  The motion of a particle in a ring of length L is influenced by a dirty metal
environment whose fluctuations are characterized by a short correlation
distance $\ell << L$. We analyze the induced decoherence process, and compare
the results with those obtained in the opposing Caldeira-Leggett limit ($\ell
>> L$). A proper definition of the dephasing factor that does not depend on a
vague semiclassical picture is employed. Some recent Monte-Carlo results about
the effect of finite temperatures on "mass renormalization" in this system are
illuminated.
