Lecture 4 Flashcards
what are 5 possible types of binocular interaction or summation?
facilitation, complete summation, partial summation, no summation and inhibition
which category of binocular interaction/summation do normal binocular observers fall under?
partial summation
what is the degree of binocular interaction characterized by?
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
what is facilitation?
both eyes together is greater than the sum of the two individual eyes (both > L + R)
what is complete summation?
both eyes together are equal to the sum of the two eyes (both = L + R)
what is partial summation?
both eyes together are slightly less than the sum of the two eyes (Both < L + R, but > L or R)
what is no summation?
each eye functions on its own (both = L or both = R)
what is inhibition?
both eyes together is worse than each eye on its own (both < L or both < R)
what is probability summation or the independent theory?
simply by adding one more detector, you have 40% better chance of detecting a stimulus than one detector (no interaction between eyes)
what is neuronal summation or interaction theory?
when stimuli are synchronous in space and time - binocular vision is stimulated (much better chance of detection than predicted by statistics)
what are some examples of visual functions that show binocular summation?
threshold light detection, CFF (goes up), contrast threshold (goes down), resolution threshold (goes up), brightness and interocular transfer
how much does our contrast sensitivity function (CSF) improve from monocular to binocular? what happens to the threshold?
about 40% improvement and threshold goes down
what type of spatial frequency does contrast sensitivity function improve with binocular vs. monocular?
all spatial frequencies (low and high)
what happens to binocular contrast sensitivity with monocular blur?
binocular contrast sensitivity declines with increasing blur - with significant blur inhibition occurs
at what amount of retinal blur is binocular sensitivity worse than monocular?
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)
what happens to critical flicker fusion frequency (CFF) with binocular summation?
the binocular percept is higher than with monocular - if it is in phase (out of phase will cancel)
what type of binocular interaction is occurring in low temporal frequency CFF?
facilitation
what type of binocular interaction is occurring in middle temporal frequency CFF?
complete summation
what type of binocular interaction is occurring in high temporal frequency CFF?
partial summation - light flickers so fast that binocular summation goes down
what type of binocular summation is seen in visual acuity testing?
partial binocular summation (binocular VA > monocular VA)
what happens to brightness when there are small interocular luminance differences?
they are averaged together
what happens to brightness when there are large interocular luminance differences?
leads to suppression of the dimmer eye (similar effect as monocular retinal blur: +10D)
what is the tilt aftereffect?
a visual illusion - fatiguing specifically tuned visual neurons monocularly
what is the interocular transfer of tilt aftereffect? (after fatiguing one eye and then viewing the target with the other eye)
the after effect isn’t as strong as viewing it with one eye - evidence for neurons receiving binocular input
will patient will disrupted binocularity (like strabismus) have an interocular transfer?
no
when is binocular summation a disadvantage?
when flashing/flickering can trigger an epileptic attack (closing one eye can decrease this effect - CFF is lower monocularly)
what is binocular suppression or rivalry?
when dissimilar images fall on corresponding points
what is gross binocular suppression?
the entire image from one retina is being suppressed
what is central (focal) binocular suppression?
when the fovea in one eye is being suppressed
when is physiological suppression unilateral?
if the different image qualities are: monovision, significant uncorrected anisometropia or monocular macular pathology
when is physiological suppression alternating?
if similar image qualities have binocular rivalry
what is physiological suppression?
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
what is pathological suppression?
suppression induced by stimulus condition which cause fusion in normals or a response to prolonged diplopia
how does the worth 4 dot underestimate suppression?
darkness, absence of a textured background, and using red/green glasses all weaken the true amount of suppression
what is the size of an exotropia binocular suppression scotoma?
usually more extensive suppression - entire temporal hemiretina
what is the size of an esotropia binocular suppression scotoma?
size correlates to the size of the angle of deviation (smaller tropia = smaller scotoma)
why might a scotoma be missed in a small angle ET when testing the worth 4 dot at near?
because the angular subtence of stimulus is larger than the scotoma size
how can you make sure that you are not missing a scotoma in a small angle ET while using the worth 4 dot test?
“walk away” = at a certain distance the stimulus will fall into the scotoma and it will be suppressed
what is binocular rivalry?
vision which alternates between the eyes in part or all of visual space
when does binocular rivalry occur?
when very different images of equal salience fall on corresponding points - similar in spatial frequency or contrast
what happens when two stimuli are of unequal strength during binocular rivalry?
the stronger stimulus will dominant a greater proportion of the time - more than 50% of the time (if equal stimuli = equal proportion)
what is binocular luster?
a special form of rivalry - when two identical images have opposite contrast signs, the fused image contains a combination of both percepts
