Msp 2 Exam 1

Front 1

what is a point spread function

Back 1

1. image that an optical system forms of a point source
2. most fundamental obj.
3. forms basis for any complex object

Front 2

what is the perfect optical system for a point spread function

Back 2

AIRY DISC

Fraunhofer diffraction pattern for a circular pupil

Front 3

what is the relationship between airy disc and pupil size

Back 3

theta=1.22(lambda)/(pupil diameter)

increase in AIRY DISC=decrease in pupil diameter

Front 4

what is the cut off frequency of a normal pupil (2.5mm) modulation transfer function

Back 4

~60 cycles/deg (aka: cpd)

spot diameter corresponding to 60cpd is approx. 30 seconds of arc.

Front 5

what if the spot diameter is smaller than 30 secs of arc

Back 5

TREATED AS A POINT!!

1. produces approx. the same spatial distribution of light on the retina (retinal light distribution)
2. light will be less for a smaller spot

Front 6

what is line spread function

Back 6

convolution of point spread functions along a straight line

Front 7

detection threshold in relation to perceived size

Back 7

1. spot larger than 30 sec of arc all have different retinal light distributions
2. perceived size of a point can depend upon the observers detection threshold

Front 8

point spread function vs. pupil size

Back 8

1. increase in pupil size = increase in aberrations
2. increase in pupil size=decrease in airy disc

Front 9

why do we treat spots smaller than 30 sec of arc as a POINT STIMULUS

Back 9

any spot smaller than 30 sec of arc will have the same light distribution on the retina

Front 10

what is the considered a complete description of the eye's optical system? why?

Back 10

1. optical MTF
2. the optical performance of the eye and the OMTF depends on pupil diameter
3. high spatial freq cutoff of the eye's OMTF is highest for a pupil diameter ~2.5mm

Front 11

pupil size for narrowest point spread functions and best acuity?

Back 11

2.0-5.0mm

Front 12

what happens when the pupil is smaller than 2mm?

larger than 5mm?

Back 12

diameter smaller than 2mm:
1. wider PSF
2. poor acuity due to diffraction

diameter greater than 5mm:
1. wider PSF
2. poorer acuity due to peripheral optical aberrations

Front 13

what is minimum visible (detection) acuity

Back 13

INCREMENT THRESHOLD

1. angular subtense of the smallest object that can be detected visually AT VERY HIGH CONTRAST
2. acuity depend on contrast of the test target
3. quoted at 1 second of arc

Front 14

what is minimum localizable acuity

Back 14

Relative Spatial Localization
Hyperacuity

1. threshold (in visible angle) for a reliably discriminating small differences in the position of one object relative to another
2. threshold 4-10 arc seconds
3. very resistant to optical blur

Front 15

what is vernier acuity

Back 15

1. subject is asked to indicate the spatial location of one target with respect to one or more other targets
2. changing the line length and spacing between the line effects the acuity

Front 16

what is another term for minimum separable acuity? what is it?

Back 16

resolution acuity: spatial resolution

the minimum visual angle between two objects or contours for them to be reliably discriminated as separated and distinct from on another

Front 17

what are the requirements for minimum separable acuity

Back 17

1. good change in luminance discrimination (low contrast threshold)
2. relative spatial localization (hyperacuity)

Front 18

what are the THREE requirements for recognition acuity

Back 18

1. good change in luminance discrimination (low contrast threshold)
2. relative spatial localization (hyperacuity)
3. prior experience of the object, memory and recognition ability

Front 19

what is recognition acuity (VA)

Back 19

the smallest visual angle of critical detail needed to accurately identify an object

Front 20

what does measurement error of acuity depend on

Back 20

1. number of measurements made
2. slope of the psychometric function (steep slope gives a narrow range of error)

Front 21

what are NINE factors contributing to visual spatial resolution and recognition acuity

Back 21

1. pupil size
2. mean luminance (adaptation level)
3. contrast
4. stimulus orientation
5. retinal position
6. optical blur
7. crowding
8. motion velocity
9. age

Front 22

what is the effect of orientation on acuity

Back 22

1. vertical orientation is best
2. horizontal orientation is just as good
3. oblique orientation result in the WORST ACUITY

Front 23

LARGER LogMAR...

LARGER SNELLEN fraction...

Back 23

1. LARGER LogMAR, worse acuity

2. LARGER SNELLEN fraction, the better the acuity

Front 24

what is crowding effect

Back 24

1. normal: VA is poorest when there are neighboring contours within 2-5 arc minutes of the test target
2. strabismic amblyopes: significantly greater effect (requires target isolation)

Front 25

what is motion effect and dynamic acuity

Back 25

1. velocities lower than ~3-4 deg/sec can be tolerated with light, VA loss
2. obj motion lower than ~60-80 deg/sec can be tolerated with little loss of acuity as long as eye and head pursuit movements are not restrained

Front 26

what is the difference between weber contrast and michelson contrast

Back 26

1. weber: used when studying the visibility of APERIODIC stimuli
2. Michelson: used when studying the visibility of PERIODIC stimuli

Front 27

what is contrast threshold

Back 27

minimum luminance modulation required for the subject to see the grating (rather than just a gray field)

Front 28

what does contrast sensitivity function combine

Back 28

the sum of the components contributed by the optics (MTF) and the neuroretinal enhancement (RTF)

Front 29

at what spatial frequency (cpd) has the highest contrast sensitivity

Back 29

6-8 cpd

cutoff is at 60cpd

Front 30

in respects to contrast sensitivity which is more debilitating...optical blur or glare

Back 30

GLARE!!!

1. people usually adapt to the refractive errors

Front 31

what is the reason for low sensitivity in infants?

what is the reason for low resolution in infants?

Back 31

1. low sensitivity: result from photoreceptor morphology
2. low resolution: results from photoreceptor density

Front 32

what animal is closest to humans in CSF

Back 32

MACAQUE

Front 33

how is MTF used

Back 33

evaluates the quality of an optical system by comparing contrast in the image to contrast of the object, for various spatial freq.

Front 34

how are square wave gratings created

Back 34

1. summing a set of sinusoidal gratings of INCREASING FREQ and DECREASING CONTRAST
2. the contrast of the lowest spatial frequency sinusoidal grating is greater than the square wave grating

Front 35

what were the results of the campbell and robson findings

Back 35

detection threshold for square wave gratings were NOT the same as the for sin gratings of the same spatial freq

at threshold, sin gratings and square wave gratings look the same (only the largest sin component of the square wave was visible)

Front 36

in respects to threshold what is the difference between sin and square wave gratings

Back 36

thresholds were typically 1.27x lower for square vs sin gratings of the same spatial freq

Front 37

what happens with CSF during mild refractive error, visual deprivation and mild amblyopia

Back 37

1. contrast sensitivity same as normal
2. high spatial freq loss

Front 38

what happens with CSF during multiple sclerosis

Back 38

1. mid to low spatial freq. loss
2. decrease in contrast sensitivity

Front 39

what happens with CSF during cataracts, severe refractive error and severe amblyopia

Back 39

BOTH contrast sensitivity AND spatial frequency DECREASES!!

Front 40

what happens with CSF during paracentral glaucoma

Back 40

looks kinda normal but a little NOTCHED

Front 41

what are some psychophysical evidence for multiple spatial frequency channels

Back 41

1. SF size adaptation
2. SF size induction
3. SF masking
4. sub-threshold summation

Front 42

spatial frequency in respects to selective adaptation

Back 42

1. prolonged viewing of a high contrast pattern makes subsequently viewed patterns harder to see

ADAPTATION RESULTS IN:
1. single mech. model: a drop in CS across all SF
2. multi. filter models: a loss in sensitivity limited to a narrow range of spatial freq centered on the adapting SF

Front 43

what happens if you stare at a specific spatial freq for a while?

Back 43

Adaptation will kick in

LOW SF will appear LOWER
HIGH SF will appear HIGHER

Front 44

what is size (SF) induction

Back 44

two same sized objects:
1. surround one with bigger objects then the original object will look smaller
2. surround one with smaller objects then the original objects will look bigger

Front 45

what is spatial frequency masking

Back 45

1. if you have a low SF object surrounded by a lot of high SF object...the high SF will MASK the low SF object
2. in order to see the low SF object amongst the chaos you have to apply a LOW PASS SPATIAL filter.

vis versa

Front 46

what are evidences of orientation channels

Back 46

1. orientation adaptation
2. orientation induction
3. orientation masking
4. sub-threshold summation

Front 47

what is subthreshold summation

Back 47

if the contrast of 2 gratings are below threshold are added together will exceed threshold and become visible...BUT ONLY IF their SF are similiar enough for them to share the same channel

if each stimulate different channels, the sum should NOT be visible