Movimento complesso: flusso ottica

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?

24. 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:

25. Superior Posterior Superior Lateral Unfolding 1 cm

26. V1 Expanding ring V2 V3

27. V1 Rotating wedge V2 V3

28. MT V1

29. Demo in dos Dos Demo

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

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

33. Translation Flow SB

34. Spatiotopic coding of visual motion in human MT

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

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

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

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

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

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

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

42. S1 S2 S3 S4

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

44. Response is specific to controlateral stimuli

45. V1 No modulation of response by gaze

46. MT: Strong modulation of response by gaze

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

48. 7 deg 2X8deg S1 S2 S3 S4 Block design: spatial selectivity with eccentric fixation F0 F1 F2 D’Avossa et al. Nat. Neurosc. 2007

49. Spatial selectivity with central fixation

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