Previous measurements of middle ear forward (FTF) and reverse transfer function (RTF) evaluated via simultaneous measurements of PEC and PSV close to the stapes (adapted from Dong and Olson 2006, Fig. 5). A FTF, defined as PSV/PEC at primary frequencies, and RTF, defined as PEC/PSV at DP frequencies. BPSV phase referenced to PEC. Red, green, cyan, and blue represent components of f1, f2, 2f1–f2, and 2f2–f1, respectively. (L1 = L2 = 90 dB SPL, f2/f1 = 1.25, wg67. The bulla was open, and the sound was delivered in a closed-field configuration).