Binocular depth processing: neural basis or stereopsis or solid 3D vision Flashcards
which two types of pictorial cues allows to achieve stereopsis with only one eye
- interposition - in real 3D world, can tell e.g. the zebra is standing in front of the striped wall as the zebra is masking the stripes on the wall i.e. it is interposed between the observer and the background
- shadowing - demonstrated when the sun is shining from one direction, it creates shadows which gives off a strong 3D piece of information
what is the origin of the ability to use 2 eyes & extract a third dimension/binocular stereopsis
optic geometry
- horizontal separation of 2 eyes - each eye has slightly different view on the world due to separation which…
- generates disparities between 2 retinal images
what is the perception of binocular stereopsis achieved from
visual cortex
- primary v1 cortex + numerous extra striate areas
- single neurons tuned to different retinal image disparities = disparity detectors (neurons in the extra striate cortex)
what part of binocular stereopsis enhances depth discrimination
- stereo acuity (clinical grades & tests)
- /~100 arc secs = coarse/reduced (defect in stereo acuity), tests are usually placed at 40cm where the two eyes can tell how far something is which can’t do with one eye
what is the vieth-muller circle also known as
the horopter
when the foveas of both eyes are looking at the same place, what property will the images have
they will have no disparity = 0 i.e. the two images are in retinal correspondence as there is no difference in how far away from you that you can perceive that fixation point to be
why is the fovea not the only part in the retina where there in retinal correspondence/0 disparity
for every point on your right retina, there will also be a part on your left retina which is looking at the same point in space = object with 0 disparity & there is correspondence
what does the horopter represent
in reality there is a hemi sphere all around the head, on this hemi sphere, every point will be the exact same distance away from you, as the fixation point is
what is non correspondence in relation to the horopter
if object is beyond or before the horopter, it will form a disparity between both eyes
what are the two points of non correspondence/properties of disparity
- sign
nearer than the horopter causes crossed (-ve) disparity
further than the horopter causes uncrossed (+ve) disparity - size
disparities increase with distance from the horopter
what is the sign of disparity when the image is to the right in the right eye and to the left in the left eye
uncrossed +ve disparity
what is the sign of disparity when the object is slightly to the left in the right eye and slightly to the right in the left eye
crossed -ve disparity
what does a large disparity cause and why
diplopia due to narrow range wither side of the horopter
what is referred to as panum’s fusional area
fixation plane in which you can fuse two images, even though they are slightly different in two eyes, that region of space is the panum’s fusional area
where is the width of panum’s fusional area narrow
around the fovea = narrow region of 3D space
where does panum’s fusional area get broader and why
further out in the eccentricity, because the brain is able to tolerate the slop is disparities in a more eccentric location, compared to a point in fixation i.e. stereo acuity is better if closer to the fovea & worse out in periphery
what are the nasal axons of RGCs that cross over at the optic chiasm and have neurons that go to certain layers of the LGN on the other side, look at the same point in space as
temporal axons of RGCs that do not cross over at the optic chiasm and have neurons that go to certain layers on the LGN on the same side
name the steps in which the neurons take after they leave the LGN
- dive into posterior limb of the internal capsule
- up the optic radiations
- end up in primary v1 cortex
- layer 4c called granule cells (little local circuit neurons) which only receive information from one eye from same point in space
- granule cells have neurons which come out & make connections with granule cells in layers above and below layer 4c
- these connections coverage from left and right eyes onto single neurons of layers above and below e.g. pyramidal cells in layer 3
- which are interested in information from both left and right eyes
which cells are only interested in information from one eye/monocular
connections from LGN to primary v1 cortex to layer 4c
which cells are interested in information from both eyes/binocularly
layers above and below layer 4c
how much % of v1 cells beyond 4c are binocularly driven (excited by stimuli presented to both eyes)
75%
what do all binocular driven cortical cells have in similarity
receptive fields in the left and right eyes
what do all binocular driven cortical cells have similar RFs in respect to
- spatial location (come from same point in space)
- preferred orientation (e.g. if likes vertical lines as seen from left eye, will like vertical lines as seen from right eye)
- preferred spatial frequency
- organisation i.e. simple, complex, hypercomplex
e. g. if complex cells will be the same in right and left eye as those binocular cells are looking at same point in space with right and left eye, so interested in the same stimulus properties
what do binocular driven cortical cells differ in
their
- preferences for horizontal stimulus disparity
- small spatial offsets in their left vs right eye RF positions (known as positional disparities) i.e. Rsf are not completely super imposed in space, sometimes they are slightly crossed in left and right eyes or uncrossed = RF offsets
what are the responses of 75% of binocularly driven cells in v1 cortex influenced by
the horizontal disparity between stimuli presented to the left and right eyes
how many % of binocularly driven cells in v1 cortex are not influenced by horizontal disparity between stimuli presented to the left and right eyes
25% do not care about disparity at all
what do different disparity tuned cells show selectivity for a specific..
- sign & size of disparity (including zero)
some are tightly tuned for size & sign of the disparity - there are some that are only interested in sign alone, responding to a range of crossed (near) OR increased (far) disparities
what are neurons in layer 4c sitting side by side receiving input from
two eyes in same point in space
in the granule cells in layer 4c have axons that go up & make excitatory connections with pyramidal cells directly above, what is there a good chance of
that this pyramidal cell will be looking at the exact point in space through both eyes together = their binocular RFs will be in perfect correspondence, with 0 disparity
what happens to the RFs is the pyramidal cells are slightly offset
RFs are disparate which contributes to disparity amongst neurons in v1
list the 6 classes of disparity tuned cell in monkey v1
- tuned excitatory near
- tuned excitatory zero
- tuned excitatory far
- tuned inhibitory near
- tuned inhibitory zero
- tuned inhibitory far
why are the 6 classes of disparity cells tuned
they like only one disparity ± a tiny bit
why are 3 classes of disparity tuned cells excitatory
because their response to their preferred disparity is based on facilitation (multiplying)
what do the horizontal lines mean in the graphs of the 6 classes of disparity tuned cell
disparity of left eye alone of disparity go right eye alone, if added together = binocular disparities = binocular summation (just adding) if (multiplying = binocular facilitation)
which RGC cellular processing acquires fine stereo acuity
parvo cellular
which RGC acquire/contribute to coarse stereo acuity
parvo % magno
what does a lesion to the parvo cellular processing cause
reduction in fine (high grade) stereo acuity
how many % of cell are tuned excitatory/inhibitory for retinal correspondence/zero disparity
25%
what are fine stereopsis disparity concerned with
size and sign
which angle of disparity is considered for fine stereopsis
<0.5 deg arc + near horopter
what accounts for 40% of fine stereopsis
tuned excitatory cells, binocular facilitation
what is coarse stereopsis disparity concerned with
sign only (unable to tell its magnitude)
which angle of disparity is considered for coarse stereopsis
± 1 deg arc crossed or uncrossed
what accounts for 33% of coarse stereopsis
near & far cells, binocular summation
which RGCs contribute to coarse stereopsis
parvo & magno
what does local stereopsis require
- disparity between isolated points in space, formed by…
- object or surface which must have a solid form (real things)
what does global stereopsis require
aka cyclopean
- disparity across multiple points in space
- generates solid ‘3D shape from disparity’
- exploited in random dot stereograms
what is local and global stereopsis two types of
disparity detection
which neurons respond similarly to both types of stereo cue (local & global)
disparity tuned v1 neurons
list the clinical grades from lowest to highest
- simultaneous perception
- binocular single vision
- depth perception/stereo acuity
what neural requirements are there for simultaneous perception
monocular inputs from each eye
i.e. two eyes which are working quite well and are fine e.g. can be a person with a squint who can do alternating fixation as they have good VAs in each eye but no stereo
what neural requirement is there for binocular single vision
combine corresponding retinal inputs in visual cortex
what type of test is required to test for binocular single vision
bagolini striated glasses
what neural requirement is there for depth perception/stereo acuity
be able to compare disparate retinal inputs in the visual cortex
what are the grades associated with depth perception/stereo acuity
fine vs coarse vs absent
what type of test is required to test for depth perception/stereo acuity
stereo-grams
what do cells in v1 respond to (i.e. where the pastor plots are the same)
lines - solid figure stereo grams
&
random dot - cyclopean stereogram
what do single cell recordings show all extra striate cortex to contain
disparity tuned cells
which part of the extra striate cortex contains the highest % in disparity tuned cells
dorsal stream - spatial-motion-action vision areas
eg V3A, V7, V5/MT & MST
as well as the dorsal stream containing most % of disparity tuned cells, which other area contains just as much & more than area v1
ventral stream eg IOT/LOC
how many % of disparity tuned cells does v1 contain
50%
list the wide spread cortical regions activated by binocular disparity (3D vs 2D stimuli)
- area v1 + occipital extra striate areas v2 - v7
- parietal cortex - banks of the IPS & SPL
- pre motor cortex
- cerebellar cortex
which areas are activated by 3D shape from disparity processing
mainly superior occipital cortex areas V3A & V7
& various areas along the intra-parietal sulcus (IPS)
with smaller foci ventrally in the posterior ITG/area LOC
what type of infarct causes impaired distance & depth perception
bilateral occipito-parietal infarcts: superior occipital V3A/V7 + inferior & caudal IPS in each hemispheres
what remains intact with someone who has impaired distance & depth perception
- VFs
- VA
- colours
- familiar/novel object size estimation & recognition
what does a patient who has impaired distance & depth perception often experience
they often misjudge distances
- bump into objects & accidentally poked people in the face
- couldn’t explain why this is happening
distance, depth & other deficits
- impaired distance estimation/perception in peri personal space
- reduced access to perceptual interposition and shadowing depth cues
- reduced (coarse) binocular stereo acuity
- moderate optic ataxia
- little/no conscious awareness of deficits: they claimed that all the tasks were extremely easy, despite numerous performance errors
