External flow is known to induce anisotropic growth of concentration fluctuations in polymer solutions close to the phase boundary. In this article, scattering dichroism measurements are used to investigate the structural dynamics of flow-enhanced concentration fluctuations in a near-critical, semidilute polymer blend solution subjected to small-amplitude oscillatory shear flow. Our measured frequency response reveals that the behavior of the shear-induced fluctuations is governed by the relaxation time of the concentration fluctuations. Predictions from a hydrodynamic model, in good agreement with the experimental results, also indicate that the dynamics are dominated by a single relaxation time. In addition, relaxation times of the concentration fluctuations at various temperatures are calculated from dichroism data and are found to agree with those previously obtained from small-angle light scattering experiments.