Fusion, Rivalry, and Suppression Flashcards
where does fusion happen in the brain
where do we stop seeing monocularly in the brain
fusion happens in the visual cortex
stop seeing mono in layer 4C of the striate cortex
what are the 2 parts of fusion process
- sensory: images near corresp points are fused
2. motor: move eyes in or out to fuse images at diff distances
what are the 2 types of diplopia, which is abnormal
physiological: nonfixated objects off the horopter
pathological: seeing 2 of the image you are paying attentino to, NOT NORMAL
what is confusion
where is it most visible in
what does it usually accompnay
another name?
when you perceive 2 diff objects to be in the exact same place in the vf
- most visible in foveal vision
- usually accompanies diplopia
- aka binocular rivalry
what is panum’s area
an area on the retina of one eye wehre an image may be placed and still fuse w/ an image at a fixed location in the fellow eye
what is panum’s space
the region of 3D space where singleness is perceived
do all points fused in panum’s area appear in the same location in visual space
no-each diff pair of retinal points in PA creates a unique stereo depth and direction in visual space so there is no loss of spatial info w/ fusion
where is the horopter in panum’s space
in the middle
what is allelotropia
the oculocentric directions of fused images are averaged to form a cyclopean direction
-direction averaging process is influenced by ocular dominance
how is PA related to retinal eccentricity
PA size increases w/ retinal eccentricity
when patients report diplopia, where is it usually from
foveal
-it is not easily observed in peripheral vision
how does PA change in the periphery
increases as you move out to the periphery
what kind of motion increase the size of PA
target motion and patient motion
higher spatial freq (sharp edges) are associated w/ ____ PA size
smaller
what are the various sizes taht have been reported for foveal panum’s area?
using what kind of things?
2’ (woo, using fine bars)
6’ (ogle, using horopter rods)
15’ (mitchell, using small flashing spots)
how is PA shaped for very brief stimuli?
how is it shaped for long duration stimuli?
how is it shaped for static targets?
how is it shaped for foveal?
- round for brief
- PA diamter slightly increased vert and greatly increased horiz (3x) for long duration
- horizontal ellipse for static
- elliptical for foveal
how is panum’s area is strabismic patients
most constant strabismus have no fusion or panum area
why do patients w/ microtropia have single peripheral vision
-ocular misalignment is too large in microtropes to allow images to fall w/in normal panum’s area in the foveal macular area
how does PA develop in pts w/ constant microtrope strab
very large panum’s areas in the periphery
what is binocular summatino
a change of nonspatial quality of vision caused by binocular interaction
what are the possible levels of mathematical binocular summation
- facilitation: when stimulus is more than twice as bright OU than w/ one eye. 1+1>2
- complete summation: when stimulus is twice as bright OW
1+1=2 - partial summation: when stimulus is brighter OU
1+1=1.5 - zero summation: when stimulus is as bright OU
1+1=1 - inhibition: when stimulus is not as bright OU
1+1<1
what is most binocular summation in terms of math
zero summation or partial summation
how do eyes behave for dim scotopic images falling outside panum’s area
weak stimuli more detected w/ 2 eyes than 1 bc you get 2 changes of detection
how is binocular summation related in CFF, contrast threshold, and resolution threshold
CFF: goes up
contrast threshold: goes down
resolution threshold: goes down bc of contrast threshold
how are small differences in luminance and large difference in luminance handled by the brain
small: averaged by the brain
large: not averaged and the dimmer eye is suppressed
what is color luster
for small differences of color btwn the 2 eyes image, we average them
what color does the eye end to see more w/ brighter luminance? dimmer luminance?
brighter: eye tends to see things more towards blue
dimmer: eye tends to see images more toward red
what does the eye do for large differences btwn colors of the 2 eyes
we do not average them
we will see rivalry (see one color then it turns into another, then back to the first)
-rate of alternation is dependent on luminance
what is interocular transfer
when does this happen
binocular vision ells get adapted to a pattern when looking at another pattern and maysee an aftereffect which affects the new pattern
-happens w motion (waterfall effect), tilt, and size
when does suppression occur
when does amblyopia occur
suppression=BINOCULAR VISION, momentary thing
amblyop=monocular vision
what is physiological suppression
a normal form of suppression associated w/ non-horopter objects
- when very dissimular images fall on corresponding points and brain can’t fuse
- when images are of equal contrast, the perosn will perceive these images to be alternating
what is binocular rivalry
2 diff images to the eyes but of equal contrast and importance and sitmulated corresponding points
-brain will go back and forth btwn which image is perceived
if binocular rivalry occurs in foveal vision, the patient will report what
confusion
is rivalry noticed in peripheral vision?
rarely
what are rivalry suppression scotomas
- how are they shaped
- what is there size in panum’s area
regions in the monocular field where the suppression (from rivalry) is occurring
- always round
- twice as large in panum’s area at the same retinal location
- larger in periphery
when is pathological suppression found
early onset binocular abnormalities
-ARC patients
what is pathological suppresion
which eye does it occur
suppresion induced by stimulus conditions which cause fusion in normals: similar images on corresponding points
-non dominant eye
does adult onset strab cause pathological suppression?
no. causes diplopia w/o it
what is a clinical test of suppresion
worth 4 dot test
-underestimates suppression in normal viewing though bc darkness, absence of textured background, red/green glasses (promotes rivalry) weakens suppression
how are pathological suppression and rivalry related
both are stronger for images on corresponding points than noncorresponding points
-image dissimilarity on corresponding points may induce rivalry in both normals and strabs
at minimum, what is the scotomoa size for pathological suppression scotomas
at min the fovea and zero-measure points
