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PSYCH 367 > Topic 4: The Visual Brain > Flashcards

Topic 4: The Visual Brain Flashcards

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1
Q

Optic Chiasm

A

an x-shaped bundle of fibers on the underside of the brain, where nerve fibers activated by stimulation of one side of the visual field cross over to the opposite side of the brain

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2
Q

Contralateral

A

side of the body opposite to the side on which a particular condition occurs

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3
Q

Lateral Geniculate Nucleus (LGN)

A

the nucleus in the thalamus that receives inputs from the optic nerve and, in turn, communicates with the cortical receiving area for vision

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4
Q

Superior Colliculus

A

an area in the brain that is involved in controlling eye movements and other visual behaviors

this area receives about 10% of all ganglion cell fibers that leave the eye in the optic nerve

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5
Q

Visual Receiving Area

A

the area of the occipital lobe where signals from the retina and LGN first reach the cortex

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6
Q

Striate Cortex

A

the visual receiving area of the cortex, located in the occipital lobe

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7
Q

Area V1

A

the visual receiving area of the brain

called area V1 to indicate that it is the first visual area in the cortex

also called the striate cortex

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8
Q

Simple Cortical Cells

A

a neuron is the visual cortex that responds best to bars of a particular orientation

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9
Q

Orientation Turning Curve

A

a function relating the firing rate of a neuron to the orientation of the stimulus

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10
Q

Complex Cells

A

a neuron in the visual cortex that responds best to moving bars with a particular orientation

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11
Q

End-Stopped Cells

A

a cortical neuron that responds best to lines of a specific length that are moving in a particular direction

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12
Q

Feature Detectors

A

a neuron that responds selectively to a specific feature of the stimulus such as orientation or direction of motion

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13
Q

Selective Adaptation

A

a procedure in which a person or animal is selectively exposed to one stimulus, and then the effect of this exposure is assessed by testing with a wide range of stimuli

typically, sensitivity to the exposed stimulus is decreased

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14
Q

Contrast Threshold

A

the intensity difference between two areas that can just barely be seen

this is often measured using grating with alternating light and dark bars

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15
Q

Selective Rearing

A

a procedure in which animals are reared in special environments

an example us the experiment in which kittens were reared in an environment of vertical striped to determine the effect on orientation selectivity of cortical neurons

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16
Q

Neural Plasticity

A

the capacity of the nervous system to change in response to experience

examples are how early visual experience can change the orientation selectivity of neurons in the visual cortex and how tactile experience can change the sizes of areas in the cortex that represent different parts of the body

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17
Q

Experience-Dependent Plasticity

A

a process by which neurons adapt to the specific environment within which a person or animal lives

this is achieved when neurons change their response properties so they become tuned to respond best to stimuli that have been repeatedly experienced in the environment

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18
Q

Retinotopic Map

A

a map on a structure in the visual system, such as the lateral geniculate nucleus or the cortex, that indicates locations on the structure that correspond to locations on the retina

in retinotopic maps, locations adjacent to each other on the retina are usually represented by locations that are adjacent to each other on the structure

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19
Q

Cortical Magnification

A

occurs when a disproportionally large area on the cortex is activated by stimulation of a small area on the receptor surface

one example of cortical magnification is the relatively large area of visual cortex that is activated by stimulation of the fovea

an example in the somatosensory system is the large area of somatosensory cortex activated by stimulation of the lips and fingers

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20
Q

Cortical Magnification Factor

A

the size of the cortical magnification effect

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21
Q

Location Columns

A

a column in the visual cortex that contains neurons with the same receptive field locations on the retina

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22
Q

Orientation Columns

A

a column in the visual cortex that contains neurons with the same orientation preference

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23
Q

Hypercolumn

A

in the striate cortex, unit proposed by Hubel and Wiessel that combines location, orientation, and ocular dominance that serve a specific area on the retina

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24
Q

Tiling

A

the adjacent (and often overlapping) location columns working together to cover the entire visual field (similar to covering a floor with tiles)

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25
Extrastriate Cortex
collective term for visual areas in the occipital lobe and beyond known as V2, V3, V4, and V5
26
Ablation
removal of an area of the brain this is usually done in experiments on animals to determine the function of a particular area also called lesioning
27
Object Discrimination Problem
the behavioral task used in Ungerleider and Mishkin's experiment in which they provided evidence for the ventral, or what, visual processing stream monkeys were required to respond to an object with a particular
28
Landmark Discrimination Problem
the behavioral task used in Ungerleider and Mishkin's experiment in which they provided evidence for the dorsal, or where, visual processing stream monkeys were required to respond to a previously indicated location
29
Ventral Pathway
pathway that conducts signals from the striate cortex to the temporal lobe also called the what pathway because it is involved in recognizing objects
30
Dorsal Pathway
pathway that conducts signals from the striate cortex to the parietal lobe the dorsal pathway has also been called the where, or how, or the action pathway by different investigators
31
Double Dissociations
in brain damage, when function A is present and function B is absent in one person, and function A is absent and function B is present in another presence of a double dissociation means that the two functions involve different mechanisms and operate independently of one another
32
Inferotemporal (IT) Cortex
an area of the brain outside Area V1 (the striate cortex), involved in object perception and facial recognition
33
Hippocampus
subcortical structure in the brain that is associated with forming and storing memory
34
Contextual Modulation
change in response to a stimulus presented within a neuron's receptive field caused by stimulation outside of the receptive field
35
What do electroencephalograms (EEGs) measure?
amplifies evoked potentials produced by large numbers of neurons
36
What do intra/extracellular recordings measure?
measure activity of a single neuron, using microelectrode
37
What is a positron emission tomography (PET) scan?
take radioactive form of glucose X-rays cause positron to be emitted shows metabolic activity
38
What is functional magnetic resonance imaging (fMRI)?
hemoglobin (which carries oxygen in the blood) contains an iron atom that has magnetic properties strong magnetic field aligns magnetic molecules radio wave pulse disorients them upon realignment, protons emit radio waves like an echo which can be measured quickly shows metabolic activity
39
What is the visual pathway of an object in the left visual field?
image passes through lens and projects on the right part of the retina in both eyes at optic chiasm, optic nerves from right side of both eyes meet optic tracts (optic nerve after the optic chiasm) project to the LGN in the thalamus then to the right half of the visual cortex in the occipital lobe
40
What are the characteristics of the parvocellular layers of the lateral geniculate nucleus?
RGC input: P-cells cell body size: small number: many conduction speed: slow response type: sustained receptive field size: small percepts: high spatial detail colour: colour
41
What are the characteristics of the magnocellular layers of the lateral geniculate nucleus?
RGC input: M-cells cell body size: large number: few conduction speed: rapid response type: transient receptive field size: large percepts: motion sensitive colour: black and white
42
What is the geniculostriate visual pathway?
P-cells, some M-cells --> LGN LGN has 6 layers; each has a retinotopic map: adjacent neurons correspond to spatially related points on the retina LGN also receives substantial feedback connections from the cortex then, optic radiations project to cortex in occipital lobe: primary visual cortex (V1, "striate cortex"), and secondary visual cortex (V2)
43
What is the tectopulvinar visual pathway?
remaining M-cells --> superior colliculi of the tectum: part of the brain stem; guide visual attention then projects to thalamus: pulvinar and lateral posterior nuclei, then to V2 and beyond controls eye movements/fixations; detection/orientation to visual stimuli, motion and location
44
What are blobs?
sensitive to wavelength, but not orientation (mostly receive input from parvo)
45
What are interblobs?
areas between blobs; sensitive to orientation, but not wavelength (receive input from parvo only)
46
What do simple cells respond best to?
layer 4 a bar, line, or edge of light in a particular location on the retina having a specific orientation
47
What do complex cells respond best to?
layers 2/3 and 6 a bar, line or edge of light in a particular location on the retina having a specific orientation and moving in a certain direction
48
What do hypercomplex/end-stopped respond best to?
beyond V1 a bar, corner, or angle having a certain length and/or width in a particular location on the retina having a specific orientation moving in a certain direction
49
What is a location column?
cells respond to stimuli from the same retinal location
50
What is a ocular dominance column?
cells respond to stimuli presented to one eye only
51
What is a orientation column?
cells respond to line stimuli having the same orientation adjacent orientation columns differ in orientation selectivity by 10 degrees
52
What is a hypercolumn?
region containing a single location column, which contain left and right ocular dominance columns, which contain the set of orientation columns from 0 degrees to 180
53
What is the V3 area?
cells sensitive to moving edges of a certain orientation believed to handle perception of forms and local motion projects to temporal lobe
54
What is the V4 area?
cells respond to perceived color of a surface (not wavelength) projects to temporal lobe
55
What is the inferior temporal (IT) cortex?
involved in identifying stimuli
56
What are primary cells?
respond best to simple stimuli, such as dots, squares, ellipses
57
What are elaborate cells?
respond best to more complex shapes, or shapes combined with color or texture
58
What is the medial temporal (MT) cortex?
V5 sensitive to overall motion (and direction) of object, but not colour projects to parietal lobe
59
What is the ventral (or temporal) pathway?
parvo --> V1 --> V2 --> V4 --> IT concerned with object recognition and identification "what" system
60
What is the dorsal (or parietal) pathway?
magno --> V1 --> V2 --> V3 --> V4 & MT (V5) --> parietal lobe involved in locating objects, motion, spatial relationships, depth "where" system
61
What is object discrimination?
show object (e.g. brick), then presented choice task (brick and cylinder) if target (brick) was moved, it would uncover a hidden well that held food reward
62
What is landmark discrimination?
one object presented food hidden in well closest to object
63
What was the effect of lesions in monkeys on the object discrimination task?
temporal-lobe lesion monkeys show much impairment parietal-lobe lesion monkeys show minimal impairment suggests "what" pathway affected
64
What was the effect of lesions in monkeys on the landmark discrimination task?
unoperated monkeys show no impairment temporal-lobe lesion monkeys show minimal impairment parietal-lobe lesion monkeys show much impairment suggests "where" pathway affected
65
What is visual agnosia?
from Greek, meaning "without knowledge" failure or deficit in perceiving or recognizing visual objects
66
What is prosopagnosia?
disruption of face perception inability to recognize/identify friends and family inability to read facial expressions/emotions may not be able to perceive a face or may have intact perception of facial features, but inability to identify face
67
What is the apperceptive category of agnosias?
failure to form a holistic percept; deficit in perception of whole objects inability to extract global structure, despite intact low-level sensory processing (acuity, color, and brightness discrimination intact) cannot recognize, discriminate, or copy complex visual forms, like shapes but they can grasp objects they cannot identify a.k.a. visual form agnosia or visual space agnosia neuropathy: caused by diffuse lesions to posterior occipital cortex (e.g., due to CO or mercury poisoning) likely a failure of "binding" features together, due to damage at early stage of visual processing
68
What is the associative category of agnosias?
deficit in associating percept with meaning ("recognition without meaning") cannot draw from memory able to copy pictures, but cannot identify them can use other senses (e.g., touch, smell) e.g. visual object agnosia: "convoluted red form with a linear green attachment" = rose neuropathy is not consistent: different subtypes may involve different perceptual impairments whole object not identified, likely due to damage to later stage of visual processing that connects visual object to semantic knowledge
69
What is category specific agnosia?
inability to identify living (or nonliving) objects, metals, fruit, vegetables, musical instruments, fabrics, or gemstones
70
What is orientation agnosia?
able to recognize drawings of objects rotated in picture-plane, but impaired at recognizing picture's orientation drawings often copied perpendicular to original
71
What is simultanagnosia?
inability to perceive more than one aspect of a visual stimulus an integrate details into coherent whole
72
What is dorsal simultanagnosia?
can only perceive one of a number of overlapping objects unattended objects not perceived often cannot localize objects bilateral damage to occipitoparietal regions
73
What is ventral simultanagnosia?
can perceive more than one object at a time, but cannot identify more than one may be able to describe one aspect of a scene without understanding the whole can localize objects damage to left inferior temporo-occipital cortex
74
What is pure alexia?
cannot read words, must go letter-by-letter reading, can write to dictation but cannot read back what has been written can copy words, which leads to recognition may be the same as ventral simulanagnosia
75
What is topographic agnosia?
impaired recognition of scenes and landmarks; get lost easily; damage to inferior medial occipito-temporal cortex (similar to prosopagnosia)
76
What is the double dissociation of extrastriate pathways?
in one case study, one ability is functioning, but another ability is not and vice-versa in another case study
77
What is Balint's syndrome?
patient had bilateral damage to superior posterior parietal lobes (very rare) optic ataxia: inability to reach for and grasp objects in field of view optic apraxia: inability to guide eye movements or change visual fixation simultanagnosia could recognize individual objects, but could not tell where they were located or reach for them intact "what" system, but damaged "where" system

PSYCH 367 (15 decks)

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