  Novel spectro-polarimetric observations of the \ion{He}{1} multiplet are used
to explore the dynamics of the chromospheric oscillation above sunspot umbrae.
The results presented here provide strong evidence in support of the
two-component model proposed by Socas-Navarro and co-authors. According to this
model, the waves propagate only inside channels of sub-arcsecond width (the
``active'' component), whereas the rest of the umbra remains nearly at rest
(the ``quiet'' component). Although the observations support the fundamental
elements of that model, there is one particular aspect that is not compatible
with our data. We find that, contrary to the scenario as originally proposed,
the active component remains through the entire oscillation cycle and harbors
both the upflowing and the downflowing phase of the oscillation.
