  We consider the motion of conductivity spectral weight at a
finite-temperature phase transition at which $d_{x^2-y^2}$ density-wave (DDW)
order develops. We show that there is a shift of spectral weight to higher
frequencies if the quasiparticle lifetime is assumed to be isotropic, but a
shift to lower frequencies if the quasiparticle lifetime is assumed to be
anisotropic. We suggest that this is consistent with recent experiments on the
pseudogap phase of the cuprate superconductors and, therefore, conclude that
the observation of a downward shift in the spectral weight at the pseudogap
temperature does not militate against the DDW theory of the pseudogap.
