Spatial Vision (M2) Flashcards Preview

II. Neurophysiology and Perception > Spatial Vision (M2) > Flashcards

Flashcards in Spatial Vision (M2) Deck (47):
1

What refers to how the visual system responds to patterns of light and dark across space?

spatial vision

2

What do low-contrast acuity charts tell the doctor about the patient?

know less than normal but not a measure of contrast sensitivity for the patient

3

What allows for Vernier acuity to be so "hyperacute"?

responses to different stimuli overlap or blur occurs

4

What acuities are impaired by strabismic amblyopia? 1. Which are not impaired? 2

1. Vernier and optotype acuities
2. grating acuity

5

What is the type of hyperacuity that is the ability to use the slightly different images in the two eyes to see in depth? 1. Is this better or worse than Vernier hyperacuity? 2

1. stereopsis
2. slightly worse

6

What are the limits on grating resolution acuity?

1. Nyquist limit
2. optical blur
3. light level
4. position on retina
5. rods vs. cones
6. infants vs. adults

7

What are the disorders that affect Vernier acuity?

1. refractive amblyopia
2. strabismic amblyopia

8

For human CSF, what value is usually the peak sensitivity?

5 cycles/degree

9

What are the differences in brightness (and color) of an object with respect to other objects in the field of view called?

contrast

10

What visual disorders can lead to reduced CSF?

1. cataracts
2. corneal conditions (especially LASIK)
3. multiple sclerosis
4. Parkinson's
5. cortical vision impairment
6. albinism

11

Which comes faster for infants: Vernier acuity or resolution acuity?

Vernier acuity (4-6months)

12

What is the reason for low spatial frequency roll-off?

bright bars stimulate whole receptive field so lateral inhibition from the surround cancels excitation in the center

13

Is the logMAR or Vernier acuity better in the visual periphery? 1. In the fovea? 2

1. logMAR better
2. Vernier

14

How many arc sec is the minimum Vernier acuity?

10 arc sec

15

For sine-wave grating, what is the contrast referred to? 1. What is the formula for this? 2

1. Michelson or grating contrast
2. grating contrast =(Lmax - Lmin)/(Lmax + Lmin)

16

What is a discrimination that is finer than the spacing of the rods and cones or by widely-spaced detectors?

hyperacuity

17

What is the overall ability of infant vernier acuity?

it is poor but not that poor once their poor contrast perception is taken into account

18

What is one disorder that does not affect Vernier acuity very much but does affect resolution and optotype acuity?

cataracts

19

What does pre-cataract surgery logMAR predict about post-op logMAR?

doesn't predict post-op logMAR as well as a pre-op hyperacuity

20

What is the shape of the contrast threshold for sine waves?

u-shaped

21

What are the well known low-contrast letter charts?

1. Pelli-Robson chart
2. Bailey-Lovie chart

22

How many arc sec is the minimum resolution acuity?

30 arc sec

23

What are the ways to tell if cataract surgery is going to be helpful to the patient?

1. helpful if no other ocular pathology (but sometimes hard to tell if it's there)
2. use hyperacuity to see if beneficial because poor hyperacuity before the surgery implies some ocular pathology other than catract

24

What is the numerator of the Snellen fraction? 1. The denominator? 2

1. distance at which test was taken
2. distance at which the smallest optotype patient can resolve subtends 5 arcmin

25

What is the minimum detectable offset of two nearly-colinear marks?

Vernier acuity

26

How many arc sec is the minimum optotype acuity?

60 arc sec

27

What is the shape of the contrast sensitivity for sine waves?

n-shaped

28

What are examples of Vernier hyperacuities?

1. leveling
2. centering/bisection
3. spatial frequency discrimination
4. orientation discrimination
5. telling time
6. measuring length

29

In the clinic, what is the minimum angle of resolution of an adult usually determined by?

optotypes rather than gratings

30

What are used as a tool to assess the sensitivity of the visual system to spatial changes in luminance?

sine-wave gratings

31

What is a person's ability to appreciate the locations of stimuli relative to each other?

Vernier acuity

32

What causes the losses in the ocular media, making the Nyquist limit hard to measure? 1-4. What do these all lead to? 5

1. defocus
2. higher-order aberrations
3. scatter in the ocular media and retina
4. stray light not absorbed by the visual pigments or the RPE
5. reduced contrast

33

How do you measure contrast sensitivity?

have subject look at sine-wave gratings of different spatial frequencies and adjust until barely visible

34

How does light affect visual acuity?

more light, more sight until maximum VA achieved

35

Is the Vernier acuity limited by the photoreceptor mosaic? 1. What does blur do to the acuity? 2. Is it better or worse int he periphery? 3

1. no
2. relatively immune to blur (like cataract)
3. worse

36

What is the highest spatial frequency the patient can see at 100% contrast called? 1. What are the common values of this? 2. What is this called overall? 3

1. high-frequency cutoff
2. 30-60 cycles/degree (30-50 in fovea)
3. grating resolution acuity

37

What is the reciprocal of the contrast threshold (the lowest contrast a patient can detect) called? 1. How is this typically measured? 2

1. contrast sensitivity
2. take log of the inverse of the threshold

38

What stops the retina from seeing the strange artifacts that form at above-Nyquist gratings?

blur

39

Do loses in the ocular media reduce contrast more at high or low frequencies?

high frequnecies

40

At the youngest ages, which is better: Vernier acuity or resolution acuity?

resolution acuity

41

What is the highest spatial frequency that can be distinguished from gray at 100% contrast?

grating resolution acuity

42

What is the optically maximum possible resolution acuity? 1. How many stripes per cones is this? 2

1. Nyquist limit
2. one stripe per cone

43

Why is the Nyquist limit not easily measured?

losses in the ocular media

44

Is our contrast better or worse at low spatial frequencies? 1. What is this called? 2

1. worse
2. low-frequency rolloff

45

What is the problem with current common visual acuity charts?

only at high frequency resolution but reduction in low and moderate spatial frequencies can be handicapping

46

What is the characteristic human contrast sensitivity function?

inverted U-shape

47

What is the center to center spacing of cones in the fovea in stripe widths? 1. In spatial frequency? 2. For the Snellen equivalent? 3

1. 30 arc sec (one stripe width)
2. 60 cy/deg
3. 20/10