FIG. 9.

Theoretical relationships among threshold and SFOAE microstructures given Eqs. (A1) and (A2), with values for each term fixed across a ∼0.5 octave span centered on 4 kHz. Here $R_{\mathrm{a}}$ was given a magnitude of 0.9 and delay of 5 ms (the approximate SFOAE delay near 4 kHz) and $R_{\mathrm{b}}$ was given a magnitude of 0.6 and delay of 0 ms (the delay associated with $R_{\mathrm{b}}$ is presumed negligible, for simplicity). For the purposes of this simplified illustration, thresholds [in (A)] were synthesized by scaling the inverse of Eq. (A1) by a nominal threshold level of 10 dB SPL, thus assuming a linear relationship between the steady-state forward-traveling-wave magnitude and the neural excitation required for behavioral threshold, and ignoring any complex spatio-temporal effects resulting from intracochlear reflection. The SFOAE pressure [the amplitude, phase, and delay of which are shown in (B)–(D)] was calculated with $P_{\text{stim}}$ equivalent to 10 dB SPL, and $G_{\text{me}}^{\text{RT}}$ with magnitude equivalent to −30 dB, and, for convenience, a negligible delay (0 ms). Thick dashed lines indicate the nominal threshold and SFOAE response values (i.e., trends) without the influence of the microstructure term, $1/(1-R_{\mathrm{a}}{R}_{\mathrm{b}})$.