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Central Visual Processes

Central Visual Processes. Central Visual Pathways. Primary Visual Cortex Receptive Field Columns Hypercolumns Spatial Frequency Nerve or Cortical Damage Higher Visual Areas. Occipital Lobe. Occipital Lobe: Calcarine Sulcus -- V1 -- Striate Cortex. Cells in V1.

charity-carlson
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Central Visual Processes

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  1. Central Visual Processes

  2. Central Visual Pathways • Primary Visual CortexReceptive Field • Columns • Hypercolumns • Spatial Frequency • Nerve or Cortical Damage • Higher Visual Areas Anthony J Greene

  3. Occipital Lobe Anthony J Greene

  4. Occipital Lobe: Calcarine Sulcus -- V1 -- Striate Cortex Anthony J Greene

  5. Cells in V1 Anthony J Greene

  6. Single-Cell Recording (Hubel & Weisel, 1962) • Attempted to discover what sorts of information cells in (cat) V1 respond to • Accidentally discovered orientation specific cells organized into columns and hypercolumns V1 Anthony J Greene

  7. Anthony J Greene

  8. Cells In V1 Inputs from Ganglion Cells Cells in V1 receive messages from certain ganglion cells such that they respond to stimuli of a certain orientation from a small portion of the retina - Orientation Specific ~ 200 Million Cells in V1 Anthony J Greene

  9. Cells In V1 • One V1 cell receives inputs from many ganglion cells • One ganglion cell may send inputs to numerous V1 cells • Stimuli from every possible orientation, and from every position in the visual field are detected by different cells in V1 • Simple Cells detect only orientation -- Complex Cells detect orientation and motion Anthony J Greene

  10. How to Make a Complex Cell • Orientation specific inputs from ganglion cells is similar to simple cells • However, the receptive field is much larger and is designed to respond maximally when inputs from sub-fields are sequential Anthony J Greene

  11. Cells in V1 Occular Dominance Anthony J Greene

  12. Columns in V1 Anthony J Greene

  13. Organization of Cells in V1 • Columns are sections of cortex which all respond to the same orientation from approximately the same region of cortex Anthony J Greene

  14. Organization of Cells in V1 • Hypercolumns are groups of columns, from both eyes, which are influenced by the same minute portion of the visual field Anthony J Greene

  15. Organization of Cells in V1 • What sort of information are these cells detecting? • Is the information from any single cell in V1 informative? Anthony J Greene

  16. Response Properties of Cells in V1 The extent to which columns will respond to stimuli with no interactions from other columns Cellular Activity Orientation Column Position on Occular Dominance Slab Anthony J Greene

  17. Lateral Inhibition The column with the strongest response to a given stimuli will suppress the respondse of neighboring columns + - Anthony J Greene

  18. Response Properties of Cells in V1 The extent to which columns will respond to stimuli with lateral inhibition from other columns Cellular Activity Orientation Column Position on Occular Dominance Slab Anthony J Greene

  19. Processing at V1 Is Edge Detection Anthony J Greene

  20. Edge Detection • While lateral inhibition normally improves the accuracy of edge detection, in this case it creates the “Deli Wall Illusion” Anthony J Greene

  21. Anthony J Greene

  22. Understanding Acuity: Spatial Frequency Analysis • Measuring visual acuity: • Eye doctors use distance (e.g., 20/20) • Vision scientists use visual angle Anthony J Greene

  23. Understanding Acuity: Spatial Frequency Anthony J Greene

  24. Understanding Acuity: Spatial Frequency Anthony J Greene

  25. Describing Processes in V1: Spatial Frequency Analysis Anthony J Greene

  26. Describing Processes in V1: Spatial Frequency Analysis (cont.) • Orientation • Frequency • Contrast Decreasing Contrast Anthony J Greene

  27. Spatial Frequency Analysis (cont.) • Fourier - French mathematician, came up with theory that one can create any complex wave through a summation of Sinusoids (or sub-parts, sub-waves) • Fourier Analysis divides all orientation specific cells in V1 according to the width of their receptive fields or Spatial Frequency • 1) Low • 2) Medium • 3) High Anthony J Greene

  28. Spatial Frequency Analysis (cont.) • Neurons can then be viewed as Spatial Filters which separately analyze differing levels of detail or scale • Any scene can then be decomposed into images with varying spatial frequencies - low frequency images are blurry and only the most prominent features are represented - high frequency images exaggerate the fine details • Construing form vision in terms of an emergent property of these different scales of receptors is referred to as the Multichannel Model Anthony J Greene

  29. Spatial frequency Analysis (cont.) Anthony J Greene

  30. Spatial frequency Analysis (cont.) Anthony J Greene

  31. Spatial frequency Analysis (cont.) • Once divided by width, cells can further be grouped according to their orientation specificity • This allows a vastly simplified organization of neural activity - 3 major variables - Spatial Frequency, Orientation & Contrast • Additionally, Fourier analysis helps explain how individual cells may contribute information to the aggregate Anthony J Greene

  32. Spatial frequency Analysis (cont.) Anthony J Greene

  33. Spatial frequency Analysis (cont.) Anthony J Greene

  34. Spatial Frequency Analysis (cont.) • 1f gives the fundamental waveform • 2f ... xf : are called harmonics - increasing details Anthony J Greene

  35. Spatial Frequency Analysis (cont.) Anthony J Greene

  36. Spatial Frequency Illusions Anthony J Greene

  37. Spatial Frequency Illusions Anthony J Greene

  38. Spatial Frequency Illusions Anthony J Greene

  39. Spatial Frequency Illusions Anthony J Greene

  40. ColoratV1 • Among cells selective for orientation are patches of cells selective for color (and not orientation), which are known as Blobs. • Other cell (orientation specific cells) regions are known as interblobs. Anthony J Greene

  41. Organization of V2 • Thin Stripes receive information from Blobs and pass it to V4 • Thick Stripes recieve information from complex cells and send it to V5 and V3 • Interstripes recieve information from simple cells and send it to V3 and V4 • Information at V2 is 3-D Anthony J Greene

  42. Nerve or Cortical Damage 1) Retina / Optic Nerve 2) Optic Chiasm 3) Optic Tract 4) V1/V2 Anthony J Greene

  43. Nerve or Cortical Damage Retina/Optic Nerve: Monocular blindness Anthony J Greene

  44. Nerve or Cortical Damage Optic Chiasm: Nasal field blindness Anthony J Greene

  45. Nerve or Cortical Damage Optic Chiasm: Bitemporal field blindness Anthony J Greene

  46. Nerve or Cortical Damage Optic Tract/LGN/Radiations: Homonymous Blindness Anthony J Greene

  47. Nerve or Cortical Damage V1: Quadrantic blindness Anthony J Greene

  48. Nerve or Cortical Damage V1/V2: • Scotoma • Complete blindness • case of Blindsight Anthony J Greene

  49. Higher Visual Areas • V3: Form & Dynamic Form • V4: Color • V5: Motion • IT: What System: Object Recognition • Lingual Gyrus of IT: Face Recognition • PP: Where System: Object Location and Navigation Anthony J Greene

  50. Simplified Functional Visual Anatomy Anthony J Greene

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