Stat4Ci

A sensitive statistical test for smooth classification images

Z=1.64, p=.05 Z=2.35, p=.01

Test Z

Pour des images ?

Gaussian Random field

Seuil non corrigé

Bonferroni Correction

Exemples

Bonf t = 4.5228 Bonf t = 3.5463 Bonf t = 3.5463RFT t = 4.06

Pixel test

Résumé

• Seulement 2 paramètres– FWHM = taille du filtre de

lissage– p = seuil de confiance

• Comment choisir FWHM ?– Pour détecter un signal donné,

le meilleur filtre est un filtre de taille comparable

• Problèmes– Si le signal est diffus, le pic est

faible

• Solution– Prendre en compte la taille et

le Z score.

• Cluster test

Cluster test

tz = 2.5

k = 350 pixels

Pixel test

tz = 3.30

La toolbox

• p=.05;

• tC=2.7; % threshold for 2D image (other test)

• FWHM=HalfMax(sigma_b);

• [Sci,h] = SmoothCi(Ci, sigma_b);

• ZSCi = ZTransCi(SCi, mean(vecCi(:)), std(vecCi(:)));

• [volumes,N]=CiVol(sum(mask(:)),D)

• [tP,k]=stat_threshold(volumes,N,FWHM,Inf,p,tC,p);

• tCi = DisplayCi(ZSCi,tC,k,tP,FWHM,p,RFTtest,background);

ZTransCi

• ZSCi = ZTransCi(SCi, mean(vecCi(:)), std(vecCi(:)));

• In ZtransCi(Ci1, n1, Ci2, n2, sigmaNoise, smoothFilter),– Ci1 = sum of white noise fields that led to a type 1 response (e.g., correct)

– n1 = number of type 1 response

– Ci2 = sum of white noise fields that led to a type 2 response (e.g., incorrect)

– n2 = number of type 2 response

– sigmaNoise = standard deviation of white noise

– smoothFilter = Gaussian filter used to smooth the classification image

stat_threshold

• [tP,k]=stat_threshold(volumes,N,FWHM,Inf,p,tC,p);

– t pixel

– k taille minimun

– volumes, num_voxels, FWHM

– df : Inf

– p_val_peak, ...

– cluster_threshold,

– p_val_extent

DisplayCi

• tCi = DisplayCi(ZSCi,tC,k,tP,FWHM,p,RFTtest,background);

t size resels Zmax x y-----------------------------------------

C [2.70] 970 0.44 4.17 122 129[2.70] 917 0.41 3.95 162 129-----------------------------------------

P 3.30 -

p-value = 0.05FWHM = 47.1Minimum cluster size = 861.7

t size resels Zmax x y-----------------------------------------

C [2.70] 970 0.44 4.17 122 129[2.70] 917 0.41 3.95 162 129-----------------------------------------

P 3.30 -

p-value = [0.05]FWHM = [47.1]Minimum cluster size = 861.7

t size resels Zmax x y-----------------------------------------

C [2.70] 1787 0.81 5.2 133208-----------------------------------------

P 3.30 -

p-value = [0.05]FWHM = [47.1]Minimum cluster size = 861.7

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