Binocular depth processing: neural basis or stereopsis or solid 3D vision

Question 1

which two types of pictorial cues allows to achieve stereopsis with only one eye

Answer 1

• 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

Question 2

what is the origin of the ability to use 2 eyes & extract a third dimension/binocular stereopsis

Answer 2

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

Question 3

what is the perception of binocular stereopsis achieved from

Answer 3

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)

Question 4

what part of binocular stereopsis enhances depth discrimination

Answer 4

• 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

Question 5

what is the vieth-muller circle also known as

Answer 5

the horopter

Question 6

when the foveas of both eyes are looking at the same place, what property will the images have

Answer 6

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

Question 7

why is the fovea not the only part in the retina where there in retinal correspondence/0 disparity

Answer 7

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

Question 8

what does the horopter represent

Answer 8

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

Question 9

what is non correspondence in relation to the horopter

Answer 9

if object is beyond or before the horopter, it will form a disparity between both eyes

Question 10

what are the two points of non correspondence/properties of disparity

Answer 10

• 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

Question 11

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

Answer 11

uncrossed +ve disparity

Question 12

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

Answer 12

crossed -ve disparity

Question 13

what does a large disparity cause and why

Answer 13

diplopia due to narrow range wither side of the horopter

Question 14

what is referred to as panum’s fusional area

Answer 14

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

Question 15

where is the width of panum’s fusional area narrow

Answer 15

around the fovea = narrow region of 3D space

Question 16

where does panum’s fusional area get broader and why

Answer 16

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

Question 17

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

Answer 17

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

Question 18

name the steps in which the neurons take after they leave the LGN

Answer 18

• 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

Question 19

which cells are only interested in information from one eye/monocular

Answer 19

connections from LGN to primary v1 cortex to layer 4c

Question 20

which cells are interested in information from both eyes/binocularly

Answer 20

layers above and below layer 4c

Question 21

how much % of v1 cells beyond 4c are binocularly driven (excited by stimuli presented to both eyes)

Answer 21

75%

Question 22

what do all binocular driven cortical cells have in similarity

Answer 22

receptive fields in the left and right eyes

Question 23

what do all binocular driven cortical cells have similar RFs in respect to

Answer 23

• 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

Question 24

what do binocular driven cortical cells differ in

Answer 24

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

Question 25

what are the responses of 75% of binocularly driven cells in v1 cortex influenced by

Answer 25

the horizontal disparity between stimuli presented to the left and right eyes

Question 26

how many % of binocularly driven cells in v1 cortex are not influenced by horizontal disparity between stimuli presented to the left and right eyes

Answer 26

25% do not care about disparity at all

Question 27

what do different disparity tuned cells show selectivity for a specific..

Answer 27

- 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

Question 28

what are neurons in layer 4c sitting side by side receiving input from

Answer 28

two eyes in same point in space

Question 29

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

Answer 29

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

Question 30

what happens to the RFs is the pyramidal cells are slightly offset

Answer 30

RFs are disparate which contributes to disparity amongst neurons in v1

Question 31

list the 6 classes of disparity tuned cell in monkey v1

Answer 31

- tuned excitatory near - tuned excitatory zero - tuned excitatory far - tuned inhibitory near - tuned inhibitory zero - tuned inhibitory far

Question 32

why are the 6 classes of disparity cells tuned

Answer 32

they like only one disparity ± a tiny bit

Question 33

why are 3 classes of disparity tuned cells excitatory

Answer 33

because their response to their preferred disparity is based on facilitation (multiplying)

Question 34

what do the horizontal lines mean in the graphs of the 6 classes of disparity tuned cell

Answer 34

disparity of left eye alone of disparity go right eye alone, if added together = binocular disparities = binocular summation (just adding) if (multiplying = binocular facilitation)

Question 35

which RGC cellular processing acquires fine stereo acuity

Answer 35

parvo cellular

Question 36

which RGC acquire/contribute to coarse stereo acuity

Answer 36

parvo % magno

Question 37

what does a lesion to the parvo cellular processing cause

Answer 37

reduction in fine (high grade) stereo acuity

Question 38

how many % of cell are tuned excitatory/inhibitory for retinal correspondence/zero disparity

Answer 38

25%

Question 39

what are fine stereopsis disparity concerned with

Answer 39

size and sign

Question 40

which angle of disparity is considered for fine stereopsis

Answer 40

<0.5 deg arc + near horopter

Question 41

what accounts for 40% of fine stereopsis

Answer 41

tuned excitatory cells, binocular facilitation

Question 42

what is coarse stereopsis disparity concerned with

Answer 42

sign only (unable to tell its magnitude)

Question 43

which angle of disparity is considered for coarse stereopsis

Answer 43

± 1 deg arc crossed or uncrossed

Question 44

what accounts for 33% of coarse stereopsis

Answer 44

near & far cells, binocular summation

Question 45

which RGCs contribute to coarse stereopsis

Answer 45

parvo & magno

Question 46

what does local stereopsis require

Answer 46

- disparity between isolated points in space, formed by... | - object or surface which must have a solid form (real things)

Question 47

what does global stereopsis require

Answer 47

aka cyclopean - disparity across multiple points in space - generates solid '3D shape from disparity' - exploited in random dot stereograms

Question 48

what is local and global stereopsis two types of

Answer 48

disparity detection

Question 49

which neurons respond similarly to both types of stereo cue (local & global)

Answer 49

disparity tuned v1 neurons

Question 50

list the clinical grades from lowest to highest

Answer 50

- simultaneous perception - binocular single vision - depth perception/stereo acuity

Question 51

what neural requirements are there for simultaneous perception

Answer 51

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

Question 52

what neural requirement is there for binocular single vision

Answer 52

combine corresponding retinal inputs in visual cortex

Question 53

what type of test is required to test for binocular single vision

Answer 53

bagolini striated glasses

Question 54

what neural requirement is there for depth perception/stereo acuity

Answer 54

be able to compare disparate retinal inputs in the visual cortex

Question 55

what are the grades associated with depth perception/stereo acuity

Answer 55

fine vs coarse vs absent

Question 56

what type of test is required to test for depth perception/stereo acuity

Answer 56

stereo-grams

Question 57

what do cells in v1 respond to (i.e. where the pastor plots are the same)

Answer 57

lines - solid figure stereo grams & random dot - cyclopean stereogram

Question 58

what do single cell recordings show all extra striate cortex to contain

Answer 58

disparity tuned cells

Question 59

which part of the extra striate cortex contains the highest % in disparity tuned cells

Answer 59

dorsal stream - spatial-motion-action vision areas | eg V3A, V7, V5/MT & MST

Question 60

as well as the dorsal stream containing most % of disparity tuned cells, which other area contains just as much & more than area v1

Answer 60

ventral stream eg IOT/LOC

Question 61

how many % of disparity tuned cells does v1 contain

Answer 61

50%

Question 62

list the wide spread cortical regions activated by binocular disparity (3D vs 2D stimuli)

Answer 62

- area v1 + occipital extra striate areas v2 - v7 - parietal cortex - banks of the IPS & SPL - pre motor cortex - cerebellar cortex

Question 63

which areas are activated by 3D shape from disparity processing

Answer 63

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

Question 64

what type of infarct causes impaired distance & depth perception

Answer 64

bilateral occipito-parietal infarcts: superior occipital V3A/V7 + inferior & caudal IPS in each hemispheres

Question 65

what remains intact with someone who has impaired distance & depth perception

Answer 65

- VFs - VA - colours - familiar/novel object size estimation & recognition

Question 66

what does a patient who has impaired distance & depth perception often experience

Answer 66

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