Steep and shallow phase gradient distortion product otoacoustic emissions arising basal to the primary tones.

Distortion product otoacoustic emission (DPOAE) level/phase maps were collected in humans with and without an interference tone (IT) near the DPOAE frequency place (f(dp)) at primary-tone levels of 75 dB SPL. A DPOAE component with the expected steep phase gradient could be extracted at f(dp), however, considerable vertical-phase banding, presumably indicative of reflection emissions, remained. An IT placed 0.33 oct above f(2) removed most of this banding, revealing DPOAE components originating basal to the IT frequency place. These findings suggest that the commonly accepted two-source model of DPOAE generation may need to be qualified when higher primary-tone levels are utilized.