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an anatomically distinguishable set of neurons
Visual cortical "area"
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How cells look in the Visual cortical "area"
similar histological characteristics; cells must look the same
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Visual cortical "area" pattern of afferent and efferent connections (connections to input from the retina)
homogenous pattern;
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What test shoes that neurons have the same response to a stimulus so they appear to have the same function in the Visual cortical "area" ?
functional MRI (fMRI)
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How does the Visual cortical "area" respond to visual stimuli?
exclusively
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In the Visual cortical "area" there is a representaton of____ of the visual field
every point
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The Visual cortical "area" comprises one (or more) complete _____ ______ of the visual world
retinotopic representation
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Optical imaging of cortex in monkey. Data is polotted in a color coded map that shows
activitiy related to orientation of the stimuli
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A neuron may act differently when it is grouped with
other neurons
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Some techniques for Extrastriate vision research
- 1. recordings of single neuron activity (cats)
- 2. Anatomical staining and labeling teq (animal) with CO
- 3. Optical imaging (animal)
- 4. lesion studies (human and animal)
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when staining with CO to determine which cells of the cortex are active. Which ones appear white and which dark
- active cells = white
- inactive cells = dark
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Optical imaging monitors a group or single neuron?
groups of neurons
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How does optical imaging measure activity?
Detects changes in cortical reflectance due to variations in bld flow (active area = incr bld flow)
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What type of techniques/study for extrastriate vision research lets you observe how a lesion affects vision or function in body?
Lesion study
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What are some modern techniques/study for extrastriate vision research?
- 1. Positron emission tomography (PET)
- 2. Functional magnetic resonance imaging (MRI)
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Which modern techniques/study for extrastriate vision research measures changes in bld oxygenation due to neurala activity?
fMRI
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Which modern techniques/study for extrastriate vision research measures changes in bld flow related to neural activity?
PET (position emission tomography)
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What does the pt do during a fMRI?
pt is assigned tasks or looks at stimuli
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Where can the primary visual cortex be seen?
Can;t be seen laterally, has to be seen if you cut corpus callosum in half and look at medial part of brain, BUT you can view with a fMRI w/o cutting brain open
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Neurons in VI have relatively SMALL receptive fields and respond to ___ features of objects in the VF
local
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Name some examples of local features that neurons in V1 respond to
- orientation, length, width, speed and direction of motion of bars and edges (spacial freq)
- wavelength of light
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Neurons in extra-striate visual areas (V2-V5,...) have much LARGER receptive fields and respond to ___ properties of objects in the VF
Global
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Name some examples of local features that neurons in V2-V5 respond to
color rather than just wavelength, specific shapes and objects irrespective of orientation, forma dn motion coherence.
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Extrastriate cortical cell properties, graph showing percentage of cells in each of first 5 cortical areas selective for orientation, direction, color and binocular disparity. Why are some of the % more than 100%??
Each cell may respond to more than one characteristic. (ex. cell can respond to both color and orientation).
Proportions vary from area to area (look at table)
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Which area is mostly for color vision>
V4 (but also has some stereo, direction and orientation)
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Which area is mostly for direction?
MT
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Which layer is VI (striate cortex) most and least pronounced with CO staining?
- Most= IIIB (koniocellular)
- Least= IVCa (Magnocel)
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Staining with CO where are the "blobs" in VI?
centered above ocular dominance colums
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What happens when you stain the V2 area with CO?
Stripes perpendicular to V1/V2 border.
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What are the "Thick stripes" when you stain the V2 area with CO?
- M pathway
- (imput from V1 layer to IVCa/ OUtput to V3 and V5 (MT))
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What are the "Thin stripes" when you stain the V2 area with CO?
- Parvo-blob pathway
- Input from V1 CO blobs/ output to V4, V3 and V5
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What are the "Pale stripes" when you stain the V2 area with CO?
- Parvo-Interblob pathway (interstripes)
- input from V1 layers 2&3 outside of CO blobs; output to V4
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What are the 3 complete retinotopic maps in V2 (Brodman's Area 18)?
- 1. Thick Dark CO stripes
- 2. Thin DArk CO stripes
- 3. Pale CO stripes
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What does the Thick Dark CO stripes represent in V2?
M pathway: motion, orientation, binocular disparity
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What does the Thin Dark CO stripes represent in V2?
P-Blob pathway: wavelength/color
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What does the Pale/Interstirpes CO stripes represent in V2?
P-Interblob pathway: orientation, binocular disparity
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In V2 what is there a high proportion of?
disparity-tuned neurons (they like depth)
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Many neurons in V2 will respond to?
"Illusory Contours"
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What is an example of "Illusory Contours"?
kaniza triangle
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What type of input does area V3 recieve?
Magno and parvo (integration!)
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What are the two parts of V3?
- 1. VP: ventral posterior area
- 2. Dorsal V3 (V3 proper)
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What does the VP and also Dorsal V3 represent?
- Upper visual field
- Lower visual field
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Where does V3 output go to?
Mostly to V5 and posterior parietal cortex, also some to V4
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Where does V3 contribute to?
integration of magno & parvo streams
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What area was believe to be part of V3, but neurons are much less selective to direction and speed of motion and projects to both temporal and parietal lobes?
V3A
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Where does V4 get its major input from and what is it info is it mainly related to?
Parvo pathway (blob & interblob); perception of color and form, some neurons specific for simple shapes and forms
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What does damage of V4 called?
achromatopsia
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What is achromotopsia often associated with and why?
prosopagnosia; due to proximity to V4 to IC in fusiform gyrus
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What is the fusiform gyrus for?
memory
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What is prosopagnosia?
can't remember and recognize faces
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What is the major input of V5(MT) from and what info is it mainly related to?
magno pathway and perception of motion
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What are the size are the reeptive fields and what are they called?
Large receptive fields, parasols
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What is V5 specific for?
PERCEPTION of motion, direction and velocity, orientation and depth
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What are two examples of illusory motion?
- 1. Barber Pole Illusion: lines look like they are moving in a certain direction when they aren't
- 2. Motion After-effects
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Damage to V5 results in?
akinetopsia
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What is akinetopsia?
motion blindness
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What happens in the 'ventral' cortical stream?
- 1. global pattern processing
- 2. object and pattern recognition (what?)
- 3. Face recognition (who?)
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What are the two "streams" of higher-order visual info processing?
- 1. ventral cortical stream
- 2. dorsal cortical stream
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What happens in the 'dorsal' cortical stream?
- 1. Global motion processing
- 2. Processing location in 3D space (where?)
- 3. provides info for visually guided actions (how?)
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The "ventral" what stream is largely from what input, and what is the function?
- Parvo and koniocellular input
- V1>V2>V4>IT
- recognition of shapes, objects, faces, color perception
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Damage to ventral stream can case what?
achromatopsia, drawing/object agnosia, prosopagnosia
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The "dorsal" where stream is largely from what input, and what is the function?
- magnocellular (but not entirely)
- VI>V2>V3&V5>LIP &7A> frontal eye fields
- LIP: lateral intraparietal area
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Damage to dorsal stream can cause?
- Akinetopsia (can't estimate speed of moving object)
- Deficits in visually guided behavior
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What is it called when we see only a small portion of our VF to which we are attending; AKA rest of our visual field is suppressed
"Inattentional" blindness
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