Chapter 3 Flashcards
more technical definition of acuity
smallest spatial detail that can be resolved
three ways to test acuity
minimum visible (absolute threshold)
minimum resolvable (stripes)
minimum recognizable (snellen test)
minimum discriminable (JND)
Snellen Eye Chart
eye doctor chart, show letters (or orientations of letters for universal use)
operationalized visual acuity based on distance relative to “average” people
20/20 - average
20/15 - above average (you can read from 20 ft away what others read at 15 ft)
20/30 - below average
acuity tests the size of _____ ______ at which you can identify a _____ in a striped grating
visual angle; cycle
cycle of acuity
one full rotation from black to white
sine wave grating
gradation between colors
smallest angle you can see shift in light = _____
acuity
why does an oriented grating appear to be gray if you are far enough away?
your cones are picking up both light and dark luminance, combining them to make gray due to a smaller cycle/frequency
this is because our photoreceptor responses are graded, so some light and some dark = medium
two factors that affect acuity
spatial frequency
- visual angle of a change from light to dark (cycle)
- aka the rate at which the luminance changes
contrast
- the amount of difference between a change in luminance
- aka the sharpness of that change in luminance
Contrast sensitivity function (CSF)
chart contrast and frequency and see where cycles become invisible on that spectrum
CSF can be _____, impacted by changes in _____ ________ and ___ _____
shifted; overall luminance and temporal frequency
temporal frequency
how fast the cycle moves
the faster the cycles go, the less acuity you have
gabor patches
grading adjusting spatial frequency and contrast
squares with a circle of vision in the middle which is impacted by spatial frequency and contrast
how do we measure ganglion activity?
rate of action potential
really low and high frequency yields ___ response for action potential, while medium frequency yields ____ response
weak; strong
phase
portion of sine wave
leaving the eye tract
optic nerve
optic chiasm
optic tract to LGN
thalamus
primary relay center of the brain
inhibited when you sleep, lowering your responses to most external stimuli
at the optic chiasm, vision is divided by ___ ____, not by ____
visual field; eye
at the optic chiasm, regardless of eye;
information for the left side of space goes _____
information for the right side of space goes ____
visual fields represented ____________
right; left; contralaterally
how many layers in the LGN
6
each side of the LGN receives input from _______ and _________ eye, meaning …
ipsilateral - same eye
contralateral - opposite eye
LGN layers 1, 4, 6 receive ______ eye input
contralateral
LGN layers 2, 3, 5 receive ______ eye input
ipsilateral
the inner two layers of the LGN are the ___________ layer
magnocellular (what M ganglion cells are named after), receiving info from periphery
outer two layers of the LGN are the ________ layer
parvocellular (what P ganglion cells are named after), receiving info from fovea
why do parvocellular layers in the LGN get more representation?
because they are receiving information from fovea which means more cells report to it
Retinotopic Map
map of what is hitting your retina
if one eye or one optic nerve is damaged, what is affected?
vision is lost only on the affected side
if the optic chiasm is damaged, what is affected?
the outer part of the visual field in both eyes is lost
if the visual pathways from the optic chiasm to the visual cortex are damaged, what is affected?
one side of the visual field is lost in both eye
ex) damage on the right side of the brain causes loss of the left visual field in both eyes
which factors influence our ability to perceive a cycle between black and white?
1) spatial frequency
2) overall luminance
3) contrast
4) all of the above
4
Dr. Rafay is an eye doctor. A patient comes to him complaining that they cannot see the right side of their visual space. Their eyes aren’t damaged at all though. What might be wrong with Dr. Rafay’s patient?
a) They have damage to their left optic nerve before the optic chiasm
b) They have damage to their left optic tract after the optic chiasm
c) They have damage to their right optic nerve before the optic chiasm
d) They have damage to their optic chiasm
B
which layer(s) of the LGN receives input from M ganglion cells of the ipsilateral eye?
a) 1
b) 2
c) 3 and 5
d) 4 and 6
B
what is the saying to remember what layers of the LGN are contralateral or ipsilateral?
seasick
1 - C
2 - I
3 - I
4 - C
5 - I
6 - C
striate cortex
aka primary visual cortex or V1
part of the occiptial lobe of your brain
receives bottom-up inputs from the LGN
maintains a retinotopic map
bottom-up
info from sensory system up into the brain
first part of cortex to receive visual input
v1/primary visual cortex
how many layers is in the striate/cellular layer
6 but DO NOT correspond to LGN layers
fovea is represented at the _____ of the retinotopic map for the striate cortex
VF is then represented extending out based on ________ from the fovea
back; eccentricity
eccentricity
distance from fovea, measured in degrees of VF
what three features are shown in the retinotopic map for the striate complex
contralateral VF (like LGN)
inverted from reality
cortical magnification of fovea
cortical magnification
dramatic scaling of information from different parts of visual fields
proportionally more cortex devoted to fovea than periphery, causing loss of acuity
susceptible to visual crowding
visual crowding
stimuli are harder to perceive because there are other stimuli around than compared to when they are in isolation
ex) being able to see a key on the left side (since it is the only item there) but not on the right side (since it is surrounded by multiple items) when staring at a red dot in the center of the image
v1 cells respond better to _________ rather than cicular/center-surround like the LGN
lines/bars
what can V1 cells code for (depending on LGN cells that feed input)?
any orientation
edges vs. bars
gratings of various frequencies
motion direction
simple cells in V1
respond to specific orientation and location
complex cells in V1
respond to specific orientation
unlike simple, respond to any location
end stopping cells in V1
respond to orientation, location and length
cortical neurons tend to have a _____ eye, called ______ ________
preferred; ocular dominance
V1 cells have an eye they prefer, but will still receive information from both eyes
cells in the V1 are grouped in ________
columns
line of cells the run perpendicular to the surface of the brain
orientation columns in the V1 reflect sets of cells that all respond to … each column is then …
the same line orientation; adjacent to columns that are of slightly shifted angle
ocular dominance organization
also columnar, but overlaps with orientation columns to form hypercolumns
hypercolumns
represent all possible orientations across both eyes for a given part of the visual field
since all orientations represent .5 mm and each eye represents .5mm, a hypercolumn is 1 mm
inside each hypercolumn are _________
CO blobs
full role unclear, part tied to color
adaption in columns of striate cortex
cells/columns are tuned for specific things (orientation, location, etc.) but they do not fire forever to that sustained stimulus
response is reduced due to sustained/prior exposure to stimulus
selective adaption
when you can downregulate responding to a specific stimulus by sustaining it
due to selective adaption: after staring at lines slanted to the left for 30 seconds, if you look at straight lines they will appear … why?
slanted to the right due to your cells becoming adapted to them
selective adaption effects for _____ and ___________
orientation; spatial frequency
high spatial frequency = ________
low spatial frequency = _________
edges are defined; shadows are defined
How is the retinotopic map of V1 organized relative to the image on the fovea?
a. The fovea is at the back of V1, and the retinotopic map stretches forward based on eccentricity
b. The fovea is at the front of V1, and the retinotopic map stretches backwards based on accommodation
c. The fovea is at the back of V1, and the retinotopic map stretches forward based on accommodation
d. The fovea is at the front of V1, and the retinotopic map stretches backwards based on eccentricity
a
We know bars of light can activate V1 Simple Cells. Which factor CANNOT influence Simple Cell firing?
a. Orientation of Bar of Light
b. Position of Bar of Light
c. Length of Bar of Light
d. Extended duration of Bar of Light
e. All of these factors can influence Simple Cell firing rate
e
Which statement the organization of columns for a given hypercolumns in V1 is TRUE?
a. Each hypercolumn contains all orientations, but with ocular dominance divided across layers
b. Each hypercolumn contains all orientations, organized based on ocular dominance
c. Each hypercolumn is coded so that columns of a given orientation are always adjacent to their opposite eye column
d. Each hypercolumn is coded based on color, organized based on ocular dominance
b
