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169 Cards in this Set
- Front
- Back
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minimum quantity of stimulus that can be detected
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threshold
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threshold and sensitivity relationship
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inversely related
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experimenter increases the stimulus intensiy incrementally from presentation to presentation; initially the stimulus is not visible
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method of ascending limits
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experimenter decreases the stimulus intensity incrementally from presenttation to presentation; initially the stimulus is visible
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method of descending limits
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ex of ascending limits
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dark adaptation
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ex of descending limits
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VA
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drawback of ascending limits
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anticipation
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drawback of descending limits
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time
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benefit of descending limits
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no anticipation
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experimenter increases the stimulus in an increasing stair case manner one step at a time and then decreases it in staircase manner
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stair case method
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ex of staircase
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automated VF
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experimenter allows subject to adjust stimulus intensity until it is just perceivable
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adjustment method
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which method has most variation and anticipation
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adjustment method
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what does forced choiced minimize
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limits the effect of threshold criteria
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forced choice
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the subject is forced to choose btw 2 alternatives
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threshold for forced choice
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75%
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what does the visual system have
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noise
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signal detection theory
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have to distinguish signal from noise; if the what you are seeing is noise or signal + noise
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what does SDT assume about noise
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noise is random
bell shape curve noise corrupts signal |
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what does SDT assume about what receiver recieve
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combination of N and S + N
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what happens when N and S + N overlap
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hard to tell them apar
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detectability
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difference btw means of S + N and N
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what happens when the signal is weak (small)
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N and N + S overlap difficult to distinguish
detectability is low |
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what happens when there is a stong (lrg) signal
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S + N and N dont overlap
detectability is high easy to distinguish |
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what can affect stimulus detection
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threshold criteria
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lax criteria
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many positives
lots of FP will almost never miss signal that is actually there |
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strict criteria
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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 |
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high threshold low sensitivity is seen in what criteria
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strict
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low th and high sensitivity is seen in
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lax
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stimulus is present and was detected
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TP
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signal was present but was not detected
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false negative
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signal was absent and was detected
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false positive
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signal was absent and was not detectd
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true negative
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describe ROC
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plots hit (correctly detects it) vs false positive
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what affects ROC
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detectability
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ROC changes when
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detectability changes
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where does lax criteria fall on ROC
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upper right
high FP high hit |
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where does strict fall on ROC
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lower left
low FP low hit |
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jnd
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detect increment th flashed on background
stimulus + bg or bg alone |
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jnd is directly proportional to
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Ib
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weber's law
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I/Ib
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magnitude of sensation (fechner)
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if intensity increased by 5, perception of brightness will increase by 5
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fechner uses
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indirecr scaling
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fechner eq and point
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S = clogI
all JND produce equal mag of sensation |
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Stevens power law
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s = I ^c
direct scaling (mag estimation) observer assess intensity on scale of 1-10 |
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x chrome CL
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act as long pass filters
tinted red shift absorption peak to long wavelengths |
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poor color discrimination in protanopes
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>546
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poor color discrimination in deuteranopes
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>546
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poor color discrimination in tritanopes
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495
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contrast equation
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C = Lmax - Lavg/Lavg
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SMTF
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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 |
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high SF means
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tightly packed, small
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what does optical defocus do to image quality
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poor image quality
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at what freq is optical defocus most affected
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high SF
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CSF
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SMTF of the eye
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the human CSF is
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band pass
4cpd |
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CSF shows
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high SF cutoff
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what does the high SF cutoff of CSF mean
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that there is limit in our ability to resolve fine detaiil
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what is the high SF cutoff related to
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VA
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why cant really small letters be seen
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bc the letters have a high SF (small) and fall above the high frequency cutoff of the CSF
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x chrome CL
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act as long pass filters
tinted red shift absorption peak to long wavelengths |
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poor color discrimination in protanopes
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>546
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poor color discrimination in deuteranopes
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>546
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poor color discrimination in tritanopes
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495
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contrast equation
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C = Lmax - Lavg/Lavg
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SMTF
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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 |
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high SF means
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tightly packed, small
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what does optical defocus do to image quality
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poor image quality
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at what freq is optical defocus most affected
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high SF
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CSF
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SMTF of the eye
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the human CSF is
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band pass
4cpd |
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CSF shows
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high SF cutoff
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what does the high SF cutoff of CSF mean
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that there is limit in our ability to resolve fine detaiil
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what is the high SF cutoff related to
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VA
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why cant really small letters be seen
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bc the letters have a high SF (small) and fall above the high frequency cutoff of the CSF
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2 reasons for high SF cutoff of CSF
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aberrations
Pr packing density |
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who stated that packing density of Pr is finite and is a cause of high SF cutoff
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Nquist
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reason for low SF cutoff
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lateral inhibition
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describe lateral inhibition
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ganglion cell has center surround anatgonism
stimulus falls on surround causing inhibition and thus limiting low freq vision |
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angle btw 2 just resolvable bars measured in arcmin (1/60 degree)
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MAR
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snellen fraction equals
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1/MAR
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what is fourier analysis
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break down visual scene into various frequencies and then add them up to get complete percept
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mach bands
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enhancement of high SF thus can see boundaries enhanced
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what do mach bands suggest
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visual system is acting like a fourier analyzer and is breaking scene into ind freq components and handling them separately
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downfall of VA
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treats only small portion of CSF
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patient has to distinguish pattern from a uniform patch; typically 40-60cpd
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resolution acuity
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recognize ototypes
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recognition acuity
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type of recognition activity
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snellen
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recognition acuity gives info soley about
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ability to detect high SF
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how small can something be to be seen; 1 arc sec
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minimum detectable acuity
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ability to sense direction, tilt; very good and resillient to refractive error
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hyperacuity
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what do we use to perceive depth
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monocular and binocular cue
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list monocular cues
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pictorial depth cures like angle, light, texture, shadow, etc
motion parallax |
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large objects appear
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closer
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small objects appear
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farther
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low SF
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large
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converging lines appear
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far
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near objects look
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closer
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relative motion btw objects gives clues about positional rel btw objects
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motion parallax
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things that are near appear to move ___ you
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against
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things that are far appear to move ___ you
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with
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what do binocular cues rely on
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comparison of location of image formed on each retina ie BINOCULAR DISPARITY
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uncrossed retinal disparity
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falls nasal
object appears farther |
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crossed retinal disparity
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falls temporal
objects appear CROSSER |
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what happens is retinal disparity is too big
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no stereo
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what are the areas of retina where stereo occurs
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panum's fusional area
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if disparity is too big where do the images fall
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not on Panum's
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diplopia occurs when
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retinal disparity is too big and the images do not fall on panum's fusional area
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stereo
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perception of depth formed by binocular disparity
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Images falling on the two foveas signal the same direction are called
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corresponding points
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Plotting these corresponding points (for a given fixation distance) results in a curved plane referred to as the
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horopter
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All points on the horopter
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stimulate corresponding retianl points and are perceived as being at the same distance
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Objects that fall relatively close to the horopter
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fused -> panums ---> stereo
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apparent motion
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perception of motion that is not real motion
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Stroboscopic motion or the phi phenomenon:
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using flashes of light to create the illusion of motion (1st order phenomenon).
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Various sensations of movement are produced by different intervals between 2 flashes of light. An interval of 60 msec produces
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realistic movement (optimum or beta movement).
looks like moving |
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An interval of less than 30 msec produce
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s no sensation of movement.
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Durations of 60 - 200 msec produce
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a partial illusion of movement (pure or phi movement).
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detecting motion is possible via
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magno pathway
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area of brain associated with motion processing
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V5 aka MT (middle temporal area)
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what do cells in V5 respond to
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global stimuli
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ex of global stimul
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random dot kinetograms
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random dot kinteogram
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stimulus with loss of randomly moving dots
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measures how far the dots have to move to give sense of motion
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min/max displacement threshold
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motion after affect
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perceived motion will appear opp to the stimulus motion
ex waterfall |
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cause for MAE
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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
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what happens to VA when stimulus is moving
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remains constant but not when critical velo is reached
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what happens to VA when critical vel is reached
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decreases because cant pursue it anymore
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why is world not smeared by magno pathway
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saccadic suppression
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spatial vision
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analysis of changes of luminance across space
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temporal vision
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analysis of changes of luminance across time
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ex of temporal vision
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detect a flicker
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temporal vision is closely related to
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motion perception
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this is analogous to contrast in spatial vision; it is PM = 100A/Lavg
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% modulation
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slow flicker
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low TF
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high freq
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fast flicker
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what happens when TF is too high
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it will reach the CFF at which flicker will no longer be resolved and appears steady
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what characterizes temporal vision
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TMTF
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low frequency TMTF limits
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cant detect very slow temporal changes
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purkinje tree
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light results in high freq changes in retina
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inability to detect perceive stabilized retinal images is due to
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low TF cutoff
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why do we have poor sensitivity for low freq stimuli
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lateral inhibition
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troxler phenomenon
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disappearance of low temporal frequency stimuli because eye constantly moving and thus threshold is exceeded
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glaucoma pts have loss of
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sensitivity to mod - high freq
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CFF
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highest or lowest temporal frequency that can be resolved at a given percentage of modulation (relative sensitivity )
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does background illumination affect CFF
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yes
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Low temporal frequencies: increasing background illumination has
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no effect
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High temporal frequencies: increasing background illumination causes
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a relative increase in sensitivity.
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law that states that high freq increases linearly with the log of retinal illumination due to increased activity of retina following light adaptation
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ferry porter law
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law that states that CFF is increased as stimulus area is increased since the periphery is better at detecting flicker than the center retina
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granit harper law
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periphery detects motion/flicker how in compared to central retina
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better
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if area increases what happens to CFF
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increases
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light flashes above threshold appear brightest when they last how long ___ per what law
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50-100msec
broca sulzer effect long/short flashes appear dimmer |
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flickering light at 10 Hz appaears brighter than steady light with same Lave
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brucke bartley effect
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flicker flickering at freq > CFF is
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fused
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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
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talbot plateau law
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stimulus that decreases visibility of another stimulus
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mask
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mask preceeds target
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forward masking
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mask follows target
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backward masking
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mask appears first then target appears but both are close together in space
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paracontrast
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mask appears second and target appears first but both are close together in space
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metacontrast
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mask and target appear at same time
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silmultaneous masking
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which masking is most evident in amblyopes
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silmultaneous masking --- crowding phenomenom
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pathway involving detail color, object size, shape; involves neurons in central retina that are sensitive to high SF
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parvo
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pathway involving motion in which peripheral retina is most sensitive at low SF
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magno
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glaucoma damages what pathway perferntially
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magno
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when is vision suppressed in saccades
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before
during after |
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why is vision suppressed in saccades
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allows the image not to be blurred with rapid eye movements
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what pathway is suppressed giving rise to saccadic suppression
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magno
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