  The creep behavior of an amorphous poly(etherimide) (PEI) polymer is
investigated in the vicinity of its glass transition in a weakly non linear
regime where the acceleration of the creep response is driven by local
configurational rearrangements. From the time shifts of the creep compliance
curves under increasing applied stresses in the range 1-15~\si{\mega\pascal},
we determine a macroscopic acceleration factor. At the start of creep, the
stress is homogeneous and the macroscopic acceleration can be assimilated to
that of the local rearrangements which is shown to vary as $f=e^{-(\sigma/Y)^n}
$ with $n=2 \pm 0.2$, where $\sigma$ is the local stress and $Y$ is a
decreasing function of compliance. This experimental result is in agreement
with the recent theory of Long \textit{et al.} (\textit{Phys. Rev. Mat.} (2018)
\textbf{2}, 105601 ) which predicts $n=2$. From a mean field approximation, we
interpret the variation of $Y$ with compliance as the result of the development
of stress heterogneities during creep.
