Magnetic field response functions, RF_B, of the Si i 10 827.1 Å  and Ca i 10 833.4 Å  lines. Panels a) and b) display RF_B of Stokes I and Stokes V of the Si i 10 827.1 Å  line, respectively, for a penumbral atmosphere where (ΔB/ Δlog τ) is positive. For the same atmosphere, RF_B of Ca i 10 833.4 Å  are shown in panels c) and d). Panels e)−h) are the same as a)−d), but represent RF_B of a penumbral atmosphere where (ΔB/ Δlog τ) is negative. Displayed RF_B are normalized to the maximum value. The absolute values of RF_B integrated along the wavelength range Δλ = ± 1.0 Å  for the Si i  and Ca i  lines are shown in panels i) and j), respectively. The red and blue curves correspond to the positive and negative (ΔB/ Δlog τ), respectively. Solid curves are for Stokes I and dashed curves are for Stokes V. Dotted horizontal or vertical lines in the panels indicate the log τ nodes used in the inversions.