Module 7 Flashcards
(210 cards)
1
Q
True or False? Some animals can see in complete darkness.
A
False. The light reflected into your eyes from the objects around you is the basis for your ability to see them; if there is no light, there is no vision.
2
Q
Light can be thought of in what 2 different ways?
A
1) As discrete particles of energy, called photons, traveling through space at about 300,000 kilometers (186,000 miles) per second
2) As waves of energy. Both theories are useful; in some ways, light behaves like particles; and in others, it behaves like waves.
3
Q
Light is sometimes defined as ________ of electromagnetic energy between 380 and 760 nanometers (billionths of a meter) in length.
A
waves
4
Q
True or False? Animals can see wavelengths that we cannot.
A
True. For example, rattlesnakes can see infrared waves, which are too long for humans to see; as a result, they can see warm-blooded prey in what for us would be complete darkness. So, if we were writing this text for rattlesnakes, we would be forced to provide a different definition of light for them.
5
Q
What 2 properties of light are of particular interest/importance?
A
1) Wavelength - it plays an important role in the perception of color.
2) Intensity - because it plays an important role in the perception of brightness.
6
Q
The amount of light reaching the retinas is regulated by what?
A
The donut-shaped bands of contractile tissue, the irises, which give our eyes their characteristic color.
7
Q
Light enters the eye through what?
A
The pupil, the hole in the iris.
8
Q
The adjustment of pupil size in response to changes in illumination represents a compromise between what 2 things?
A
Sensitivity (the ability to detect the presence of dimly lit objects) and acuity (the ability to see the details of objects).
9
Q
When the level of illumination is high and sensitivity is thus not important, the visual system takes advantage of the situation by doing what?
A
Constricting the pupils. When the pupils are constricted, the image falling on each retina is sharper and there is a greater depth of focus; that is, a greater range of depths is simultaneously kept in focus on the retinas. However, when the level of illumination is too low to adequately activate the receptors, the pupils dilate to let in more light, thereby sacrificing acuity and depth of focus.
10
Q
Behind each pupil is a________, which focuses incoming light on the retina.
A
lens
11
Q
When we direct our gaze at something near, the tension on the ligaments holding each lens in place is adjusted by the _________ muscles, and the lens assumes its natural cylindrical shape.
A
ciliary
(This increases the ability of the lens to refract (bend) light and thus brings close objects into sharp focus.)
12
Q
When we focus on a distant object, the lens is flattened. The process of adjusting the configuration of the lenses to bring images into focus on the retina is called ______________.
A
accomodation
13
Q
What is one reason vertebrates have two eyes?
A
Vertebrates have two sides: left and right. By having one eye on each side, which is by far the most common arrangement, vertebrates can see in almost every direction without moving their heads.
14
Q
But why do some vertebrates, including humans, have their eyes mounted side-by-side on the front of their heads?
A
This arrangement sacrifices the ability to see behind so that what is in front can be viewed through both eyes simultaneously—an arrangement that is an important basis for our visual system’s ability to create three-dimensional perceptions (to see depth) from two- dimensional retinal images.
15
Q
The movements of your eyes are coordinated so that each point in your visual world is projected to corresponding points on your two retinas. To accomplish this, your eyes must _______.
A
converge (turn slightly inward).
16
Q
Convergence (eyes turning slightly inward) is greatest when you are inspecting things that are________.
A
close
(But the positions of the images on your two retinas can never correspond exactly because your two eyes do not view the world from exactly the same position.)
17
Q
What is binocular disparity?
A
The difference in the position of the same image on the two retinas—is greater for close objects than for distant objects; therefore, your visual system can use the degree of binocular disparity to construct one three- dimensional perception from two two-dimensional retinal images.
18
Q
Why do a few vertebrate species have their eyes side-by-side on the front of the head while most species have one eye on each side?
A
Predators tend to have the front-facing eyes because this enables them to accurately perceive how far away prey animals are;
prey animals tend to have side-facing eyes because this gives them a larger field of vision and the ability to see predators approaching from most directions.
19
Q
After light passes through the pupil and the lens, it reaches the ________.
A
retina
(The retina converts light to neural signals, conducts them toward the CNS, and participates in the processing of the signals.
20
Q
The retina is composed of what 5 different types of neurons?
A
Receptors, horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells.
21
Q
In the retina, amacrine cells and the horizontal cells are specialized for what?
A
lateral communication (communication across the major channels of sensory input).
22
Q
True or False? Retinal neurons communicate both chemically via synapses and electrically via gap junctions.
A
True.
23
Q
The retina is in a sense inside-out. Why?
A
Light reaches the receptor layer only after passing through the other layers. Then, once the receptors have been activated, the neural message is transmitted back out through the retinal layers to the retinal ganglion cells, whose axons project across the outside of the retina before gathering together in a bundle and exiting the eyeball.
24
Q
This inside-out arrangement of the retina creates what 2 visual problems?
A
1) The incoming light is distorted by the retinal tissue through which it must pass before reaching the receptors.
2) For the bundle of retinal ganglion cell axons to leave the eye, there must be a gap in the receptor layer; this gap is called the blind spot. The first of these two problems is minimized by the fovea.
25
What is the fovea?
An indentation at the center of the retina that is specialized for high-acuity vision (for seeing fine details). The thinning of the retinal ganglion cell layer at the fovea reduces the distortion of incoming light.
26
The blind spot requires a more creative solution called what?
Completion (or filling in). The visual system uses information provided by the receptors around the blind spot to fill in the gaps in your retinal images.
27
The __________ phenomenon is one of the most compelling demonstrations that the visual system does much more than make a faithful copy of the external world.
Completion
28
True or False? The completion phenomenon is just a response to blind spots.
False.
It also plays an important role in normal vision. When you look at an object, your visual system does not conduct an image of that object from your retina to your cortex. Instead, it extracts key information about the object—primarily information about its edges and their location—and conducts that information to the cortex, where a perception of the entire object is created from that partial information.
29
The color and brightness of large unpatterned surfaces are not perceived directly but are filled in (completed) by a completion process called ____________.
surface interpolation
30
What is surface interpolation?
The process by which we perceive surfaces; the visual system extracts information about edges and from it infers the appearance of large surfaces.
31
What are the two different types of receptors in the human retina?
Cone-shaped receptors called cones and rod-shaped receptors called rods.
32
What is the duplexity theory of vision?
The theory that cones and rods mediate different kinds of vision.
33
How did the duplexity theory of vision emerge?
From the observation that that species active only in the day tend to have cone-only retinas, and species active only at night tend to have rod-only retinas.
34
What type of vision predominates in good lighting conditions and provides high-acuity colored perceptions of the world?
Photopic vision (cone-mediated vision)
35
What type of vision predominates in dim illumination and lacks both detail and color?
Scotopic vision (rod-mediated vision)
36
In which system, photopic or scotopic, does the output of several hundred receptors converge on a single retinal ganglion cell?
Scotopic system
37
What is the result of convergence in the scotopic system?
Sensitivity at the cost of acuity
38
What is the region in the retina where there are no rods, only cones?
Fovea
39
What is the effect observed when lights of the same intensity but different wavelengths are perceived with different brightness?
Spectral sensitivity
40
What are the two spectral sensitivity curves found in humans and other animals with both cones and rods?
Photopic and scotopic spectral sensitivity curves
41
Under photopic conditions, the visual system is maximally sensitive to wavelengths of about how many nanometers?
About 560 nanometers
42
Under scotopic conditions, the visual system is maximally sensitive to wavelengths of about how many nanometers?
About 500 nanometers
43
What visual effect describes the shift in relative brightness observed during the transition from photopic to scotopic vision?
Purkinje effect
44
Describe the Purkinje effect.
The relative brightness of objects shifts during the transition from photopic to scotopic vision, causing some colors to appear brighter in different lighting conditions.
45
How can cones accomplish their task of mediating high-acuity color vision when most of them are crammed into the fovea?
Through temporal integration and eye movements that continuously scan the visual field.
46
What are the three kinds of involuntary fixational eye movements?
Tremor, drifts, and saccades.
47
What is the purpose of fixational eye movements?
To keep images moving on the retina, enabling us to see during fixation.
48
What is transduction?
The conversion of one form of energy to another.
49
What is visual transduction?
The conversion of light to neural signals by the visual receptors.
50
What is the name of the red pigment extracted from rods in 1876?
Rhodopsin.
51
What is the first step in rod-mediated vision?
Rhodopsin's absorption of light and bleaching.
52
What is the relationship between rhodopsin's absorption spectrum and the human scotopic spectral sensitivity curve?
They are nearly identical, indicating that sensitivity to various wavelengths under scotopic conditions is directly influenced by rhodopsin's ability to absorb them.
53
What type of receptor is rhodopsin?
A G-protein-coupled receptor.
54
What happens to rods when rhodopsin receptors are bleached by light?
Sodium channels close, rods hyperpolarize, and the release of glutamate reduces.
55
Although we are not aware of it, the eyes continually scan the visual field, and our visual perception at any instant is a summation of recent visual information. It is because of this __________________ that the world does not vanish momentarily each time we blink.
temporal integration
56
What is a pigment?
any substance that absorbs light
57
The transduction of light by rods exemplifies an important point: Signals are often transmitted through neural systems by __________________.
decreases in activity.
58
True or False: The retina-geniculate-striate pathways are the largest and most thoroughly studied visual pathways in the brain.
True
59
How do signals from the left visual field reach the right primary visual cortex?
Answer: Signals from the left visual field reach the right primary visual cortex either ipsilaterally from the temporal hemiretina of the right eye or contralaterally via the optic chiasm from the nasal hemiretina of the left eye.
60
What is the primary visual cortex also known as?
Striate cortex or V1
61
How many layers does each lateral geniculate nucleus have?
Six layers
62
Which part of the lateral geniculate nucleus receives visual input from the contralateral visual field?
Each lateral geniculate nucleus receives visual input only from the contralateral visual field, with three layers receiving input from one eye and three layers receiving input from the other.
63
Where do most lateral geniculate neurons that project to the primary visual cortex terminate?
In the lower part of cortical layer IV, producing a characteristic stripe or striation.
64
What is the primary visual cortex often referred to as due to its characteristic stripe when viewed in cross-section?
Striate cortex
65
What does it mean for the retina-geniculate-striate system to be retinotopic?
It means that each level of the system is organized like a map of the retina, where two stimuli presented to adjacent areas of the retina excite adjacent neurons at all levels of the system.
66
What proportion of the primary visual cortex is dedicated to the analysis of input from the fovea?
About 25 percent
67
What was the dramatic demonstration of the retinotopic organization of the primary visual cortex provided by Dobelle, Mladejovsky, and Girvin in 1974?
They implanted an array of electrodes in the primary visual cortex of blind patients, and by administering electrical current through specific electrodes, they elicited the perception of shapes.
68
What could recent research on retinal implants and the findings of Dobelle, Mladejovsky, and Girvin in 1974 potentially lead to?
The development of visual prostheses that could benefit blind individuals.
69
How many parallel channels of communication flow through each lateral geniculate nucleus?
At least two parallel channels.
70
What are the top four layers of the lateral geniculate nucleus called?
Parvocellular layers (P layers).
71
What type of neurons are found in the parvocellular layers?
Neurons with small cell bodies.
72
What are the bottom two layers of the lateral geniculate nucleus called?
Magnocellular layers (M layers).
73
What type of neurons are found in the magnocellular layers?
Neurons with large cell bodies.
74
What are parvocellular neurons particularly responsive to?
Color, fine pattern details, and stationary or slowly moving objects.
75
What are magnocellular neurons particularly responsive to?
Movement.
76
Which visual receptors provide the majority of input to the parvocellular layers?
Cones.
77
Which visual receptors provide the majority of input to the magnocellular layers?
Rods.
78
What is the receptive field of a visual neuron?
The area of the visual field within which it is possible for a visual stimulus to influence the firing of that neuron.
79
What is the method used by David Hubel and Torsten Wiesel to study single neurons in the visual systems of laboratory animals?
A technique involving microelectrodes to study receptive fields and record neuron responses to stimuli.
(the tip of a microelectrode is positioned near a single neuron in the part of the visual system under investi- gation. During testing, eye movements are blocked by para- lyzing the eye muscles, and the images on a screen in front of the subject are focused sharply on the retina by an adjust- able lens. The next step in the procedure is to identify the receptive field of the neuron. The receptive field of a visual neuron is the area of the visual field within which it is pos- sible for a visual stimulus to influence the firing of that neu- ron. The final step in the method is to record the responses of the neuron to various simple stimuli within its recep- tive field in order to characterize the types of stimuli that most influence its activity. Then the electrode is advanced slightly, and the entire process of identifying and character- izing the receptive field properties is repeated for another neuron, and then for another, and another, and so on. The general strategy is to begin by studying neurons near the receptors and gradually work up through “higher” and “higher” levels of the system in an effort to understand the increasing complexity of the neural responses at each level.)
80
What is the receptive field of a visual neuron?
The area of the visual field within which it is possible for a visual stimulus to influence the firing of that neuron.
81
How does the research of David Hubel and Torsten Wiesel contribute to understanding vision?
Their research revealed much about the neural mechanisms of vision, particularly in understanding how visual neurons respond to stimuli.
82
Light reflected from objects enters the eye though the _______.
pupil
83
Depending on how close or far away an object is, the lens is adjusted using the _______ muscles.
ciliary
84
About 25 percent of the primary visual cortex is dedicated to analyzing input from the _______.
fovea
85
_______ is the process by which the lenses adjust their shape to bring images to focus on the retina.
Accomodation
86
The difference in the position of the same image on the two retinas is called _______.
binocular disparity
87
Nasal hemiretina of the right visual field project to the _______ hemisphere, while temporal hemiretina project to the _______ hemisphere.
ipsilateral, contralateral,
88
The location on the retina where a bundle of cell axons leaves the eye is called the _______.
blind spot
89
The theory that the two types of retinal receptors, rods and cones, mediate different kinds of vision is called the _______ theory.
duplexity
90
There are two _______ channels that run through the lateral geniculate nucleus called M and P channels.
parallel
91
How did Hubel and Wiesel begin their studies of visual system neurons?
They started by recording from the three levels of the retina-geniculate-striate system: first from retinal ganglion cells, then from lateral geniculate neurons, and finally from the striate neurons of lower layer IV.
92
What type of light did Hubel and Wiesel use to test the neurons?
Stationary spots of achromatic (uncolored) light.
93
True or False: There was significant change in receptive fields as Hubel and Wiesel worked through the levels of the retina-geniculate-striate system.
False.
94
What were the commonalties observed by Hubel and Wiesel in the receptive fields recorded from retinal ganglion cells, lateral geniculate nuclei, and lower layer IV striate neurons?
1) Receptive fields in the foveal area were smaller than those at the periphery.
2) All neurons had circular receptive fields.
3) All neurons were monocular (each neuron had a receptive field in one eye but not the other)
4) Many neurons had receptive fields with an excitatory area and an inhibitory area separated by a circular boundary.
95
Describe the response of neurons in the retina-geniculate-striate pathway to a spot of achromatic light.
Neurons responded with either "on" firing or "off" firing, depending on the location of the spot of light in the receptive field.
96
What are on-center cells and off-center cells?
On-center cells respond to lights shone in the central region of their receptive fields with "on" firing and to lights shone in the periphery with inhibition, followed by "off" firing when the light is turned off.
Off-center cells display the opposite pattern.
97
What is one function of many neurons in the retina-geniculate-striate system according to Hubel and Wiesel?
To respond to the degree of brightness contrast between the two areas of their receptive fields.
98
What did Hubel and Wiesel conclude about the most effective way to influence the firing rate of on-center or off-center cells?
Maximizing the contrast between the center and the periphery of its receptive field.
99
True or False: Most visual system neurons are continually active even when there is no visual input.
True.
100
What is characteristic of most cerebral neurons in terms of activity?
Spontaneous activity, and responses to external stimuli consume only a small portion of the energy required for ongoing brain activity.
101
What distinguishes simple striate cells from lower layer IV neurons?
Simple cells have straight-line borders between "on" and "off" regions in their receptive fields, while lower layer IV neurons have circular borders.
102
How do simple cells respond to stimuli?
They respond best to bars of light in a dark field, dark bars in a light field, or single straight edges between dark and light areas.
103
What is a characteristic of the receptive fields of simple cortical cells?
They are rectangular rather than circular.
104
What distinguishes complex striate cells from simple cells?
Complex cells have larger receptive fields, respond best to straight-line stimuli regardless of position within the field, and many are binocular.
105
How do complex cells respond to a particular straight-edge stimulus?
They respond continuously to it as it moves across their receptive field.
106
What is the difference in receptive field organization between simple and complex cells?
Simple cells have receptive fields with clear "on" and "off" regions, while complex cells do not.
107
What is the characteristic response of binocular complex striate cells to stimulation through both eyes?
They usually fire more robustly than if only one eye is stimulated.
108
What is ocular dominance in the context of binocular cells?
It refers to the tendency of some binocular cells to respond more robustly to stimulation of one eye than the other.
109
How do some binocular cells respond to stimuli presented to both eyes simultaneously?
Some respond best when the same stimulus is presented to both eyes at slightly different positions on the two retinas, indicating a preference for retinal disparity.
110
What conclusions did Hubel and Wiesel reach about the organization of the primate visual cortex?
The primary visual cortex is organized into functional vertical columns.
Columns in the primary visual cortex analyzing input from one area of the retina are clustered together.
Neurons with simpler preferences converge onto neurons with more complex preferences as the visual processing progresses.
111
Go back here and look at the explanation of Mrs. Richard's case study on page 169.
112
How many distinct sorts of retinal ganglion cells have been identified in primates and mice?
Approximately 20 in primates and 40 in mice.
113
Besides on-center and off-center receptive fields, what other receptive field characteristics have been discovered in retinal ganglion cells?
Receptive fields selective to uniform illumination, orientation, motion, and direction of motion.
114
What are some receptive field characteristics of lateral geniculate cells beyond on-center and off-center?
Sensitivity to orientation, motion, and direction of motion.
115
How do recent studies challenge traditional assumptions about visual processing?
They suggest that receptive field properties of neurons are not static and can be influenced by contextual factors.
116
What are contextual influences in the context of visual processing?
Influences on a visual neuron's activity caused by stimuli outside its receptive field.
117
How do contextual influences affect a visual neuron's receptive field?
They continually fine-tune the receptive field based on prior experience and current signals from the environment.
118
What determines the perception of an object's color?
It depends largely on the wavelengths of light that the object reflects into the eye.
119
What does the perception of an object's color depend on besides reflected wavelengths?
It also depends on the complex mixtures of wavelengths present in the ambient light and how objects absorb and reflect these wavelengths.
120
What is another term for colors, as discussed in the module?
Hues.
121
How is the perception of colors such as blue, green, and yellow related to wavelengths of light?
It depends on the mixture of wavelengths that objects reflect, influencing our perception of their color.
122
Who proposed the component theory (trichromatic theory) of color vision, and when?
Thomas Young in 1802, refined by Hermann von Helmholtz in 1852.
123
According to the component theory, how many different kinds of color receptors (cones) are there?
Three, each with a different spectral sensitivity.
124
What observation led to the development of the component theory of color vision?
Any color of the visible spectrum can be matched by mixing together three different wavelengths of light in different proportions.
125
Who proposed the opponent-process theory of color vision, and when?
Ewald Hering in 1878.
126
According to the opponent-process theory, how many different classes of cells in the visual system encode color?
Two classes for encoding color and another class for encoding brightness.
127
What are complementary colors, as described in the opponent-process theory?
Pairs of colors that produce white or gray when combined in equal measure, such as green and red.
128
How did research in the 1960s confirm the component theory of color vision?
By measuring the absorption spectrum of the photopigment in a single cone, confirming the presence of three different kinds of cones with different absorption spectra.
129
What is the difference between trichromats and dichromats in terms of color vision?
Trichromats possess three color vision photopigments, while dichromats possess only two, lacking the photopigment sensitive to long wavelengths.
130
Which animals have been found to have four or more color vision photopigments?
Some birds, fish, and reptiles have four photopigments, while some insects have five or more photopigments.
The dragonfly wins first place with ten.
131
What was the result of inserting a gene for a third photopigment into mice in a study by Jacobs and colleagues (2007)?
The transgenic mice acquired the ability to see additional wavelengths of light, converting them from dichromats to trichromats.
132
What is color constancy?
Color constancy refers to the perceived color of an object remaining the same despite changes in the wavelengths of light that it reflects.
133
Why is color constancy important for vision?
Color constancy improves our ability to recognize objects consistently despite changes in illumination, enhancing our ability to interact with the environment.
134
Describe Edwin Land's laboratory demonstration of color constancy.
Edwin Land used projectors emitting different wavelengths of light to illuminate a test display. Despite adjusting the wavelengths of light reflected by the display, the perceived colors remained unchanged.
135
According to Land's retinex theory of color vision, how is the color of an object determined?
The color of an object is determined by its reflectance, which is the proportion of light of different wavelengths that a surface reflects. The visual system compares the light reflected by adjacent surfaces in at least three different wavelength bands to perceive colors.
136
According to Land's retinex theory of color vision, how is the color of an object determined?
The color of an object is determined by its reflectance, which is the proportion of light of different wavelengths that a surface reflects. The visual system compares the light reflected by adjacent surfaces in at least three different wavelength bands to perceive colors.
137
What is the primary function of the occipital cortex in the human visual system?
The occipital cortex is involved in processing visual information received from the eyes and plays a crucial role in vision.
138
What is a scotoma?
A scotoma is an area of blindness in the visual field, typically resulting from damage to the primary visual cortex.
139
Describe blindsight.
Blindsight is the ability to respond to visual stimuli within a scotoma without conscious awareness of them, often observed in patients with damage to the primary visual cortex.
140
What are the two proposed neurological interpretations of blindsight?
One interpretation suggests that functional cells in the remaining areas of the striate cortex mediate some visual abilities without conscious awareness. The other proposes that visual pathways bypassing the primary visual cortex maintain visual abilities without cognitive awareness.
141
How do patients with blindsight typically respond to visual stimuli?
Patients with blindsight can respond to visual stimuli within their scotomas, such as reaching out to grab moving objects, despite claiming not to see them consciously.
142
Why is blindsight considered a phenomenon that challenges traditional concepts of perception?
Blindsight demonstrates that visual perception can occur without conscious awareness, challenging the traditional assumption that perception and conscious awareness are inseparable processes.
143
How many different functional areas of visual cortex have been identified in the macaque monkey?
32 different functional areas of visual cortex have been identified, including primary visual cortex, secondary visual cortex, and association visual cortex
144
What types of stimuli do neurons in secondary visual cortex respond most vigorously to?
Neurons in secondary visual cortex respond most vigorously to different aspects of visual stimuli, such as color, movement, or shape.
145
How are various functional areas of secondary and association visual cortex in the macaque monkey interconnected?
They are interconnected via more than 300 interconnecting pathways, with virtually all connections being reciprocal.
146
How have PET, fMRI, and evoked potentials been used to identify various areas of visual cortex in humans?
By monitoring brain activity while volunteers inspect various types of visual stimuli, researchers have delineated about a dozen different functional areas of human visual cortex.
147
What are the two major streams of visual information processing in the cortex?
The dorsal stream and the ventral stream.
148
What is the primary function of the dorsal stream in visual processing?
The dorsal stream is involved in the perception of "where" objects are located and their direction of movement.
149
What is the primary function of the ventral stream in visual processing?
The ventral stream is involved in the perception of "what" objects are, including their characteristics such as color and shape.
150
Describe the "where" versus "what" theory of vision.
The "where" versus "what" theory proposes that the dorsal stream primarily mediates the location and movement of objects, while the ventral stream primarily mediates the conscious perception of objects.
151
What is blindsight?
Blindsight is the ability to respond to visual stimuli within a scotoma without conscious awareness of them, often observed in patients with damage to the primary visual cortex.
152
What are prosopagnosia and akinetopsia?
Prosopagnosia refers to a difficulty in recognizing faces, while akinetopsia refers to a difficulty in perceiving visual motion.
153
What is prosopagnosia?
Prosopagnosia is a visual agnosia for faces, characterized by a specific difficulty in recognizing faces while other aspects of vision remain intact.
154
What is agnosia?
Agnosia is a failure of recognition that is not attributable to a sensory deficit or to verbal or intellectual impairment.
155
What is visual agnosia?
Visual agnosia is a specific agnosia for visual stimuli, where individuals can see things but have difficulty recognizing or identifying them.
156
How are visual agnosias often specific to particular aspects of visual input?
Visual agnosias are often specific to particular aspects of visual input and are named accordingly; for example, movement agnosia, object agnosia, and color agnosia are difficulties in recognizing movement, objects, and color, respectively.
157
What is the primary difficulty faced by prosopagnosics?
Prosopagnosics have a specific difficulty in recognizing faces, including problems recognizing whose face it is. In extreme cases, they may not recognize themselves in photos.
158
Is prosopagnosia specific to faces?
While prosopagnosia is often described as a deficit specific to face recognition, some evidence suggests that prosopagnosics may have recognition difficulties not limited to faces but also involving specific objects belonging to complex classes.
159
What brain areas are associated with prosopagnosia?
Acquired prosopagnosia is associated with damage to the fusiform face area (FFA) and the occipital face area (OFA), along with the lateral prefrontal cortex playing an important role in face identification.
160
What role does the fusiform face area (FFA) play in face identification?
The FFA, located on the ventral surface of the boundary between the occipital and temporal lobes, is implicated in face identification because parts of it are selectively activated by human faces.
161
Can prosopagnosics perceive faces in the absence of conscious awareness?
Yes, prosopagnosics can recognize faces in the absence of conscious awareness, as demonstrated by studies showing physiological responses to familiar faces despite the subjects' claims of not recognizing them consciously.
162
What is akinetopsia?
Akinetopsia is a deficiency in the ability to see movement progress in a normal smooth fashion, where individuals affected by it only see periodic snapshots of the world.
163
Can akinetopsia be a transient result of taking high doses of certain antidepressants?
Yes, akinetopsia can be a transient result of taking high doses of certain antidepressants.
164
What brain area is often associated with acquired akinetopsia due to brain injury?
Acquired akinetopsia is often associated with damage to the middle temporal area (MT) of the cortex.
165
What is the function of the middle temporal area (MT)?
The function of MT appears to be the perception of motion.
166
What percentage of neurons in MT respond specifically to directions of movement?
95 percent of neurons in MT respond to specific directions of movement and little else.
167
How do neurons in MT differ from those in the primary visual cortex regarding the perception of movement?
Neurons in MT respond specifically to directions of movement and have large binocular receptive fields, unlike neurons in the primary visual cortex.
168
What lines of research implicate MT in the visual perception of motion and akinetopsia?
Four lines of research implicate MT in the visual perception of motion and akinetopsia:
(1) patients with akinetopsia tend to have unilateral or bilateral damage to MT,
(2) activity in MT increases when humans view movement as measured by fMRI,
(3) blocking activity in MT with transcranial magnetic stimulation (TMS) produces motion blindness, and
(4) electrical stimulation of MT in human patients induces the visual perception of motion.
169
Disrupted somatosensory transmission, particularly pain perception, has what drastic consequences for the health and survival compared to blindness?
Patients suffering from a rare, genetic condition called congenital insensitivity to pain are unable to perceive pain. Many individuals afflicted by this condition sustain numerous, severe injuries and often die at a young age, since they are completely unaware that their body is sustaining tissue damage.
170
Subjectively, ________ seems to be our primary sensory system to perceive and interact with the world.
vision
171
What is the V1 (primary visual cortex) responsible for
Detection of straight lines; analysis of orientation, movement, and colour.
172
What is the Dorsal Stream to Parietal Lobe responsible for?
Analvsis of location (where?) and visuallv-guided movement (how?).
173
What is the V4 responsible for?
Color perception.
174
What is the MT responsible for?
Movement perception (speed, direction etc).
175
What is Ventral Stream to Temporal Lobe responsible for?
Visual pattern recognition (e.g., objects, faces, scenes); conscious visual perception.
176
What is the Functional
Segregation/Specialization among visual areas?
This is related to the point about Parallel
Processing and refers to the fact that separate, functionally specialized areas and pathways exist within the visual system (e.g., for movements; color, 3D object perception; face perception; spatial localization).
177
What is the Hierarchical Organization among visual areas?
Visual processing is hierarchical, that is, processing becomes more complex from lower to higher visual areas. For example, cells in VI (purple) respond to simple lines of a specific orientation; cells in the temporal lobe respond to, 3-D objects, faces, or complex scenes.
178
What is the Parallel Processing among visual areas?
Separate channels process different aspects of visual stimuli (e.g., the M/magnocellular channel for movement and overall illumination vs. the P/parvocellular channel for color and fine detail).
179
What is the Complexity among visual areas?
Connectivity is highly complex, with numerous pathways connecting visual centers throughout the cortex.
180
The organization of the visual system is characterized by what 4 fundamental principles?
Complexity
Hierarchy
Parallel processing
Functional segregation/specialization
(These principles apply not only to the visual system, but to other sensory systems and the brain as a whole.)
181
The existence of the M- and P-channels of visual processing are in line with which of the following principles?
a). complexity
b). hierarchy
c). parallel processing
d). functional segregation/specialization
e). both (c) and (d)
f). (b), (c), and (d)
e). both (c) and (d)
182
According to the anatomical diagrams by Feller and Van Essen, which of the four lobes contains the smallest number of visual areas?
a) frontal lobe
b) parietal lobe
c) temporal lobe
d) occipital lobe
e) all lobes contain about the same number of visual areas
a) frontal lobe
183
You see activation of brain areas MT and V4 in a human in a fMRI scanner. What kind of visual stimulus are they likely to see?
a) a black line of a specific orientation against a white background
b) a fast-moving, colourful sports car
c) a human face with a strong emotional expression
d) a scene of a park with a couple sitting together on a bench
b) a fast-moving, colourful sports car
184
The _____________ has become somewhat of a model system, not only for the organization of cortical sensory areas, but also for the entire neocortical mantle.
primary visual cortex (V1)
185
The ground-breaking work to characterize V1 was started by David Hubel and Torsten Wiesel, who together received the Nobel prize for their contributions in 1981. Hubel and Wiesel, working mostly on (anesthetized) cats, started their pioneering experiments by recording the activity of single neurons in V1 and describing their responses to visual stimuli.
Why do you think that Hubel and Wiesel used cats as experimental subjects, rather than rodents?
Cats have a well-developed visual system, much more so than rodents. For example, cats, but not rodents, can see fine detail and color. Thus, cats make a better model for learning about the visual system, with results that will also apply to humans.
186
What are the two principles of V1 organization?
1. Ocular Dominancy Columns
2. Orientation Columns
187
Describe the Ocular Dominancy Columns (a principle of V1 organization).
inputs carrying information from the left and right eye are initially kept separate in V1. Axons from the eyes and LGN arrive in layer 4 (IV), the major input layer of the six layers of the neocortex.
Panel A: Over prenatal and early postnatal brain development, there is an initial overlap of axons terminal from the left (blue axons) and right (red axons) eye.
Panel B: However, as the brain develops, these axon terminals (presented in Panel A) become separated, so that there is little overlap between inputs from the two eyes. These separate areas in V1 are referred to as ocular dominance columns, as one eye is dominant in each of these columns.
Ocular dominance columns are repeated in a systematic fashion (that is: LEFT EYE - RIGHT EYE - LEFT EYE - RIGHT EYE - LEFT EYE - RIGHT EYE...etc.) across the entire extent of V1. Functionally, ocular dominance columns can be demonstrated by showing that V1 cells fire action potentials much more strongly (or only) to stimulation of only one of two eyes. That is, a light shown into the left eye will fire off neurons in the left-eye ocular dominance columns, but not in the right-eye ocular dominance columns, and vice versa.
188
Describe the Orientation Columns (a principle of V1 organization).
cells in V1 respond best to lines of a specific orientation. There are small chunks of V1 where all cells, from the brain surface to the deepest layers of the neocortex, have the same orientation preference - they all respond optimally to lines of the same orientation. These small chunks of cortex are referred to as orientation columns.
There is a systematic arrangement (or map) of all possible orientation across V1; each column of neurons responds to an orientation slightly different from the previous column, and this sequence is repeated until all orientations (i.e., lines across an entire 360 degree cycle) are covered.
circular 'blobs" in the center of the ocular dominance columns contain neurons responsive to colors, as opposed to neurons outside the blobs, which only respond to various shadings along the black-white dimension.
189
V1 is characterized by its well-organized, systematic structure. Both eyes are represented in equal amounts in V1 by their respective ocular dominance columns. What happens to this V1 arrangement when signals from one eye are poor or entirely absent during early life, for example by some congenital abnormality in one of the two eyes?
(Go back and watch video in Mod 7.2).
190
The functional structure of V1 is highly organized and systematic. What are the 3 main functional components of V1?
Ocular dominance columns
Orientation columns
Blobs
191
Evidence of ocular dominance plasticity provides support for...
a). the role of nature over nurture in brain development
b). the role of nurture over nature in brain development
c). experience-dependent brain development
d). the importance of genetic-developmental programs in brain maturation
e). b and c are correct
e). b and c are correct
192
Amblyopia treatments involve...
a) surgical restoration of the impaired eye and blocking vision in the good/functional eye
b) surgical restoration of the impaired eye and blocking vision in the impaired eye
c) surgical enhancement of the good/functional eye and blocking vision in the functional eye
d) none of the above are correct
a) surgical restoration of the impaired eye and blocking vision in the good/functional eye
193
Selective damage to "blobs" in V1 will impair:
a) orientation perception
b) color perception
c) movement perception
d) black-and-white perception
b) color perception
194
What are the receptive field (RF) characteristics of neurons in the retinal ganglion cell visual area?
Circular RF with center-surround organization.
195
What are the receptive field (RF) characteristics of neurons in the Lateral Genuculare Nucleus visual area?
Circular RF with center-surround organization.
196
What are the receptive field (RF) characteristics of neurons in the Lower Layer IV of V1 visual area?
Circular RF with center-surround organization.
197
What are the receptive field (RF) characteristics of neurons in the Simple Cells in V1 visual area?
Orientation-specific rectangular RF with on-off regions.
198
What are the receptive field (RF) characteristics of neurons in the Complex Cells in V1 visual area?
Orientation-specific rectangular RF without on-off regions; often respond best to moving stimuli.
199
As we move from the visual cortex into higher-level, more specialized visual areas, the properties of receptive field become progressively more complex and specific. In the most extreme cases, you will have neurons that respond, for example, only to specific objects (cars, houses, spoons, apples, etc.), faces, or even a specific face of one individual.
These changes in receptive field characteristics from lower to higher visual areas raise an important question: how do we get from light detectors to line detectors to face detectors (as one example)?
6 LGN neurons (responds to circular light) all have axons that project to one neuron in VI, one of those simple cells (rectangular) that gets input from these 6 neurons .....
if the 6 LGN neurons all fire together, and they all send these signals to the cortical neuron in the primary V1, then that neuron will respond only when the lights are lined up in a specific orientation. Now it's turned into a line detector.
Now let's say 6 individual simple V1 cells (rectanguar) all respond to these lines ....
(go back to video in Module 7.3)
200
Our conscious visual perception of the world combines all features of vision into one unified, coherent visual image. If you see a beautiful sports car driving down the 401, you will see and be conscious of one unified, coherent picture, that of the car driving on the highway.
However, the direction and speed of the movement of the car is processed in area _______; the colour of the car is processed in ______, and the car itself in the _____________. How does the brain combine all these cues into one image? This question is referred to as the ________ problem: how does the brain bind together activity in widely distributed cortical areas into one perceptual, conscious image?
MT
V4
temporal cortex
binding
201
What is the Single neuron/feature detector hypothesis proposed by H. B. Barlow?
The Single neuron/feature detector hypothesis suggests that single neurons act as specialized feature detectors that code for all stimulus features of an object.
202
What is a limitation of Barlow's Single neuron/feature detector hypothesis?
One limitation is the requirement for a large number of feature detectors to represent an unlimited number of combined visual features, which seems not very economical or possible for the brain to achieve.
203
What is the Assembly coding/distributed recognition system hypothesis?
The Assembly coding/distributed recognition system hypothesis proposes that the brain combines activity in separate cortical regions to form a unified, conscious perception.
204
How do receptive field characteristics change along the visual pathway?
Receptive field characteristics exhibit major changes along the retinal-LGN-V1 pathways, as well as into visual association cortex and higher visual pathways (dorsal and ventral streams).
205
How does the brain achieve increasing complexity and specificity of receptive fields along the visual pathway?
The brain achieves this by a greater convergence of visual features, which combine more and more discrete visual cues into the stimulus that will excite a neuron.
206
What are two competing theories attempting to account for visual integration?
The two competing theories are the Single neuron/feature detector hypothesis and the Assembly coding/distributed recognition system hypothesis.
207
Flip for a summary of Module 7.3.
Receptive field characteristics exhibit major changes along the retinal-LGN-V1 pathways, as well as into visual association cortex and higher visual pathways (dorsal and ventral streams).
The increasing complexity and specificity of receptive fields along the visual pathway is achieved by a greater convergence of visual features, which combine more and more discrete visual cues into the stimulus that will excite a neuron. In this way, highly selective cells emerge that respond only to a combination of complex and specialized visual cues.
The precise mechanism that allow the brain to integrate visual information remain unclear, with at least two competing theories (the single neuron/feature detector hypothesis and the assembly coding/distributed recognition system) attempting to account for visual integration. It is possible that the brain relies on a co
208
You are locked up in a (very old-fashioned) prison cell with vertical black metal bars forming one side of the cell. As you look at these bars, where would you expect to see neurons that respond to this visual input?
a). retina
b). LGN
c). V1
d). temporal lobe
e). c and d are correct
f). a, b, c, and d are correct
f). a, b, c, and d are correct
209
The main difference between simple and complex cells in V1 is that...
a) simple and complex cells respond best to simple and complex visual stimuli, respectively
b) simple and complex cells have circular and rectangular receptive fields, respectively
c) complex cells often respond to movement, whereas simple cells do not
d) simple cells respond to black & white stimuli, whereas complex cells respond to colours
c) complex cells often respond to movement, whereas simple cells do not
210
Imagine that you are a person with brain damage who is looking at the picture of a blue guitar. What type of brain damage should cause a greater deficit in your ability to perceive the guitar? According to the single neuron/feature detector hypothesis, you would expect a greater deficit with ________________________, while the assembly coding/distributed recognition system hypothesis predicts a more severe impairment with ____________.
a) localized damage to the inferior temporal lobe / disrupted EEG activity due to seizures
b) localized damage to the prefrontal cortex / localized damage to the temporal lobe
c) disrupted EEG activity due to seizures / localized damage to the inferior temporal lobe
d) localized damage to V1 / localized damage to the LGN
a) localized damage to the inferior temporal lobe / disrupted EEG activity due to seizures
