Optical measurements of the individual ferroelectric/ferroelastic domain wall oscillations in the ac electric field were carried out up to the transition temperature. The amplitude of the wall vibrations fell abruptly to zero so that the wall was at rest during the phase transition. The change of oscillation characteristics with temperature is shown to be dependent on the history of motion, in part on the initial amplitude and the presence of the shell of mobile defects or charge carriers. Change of material parameters, influence of screening or defects shell, and critical damping are discussed as possible mechanisms of the effect. The last assumption is shown to be in a good agreement with the experimental data. The measurements of the amplitude of domain wall vibrations may be used as a simple method for investigations on critical phenomena in ferroelectrics. ©1996 American Institute of Physics.