High-precision lifetime measurements have been performed in superdeformed (SD) bands of 1 5 1 , 1 5 2 Dy and 1 5 1 Tb with the Doppler-shift attenuation method. Differences found in the quadrupole moments Q 0 of the yrast SD bands are understood in terms of shape polarization effects by the high-N intruder orbitals. Q 0 moments are also presented for three excited SD bands in 1 5 1 Dy. Recent calculations can account for most of the observations.