Response functions for Stokes I (upper left panel), V (lower left panel), Q (upper right panel), and U (lower right panel) to a 1 G perturbation applied to the FAL-C atmospheric model, permeated by a horizontal magnetic field with χ_B = 0°, over intensity. An LOS with μ = 0.2 is considered. The R_i/I in each panel is normalized to the largest absolute value. For each panel, the corresponding Stokes I, V/I, Q/I, or U/I profiles are overplotted in magenta curves, in order to highlight the impact of the magnetic field. The solid curves represent the profiles obtained in the presence of the unperturbed magnetic field, whereas the dash-dotted curves represent those obtained in the case that a perturbation is applied at all height points.