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TMTV > Chapter 3-Spatial Vision > Flashcards

Chapter 3-Spatial Vision Flashcards

1
Q

what is spatial vision

A

concerned w/ the ability of the visual system on detecting/discriminating spatially defined features

-changes in space

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2
Q

what does the luminance of a square wave grating change as

A

as a step function (only min and max luminace values, no intermediate)

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3
Q

what is the luminance of a sine wave grating change as

A

sinusoidal function

-not only min and max but intermediate also

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4
Q

a luminance grating is defined by its

A

spatial frequency
phase
orientation
contrast

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5
Q

waht is spatial frequency

A

the number of cycles per degree of visual angle

-1 cycle is a dark and a bright stripe

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6
Q

high spatial frequency = ____ cycles per degree of visual angle
low spatial freq = _____ cycles per degree of visual angle

A

more

less

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7
Q

what does phase refer to

A

refers to the position of the cycle that the luminance grating is in at any given time

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8
Q

what is contrast

A

contrast is the difference in luminance often expressed as % contrast

  • detecting the difference in luminance btwn objects
  • difference btwn max and min luminance
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9
Q

if you have a grating w/ a luminance value of 0, how much percent contrast will you have, no matter what the luminance

A

100%

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10
Q

what is spatial resolution

A

the smallest spatial detail that can be detected, recognized or resolved

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11
Q

what is target detection

A

the perception (or not) of the presence of an object

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12
Q

what is target recognition

A

recognition and naming of the target (snellen)

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13
Q

what is target resolution

A

the minimum angular size at which 2 objects can be discriminated as 2 diff objects

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14
Q

what is target localization

A

requires discrimination in the spatial position of objects (vernier acuity)

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15
Q

all the tests for spatial resolution, involving or not cognitive mech, are limited by what

A

optical and neural factors that determine the lmit of spatial resolution

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16
Q

target localization, detection and resolution give VA higher than the typical VA (landolt C or recognition) indicating that mechanisms involved in making such judgements (recognition) are…

A

not restricted to the retinal level

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17
Q

what are the limiting factors for the spatial resolution if we assume that the eye’s optical system are aberrations free

A

optical: diffraction
neuronal: cone density

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18
Q

what is diffraction

A

pheno when a lightwave encounters an obstacle

-due to diffraction the light wave bends and separates

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19
Q

what is the point spread function

A

describes the transformation that a point source undergoes as it passes through the optical elements of the eye

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20
Q

in photopic conditions, our spatial resolution limit due to diffraction cant be any better than waht

A

0.4 arcmins

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21
Q

if there are no aberrations in the eye’s optical system then a point source would be the size of an airy disk and the optical system is limited by….

A

diffraction

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22
Q

will high or low freq be afftected more by diffraction

A

high

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23
Q

what is the rayleigh criterion

A

2 point sources can be resolved as 2 separate point sources only when the centers of their airy disks are no closer than the radius of the airy disks

24
Q

what does the rayleigh criterion mean for the spatial resolution of the visual system?

A

in order to resolve 2 point sources, 2 cones must be stimulated w/ light while there is an unstimulated ocne btwn them

25
Q

what is the cone spacing in the fovea

A

2.8 micrometers

26
Q

what is aliasing

A

the effect that causes diff signals to become indistinguishable

27
Q

when does aliasing start

A

for freq higher than the nyquist limit

28
Q

what is the max freq called

A

nyquist limit

29
Q

what is the resolution of smaller pupils limited by

A

diffraction

30
Q

what is the resolution of larger pupils limited by

A

cone density

31
Q

what are some disadvantages to the snellen chart

A

the letter size doesnt chnage uniformly throughout the test

  • not equal number of letters on each line
  • not regular spacing btwn the letters
32
Q

what does the logMAR chart use

A

log of the MAR to get a uniform progression of letter size throughout the chart

33
Q

what are the advantages to logMAR

A

uniform profession in letter size from line to line

  • same number of letters on each line (crowding)
  • regular spacing btwn lines
  • greater accuracy
34
Q

for VA charts,
rule 1: the MAR is the ____ of decimal VA
rule 2: the spatial freq (in cycles/degree) is equal to the decimal x ____

A

reciprocal

30.00

35
Q

what are the factors affecting spatial resolution

A 
refractive error
pupil size
illumination
contrast
retinal area
36
Q

we need higher contrast for detecting what?

we need lower contrast for detecting what?

A

high spatial frequency gratings

low spatial freq gratings

37
Q

what does the contrast sensitivity function describe

A

the contrast sensitivy of the human visual system for diff spatial freq

38
Q

what is the highest contrast sensitivity that occurs for spatial freq

A

~4c/deg

39
Q

for freq lower and higher than 4c/deg there is a what

A

low freq drop-off and a high freq cut off

40
Q

what is CSF often described as

A

band-pass function

41
Q

waht does CSF tell us (contrast sensitivity function)

A

that our visual system is more sensitive for spatial freq around 4cycles/degree
-either side of this freq, our contrast sensitivity drops

42
Q

what does the peak contrast sensitivity at 4c/deg mean

A

the majority of the receptive fields respond optimally at this spatial freq
OR
the majority of the receptive fields have such a size so as to respond to 4c/deg

43
Q

waht is the low freq drop out

A

the decline in contrast sensitivty at low spatial freq provides info about the strenth of spatial antagonism (or later inhibition)

44
Q

what is peak sensitivyt

A

the most effective spatial freq provides info about the overall size of the receptive fields

45
Q

in low freq drop off…
as the spatial freq increases a single bring (or dark) band occupies both the center and the surround of the recptive field, cuasing what

A

lateral inhibition

-this means that the center respons to the band but the surround doesnt, resulting in NO REPONSE from this RF

46
Q

in high freq cut-off..
the decline in contast sensitity at high spatial freq is bc the stimulus is avged by the center and surround of the receptive field, doing what

A

diminishing the cell’s response

47
Q

in high freq cut off

as the spatial freq decreases, the avg response of the center and the surround is decreasing, resulting in what

A

a decrease in contrast sensitivity

48
Q

waht is our maximum cycles/degree

A

60 cyc/deg

49
Q

if the highest spatial freq is 60c/deg then snellen VA will be what, if its 30c/deg what will it be

A

20/10

20/20

50
Q

how is snellen VA related to CSF

A

snellen VA is just a point on the CSF

so CSF provies much more info about the integrity of the visual system than VA

51
Q

what are the factors affecting contrast sensitivty

A
  1. retinal illumination
  2. refractive error
  3. media transparency
  4. reintal and systemic diseases
  5. sine vs square wave gratings
52
Q

what is band pass

A

certain range of visible freq that can be seen in photopic conditions

53
Q

is the human visual system more sensitive to square or wine wave gratings

A

square
1.27x more for frequ more than 1c/deg
for sptial freq less than 1c/deg the ratio increases

54
Q

what happens for spatial freq lower than 1c/deg on the CSF

A

the contrast sensitivity of a square-wave grating is defined by the contrast sensitivy of a series of sine-wave grating

55
Q

for spatial freq lower than 1c/deg the contrast sensitivity of a square-wave grating is defined by what

A

the fundamental and higher order harmonics

56
Q

if someone adapts (stares for a prolonged time( to a sine wave grating of ex. 4c/deg then there is a reduction in the CSF around….

A

4c/deg

TMTV (5 decks)

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