Test 2: lecture 19: visual Flashcards
___converts “optical image” in to a ”neural image” for transmission
down the optic nerve to the brain for further analysis.
Retina
how does light get to optic nerve
vertical pathway
comes in hits retina
cone → bipolar cell → ganglion cell → optic nerve
transduction of the image by photoreceptors take physical energy photons and convert them to ____
electrochemical energy
light → cones/rods → bipolar cells → ganglion cells
lateral information flow in the retina
amacrine cells and horizontal cells inhibit the transmission of info to the optic nerve
cells that can see light
rod (night vision)
cones (day vision (color))
Retina uses different cell types to create ___ for simultaneous transmission of multiple neural images to the brain (for motion,form,color,…)
parallel circuits
(needs a bunch of cells working together to reform an optic image into a neural image → each cell type has a different job)
receptive field of a retinal ganglion cell
the area of cells that stimulate the ganglion cell → vertical pathway
the area of cell outside a specific area that will inhibit the vertical pathway by interacting with the horizontal cells → lateral pathway
vertical pathway in the eye
photoreceptor → bipolar cell → ganglion cell
forms the center of the receptive field
lateral pathway of the eye
photoreceptor → horizontal cell (amacrine) → bipolar cell → inhibits ganglion cell
forms the inhibitory surround of the receptive field
___ : The part of the visual field in which various visual stimuli can affect the discharge rate of the cell
receptive field
on center ganglion cells vs off center ganglion cells
on → stimulated by center
off → stimulated by surround
The RF of a ganglion cell has two parts called a ____ and they are mutually antagonistic
center and surround
Because of this center-surround RF organization, the signal leaving the retina is a ___signal (the difference between center and surround)
contrast
P ganglion cells
can be on or off ganglion
- small receptive fields
- selective to particular wavelengths of light (color)
- concerned with analysis of fine detail and color
- terminate in P (parvocellular) layers of LGN
M ganglion cells
- large receptive fields
- not wavelength selective
- respond well to large objects and movement
- terminate in M (magnocellular) layers of LGN
___ type of ganglion cells respond to a specific cone or color
P cell
selective to a particular wavelength of light → fine detail and color
P ganglion cells project to the ___
parvocellular layer of the LGN
M ganglion cells project to the ___
magnocellular layers of the LGN
information leaving the retina is packaged into parallel pathways ___
on and off center
M (motion)/P (color)
left and right eye
For every point in the visual field we have at least 4 ganglion cell types processing information concerning the image:
ON-M, OFF-M, ON-P and OFF-P
retinal ganglion cells will project to
Thalamus: lateral geniculate nucleus (LGN)
Hypothalamus: suprachiasmatic nucleus [SCN] (circadian rhythms)
Midbrain: superior colliculus [SC] (orienting the movement of head and eyes), pretectum (pupillary light reflex)
fovea separates the retina into __
temporal and nasal retina
temporal retina → stays on the same side
nasal retina → changes sides
Axons of retinal ganglion cells in the ___cross to the opposite side of the brain at the optic chiasm
nasal hemiretina
Axons in the ___do not cross.
temporal hemiretina
anything in the left visual field will end up where ___
on the nasal hemiretina of the L eye
on the temporal hemiretina of the R eye →
both will lead to the R optic tract
anopsias
large visual field deficits
scotomas
small visual field deficits
what can each eye see at A?
left normal
right → nothing (anopsias)
what can each eye see at B?
only see the center of each field (the nasal hemiretina are cut → can’t cross over)
heteronomous, hemianopsia
what can each eye see at C?
left homonomous hemianopsia
left eye → far left is cut off cause the nasal hemiretina is cut
right eye → the temporal hemiretina is cut can’t see the center
what would cause this
Lesion of optic tract, LGN or 1o Visual cortex e.g., tumor, stroke Left homonomous hemianopsia (varying degrees)
cut at C
what would cause this?
Lesion of optic chiasm e.g., pituitary tumor
Heteronomous hemianopsia (both sides loss of half of the visual field)
tunnel vision
what would cause this?
Lesion of optic nerve e.g., optic neuritis
Right eye blindness
cut at A
layers of the LGN
2 magnocellular layers
4 parvocellular layers
in the thalamus → visual comes from optic nerve
parallel pathways for M/P, left/right, On/off center
LGN → ___ → striate cortex
optic radiations
striate cortex also called the primary visual cortex
the left visual field projects to the ___
right primary visual cortex
(contralateral visual hemifield)
LGN leads to what layer of the primary visual cortex?
layer 4C
everything remains separate (segregated)
there are specific spots for M/P, On/Off, Center/surround, left/right
where are binocular cells?
layer 1-3 of the neocortex of the primary visual cortex
receive info from both eyes from the 4C layer
___ are functional columns of cells extending from pia to white matter that all share the same eye
ocular dominance columns
where does convergence of the visual field take place
in the primary visual cortex
input goes to layer 4c then mixes in layer 1,2,3
binocular cells are important for ___
depth perception
Many binocular cells code for ___- differences in images from the left and right eye that the brain uses as a binocular cue (___) to determine depth or distance of an object.
retinal disparity
stereopsis
(depth perception)
what happens to the on/off subregions from layer 4c to upper layers
they elongate → change what will trigger them (orientating tuning)
convergence of inputs from rows of On/off center cells
lines up at a particular orientation → good stimulus
(orientation selective)
Bad stimulus → going over + and - areas would not lead to good stimulus
(orientation selective)
orientation selectivity
layers 1-3 of the visual cortex are elongated in a way that specific directions of light give a good or bad stimulus
___ are functional columns of cells extending from pia to white matter that all share the same orientation preference.
orientation columns
prefer bar of light in specific direction
Orientation selectivity is the first step in visual processing to make out the ___ of objects.
contours
Visual system uses information about local orientation and contrast to construct the contours and surfaces of objects
Visual system uses information about ___and contrast to construct the contours and surfaces of objects
local orientation
direction selectivity
parts of the primary visual cortex are selective for a specific direction of light → it will send a signal if going the correct direction (preferred or null direction)
receptive field properties emerging in V1
Disparity tuning – for depth perception
Orientation selectivity – for form perception
Direction selectivity – for motion perception
M/P pathways are still segregated
dorsal vision pathway
where” spatial relationships, depth, motion
locating and grasping
M pathway
ventral object recognition pathway
what? who color form
recognizing an object
P Pathway
akinetopsia
inability to see motion
lesion in MT → where pathway
lesion in MT causes
akinetopsia (inability to see movement)
issue with the dorsal pathway (where pathway)
lesion at V4
involved in color perception
ventral pathway (P pathway → what, who pathway)
achromatopsia
achromatopsia
lesion at V4
involved in color perception
ventral pathway (P pathway → what, who pathway)
lesion at IT
in the temporal lobe
part of the ventral pathway → what pathway (P pathway)
prosopagnosia → can’t see faces
object agnosia → can’t recognize objects
patients have no trouble recognizing faces, but cannot recognize common objects
Object agnosia
Bilateral lesions of inferotemporal cortex
issue with ventral pathway (P pathway → what/who pathway)
patients cannot recognize peoples faces but basic object recognition is spared
Prosopagnosia
Bilateral lesions of inferotemporal cortex (IT)
issue with the ventral pathway → P pathway (what/who pathway)
