Exam 2 Flashcards
range of electromagnetic waves we see?
400-700 nm
what’s the order that light passes through the eye
- cornea
- lens
- vitreous humor
- retina
- fovea
- blind spot
RODS
- sensitive to what?
- ____ view?
- acrhomatic or trichromatic?
- located where?
- light - help you see in the dark
- peripheral
- achromatic
- outisde the fovea
CONES
- need more ____ to function?
- enable what? how?
- located where?
- light
- you to see color, combination of three cones
- in the fovea
function of photoreceptors
transduce light into nervous impulse
order of neurons in the retina from anterior to posterior
- ganglion cells (form the optic nerve
- bipolar cells
- photoreceptors
cells that allow for communication between bipolar and ganglion cells
amacrine
cells that allow for communicatino between photoreceptors and bipolar cells
horizontal
why do rods function the way they do?
many rods converge to ONE ganglia - you lose detail because the cells merge (3 units of activation example)
- convergence: high light sensitivity, low visual acuity
why do cones function the way they do?
the signals are separated, there’s no converging of info so you don’t lose detail
what happens in color deficiency or color blindness?
one or more cone type is missing
how does an ON center ganglion cell work?
if light is projected on the center of the cell, the firing rate of APs increases. if light is projected on the surround, the firing rate decreases
what type of receptive fields do ganglion cells have?
- explain what this means
center surround
- center is excitatory or inhibitory and surround is opposite
on center cell:
- receives stimulation only in surround?
- fully on center?
- covering everything?
- then it’ll be maximally inhibited
- maximum stimulation
- average out, back to baseline
what does having the center surround receptive fields cause?
luminance contrast - causes an edge of light to be sharpened by enhancing the change in activation at the boundary point
perceiving areas of different brightness because of adjacent areas
simultaneous contrast
explain why on pic on left the middle square seems darker (has lighter surround)
- due to what cells?
- lighter surround - receiving less inhibition, so it appears darker
what is color constancy?
- why does this happen?
a color appears to remain the same relative to other colors despite changes in light
- contrast with other colors
explain where input from each visual field ends up in the brain
- BOTH eyes receive input from BOTH visual fields
- fibers coming from lateral portion of retina stay on the same side
- medial fibers cross to the other hemisphere
- so each hemisphere receives only the contralateral visual field
- each hemisphere receives _____ visual field
- each hemisphere receives input from _____
- contralateral
- both
order of “stops” of info starting with ganglion cells
- ganglion
- optic nerve (…. to brain)
- optic chiasm
- LGN of thalamus
receptive field of neurons in the LGN is the same as what other receptive fields?
the GANGLION cells - center-surround
where does the info go from the LGN?
to the CORTEX
first area of cortex that receives visual input?
primary visual cortex of the occipital lobe
what does it mean that there’s a topological organization of visual stimuli on the primary visual cortex?
- what’s this called?
the spatial properties of visual stimuli are preserved in the brain
- retinotopic map - map of retina that projects onto brain (2 areas that are close to each other in retina are close on brain)
3 important things to remember about the retinotopic map
- DISTORTED representation - over-representation of HIGHER ACUITY areas of the visual field
- Contralateral - L visual field projected on R hemisphere and vice versa
- Upside-down
fovea takes only ___ % of surface of eye, but ___ % of V1 is devoted to processing it
- 1
- 50
you’ll have an edge detector and a bar detector for what?
- every possible orientation - how we begin to perceive shape
look at pics of edge detectors
look at them
how could you create an edge detector?
by combining on center and off center cells (look at pic)
- a column of on center, and a column of off center
how could you create a bar detector?
by combing on center cells into a column
orientation selectivity in V1 - what does this mean?
neurons are set to be maximally activated to the specific orientation of a bar (?)
Damage to the visual system BEFORE the optic chiasm will result in what? what does this mean?
monocular blindness - partial or complete damage that’s only relevant to ONE eye. So the person can see the entire visual field (one eye is fine). They have no problem determining what an object is. But will have issues perceiving it’s depth.
Damage to regions FOLLOWING the optic chiasm (LGN or V1) will result in what?
- name and explain the three options
blindness in a portion of the visual field
- hemianopia: complete loss of a visual hemifield (L or R)
- quadrantanopia: loss of a portion of the visual field
- scotoma: small blind spot
if the R half of the visual field is lost where would you expect to see damage?
in the LEFT LGN or LEFT V1
blindsight
- damage to?
- what is this phenomena?
- COMPLETE damage to V1
- cannot see anything. but in some cases, there’s signs of them having UNCOUSCIOUS vision (they avoid obstacles unconsciously, but have no idea why). areas before V1 that are impt for unconscious vision aren’t damaged.
list the impariements that result due to damage to the DORSAL stream
visual neglect, optic ataxia, motion blindness
list the impairments that result due to damage in the VENTRAL stream
prosopagnnosia, object agnosia, cortical color blindness
damage to dorsal stream is going to result in what?
deficit in LOCATING objects and VISUALLY-GUIDED ACTION
- visual neglect
damage to the ventral stream is going to result in what?
deficits in RECOGNIZING objects
cortical colorblindness results due to damage where?
V4 - an area impt for processing color
what is visual agnosia?
inability to recognize objects (can become very specific to a cateogry (ex/ color, shape, tools, animals, hands)
visual agnosia is an impairment in _____
- what does this mean
visual perception, NOT memory
- when asked to draw an apple from memory, they can, but they won’t be able to recognize it after awhile
- also, most of the time, when patient is presented with object with ANOTHER SENSE, then they can recognize it
what is apperceptive agnosia? where is damage?
more severe - can’t copy or recognize even most basic objects
- occipital lobe
what is associative agnosia?
- damage where?
- only impairment with complex objects, possibly specific to a single category of objects
- ventral gemporal cortex
visual agnosia is damage to WHAT pathway
ventral
can patients with visual agnosia execute visually guided action?
- give ex/
YES
- ex/ can’t describe alignment of a slot or try to align letter with slot but they can actually INSERT the letter just fine
prosopagnosia results from damage to what part of brain?
- explain what happens?
Fusiform Face Area - inferior temporal lobe
- lose ability to recognize faces
explain our ability to recognize faces
- we are predisposed to be VERY good at perceiving faces when they’re upright and NOT scrambled
- this becomes much more difficult if face is turned upside down or object is scrambled
what is optic ataxia? damage to what pathway?
problems locating objects and visually guided action
- can’t tell where object is or accurately reach for it
- dorsal
with damage to ventral pathway, an individual could ____ with an apple but not _____
interact with, idenify
damage to what area leads to motion blindness?
- what is this?
MT (V5)
- patient perceives a pattern/sequence of still images that change every now and then
visual neglect
- what pathway damaged?
- specific lobe?
- DORSAL
- R parietal lobe
visual neglect - deficit in ___ rather than ____
attention, visual perception
what is visual neglect?
- explain
inability to attend to one half of the visual field (usually L half)
- impairment in attn, not perception. they see it, they just don’t focus on it.
how is visual neglect DIFFERENT from visual agnosia?
- CAN’T draw an intact object from memory - still miss L side of object
- patient with visual neglect doesn’t attend to all of left modalities (touch, hearing, etc
study OCULAR DOMINANCE columns and HYPERCOLUMNS
study
the way ocular dominance works is an example of what?
plasticity
ONE hypercolum processes what?
- the sub-divisions/columns process what?
a certain particular PART of the visual field
- certain PROPERTIES within that aspect of the visual field
after V1, what does visual info do?
it splits - it’s no longer linear pathway from one structure to the next. there are two main streams of info:
1) ventral stream
2) dorsal stream
what does parallel processing mean?
- downside?
- there are around 30 areas in the cortex that process visual info
- each area is specialized for a particular aspect of vision
- it’s more efficient and faster
- 2 main streams - ventral and dorsal
- downside = have to be able to put all of this info into one cohesive unit?
ventral stream: the ____ pathway
- allows you to do what?
- reaches?
- maturation?
- includes?
what
- ID objects and familiar features (form and color)
- the temporal lobe
- slightly later maturation
- V4
dorsal stream: the ___ pathway
- does what?
- reaches?
- maturation?
- includes?
where
- processes visual space (determine where an object is in space and allows for visually guided action) - ex/ shooting hoops, reaching for an objects
- matures earlier (child better at IDing motion/location than IDing objects
- MT
lateral occipital complex - does what? as opposed to?
- interprets MEANING - activity decreases as you scramble image because it’s no longer meaningful
- a neuron in V1 still responds even when image is scrambled because basic visual components are the same
V4 is involved in?
color perception and IDing angles
MT is impt for?
detection of motion
FFA is important for?
recognizing faces
Parahippocampal place area is located where?
- mostly activated when?
- specifically devoted to?
- crucial for recognizing?
inferior temporal lobe
- when presented with landscapes and city scapes
- landmarks
- where you’re at and figuring out where to go
explain what hierarchial organization of the visual system means
as you move away from V1 towards temporal lobe in the what pathway, the info you process gets more and more complex and abstract
- from lower to higher: properties become more complex and abstract
STUDY METHODS!!!!
study!
