  The viscoelastic response of complex fluids is length- and time-scale
dependent, encoding information on intrinsic dynamic correlations and
mesoscopic structure. We derive the subdominant response of such fluids at
intermediate distances and show that it governs their dynamics over
surprisingly large length scales. Generalizing the framework of microrheology
to include this response, we experimentally confirm the theory, thereby
measuring the dynamic correlation length of F-actin networks, as well as their
bulk and local viscoelastic properties.
