Lecture 5: Spatial Vision Flashcards

1
Q

state what is spatial vision

A

visual system’s ability to detect and analyse changes in brightness across space

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2
Q

explain detection acuity task

A

perception of the absence or presence of an aspect of the stimuli

eg. landolt C, tumbling E

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3
Q

explain recognition acuity task

A

requires naming of a target

eg. snellen letter chart, near reading chart

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4
Q

explain resolution acuity task

A

ability to detect a gap/separation

eg. grating acuity

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5
Q

explain localisation acuity task

A

ability to discriminate differences in spatial position (stimulus aligned or not) of a test object

eg. vernier acuity

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6
Q

explain hyperacuity

A

when some aspects of vision are so sensitive that they cannot be explained by dense packing of cones. hyperacuity arises from cortical processing

eg. vernier acuity, stereoacuity (3D), sharpness/roughness of an edge

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7
Q

explain diffraction

A

diffraction is the spreading of light (in airy pattern) after it passes through an aperture (pupil)

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8
Q

explain rayleigh’s criterion and equation (MAR)

A

rayleigh’s criterion states that 2 objects will just be resolved if the diffraction minima of 1 light source corresponds with the maxima of another

angular resolution = 1.22(lamda) divide by pupil diameter

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9
Q

explain scoring in LOGMAR charts

A

tested at 4m, snellen notation as eg. 4/10

score for each decreases by 0.1 starting from 1.0

wrong answer plus 0.02. bigger the score, the worse the VA

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10
Q

explain spatial modulation transfer and contrast sensitivity function

A

SMTF describes how an optical system transfers information. CSF presents how humans ‘transfer and process’ visual information

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11
Q

explain how to obtain CSF

A

(1) present a grating of a specific spatial frequency
(2) slowly increase the contrast of grating from NS to S (sensitivity = 1/threshold)
(3) repeat for a range of spatial frequencies

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12
Q

explain shape of CSF (receptive fields)

A

*anything under graph is SEEN

a ganglion cell’s receptive field has an ON centre and OFF surrounding

ON - cell is excited, OFF - cell is inhibited

at middle spatial frequencies, there is HIGHER EXCITATION as the light part of the sine grating falls on the ON centre while the dark parts falls on the OFF surround.

at low spatial frequencies, there is LESS RESPONSE as light parts fall on ON centre & OFF surround simultaneously. OFF surround cancels some excitation response in the centre hence lateral inhibition

the cut off at high spatial frequencies (30cpd/60cpd), due to the limitation of optical system to resolve details

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13
Q

explain relation between CSF & resolution acuity

A

CSF tests the eyes ability to resolve details for various contrasts. typical snellen acuity tests only for high contrast

  • 30 cpd = 6/6
  • 60 cpd = 6/3
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14
Q

explain CSF in refractive error vs cataract

A

uncorrected refractive error results in loss at HIGH spatial frequencies

cataract results in loss at ALL spatial frequencies

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15
Q

explain effect of luminance + location of ret on CSF

A

CSF declines with luminance

CSF varies with retinal eccentricity (reduced in periphery & highest in central)

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