  We present the first results of a pilot study aimed at understanding the
influence of bars on the evolution of galaxy discs through the study of their
stellar content. We examine here the kinematics, star formation history,
mass-weighted, luminosity-weighted, and single stellar population (SSP)
equivalent ages and metallicities for four galaxies ranging from lenticulars to
late-type spirals. The data employed extends to 2-3 disc scalelengths, with
S/N(A)>50. Several techniques are explored to derive star formation histories
and SSP-equivalent parameters, each of which are shown to be compatible. We
demostrate that the age-metallicity degeneracy is highly reduced by using
spectral fitting techniques --instead of indices-- to derive these parameters.
We found that the majority of the stellar mass in our sample is composed of old
(~10 Gyr) stars. This is true in the bulge and the disc region, even beyond two
disc scalelengths. In the bulge region, we find that the young, dynamically
cold, structures produced by the presence of the bar (e.g., nuclear discs or
rings) are responsible for shaping the bulges' age and metallicity gradients.
In the disc region, a larger fraction of young stars is present in the external
parts of the disc compared with the inner disc. The disc growth is, therefore,
compatible with a moderate inside-out formation scenario, where the luminosity
weighted age changes from ~10 Gyrs in the centre, to ~4 Gyrs at two disc
scalelengths, depending upon the galaxy. For two galaxies, we compare the
metallicity and age gradients of the disc major axis with that of the bar,
finding very important differences. In particular, the stellar population of
the bar is more similar to the bulge than to the disc, indicating that, at
least in those two galaxies, bars formed long ago and have survived to the
present day. (abridged)
