This paper aims at exploring the invariant parameters involved in auditory normalization of French vowels. A set of 490 stimuli, including the ten French vowels produced by an articulatory model simulating seven growth stages and seven fundamental frequency values, has been submitted as a perceptual test to 43 subjects. Results confirm the important effect of the tonality distance between F1 and F0 in perceived height. Regarding place of articulation, F2-F1, and F3-F2, in Bark, appear to be good predictors of the perceived front-back dimension. Roundedness is also examined and correlated to the effective second formant, involving spectral integration of higher formants within the 3.5-Bark critical distance.