1. 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

2. 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

3. Magnocellular (M-pathway) The Table Setter Coarse visual form Moving (or modulating)target Processing time: rapid Peripheral fusion Coarse stereopsis

4. Parvocellular (P-pathway) The Details Spatial detail Chromatic detail Stationary (or moving slowly) target Processing time: slow Fine stereopsis

5. 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

6. Primary Visual Cortex (V 1 ) Located along calcarine sulcus M and P pathways continue in different paths as they reach layer 4 of V 1 –M pathway to layer 4 C  –P pathway to layer 4C  and layer 4A Organized into ocular dominance zones –Monocular cells in layer 4C –Binocular driven cells outside of layer 4C

8. Parallel Pathways in V 1 M pathway: –From 4C  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

9. Parallel Pathways in V 1 P pathway: –From 4C  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

10. Parallel Pathways in V 1 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

11. M and P Pathways In V 2 V 2 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

14. Other Visual Areas V 2 : in area 18, flanking V 1 –Thin/inter stripe regions (P pathway) projects to V4 –Thick stripe (M pathway) projects to V3 and MT –Some overlap in response characteristics in V 2 due to “cross-talk” between M and P at blob region

15. Other Visual Areas V 3 : in area 18 flanking V 2 –Receives M pathway input –Output to middle temporal area (MT) –Also output to V4!?! V 4 –Receives P-pathway input from thin/inter stripe regions of V2 –Receives strong M- input

16. 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

17. Vision Association Areas Inferotemporal cortex P-input (V 4 ): fine stereopsis, color vision, fine pattern vision Complex object recognition: faces Posterior parietal cortex M-input (MT/V 4 ): coarse stereopsis, low spatial freq., fast flicker and motion Spatial position and object motion

18. 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

19. Ocular Dominance Columns Vertical columns that respond most strongly to one eye Extends through the full thickness of V 1 Absent in areas outside V 1 Binocular cells outside layer 4C respond predominantly to one eye over the other

20. Orientation Columns If ocular dominance columns are loaves of bread, orientation selective columns are slices (parallel to pia) Orientation selectivity is interrupted by blobs

21. Binocular Cells and Stereopsis Binocular cells in V 1 receptive fields for each eye share most characteristics –Corresponding retinal loci –Latency –Size/shape of receptive field

22. 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 in V 1 receptive fields for each eye share most characteristics –Corresponding retinal loci –Latency –Size/shape of receptive field Binocular Cells and Stereopsis

23. 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

24. 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

25. 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