Week 2 - Central Visual Processing I Flashcards
what does retinotopy and receptive field refer to?
the faithful spatial representation of visual space/position from the retina
what does intensity and luminance refer to?
photons absorbed/transduced by photo-pigments, rods VS cones
what does differential spectral absorption refer to?
3 cone types and color opponency
what does spatial contrast refer to?
center-surround receptive fields and edge-detection
what does ON vs OFF refer to for the retina?
positive and negative signs of contrast, luminance increments and decrements
what aspects of vision do these contrasts refer to?
- spatial
- cone
- temporal
- ocular
- form/contour
- color
- motion
- 3D/depth
how does info from the retina get to the LGN? what happens with this information?
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)
what is the hypothalamus for?
regulation of circadian rhythms
what is the pretectum for?
reflex control of pupil and lens
what is the superior colliculus for?
orienting the movements of head and eyes
what are the first neurons to get bilateral visual input?
striate cortex (NOT LGN); until then, signals are kept separate
what visual defect do you get if the right optic nerve is cut?
left eye: normal
right eye: totally blind
what visual defect do you get if the optic chiasm is cut?
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)
what visual defect do you get if the right optic tract is cut?
left eye: temporal side blind
right eye: nasal side blind
what visual defect do you get if the right optic radiations are cut?
left eye: one of the temporal quarters is bind
right eye: one of the nasal quarters is blind
what visual defect do you get if the right striate cortex is cut?
left eye: most of temporal side is blind, but macular sparring
right eye: most of nasal side is blind, but macular sparring
from the LGN, where do fibers representing the superior and inferior visual fields go?
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
what is the primary visual cortex (and other names for it)? what is right next to it?
Visual area 1 (V1)
-AKA striate cortex or Brodman’s area 17
right next to V2 = extra-striate cortex = Brodman’s area 18
what is the Magnocellular pathway?
M-channel
-parasol cells in retina send info through to ventral LGN (1 contralateral, 1 ipsilateral) to ventral primary visual cortex
what is the Parvocellular pathway?
P-channel
-midget cells in retina send info through to dorsal LGN (2 contralateral, 2 ipsilateral) to dorsal primary visual cortex
what are the differential specializations of P and M pathways for
- color
- luminance contrast
- spatial acuity
- temporal resolution
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)
what are common properties of receptive fields in retina and LGN (for both M, P, and K-channels)
- 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)
where do LGN inputs enter and terminate?
they enter V1 and terminate in layer 4
-comes in eye-specific way, so columns are either contralateral or ipsilateral
what does flattening the neocortex show us?
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
how does most cortical circuitry run? what are some examples?
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)
what does the Hubel/Wiesel Serial Model show us?
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
what is the hierarchial elaboration of form/receptive fields for isolated and combined?
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)
what is color vision based on? what does this mean?
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
what are double-opponent receptive fields?
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
what do Type I vision cells show?
R+ center, G- periphery
- spatial opponency
- weak color bias
- retina = midget system
- LGN = P-pathway
- V1 = P-pathway and CO blobs
what do Type II vision cells show?
R+ and G- center only
- chronatic opponency
- no spatial opponency
- retina = unknown
- LGN = P-pathway
- V1 = P-pathway and CO blobs
what do double opponent vision cells show?
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
how do cells change throughout cortical circuitry?
increasing sophistication of receptive field properties through cortical circuitry
-Type I –> Type II –> double opponent
how is V1 organized functionally? what would vertical VS oblique (horizontal) electrode penetration do?
in cortical columns
- vertical: cells are all the same orientation and ocular dominance
- horizontal: progression of orientation
how are CO blob and interblob cells tuned?
CO: color tuned (from K pathway)
interblob: orientation tuned
what are the 3 “dimensions” of retinotopy? what parameters do they help for vision?
orientation (horizontally) - form CO blobs (vertically) - color ocular dominance (diagonally) - depth
what does a hypercolumn refer to?
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
what are the V2 parameters and what do they correspond to?
thick - orented, disparity, motion, depth
pale - oriented, end-stopped, form
thin - unoriented, color
what is the object discrimination task used for? what “question” does this ask?
bilateral lesion of temporal lobe leads to behavioral deficit in a task that requires discrimination of objects
-“what” - temporal
what is the landmark discrimination task used for? what “question” does this ask?
bilateral lesion of parietal lobe leads to behavioral deficit in a task that requires discriminations of locations
-“where” - parietal
what is parietal neglect?
hemispatial/hemiagnosia neglect
-will ignore the complete left side of the body and drawings
what is the parietal path for V2?
V2 –> MT (via dorsal/spatial vision pathway) in parietal lobe
-asks “where”
what is the temporal path for V2?
V2 –> V4 via ventral (object recognition) pathway in temporal lobe
-asks “what”
