Movimento complesso flusso ottica
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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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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. 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.


Neural response in MSTdDuffy & Wurtz, 1991


Psychophysical evidence for detection of optic flow in humans?


Spatial summation


Signal-to-noise Predictions

  • S α Nsectors

  • σ2α Nsectors σα √Nsectors

  • S/σα √Nsectors


Spatial summation in noise


Signal-to-noise Predictions

  • S α Nsectors

  • σ2= k (constant)

  • S α Nsectors


Spatial summation of contrast


Σ

Two-stage motion analysis

Local motion detectors

Contrast thresholded

Complex motion

integrator


Spatial summation of contrast in noise


Spatial summation of contrast in noise


Temporal summation of contrast sensitivity


10 secs

Motion coherence sensitivity

signal

noise


Summation constants


Segmentation has different temporal integration.

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


Summation with large fields


Summation with large fields in noise


Spatial summation for flow is extensive


Spatial summation of contrast sensitivity of sinusoidsAnderson and Burr, 1987


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°.


A neural centre for optic flow?


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:


Superior

Posterior

Superior

Lateral

Unfolding

1 cm


V1

Expanding ring

V2

V3


V1

Rotating wedge

V2

V3


MT V1


Demo in dos

Dos Demo


FLOW (30 s) NOISE (30 s)

2 s

2 s

Inverting Direction

2 s

2 s

Rotation

Radial

Translation


MT

a

Inverting Rotation / Inverting Noise

d

e

b

Continuous Rotation / Noise

Response

f

c

Gradually Changing Flow / Noise

MC

Time (s)


Translation

Flow

SB


Spatiotopic coding of visual motion in human MT


Motion signals integrate spatiotopically across saccades

Two motion signals separated by delay

Melcher & Morrone

Nat. Neurosc. 2003


Summation of motion signals

Two motion signals

separated by delay

one fixation

Percent correct

two different fixations


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

Cortex

Cortex


RETINOTOPIC MAP

Monkey anatomy

Tootel et al, Science, 1982


‘Retinotopic’ visual areas

RETINOTOPIA: Neuroni vicini della retina poiettano a

Neuroni vicini della corteccia


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


S1 S2 S3 S4


FLOW - NOISE

Left

Hemisfere

Left VF – Right VF

15˚

4.5˚

-4 0 4

GDA

Human MT complex


Response is specific to controlateral stimuli


V1

No modulation of response by gaze


MT: Strong modulation of response by gaze


Gaze modulation of MT and V1

Central target

Eccentric target

D’Avossa et al.

Nat. Neurosc. 2007


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 with central fixation


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.

D’Avossa et al.

Nat. Neurosc. 2007


Spatiotopicity of V1 and MT

D’Avossa et al.

Nat. Neurosc. 2007


Left MT


Indexes


Fig1


Fig 2


Fig 3


Fig 4


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

Biological motion


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