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169 Cards in this Set

  • Front
  • Back
minimum quantity of stimulus that can be detected
threshold
threshold and sensitivity relationship
inversely related
experimenter increases the stimulus intensiy incrementally from presentation to presentation; initially the stimulus is not visible
method of ascending limits
experimenter decreases the stimulus intensity incrementally from presenttation to presentation; initially the stimulus is visible
method of descending limits
ex of ascending limits
dark adaptation
ex of descending limits
VA
drawback of ascending limits
anticipation
drawback of descending limits
time
benefit of descending limits
no anticipation
experimenter increases the stimulus in an increasing stair case manner one step at a time and then decreases it in staircase manner
stair case method
ex of staircase
automated VF
experimenter allows subject to adjust stimulus intensity until it is just perceivable
adjustment method
which method has most variation and anticipation
adjustment method
what does forced choiced minimize
limits the effect of threshold criteria
forced choice
the subject is forced to choose btw 2 alternatives
threshold for forced choice
75%
what does the visual system have
noise
signal detection theory
have to distinguish signal from noise; if the what you are seeing is noise or signal + noise
what does SDT assume about noise
noise is random
bell shape curve
noise corrupts signal
what does SDT assume about what receiver recieve
combination of N and S + N
what happens when N and S + N overlap
hard to tell them apar
detectability
difference btw means of S + N and N
what happens when the signal is weak (small)
N and N + S overlap difficult to distinguish
detectability is low
what happens when there is a stong (lrg) signal
S + N and N dont overlap
detectability is high
easy to distinguish
what can affect stimulus detection
threshold criteria
lax criteria
many positives
lots of FP
will almost never miss signal that is actually there
strict criteria
fewer hits
less FP
guess that there is no signal when there is actually one, but will rarely guess that there is a signal when there is not one
high threshold low sensitivity is seen in what criteria
strict
low th and high sensitivity is seen in
lax
stimulus is present and was detected
TP
signal was present but was not detected
false negative
signal was absent and was detected
false positive
signal was absent and was not detectd
true negative
describe ROC
plots hit (correctly detects it) vs false positive
what affects ROC
detectability
ROC changes when
detectability changes
where does lax criteria fall on ROC
upper right
high FP
high hit
where does strict fall on ROC
lower left
low FP
low hit
jnd
detect increment th flashed on background

stimulus + bg or bg alone
jnd is directly proportional to
Ib
weber's law
I/Ib
magnitude of sensation (fechner)
if intensity increased by 5, perception of brightness will increase by 5
fechner uses
indirecr scaling
fechner eq and point
S = clogI

all JND produce equal mag of sensation
Stevens power law
s = I ^c

direct scaling (mag estimation)

observer assess intensity on scale of 1-10
x chrome CL
act as long pass filters
tinted red
shift absorption peak to long wavelengths
poor color discrimination in protanopes
>546
poor color discrimination in deuteranopes
>546
poor color discrimination in tritanopes
495
contrast equation
C = Lmax - Lavg/Lavg
SMTF
tells how well a system (lens) transform input into output in terms of contrast

ex. if object has high contrast, will image have less contrast
high SF means
tightly packed, small
what does optical defocus do to image quality
poor image quality
at what freq is optical defocus most affected
high SF
CSF
SMTF of the eye
the human CSF is
band pass

4cpd
CSF shows
high SF cutoff
what does the high SF cutoff of CSF mean
that there is limit in our ability to resolve fine detaiil
what is the high SF cutoff related to
VA
why cant really small letters be seen
bc the letters have a high SF (small) and fall above the high frequency cutoff of the CSF
x chrome CL
act as long pass filters
tinted red
shift absorption peak to long wavelengths
poor color discrimination in protanopes
>546
poor color discrimination in deuteranopes
>546
poor color discrimination in tritanopes
495
contrast equation
C = Lmax - Lavg/Lavg
SMTF
tells how well a system (lens) transform input into output in terms of contrast

ex. if object has high contrast, will image have less contrast
high SF means
tightly packed, small
what does optical defocus do to image quality
poor image quality
at what freq is optical defocus most affected
high SF
CSF
SMTF of the eye
the human CSF is
band pass

4cpd
CSF shows
high SF cutoff
what does the high SF cutoff of CSF mean
that there is limit in our ability to resolve fine detaiil
what is the high SF cutoff related to
VA
why cant really small letters be seen
bc the letters have a high SF (small) and fall above the high frequency cutoff of the CSF
2 reasons for high SF cutoff of CSF
aberrations
Pr packing density
who stated that packing density of Pr is finite and is a cause of high SF cutoff
Nquist
reason for low SF cutoff
lateral inhibition
describe lateral inhibition
ganglion cell has center surround anatgonism

stimulus falls on surround causing inhibition and thus limiting low freq vision
angle btw 2 just resolvable bars measured in arcmin (1/60 degree)
MAR
snellen fraction equals
1/MAR
what is fourier analysis
break down visual scene into various frequencies and then add them up to get complete percept
mach bands
enhancement of high SF thus can see boundaries enhanced
what do mach bands suggest
visual system is acting like a fourier analyzer and is breaking scene into ind freq components and handling them separately
downfall of VA
treats only small portion of CSF
patient has to distinguish pattern from a uniform patch; typically 40-60cpd
resolution acuity
recognize ototypes
recognition acuity
type of recognition activity
snellen
recognition acuity gives info soley about
ability to detect high SF
how small can something be to be seen; 1 arc sec
minimum detectable acuity
ability to sense direction, tilt; very good and resillient to refractive error
hyperacuity
what do we use to perceive depth
monocular and binocular cue
list monocular cues
pictorial depth cures like angle, light, texture, shadow, etc

motion parallax
large objects appear
closer
small objects appear
farther
low SF
large
converging lines appear
far
near objects look
closer
relative motion btw objects gives clues about positional rel btw objects
motion parallax
things that are near appear to move ___ you
against
things that are far appear to move ___ you
with
what do binocular cues rely on
comparison of location of image formed on each retina ie BINOCULAR DISPARITY
uncrossed retinal disparity
falls nasal
object appears farther
crossed retinal disparity
falls temporal
objects appear CROSSER
what happens is retinal disparity is too big
no stereo
what are the areas of retina where stereo occurs
panum's fusional area
if disparity is too big where do the images fall
not on Panum's
diplopia occurs when
retinal disparity is too big and the images do not fall on panum's fusional area
stereo
perception of depth formed by binocular disparity
Images falling on the two foveas signal the same direction are called
corresponding points
Plotting these corresponding points (for a given fixation distance) results in a curved plane referred to as the
horopter
All points on the horopter
stimulate corresponding retianl points and are perceived as being at the same distance
Objects that fall relatively close to the horopter
fused -> panums ---> stereo
apparent motion
perception of motion that is not real motion
Stroboscopic motion or the phi phenomenon:
using flashes of light to create the illusion of motion (1st order phenomenon).
Various sensations of movement are produced by different intervals between 2 flashes of light. An interval of 60 msec produces
realistic movement (optimum or beta movement).

looks like moving
An interval of less than 30 msec produce
s no sensation of movement.
Durations of 60 - 200 msec produce
a partial illusion of movement (pure or phi movement).
detecting motion is possible via
magno pathway
area of brain associated with motion processing
V5 aka MT (middle temporal area)
what do cells in V5 respond to
global stimuli
ex of global stimul
random dot kinetograms
random dot kinteogram
stimulus with loss of randomly moving dots
measures how far the dots have to move to give sense of motion
min/max displacement threshold
motion after affect
perceived motion will appear opp to the stimulus motion

ex waterfall
cause for MAE
motion cells become adapted after prolong exposure and become LESS SENSITIVE to motion in direction and consquently stationary stimuli appear to move in opp direction
what happens to VA when stimulus is moving
remains constant but not when critical velo is reached
what happens to VA when critical vel is reached
decreases because cant pursue it anymore
why is world not smeared by magno pathway
saccadic suppression
spatial vision
analysis of changes of luminance across space
temporal vision
analysis of changes of luminance across time
ex of temporal vision
detect a flicker
temporal vision is closely related to
motion perception
this is analogous to contrast in spatial vision; it is PM = 100A/Lavg
% modulation
slow flicker
low TF
high freq
fast flicker
what happens when TF is too high
it will reach the CFF at which flicker will no longer be resolved and appears steady
what characterizes temporal vision
TMTF
low frequency TMTF limits
cant detect very slow temporal changes
purkinje tree
light results in high freq changes in retina
inability to detect perceive stabilized retinal images is due to
low TF cutoff
why do we have poor sensitivity for low freq stimuli
lateral inhibition
troxler phenomenon
disappearance of low temporal frequency stimuli because eye constantly moving and thus threshold is exceeded
glaucoma pts have loss of
sensitivity to mod - high freq
CFF
highest or lowest temporal frequency that can be resolved at a given percentage of modulation (relative sensitivity )
does background illumination affect CFF
yes
Low temporal frequencies: increasing background illumination has
no effect
High temporal frequencies: increasing background illumination causes
a relative increase in sensitivity.
law that states that high freq increases linearly with the log of retinal illumination due to increased activity of retina following light adaptation
ferry porter law
law that states that CFF is increased as stimulus area is increased since the periphery is better at detecting flicker than the center retina
granit harper law
periphery detects motion/flicker how in compared to central retina
better
if area increases what happens to CFF
increases
light flashes above threshold appear brightest when they last how long ___ per what law
50-100msec

broca sulzer effect

long/short flashes appear dimmer
flickering light at 10 Hz appaears brighter than steady light with same Lave
brucke bartley effect
flicker flickering at freq > CFF is
fused
flicker flickering at freq > CFF is percived to be equally bright as a nonflickering stimulus with a luminance equal to time ave luminace of flickering stimuli
talbot plateau law
stimulus that decreases visibility of another stimulus
mask
mask preceeds target
forward masking
mask follows target
backward masking
mask appears first then target appears but both are close together in space
paracontrast
mask appears second and target appears first but both are close together in space
metacontrast
mask and target appear at same time
silmultaneous masking
which masking is most evident in amblyopes
silmultaneous masking --- crowding phenomenom
pathway involving detail color, object size, shape; involves neurons in central retina that are sensitive to high SF
parvo
pathway involving motion in which peripheral retina is most sensitive at low SF
magno
glaucoma damages what pathway perferntially
magno
when is vision suppressed in saccades
before
during
after
why is vision suppressed in saccades
allows the image not to be blurred with rapid eye movements
what pathway is suppressed giving rise to saccadic suppression
magno