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Seeing Things 2 Visual Processing in the Brain

How Your Brain Works - Week 4 Dr. Jan Schnupp jan.schnupp@dpag.ox.ac.uk HowYourBrainWorks.net. Seeing Things 2 Visual Processing in the Brain. Visually Guided Behaviour.

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Seeing Things 2 Visual Processing in the Brain

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  1. How Your Brain Works - Week 4 Dr. Jan Schnupp jan.schnupp@dpag.ox.ac.uk HowYourBrainWorks.net Seeing Things 2Visual Processing in the Brain

  2. Visually Guided Behaviour • To catch a prey, your sensory system has to “represent” the target to be caught in a manner that can “instruct” the appropriate motor commands. • In reptiles and amphibia, this representation most likely resides in the optic lobe, also called the optic tectum, or (in mammals)superior colliculus.

  3. Motor Maps in the Superior Colliculus Retinotopic Map Motor Map • Microstimulation studies have shown that the SC contains a “motor map”, which is in register with the retinotopic sensory map

  4. There is more to vision than visual reflexes • Often we have to balance the desire to catch one object with the need to dodge another, or choose which from a variety of objects is most worth pursuing. • Which objects need catching, and which need dodging, may change over time. This creates a need for quite abstract representations of objects within a flexible, rapidly adaptable system. Is that what sensory cortex is for?

  5. Primary and “Extrastriate” Visual Cortex

  6. Decoding Brain Activity • Miawake et al. Neuron 2008 • Observed activity of ca 1500 voxels of (3mm)3. • Reconstructed the image shown from recorded activity

  7. Seeing Lines

  8. Simple Cell Receptive Fields

  9. Cortical Layers • 1: “tufts” of apical dendrites receive cortico-cortical connections. • 2/3: gets input from layer 4. Many simple cells. Outputs to other parts of cortex. • 4: gets most input from LGN. Many LGN-like, non-oriented cells. Output to layers 2/3. • 5/6: inputs from layers 2/3. Output to subcortical targets

  10. Cortical Columns as “Computational Modules” • Surface • Supra- • granular • Granular • Infra- • Granular • White • matter I II/III IV V VI Subcortical Targets From Thalamus

  11. Representing Shape and Position Within an “Orientation Map” • Pseudocolour “orientation tuning” map of ferret primary visual cortex (revealed with intrinsic optical imaging).

  12. Binocular Vision

  13. Binocular Fusion • Try “shooting a hole” into your hand by rolling up a piece of paper into a tube, holding it in front of one eye, and holding your free hand flat in front of the other eye, as shown here. • Your brain will try, as best it can, to paint a single scene out of the disparate images seen by each eye.

  14. Stereopsis (Stereo vision for depth)

  15. Ocular dominance

  16. Cytochrome Oxidase Blobs

  17. Cortical Hypercolumns

  18. Break

  19. Cortical Hypercolumns

  20. Stripe Rearing

  21. What would the world look like to a stripe reared kitten?

  22. Three-eyed Frogs means that if you want to predict the PSTH of means that if you want to predict the PSTH of

  23. Strabismus

  24. Amblyopia • Inputs from each eye are thought to “compete” for cortical territory during early development. • If one eye is “weaker” (e.g. due to an optical defect), it may fail to get properly connected to the visual cortex. • This in principle essentially healthy eye can then become functionally blind. • To prevent amblyopia, children at risk sometimes have their stronger eye temporarily deprived of input.

  25. Meltzoff & Moore 1977 • Neonates are said to be able to mimic facial or hand gestures after 14 to 21 days. • Wilderbeast run with the herd after just a few hours. • Experience dependent maturation of the visual system may need to be rapid. means that if you want to predict the PSTH of

  26. Enriching Early Experience

  27. Parallel Pathways LGN Retina V1 Extrastriate cortex Layer IVCαβthen IVB M Magnocellular V5 (MT) motion Layer IVCβinterblob shape P Parvocellular V2 non-Mnon-P Koniocellular blob V4 colour

  28. Higher order Visual Pathways "Where stream" "What Stream"

  29. Shape processing hierarchy

  30. Face Cells • Infero-temporal cortex contains neurons that appear to be selective for visual objects, such as faces or hands. • Damage to these areas can lead to “visual agnosia”, and inability to recognize objects by sight even though there is no blindness. means that if you want to predict the PSTH of

  31. Motion Sensitivity

  32. Newsome’s Moving Random Dots

  33. Neurometric Curves • Hatched Bars: responses to movement in preferred direction • Filled black bars: responses to movement in null direction • Open (white) circles: psychometric function (animal’s choices) • Filled (black) circles: neurometric function (neuron’s “choice”) • From Newsome, Britten, Movshon (1989) Nature 341:52

  34. Microstimulation Biases Perceptual Choice • From Salzman, Britten, Newsome (1989) Nature 346:174

  35. The Motion Aftereffect Illusion http://www.michaelbach.de/ot/mot_adapt/index.html Go

  36. Hemineglect Syndrome • Drawing of a clock by a patient with a lesion in the right posterior parietal lobe. means that if you want to predict the PSTH of

  37. Form from Motion means that if you want to predict the PSTH of means that if you want to predict the PSTH of

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