Week 2 - Central Visual Processing I

Question 1

what does retinotopy and receptive field refer to?

Answer 1

the faithful spatial representation of visual space/position from the retina

Question 2

what does intensity and luminance refer to?

Answer 2

photons absorbed/transduced by photo-pigments, rods VS cones

Question 3

what does differential spectral absorption refer to?

Answer 3

3 cone types and color opponency

Question 4

what does spatial contrast refer to?

Answer 4

center-surround receptive fields and edge-detection

Question 5

what does ON vs OFF refer to for the retina?

Answer 5

positive and negative signs of contrast, luminance increments and decrements

Question 6

what aspects of vision do these contrasts refer to?

• spatial
• cone
• temporal
• ocular

Answer 6

• form/contour
• color
• motion
• 3D/depth

Question 7

how does info from the retina get to the LGN? what happens with this information?

Answer 7

visual pathway

• optic nerve –> optic chiasm –> optic tract –> LGN
• -some may go from OT to hypothalamus, pretectum, or superior colliculus
• if pupils must be dilated/constricted, then LGN –> pretectum –> Edinger-Westphal nucleus –> CN III (pregang para) –> ciliary ganglion –> postgang para –> ciliary muscles to constrict (if relax, then dilate)

Question 8

what is the hypothalamus for?

Answer 8

regulation of circadian rhythms

Question 9

what is the pretectum for?

Answer 9

reflex control of pupil and lens

Question 10

what is the superior colliculus for?

Answer 10

orienting the movements of head and eyes

Question 11

what are the first neurons to get bilateral visual input?

Answer 11

striate cortex (NOT LGN); until then, signals are kept separate

Question 12

what visual defect do you get if the right optic nerve is cut?

Answer 12

left eye: normal

right eye: totally blind

Question 13

what visual defect do you get if the optic chiasm is cut?

Answer 13

left eye: temporal side blind
right eye: temporal side blind

(b/c nasal retina = temporal vision, which crosses; temporal retina = nasal vision, which stays on the same side)

Question 14

what visual defect do you get if the right optic tract is cut?

Answer 14

left eye: temporal side blind

right eye: nasal side blind

Question 15

what visual defect do you get if the right optic radiations are cut?

Answer 15

left eye: one of the temporal quarters is bind

right eye: one of the nasal quarters is blind

Question 16

what visual defect do you get if the right striate cortex is cut?

Answer 16

left eye: most of temporal side is blind, but macular sparring
right eye: most of nasal side is blind, but macular sparring

Question 17

from the LGN, where do fibers representing the superior and inferior visual fields go?

Answer 17

superior visual field = inferior retinal quadrants
-travel through temporal lobe, and are more susceptible to damage via Meyer’s loop

inferior visual field = superior retinal quadrants
-travel through parietal lobe, and less susceptible to damage via Baum’s loop

Question 18

what is the primary visual cortex (and other names for it)? what is right next to it?

Answer 18

Visual area 1 (V1)
-AKA striate cortex or Brodman’s area 17

right next to V2 = extra-striate cortex = Brodman’s area 18

Question 19

what is the Magnocellular pathway?

Answer 19

M-channel
-parasol cells in retina send info through to ventral LGN (1 contralateral, 1 ipsilateral) to ventral primary visual cortex

Question 20

what is the Parvocellular pathway?

Answer 20

P-channel

-midget cells in retina send info through to dorsal LGN (2 contralateral, 2 ipsilateral) to dorsal primary visual cortex

Question 21

what are the differential specializations of P and M pathways for

• color
• luminance contrast
• spatial acuity
• temporal resolution

Answer 21

P: color, low luminance, high spatial acuity, low temporal resolution (speed/movement)

M: no color, high luminance contrast (fine shades of gray), low spatial acuity, high temporal resolution (speed/movement)

Question 22

what are common properties of receptive fields in retina and LGN (for both M, P, and K-channels)

Answer 22

• center-surround (spatially opponent) organization (usually)
• mix of cells with on- and off-center
• retinotopically (spatially) ordered and specific
• maybe color-opponent (red/green or blue/yellow)

Question 23

where do LGN inputs enter and terminate?

Answer 23

they enter V1 and terminate in layer 4

-comes in eye-specific way, so columns are either contralateral or ipsilateral

Question 24

what does flattening the neocortex show us?

Answer 24

it’s a thin layer of simple monocular cells organized into ocular dominance columns and orientation columns

• at the very top they become complex (binocular) cells
• it has a very highly conserved laminar architecture with canonical spread

Question 25

how does most cortical circuitry run? what are some examples?

Answer 25

vertically, across cell layers - ex) monocular inputs from LGN (K, P, or M channels) - ex) resident cells (output to higher areas like V2, or feedback output to LGN)

Question 26

what does the Hubel/Wiesel Serial Model show us?

Answer 26

orientation tuning - certain cells will respond to light bars in a certain orientation (horizontal, vertical, diagonal) with more APs than other orientations; unique to cell - there's a hierarchial/serial elaboration of higher order receptive field properties

Question 27

what is the hierarchial elaboration of form/receptive fields for isolated and combined?

Answer 27

isolated: white spots (retina) --> bars (V1) combined: white/black spots (retina) --> sinusoidal gratings (V1) --> non-cartesian gratings (V2) --> 3D shape primitives (V4) --> faces/objects (temporal)

Question 28

what is color vision based on? what does this mean?

Answer 28

cone-opponency (2 color opponent mechanisms) - R/G (red VS green) and B/Y (blue VS red/green) - can't see red w/o absence of green

Question 29

what are double-opponent receptive fields?

Answer 29

encode both spatial and chromatic contrast - both spatial and spectral attributes of stimulus contribute to receptive field - visual system is constructed to extract and emphasize contrasts

Question 30

what do Type I vision cells show?

Answer 30

R+ center, G- periphery - spatial opponency - weak color bias - retina = midget system - LGN = P-pathway - V1 = P-pathway and CO blobs

Question 31

what do Type II vision cells show?

Answer 31

R+ and G- center only - chronatic opponency - no spatial opponency - retina = unknown - LGN = P-pathway - V1 = P-pathway and CO blobs

Question 32

what do double opponent vision cells show?

Answer 32

R+ and G- center, R- and G+ periphery - chromatic opponency - spatial opponency - not in retina or LGN - V1 = P-pathway and CO blobs - V2 = thin stripes and higher cortex

Question 33

how do cells change throughout cortical circuitry?

Answer 33

increasing sophistication of receptive field properties through cortical circuitry -Type I --> Type II --> double opponent

Question 34

how is V1 organized functionally? what would vertical VS oblique (horizontal) electrode penetration do?

Answer 34

in cortical columns - vertical: cells are all the same orientation and ocular dominance - horizontal: progression of orientation

Question 35

how are CO blob and interblob cells tuned?

Answer 35

CO: color tuned (from K pathway) interblob: orientation tuned

Question 36

what are the 3 "dimensions" of retinotopy? what parameters do they help for vision?

Answer 36

``` orientation (horizontally) - form CO blobs (vertically) - color ocular dominance (diagonally) - depth ```

Question 37

what does a hypercolumn refer to?

Answer 37

complete set of all possibilities for a given parameter (ocular dominance, orientation, etc.) -AKA collection of cortical columns whose receptive field properties span entire range of possibilities for a given point in visual space

Question 38

what are the V2 parameters and what do they correspond to?

Answer 38

thick - orented, disparity, motion, depth pale - oriented, end-stopped, form thin - unoriented, color

Question 39

what is the object discrimination task used for? what "question" does this ask?

Answer 39

bilateral lesion of temporal lobe leads to behavioral deficit in a task that requires discrimination of objects -"what" - temporal

Question 40

what is the landmark discrimination task used for? what "question" does this ask?

Answer 40

bilateral lesion of parietal lobe leads to behavioral deficit in a task that requires discriminations of locations -"where" - parietal

Question 41

what is parietal neglect?

Answer 41

hemispatial/hemiagnosia neglect | -will ignore the complete left side of the body and drawings

Question 42

what is the parietal path for V2?

Answer 42

V2 --> MT (via dorsal/spatial vision pathway) in parietal lobe -asks "where"

Question 43

what is the temporal path for V2?

Answer 43

V2 --> V4 via ventral (object recognition) pathway in temporal lobe -asks "what"