Stat4Ci A sensitive statistical test for smooth classification images
Aspects théorique Image de classification Multiple comparaisons –Aucune correction –Bonferroni Random field theory –Pixel –Cluster –Scale Space
.* = Original imageMask of bubblesStimulus Stimuli creation Bubbles stimulus
Bubble task: gender discrimination Men or women?
Creation of the Ci +…+++++ Expected proportion = …, …,,,,, ==./ =
(Gibson, Gosselin, Schyns & Wasserman, Psychonomics, 2002) (Gosselin & Schyns, Vision Research, 2001) Bubble classification images
Visage à lendroit Visage à lenvers
Image de classification Régression multiple i=1..n, n nombre dessais u est une variable despace Pour n suffisamment grand
Test t p = [ 96,127,127,137,114,119,109,109,143,109,116,114,143,109,117,127,112,112,98, 37,112,109,119,106,109 ] Moyenne = 117.2, 2 = 160 v = [ 114,88,102,127,104,104,91,96,104,106,91,102,104,100,114,109,109,119, 91,81,114,119,102,111,80,119,119,123,119,114,132 ] Moyenne = , 2 = 167 t=1.97
Test t~Z score T(12)=3.56 t=1.97 Z=1.64, p=.05Z=2.35, p=.01
Comparaison multiple Aucune correction –p = % de chance de faux positif Bonferroni –p = p/N N est le nombre de comparaison –Soit 5 faux positif pour 100 images 1 test 2 tests 16*16 tests
Comparaison multiple p=.05, z=1.65 p=.05, z=1.92 p=.05, z=3.54 p=.05, z=3.89 P=
? p=.05, z=4.80 P=
Solutions Bonf t = Bonf t = RFT t = 4.06
Random Field theory
Expected Euler Characteristic
Gaussian Random field
Seuil non corrigé
Bonferroni Correction
Pixel test
t z = 3.30
tsize resels Zmax x y C[2.70] [2.70] P3.30- p-value = [0.05] FWHM = [47.1] Minimum cluster size = 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
tsize resels Zmax x y C[2.70] [2.70] P3.30- p-value = [0.05] FWHM = [47.1] Minimum cluster size = t size resels Zmax x y C[2.70] P3.30- p-value = [0.05] FWHM = [47.1] Minimum cluster size = 861.7
Cluster test t z = 2.5 k = 350 pixels
Scale space r=w 1 /w 2
Scale space t z = 4
Scale space t z = 2.5 k = 350 pixels