Dielectric measurements on two samples of banana-shaped molecules showing a B-2 and a B-7 phase were carried out. The low frequency dispersion in the B-2 phase is interpreted as a collective motion of ferroelectric clusters and the high frequency one as the reorientation of single molecules with a strong positive dipole correlation. In the B-7 phase a ,,soft mode-like" behavior was detected pointing to an additional phase transition. AFM measurements support the existence of helical super-structures which probably appear in B-7 and in the low temperature phase B-x.