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Movimento complesso: flusso ottica

Movimento complesso: flusso ottica. Lettura. Morrone, M.C., Burr, D.C., and Vaina, L. (1995). Two stages of visual processing for radial and circular motion. Nature 376 , 507-509.

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Movimento complesso: flusso ottica

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  1. Movimento complesso: flusso ottica

  2. Lettura • Morrone, M.C., Burr, D.C., and Vaina, L. (1995). Two stages of visual processing for radial and circular motion. Nature376, 507-509. • Morrone, M.C., Tosetti, M., Montanaro, D., Burr, D.C., Fiorentini, A., and Cioni, G. (2000). A cortical area that responds specifically to optic flow, revealed by function Magnetic Resonance Imaging. Nature Neuroscience3, 1322-1328. • d'Avossa, G. et al. (2007). Spatiotopic selectivity of BOLD responses to visual motion in human area MT. Nat Neurosci 10, 249-255.

  3. Neural response in MSTdDuffy & Wurtz, 1991

  4. Psychophysical evidence for detection of optic flow in humans?

  5. Spatial summation

  6. Signal-to-noise Predictions • S α Nsectors • σ2α Nsectors σα √Nsectors • S/σα √Nsectors

  7. Spatial summation in noise

  8. Signal-to-noise Predictions • S α Nsectors • σ2= k (constant) • S α Nsectors

  9. Spatial summation of contrast

  10. Σ Two-stage motion analysis Local motion detectors Contrast thresholded Complex motion integrator

  11. Spatial summation of contrast in noise

  12. Spatial summation of contrast in noise

  13. Temporal summation of contrast sensitivity

  14. 10 secs Motion coherence sensitivity signal noise

  15. Summation constants

  16. Segmentation has different temporal integration. Even a weak signal embedded in noise can be seen given a long enough view

  17. Summation with large fields

  18. Summation with large fields in noise

  19. Spatial summation for flow is extensive

  20. Spatial summation of contrast sensitivity of sinusoidsAnderson and Burr, 1987

  21. Interim Conclusions There exists psychophysical evidence for detectors tuned to complex optical flow. Evidence suggest that the detectors are “second-stage” after contrast thresholding. Temporal summation is extensive: ~ 3 sec. Spatial summation is extensive, ~ 70°.

  22. A neural centre for optic flow?

  23. Brain Physics Increased brain activity Oxygenated and De- produces a local increase oxygenated blood have in blood oxygenation different magnetic properties MR images are brighter where there is greater brain activity How Functional Magnetic Resonance Imaging (fMRI) Works:

  24. Superior Posterior Superior Lateral Unfolding 1 cm

  25. V1 Expanding ring V2 V3

  26. V1 Rotating wedge V2 V3

  27. MT V1

  28. Demo in dos Dos Demo

  29. FLOW (30 s) NOISE (30 s) 2 s 2 s Inverting Direction 2 s 2 s Rotation Radial Translation

  30. MT a Inverting Rotation / Inverting Noise d e b Continuous Rotation / Noise Response f c Gradually Changing Flow / Noise MC Time (s)

  31. Translation Flow SB

  32. Spatiotopic coding of visual motion in human MT

  33. Motion signals integrate spatiotopically across saccades Two motion signals separated by delay Melcher & Morrone Nat. Neurosc. 2003

  34. Summation of motion signals Two motion signals separated by delay one fixation Percent correct two different fixations

  35. Integration of motion at threshold across saccades is spatiotopic Where in the human brain does the spatiotopic integration occur?

  36. David Hubel and Torsten Wiesel:Spatially localized receptive fields in primary visual cortex Cortex Cortex

  37. RETINOTOPIC MAP Monkey anatomy Tootel et al, Science, 1982

  38. ‘Retinotopic’ visual areas RETINOTOPIA: Neuroni vicini della retina poiettano a Neuroni vicini della corteccia

  39. Each visual brain area contains a map of the visual world and performs a different function.

  40. S1 S2 S3 S4

  41. FLOW - NOISE Left Hemisfere Left VF – Right VF 15˚ 4.5˚ -4 0 4 GDA Human MT complex

  42. Response is specific to controlateral stimuli

  43. V1 No modulation of response by gaze

  44. MT: Strong modulation of response by gaze

  45. Gaze modulation of MT and V1 Central target Eccentric target D’Avossa et al. Nat. Neurosc. 2007

  46. 7 deg 2X8deg S1 S2 S3 S4 Block design: spatial selectivity with eccentric fixation F0 F1 F2 D’Avossa et al. Nat. Neurosc. 2007

  47. Spatial selectivity with central fixation

  48. Spatial selectivity of BOLD responses in hMT is modulated by eye position D’Avossa et al. Nat. Neurosc. 2007

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