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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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lettura
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.
signal to noise predictions
Signal-to-noise Predictions
  • S α Nsectors
  • σ2α Nsectors σα √Nsectors
  • S/σα √Nsectors
signal to noise predictions1
Signal-to-noise Predictions
  • S α Nsectors
  • σ2= k (constant)
  • S α Nsectors
two stage motion analysis
ΣTwo-stage motion analysis

Local motion detectors

Contrast thresholded

Complex motion

integrator

slide16
Segmentation has different temporal integration.

Even a weak signal embedded in noise can be seen given a long enough view

spatial summation of contrast sensitivity of sinusoids anderson and burr 1987
Spatial summation of contrast sensitivity of sinusoidsAnderson and Burr, 1987
interim conclusions

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°.

how functional magnetic resonance imaging fmri works
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:
unfolding
Superior

Posterior

Superior

Lateral

Unfolding

1 cm

demo in dos
Demo in dos

Dos Demo

slide30
FLOW (30 s) NOISE (30 s)

2 s

2 s

Inverting Direction

2 s

2 s

Rotation

Radial

Translation

slide31
MT

a

Inverting Rotation / Inverting Noise

d

e

b

Continuous Rotation / Noise

Response

f

c

Gradually Changing Flow / Noise

MC

Time (s)

slide35
Motion signals integrate spatiotopically across saccades

Two motion signals separated by delay

Melcher & Morrone

Nat. Neurosc. 2003

slide36
Summation of motion signals

Two motion signals

separated by delay

one fixation

Percent correct

two different fixations

slide37
Integration of motion at threshold across saccades is spatiotopic

Where in the human brain does the spatiotopic integration occur?

david hubel and torsten wiesel spatially localized receptive fields in primary visual cortex
David Hubel and Torsten Wiesel:Spatially localized receptive fields in primary visual cortex

Cortex

Cortex

slide39
RETINOTOPIC MAP

Monkey anatomy

Tootel et al, Science, 1982

retinotopic visual areas
‘Retinotopic’ visual areas

RETINOTOPIA: Neuroni vicini della retina poiettano a

Neuroni vicini della corteccia

human mt complex
FLOW - NOISE

Left

Hemisfere

Left VF – Right VF

15˚

4.5˚

-4 0 4

GDA

Human MT complex
slide45
V1

No modulation of response by gaze

gaze modulation of mt and v1
Gaze modulation of MT and V1

Central target

Eccentric target

D’Avossa et al.

Nat. Neurosc. 2007

block design spatial selectivity with eccentric fixation
7 deg

2X8deg

S1 S2 S3 S4

Block design: spatial selectivity with eccentric fixation

F0

F1

F2

D’Avossa et al.

Nat. Neurosc. 2007

spatial selectivity of bold responses in hmt is modulated by eye position
Spatial selectivity of BOLD responses in hMT is modulated by eye position

D’Avossa et al.

Nat. Neurosc. 2007

spatial selectivity of hmt is invarient in external but not retinal coordinates
Spatial selectivity of hMT is invarient in external but not retinal coordinates.

D’Avossa et al.

Nat. Neurosc. 2007

spatiotopicity of v1 and mt
Spatiotopicity of V1 and MT

D’Avossa et al.

Nat. Neurosc. 2007

conclusion
Conclusion

A specific portion of the hMT complex shows spatiotopic tuning, suggestion that the transformation from retinal to external coordinates may occur within this structure.

The spatiotopicity requires attention.

experiment in dos
Experiment in dos

Biological motion

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