A comparison of OAEs arising from different generation mechanisms in guinea pig

Otoacoustic emissions provide unambiguous evidence that the cochlea supports energy propagation both towards, and away from, the stapes. The standard wave model for energy transport and cochlear mechanical amplification provides for compressional and inertial waves to transport this energy, the compressional wave through the fluids and the inertial wave along the basilar membrane via fluid coupling. It is generally accepted that energy propagation away from the stapes is dominated by a traveling wave mechanism along the basilar membrane. The mechanism by which energy is predominantly transported back to the stapes remains controversial. Here, we compared signal onset delay measurements and rise/steady-state/fall times for SFOAEs and 2f₁ - f₂ OAEs (f₂/f₁ = 1.2) obtained using a pulsed-tone paradigm in guinea pig. Comparison of 2f₁ - f₂ OAE signal onset delay for the OAE arising from the f₂ region with SFOAE signal onset delay (matched to the f₂ stimulus frequency) based on signal onset occurring at 10% of the peak signal amplitude was suggestive of a bi-directional traveling wave mechanism. However, significant variability in signal onset delay and signal rise, steady-state duration, and fall times for both the 2f₁ - f₂ OAE and SFOAE was found, qualifying this interpretation. Such variability requires explanation, awaiting further studies.