  In piezoresponse force microscopy a lateral signal at the domain boundaries
is occasionally observed. In recent years, a couple of experiments have been
reported and varying explanations for the origin of this lateral signal have
been proposed. Additionally, elaborated theoretical modeling for this
particular issue has been carried out. Here we present experimental data
obtained on different crystallographic cuts of $\rm LiNbO_3$, $\rm BaTiO_3$,
and $\rm KTiOPO_4$ single crystals. We could thereby rule out some of the
explanations proposed so far, introduce another possible mechanism, and
quantitatively compare our results to the existing modeling.
