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Anatomy/Physiology of Binocular Vision. Goals Follow the M and P pathway out of primary visual cortex Answer where binocularly and disparity driven cells appear Learn a bit about stereopsis

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anatomy physiology of binocular vision
Anatomy/Physiology of Binocular Vision
  • Goals
    • Follow the M and P pathway out of primary visual cortex
    • Answer where binocularly and disparity driven cells appear
    • Learn a bit about stereopsis
    • Answer (partially) how an oculocentric neuronal organization gives rise to an egocentric visual perception
parallel pathways magnocellular m and parvocellular p
Parallel Pathways: Magnocellular (M) and Parvocellular (P)
  • Each pathway is sensitive to specific visual stimuli
  • Each pathway has its own timing characteristics
  • Each pathway is NOT strictly parallel!
    • More of a “Bob ‘N Weave” pathway arrangement
magnocellular m pathway the table setter
Magnocellular (M-pathway) The Table Setter
  • Coarse visual form
  • Moving (or modulating)target
  • Processing time: rapid
  • Peripheral fusion
  • Coarse stereopsis
parvocellular p pathway the details
Parvocellular (P-pathway) The Details
  • Spatial detail
  • Chromatic detail
  • Stationary (or moving slowly) target
  • Processing time: slow
  • Fine stereopsis
parallel pathways on the move
Parallel Pathways On the Move
  • Lateral geniculate nucleus
  • Segregation of P and M pathways into layers (1-2 Magno.; 3-6 Parvo.)
  • LGN serves as a relay station to primary visual cortex (18)
    • Where vision will become a conscious event
    • Where stereopsis and fusion takes place
    • Where visual and cognitive processing take place
primary visual cortex v 1
Primary Visual Cortex (V1)
  • Located along calcarine sulcus
  • M and P pathways continue in different paths as they reach layer 4 of V1
    • M pathway to layer 4 Ca
    • P pathway to layer 4Cb and layer 4A
  • Organized into ocular dominance zones
    • Monocular cells in layer 4C
    • Binocular driven cells outside of layer 4C
parallel pathways in v 1
Parallel Pathways in V1
  • M pathway:
    • From 4Ca to layer 4B in same vertical column (1 mm wide)
    • From 4B to layers 2/3 in same vertical column (1 mm wide)and neighboring columns
parallel pathways in v 19
Parallel Pathways in V1
  • P pathway:
    • From 4Cb to layers 4A and 3 in same vertical column (1 mm wide)
    • In layer 3, cytochrome oxidase, a metabolic marker, has dense staining in layer 2/3; absent in layer 4
    • Called “blobs”
    • Although considered “P-cells only”, a significant M-pathway input exists
parallel pathways in v 110
Parallel Pathways in V1
  • Blob and interblob regions:a split in the parvocellular pathway
  • Blob regions are situated in the center of ocular dominance columns
    • Blob regions: color opponency, low contrast and spatial frequency, not orientation selective
    • Interblob regions: little color opponency, high contrast and spatial frequency, very orientation selective
m and p pathways in v 2
M and P Pathways In V2
  • V2 has areas of high cytochrome oxidase activity in form of thick and thin stripes
  • M pathways project to thick stripes
  • P pathway
    • Blob cells: thin stripes
    • Interblob cells: inter stripes
other visual areas
Other Visual Areas
  • V2: in area 18, flanking V1
    • Thin/inter stripe regions (P pathway) projects to V4
    • Thick stripe (M pathway) projects to V3 and MT
    • Some overlap in response characteristics in V2 due to “cross-talk” between M and P at blob region
other visual areas15
Other Visual Areas
  • V3: in area 18 flanking V2
    • Receives M pathway input
    • Output to middle temporal area (MT)
    • Also output to V4!?!
  • V4
    • Receives P-pathway input from thin/inter stripe regions of V2
    • Receives strong M-input
slide16

Vision Association Areas

  • Area MT
    • In parietal lobe
    • M-pathway input
    • Output to parietal areas and V4
    • Sensitive to motion
    • Some areas have receptive fields in head-centric coordinates, NOT oculocentric
vision association areas
Vision Association Areas
  • Posterior parietal cortex
  • M-input (MT/V4): coarse stereopsis, low spatial freq., fast flicker and motion
  • Spatial position and object motion
  • Inferotemporal cortex
  • P-input (V4): fine stereopsis, color vision, fine pattern vision
  • Complex object recognition: faces
final words about m p pathways
Final Words About M/P Pathways
  • Significant cross-talk in V1, V4 and beyond
  • Ultimately, these two independent, yet overlapping streams must converge to form unitary perceptions of objects
  • We do not process the world like a poorly printed photograph, with the colors offset
ocular dominance columns
Ocular Dominance Columns
  • Vertical columns that respond most strongly to one eye
  • Extends through the full thickness of V1
  • Absent in areas outside V1
  • Binocular cells outside layer 4C respond predominantly to one eye over the other
orientation columns
Orientation Columns
  • If ocular dominance columns are loaves of bread, orientation selective columns are slices (parallel to pia)
  • Orientation selectivity is interrupted by blobs
binocular cells and stereopsis
Binocular Cells and Stereopsis
  • Binocular cells in V1 receptive fields for each eye share most characteristics
    • Corresponding retinal loci
    • Latency
    • Size/shape of receptive field
binocular cells and stereopsis22
If perfect overlap of receptive fields exist, it argues for a creation of an EGOCENTRIC PERCEPTION early in visual processing

It cannot explain, however, why we are sensitive to binocular disparity (stereopsis)

Binocular Cells and Stereopsis
  • Binocular cells in V1 receptive fields for each eye share most characteristics
    • Corresponding retinal loci
    • Latency
    • Size/shape of receptive field
binocular disparity
Results from different perspective of each eye to a particular visual target

Neurons tuned to disparity have been found in V1

Receptive fields for each eye do not PERFECTLY overlap

More prevalent in V2 (75% cells tuned to disparity)

4 main classifications of disparity tuned cells

Near cells/ Far cells

Excitatory cells tuned to zero disparity

Tuned excitatory

Tuned inhibitory

Binocular Disparity
profiles of disparity tuned cells
Profiles of Disparity Tuned Cells
  • Near cells: resp. to targets closer than fixation distance
  • Far cells: resp. to targets farther than fixation distance
  • Excitatory cells tuned to zero disparity: narrow peak responses around zero disparity
profiles of disparity tuned cells25
Profiles of Disparity Tuned Cells
  • Tuned excitatory: stim. by stimuli near zero disparity BUT ON EITHER SIDE/ suppressed by uncorrelated images
  • Tuned inhibitory: suppressed by stimuli near zero disparity BUT ON EITHER SIDE / stim. by uncorrelated images