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Vision Science 5 > Lecture 4 > Flashcards

Lecture 4 Flashcards

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1
Q

what are 5 possible types of binocular interaction or summation?

A

facilitation, complete summation, partial summation, no summation and inhibition

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2
Q

which category of binocular interaction/summation do normal binocular observers fall under?

A

partial summation

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3
Q

what is the degree of binocular interaction characterized by?

A

whether the binocular performance on a task (sensitivity for detecting contrast or an acuity target) is greater than, equal to or less than the performance of either eye alone

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4
Q

what is facilitation?

A

both eyes together is greater than the sum of the two individual eyes (both > L + R)

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5
Q

what is complete summation?

A

both eyes together are equal to the sum of the two eyes (both = L + R)

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6
Q

what is partial summation?

A

both eyes together are slightly less than the sum of the two eyes (Both < L + R, but > L or R)

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7
Q

what is no summation?

A

each eye functions on its own (both = L or both = R)

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8
Q

what is inhibition?

A

both eyes together is worse than each eye on its own (both < L or both < R)

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9
Q

what is probability summation or the independent theory?

A

simply by adding one more detector, you have 40% better chance of detecting a stimulus than one detector (no interaction between eyes)

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10
Q

what is neuronal summation or interaction theory?

A

when stimuli are synchronous in space and time - binocular vision is stimulated (much better chance of detection than predicted by statistics)

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11
Q

what are some examples of visual functions that show binocular summation?

A

threshold light detection, CFF (goes up), contrast threshold (goes down), resolution threshold (goes up), brightness and interocular transfer

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12
Q

how much does our contrast sensitivity function (CSF) improve from monocular to binocular? what happens to the threshold?

A

about 40% improvement and threshold goes down

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13
Q

what type of spatial frequency does contrast sensitivity function improve with binocular vs. monocular?

A

all spatial frequencies (low and high)

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14
Q

what happens to binocular contrast sensitivity with monocular blur?

A

binocular contrast sensitivity declines with increasing blur - with significant blur inhibition occurs

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15
Q

at what amount of retinal blur is binocular sensitivity worse than monocular?

A

more than +1.50D to +2.00D (why monovision patients may not be able to accept more than this difference in focus between both eyes)

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16
Q

what happens to critical flicker fusion frequency (CFF) with binocular summation?

A

the binocular percept is higher than with monocular - if it is in phase (out of phase will cancel)

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17
Q

what type of binocular interaction is occurring in low temporal frequency CFF?

A

facilitation

18
Q

what type of binocular interaction is occurring in middle temporal frequency CFF?

A

complete summation

19
Q

what type of binocular interaction is occurring in high temporal frequency CFF?

A

partial summation - light flickers so fast that binocular summation goes down

20
Q

what type of binocular summation is seen in visual acuity testing?

A

partial binocular summation (binocular VA > monocular VA)

21
Q

what happens to brightness when there are small interocular luminance differences?

A

they are averaged together

22
Q

what happens to brightness when there are large interocular luminance differences?

A

leads to suppression of the dimmer eye (similar effect as monocular retinal blur: +10D)

23
Q

what is the tilt aftereffect?

A

a visual illusion - fatiguing specifically tuned visual neurons monocularly

24
Q

what is the interocular transfer of tilt aftereffect? (after fatiguing one eye and then viewing the target with the other eye)

A

the after effect isn’t as strong as viewing it with one eye - evidence for neurons receiving binocular input

25
Q

will patient will disrupted binocularity (like strabismus) have an interocular transfer?

A

no

26
Q

when is binocular summation a disadvantage?

A

when flashing/flickering can trigger an epileptic attack (closing one eye can decrease this effect - CFF is lower monocularly)

27
Q

what is binocular suppression or rivalry?

A

when dissimilar images fall on corresponding points

28
Q

what is gross binocular suppression?

A

the entire image from one retina is being suppressed

29
Q

what is central (focal) binocular suppression?

A

when the fovea in one eye is being suppressed

30
Q

when is physiological suppression unilateral?

A

if the different image qualities are: monovision, significant uncorrected anisometropia or monocular macular pathology

31
Q

when is physiological suppression alternating?

A

if similar image qualities have binocular rivalry

32
Q

what is physiological suppression?

A

two eyes are equal in their contribution to the binocular system - the eye presented with the weaker (less salient) image will be suppressed = dimmer, lower contrast, blurred

33
Q

what is pathological suppression?

A

suppression induced by stimulus condition which cause fusion in normals or a response to prolonged diplopia

34
Q

how does the worth 4 dot underestimate suppression?

A

darkness, absence of a textured background, and using red/green glasses all weaken the true amount of suppression

35
Q

what is the size of an exotropia binocular suppression scotoma?

A

usually more extensive suppression - entire temporal hemiretina

36
Q

what is the size of an esotropia binocular suppression scotoma?

A

size correlates to the size of the angle of deviation (smaller tropia = smaller scotoma)

37
Q

why might a scotoma be missed in a small angle ET when testing the worth 4 dot at near?

A

because the angular subtence of stimulus is larger than the scotoma size

38
Q

how can you make sure that you are not missing a scotoma in a small angle ET while using the worth 4 dot test?

A

“walk away” = at a certain distance the stimulus will fall into the scotoma and it will be suppressed

39
Q

what is binocular rivalry?

A

vision which alternates between the eyes in part or all of visual space

40
Q

when does binocular rivalry occur?

A

when very different images of equal salience fall on corresponding points - similar in spatial frequency or contrast

41
Q

what happens when two stimuli are of unequal strength during binocular rivalry?

A

the stronger stimulus will dominant a greater proportion of the time - more than 50% of the time (if equal stimuli = equal proportion)

42
Q

what is binocular luster?

A

a special form of rivalry - when two identical images have opposite contrast signs, the fused image contains a combination of both percepts

Vision Science 5 (14 decks)

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