming from rather than from which eye does the information come from
15
Q
Why is there a cross-over point (optic chiasm)?
A
The brain is reorganising how its going to represent and process visual information
16
Q
How many optic nerves are there? And what are their roles?
A
There are 2
1) Left = processes info from the left eye
2) Right = processes info from the right eye
17
Q
In the optic chiasm, do all fibres cross over?
A
No, some fibres cross over and some don’t
18
Q
The cross-over point in the eye is called…?
A
Optic chiasm
19
Q
Beyond the optic chiasm is called…?
A
Optic tract
20
Q
What happens in the optic tract?
A
The info is now represented in terms of where in the world that info is coming from rather than which eye is it coming from
21
Q
At the cross-over point (optic chiasm) what happens to the information seen in the left eye about the right side of the world?
A
The info falls on the left side of the retina and remains on the left side even at the optic tract
22
Q
At the cross-over point (optic chiasm) what happens to the information seen in the left eye about the left side of the world?
A
The info falls on the right side of the retina and crosses over to the right side at the optic tract
23
Q
At the cross-over point (optic chiasm) what happens to the information seen in the right eye about the left side of the world?
A
The info falls on the right side of the retina and remains on the right side even at the optic tract
24
Q
At the cross-over point (optic chiasm) what happens to the information seen in the right eye about the right side of the world?
A
The info falls on the left side of the retina and crosses over to the left side at the optic tract
25
What does the left optic tract process?
Information coming from the right hand side of the world
26
What does the right optic tract process?
Information coming from the left hand side of the world
27
What happens to info at the optic tract?
Information is now separated by visual field rather than by eye
28
At the optic tract, information from the right visual field is represented ...... hemisphere?
Left
29
At the optic tract, information from the left visual field is represented ...... hemisphere?
Right
30
Where does the optic tract feed into?
Lateral Geniculate Nucleus (LGN)
31
Define LGN
It is a bilateral structure (one in the left hemisphere and one in the right)
32
Beyond optic chiasm the optic nerve becomes...?
Optic tract
33
What does the LGN do?
Each LGN receives input from the left and right eyes but keeps these inputs separate
34
What kind of receptive fields does the LGN have?
Centre-surround antagonism (the same receptive field organisation as retinal ganglion cells)
35
The receptive fields for LGN are ideal for detecting...?
Detecting spots of light and edges
36
The receptive fields for LGN are not ideal for detecting...?
Detecting orientation of bars/ edges
37
What is V1?
The Primary visual cortex
38
Where is V1 located?
Occipital lobe (back of the brain; away from the eyes)
39
Where does V1 receive its input from?
LGN
40
What unique pattern does V1 have?
Stripes
41
V1 (or primary visual cortex) is also known as...?
Striate cortex - because it is stripey
42
What is the physiological approach to measuring cell activity?
Single-cell recording
43
What happens in single-cell recording in a V1 cell? List 3 things
1) Stimulus is presented to an animal
2) An electrode is inserted into a neuron (e.g. V1 cell) and measures the electrical activity of a SINGLE neuron
3) Record what stimuli make that particular neuron the most active by measuring the cell firing rate over time
44
Who ran multiple experiments investigating what stimulus activates the V1 cell?
Hubel and Weisel
45
Hubel and Weisel ran multiple experiments investigating what stimulus activates the V1 cell in what time period?
Lat 50s to early 60s
46
When you don't present a stimulus to the V1 cell, what happens to the firing rate of the cell?
V1 cells fire at baseline level (low firing rate) with infrequent action potential
47
What did Hubel and Wiesel discover about the V1 cell in the 1950s?
In the 1950s, Hubel and Wiesel could not find a stimulus to excite the V1 cell
They were aware that ganglion cells can be activated by spots of light and tried the same stimuli on V1
V1 was not triggered by spots of light
48
In the 1960s, what did Hubel and Wiesel discover about V1 cells?
Rectangular glass slides were put into the projector slot so the line passing over the retina made V1 fire
They found a big response from V1 when the edge of the slide moved across the receptive field
From this, they realised V1 cells like lines moving across the retina instead of spots
49
True or False
V1 cells like spots instead of lines moving across the retina
False
V1 cells like lines moving across the retina instead of spots
50
What is it called when a cell prefers lines of a particular orientation?
Orientation selectivity
51
Define orientation selectivity
When a cell prefers lines of a particular orientation
52
What makes V1 cells active?
Lines of light
53
What do V1 cells prefer?
Lines of light of a particular orientation
54
According to orientation selectivity, V1 cells perform best when...?
They encounter a stimulus of their preferred line orientation
e.g. a V1 cell likes horizontal lines and therefore will only respond strongly (high firing rate) when a horizontal line of light is presented
55
What is it called when objects close together in the visual scene are analysed by neighbouring parts of V1?
Retinotopic mapping
56
Define retinotopic mapping
When objects close together in the visual scene are analysed by neighbouring parts of V1
Simply = When cells in V1 that are close together process bits of the stimulus that are close together
57
When cells in V1 that are close together process bits of the stimulus that are close together
This is known as...?
Retinotopic mapping
58
True or False?
V1 is a structure that forms a map of the image that is falling on the retina
True
59
The amount of cortex devoted to representing each part of the retinal field is called?
Simply= How many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size
Cortical magnification
60
Define cortical magnification
The amount of cortex devoted to representing each part of the retinal field is distorted
Simply = How many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size
61
The amount of the cortex that is devoted to representing each bit of the stimulus
This is known as...?
Cortical magnification
62
Why is the amount of cortex devoted to representing each part of the retinal field distorted?
Bits of the image falling on the fovea get more of the cortex to process it
63
The fovea is represented by a large area of...?
Cortex
64
Fovea accounts for ...... of the retina but is represented by ......... of V1
Fovea accounts for 0.01% of the retina but is represented by 8- 10% of V1
65
A stimulus that is closest to the fovea appears larger because...?
There's a huge amount of cortex of V1 that's devoted to processing bits of the stimulus closest to the fovea
66
A stimulus that falls into the peripheral appears smaller because...?
There is far less of the cortex of V1 that's devoted to processing bits of the stimulus that fall into the peripheral
67
True or False?
Orientation preferences of V1 cells arranged in a random way
False
Orientation preferences of V1 cells arranged in an ordered way
68
Orientation preferences of V1 cells arranged in an ordered way
This organisation was investigated by ...? List 2 ways
1) Recording from an electrode penetrating the cortex perpendicular to the surface of a V1 chunk
2) Recording from an electrode penetrating the cortex at an angle to the surface of a V1 chunk
69
When electrodes are inserted perpendicular to the surface of the V1 chunk, all cells have ...?
The same orientation preference (an orientation column)
70
All cells of the V1 chunk have the same orientation preference when the electrode is inserted...?
Perpendicularly
71
All cells of the V1 chunk have varied orientation preferences when the electrode is inserted...?
At an angle
72
When electrodes are inserted at an angle to the surface of the V1 chunk, the cells’ orientation preferences ....?
Vary systematically
73
Within a column of V1, all cells have...?
The same preferred orientation
74
The next column along a V1 chunk has a ....?
Different preferred orientation to the previous column (it's neighbouring column)
75
How do you find a column's orientation preference in a V1 cell?
Insert an electrode and hit one neuron at a time to record its activity to find its orientation preference
76
Cells in LGN are
a. Binocular
b. Monocular
b. Monocular
They respond to input from either the left or right eye, but not both
77
What is a monocular cell?
They respond to input from either the left or right eye, but not both
78
% cells in V1 are binocular (respond to input from both eyes)
80%
79
Most binocular cells respond better to one eye than other
This is known as...?
Ocular dominance
80
Define ocular dominance
Most binocular cells respond better to one eye than to other
81
Cells in V1 are
a. Binocular
b. Monocular
a. Binocular
They respond to input from both eyes
82
What is a binocular cell?
They respond to input from both eyes
83
Cells with the same ocular dominance (i.e. same eye preference) are arranged in ...?
Columns within V1
84
Define orientation columns
Columns where all of the cells within a column have the same orientation preference
85
Columns where all of the cells within a column have the same orientation preference
This is known as...?
Orientation columns
86
Define ocular dominance columns
All cells within the L column give a better response to the left eye input and all cells within the R column give a better response to the right eye input
87
All cells within the L column give a better response to the left eye input and all cells within the R column give a better response to the right eye input
Ocular dominance columns
88
How many different types of cells in V1 are there?
3
89
There are 3 different types of cells in V1 each with a distinct receptive field organisation
List all 3
1) Simple cells
2) Complex cells
3) Hypercomplex cells
90
List the order in which visual information is transferred and processed from the eye to the brain
1) Photoreceptors
2) Ganglion cells
3) LGN cells
4) Simple cells (V1)
5) Complex cells (V1)
6) Hypercomplex cells (V1)
91
The 3 different types of cells in V1 each have...?
A distinct receptive field organisation
92
What do simple cells in V1 respond to?
Simple cells respond to oriented bars and edges
93
What kind of receptive field do simple cells in V1 have?
The receptive field has excitatory and inhibitory regions, but they are elongated
94
Which cell responds to oriented bars and edges in V1?
Simple cells
95
The receptive field has excitatory and inhibitory regions, but they are elongated
Which cell in V1 does this apply to?
Simple cells
96
What is an elongated receptive field?
Where the inhibitory and excitatory areas are side by side
97
What stimuli cause simple cells to produce a big excitatory response?
A vertical bar that covers only the excitatory region, causing a big excitatory response
(Simple cells respond best to bars of light falling within the receptive field that are perfectly aligned with their receptive field)
98
Which cell in V1 responds best to ...
A vertical bar covers only the excitatory region causing a big excitatory response
Simply = bars of light falling within the receptive field that are perfectly aligned with their receptive field
Simple cells
99
What happens to the activity level of simple cells when a bar of light is slightly tilted away from vertical?
A bar tilted slightly away from vertical covers some of the excitatory region but also some inhibitory region causing a weaker excitatory response
100
What happens to the activity level of simple cells when a bar of light is placed horizontally?
A horizontal bar covers only a small part of the excitatory region but a larger part of the inhibitory region causing an inhibitory response
101
If you change the orientation of lines, ganglion or LGN cells change their response
True or False?
False
If you change the orientation of lines, ganglion or LGN cells don't change their response
102
If you change the orientation of lines, simple cells don't change their response
True or False?
False
If you change the orientation of lines, simple cells change their response
103
Define orientation tuning
Orientation-tuned neurons respond best to their preferred orientation but also respond to other similar orientations
104
Neurons respond best to their preferred orientation but also respond to other similar orientations
This is called...?
Orientation tuning
105
The receptive field of simple cells tunes to ....?
Vertical bars
106
Some simple cells have ON-centre RFs and some have Off-centre RFs, but all have ...?
A preferred orientation
107
Some simple cells only have one excitatory and one inhibitory region
This is called...?
Edge detectors
108
Define edge detectors (simple cell receptive fields)
Simple cells that only have one excitatory and one inhibitory region
109
Define bar detectors (simple cell receptive fields)
Simple cells that have more than one excitatory and more than one inhibitory region
110
Simple cells that have more than one excitatory and more than one inhibitory region
This is known as...?
Bar detectors
111
When do bar detectors give the strongest response?
When the bar of light falls right within the centre of their receptive field
112
When do edge detectors give the strongest response?
When the bar of light extends beyond its receptive field
113
What do complex cell receptive fields look like?
Similar to simple cells, they are elongated
But they have no separate on-and-off regions (on-and-off regions are combined)
114
What do complex cell receptive fields respond to? Name 2 things
1) Moving oriented bars and edges
2) Respond best to a particular direction of movement
115
Which cell responds to oriented lines but has no discrete ON and OFF regions?
Complex cells
116
When do complex cell receptive fields with vertical orientation selectivity give their best response to a stimulus?
When the stimulus is a vertical line of light falling within the receptive field
But it will also give the same response if that line of light moves towards the edge of the receptive field
117
Complex cells with vertical orientation selectivity respond best when the stimulus is a vertical line of light falling within the receptive field
But it will also give the same response if that line of light moves towards the edge of the receptive field
Why?
Because it does not have distinct excitatory and inhibitory regions
118
Define phase sensitive
When a cell changes its response if you move the line of light to different parts of the receptive field
AKA the response depends on the position of the bar within the receptive field
119
Define phase insensitive
When a cell does not change its response if you move the line of light to different parts of the receptive field
AKA the response does not depend on the position within the receptive field
120
When a cell does not change its response if you move the line of light to different parts of the receptive field
This is known as..?
Phase insensitive
121
Are complex cells phase-sensitive or insensitive?
Phase insensitive
122
Are simple cells phase-sensitive or insensitive?
Phase-sensitive
123
Simple cells are phase sensitive meaning...?
Their response depends on the position of the bar within the RF
124
Complex cells are phase insensitive meaning...?
Their response does not depend on the position within the RF
125
What are the 2 stimuli/light conditions that complex cell receptive fields respond to?
1) Light must be moving oriented bars and edges
2) They respond best to a particular direction of
movement
e.g. a complex cell may prefer horizontal bars of light that move in a downward direction
126
What is the stimuli/light condition that simple cell receptive fields respond to?
1) Light must be in the form of oriented bars and edges
127
What are the 3 stimuli/light conditions that hypercomplex cell receptive fields respond to?
1) Light must be moving oriented bars and edges
2) They respond best to a particular direction of
movement
3) They respond best to a particular length of line/light
128
Hypercomplex cells are also known as ...?
End stopped cells
129
Hypercomplex cell receptive fields respond best when...?
The bar of light is its preferred line orientation, the light is moving in its preferred direction and the light is at perfect length which fits the RF
130
If a bar of light is too long for the receptive field of a complex cell, will the cell change its response?
No
131
If a bar of light is too long for the receptive field of a hypercomplex cell, will the cell change its response?
Yes, its response will reduce dramatically
132
True or False?
Receptive fields increase in complexity as you move along photoreceptors to hypercomplex V1 cells
True
133
What is the characteristic of RF of the Retinal Ganglion Cell? List 2
- Centre-surround receptive field
- Responds best to spots of light
134
What is the characteristic of RF of the LGN cell? List 2
- Centre-surround receptive field
- Responds best to spots of light
135
What is the characteristic of RF of V1 simple cell? List 2
- Excitatory and inhibitory areas are arranged side-by-side and are elongated
- Responds best to bars of a particular orientation (orientation selectivity)
136
What is the characteristic of RF of V1 complex cells? List 3
- Responds best to a bar of a particular orientation (orientation selectivity)
- Responds best to the movement of a bar
- Responds best to a particular direction of movement
137
What is the characteristic of RF of V1 hypercomplex cells? List 3
- Responds to bars of light of a particular orientation (orientation selectivity)
- Responds to bars moving in a particular direction
- Responds to bars of a particular length
138
Responds to bars of light of a particular orientation and length moving in a particular direction
What cell does this?
V1 hypercomplex cells
139
Excitatory and inhibitory areas are arranged side-by-side. Responds best to bars of a particular orientation
Which cell does this?
V1 simple cells
140
Centre-surround receptive field and responds best to spots of light
Which cells do this?
Retinal ganglion cells and LGN cells
141
Responds best to the movement of a bar of a particular orientation. Many respond best to a particular direction of movement.
Which cell does this?
V1 complex cells
142
How many visual areas are there beyond V1?
30
143
What does visual area V3 specialise in?
Form
144
What does visual area V4 specialise in?
Colour
145
What does visual area V5 specialise in?
Motion
146
True or False?
All visual areas have a simple separation of function
False
All visual areas interconnected – no simple separation of function
147
Name the 2 processing streams
What and Where streams
148
What is the "What is it?" processing stream called?
Ventral visual stream
149
The ventral visual stream is known as the...?
"What is it?" processing stream
150
What is the "Where is it?" processing stream called?
Dorsal visual stream
151
The dorsal visual stream is known as the...?
"Where is it?" processing stream
152
What happens after visual information is processed by V1?
It goes through 2 processing pathways
1) A pathway of visual info being sent down the temporal lobe (ventral visual stream)
2) A pathway of visual info being sent up the parietal lobe (dorsal visual stream)
153
A pathway of visual info is sent down the temporal lobe
This is known as...?
Ventral visual stream
154
A pathway of visual info being sent up the parietal lobe
This is known as...?
Dorsal visual stream
155
Which stream travels ventrally to the inferotemporal cortex?
Ventral visual stream
156
Which stream is important for recognising and discriminating objects?
Ventral visual stream
157
Which stream travels dorsally to the posterior parietal cortex?
Dorsal visual stream
158
Which stream is important for determining where an object is and how to
act upon it?
Dorsal visual stream
159
Which stream is sometimes referred to as the ‘How’ stream?
Dorsal visual stream
160
Who conducted the Monkey lesion study testing the existence of dorsal and ventral visual streams?
Ungerleider and Mishkin, 1982
161
What happened in the Monkey lesion study testing the existence of dorsal and ventral visual streams?
Task 1: Object discrimination.
Food is always under the triangular prism and monkeys had to find the food
(must differentiate between triangular and square prism to find food)
Task 2: Landmark discrimination.
Food is always close to the cylinder and monkeys had to find the food
(must know where the cylinder is to find the food)
162
What were the results of the Monkey lesion study testing the existence of dorsal and ventral visual streams?
1) Lesion to the inferotemporal cortex (what pathway/ventral visual pathway) causes problems for the object discrimination task but not the landmark discrimination task
Simply = If the ventral pathway was damaged, monkeys could not discriminate between triangular and square prism, thus could not find the food. But they could still locate the cylinder in task 2 to find the food
2) Lesion to the posterior parietal cortex (where pathway/dorsal visual pathway) causes problems for the landmark discrimination task but not the object discrimination task
Simply = If the dorsal pathway was damaged, monkeys could still discriminate between triangular and square prism, thus could find the food. But they could not locate the cylinder in task 2 to find the food
163
What is it called when someone has damage to their ventral pathway (‘what’ stream) and cannot identify objects despite knowing their features?
Visual form agnosia
164
Define visual form agnosia
When someone has damage to their ventral pathway (‘what’ stream) and cannot identify objects despite knowing their features
165
Who conducted a study on visual form agnosia?
Milner and Goodale
166
What did Milner and Goodale do in their study investigating their visual form agnosia?
1) Control Ps and VFA Ps performed a perceptual orientation matching task; they had to match the orientation of a block with the particular orientation slot
2) Control Ps and VFA Ps performed a visuomotor posting task; they had to not only match the orientation of a block with the particular orientation slot but also fit the block through the slot (action task)
167
What did Milner and Goodale discover in their study investigating their visual form agnosia?
1) In the perceptual orientation matching task, VFA Ps could not find the right orientation of the block to match the slot, unlike control Ps
2) In the visuomotor posting task, VFA Ps could successfully find the correct orientation of the block to fit it through the slot, just as well as control Ps
168
What is it called when there's damage to the dorsal pathway (‘where/ how’ streams)?
Optic ataxia
169
Define Optic ataxia
When there's a damage to dorsal pathway (‘where/ how’ stream)
170
What happens when someone has optic ataxia?
They cannot reach to grasp objects but can recognise and describe them
They have opposite deficits to those shown in patients with visual form agnosia (e.g. patient DF)
171
They cannot reach to grasp objects but can recognise and describe them
What do these people struggle with?
Optic ataxia (damage to the dorsal pathway (‘where/ how’ stream))
172
True or False?
Pathways in the brain are not totally separate
True
There are many connections between the pathways in the brain
173
Processing stream signals flow both ...?
Upwards and Backwards
174
Define feature detectors
Cells that respond to particular features of an image
175
Which cells can be thought of as feature detectors?
V1 cells
176
Cells in V1 can be thought of as ‘feature detectors’
What does this mean?
They respond to particular features of an image
177
As we move higher up in the visual system, receptive fields get more ...... and features they respond to become .........
1) More complex
2) More specific
178
In area IT (inferior temporal gyrus) we find cells that respond to ...?
Faces
179
Monkey Area IT (inferior temporal gyrus) contains face-sensitive cells
What kind of response will the cells in the area IT produce when a face stimulus is presented?
Strong excitatory response
180
Monkey Area IT (inferior temporal gyrus) contains face-sensitive cells
What kind of response will the cells in the area IT produce when a stripe-patterned stimulus is presented?
Baseline response
