Suppression of distortion product otoacoustic emissions (DPOAE) near 2f1−f2 removes DP-gram fine structure—Evidence for a secondary generator

Abstract

Since the discovery of distortion product otoacoustic emissions (DPOAE) there has been a controversial discussion about their cochlear generation sites. Suppression experiments suggest that the place near f2 is the main generation site. On the other hand, the fact that DPOAE can be perceived subjectively indicates that there is also a cochlear excitation at the place of 2f1−f2 resulting in a stimulus frequency otoacoustic emission (SFOAE). The contribution of this SFOAE to the overall emission is still unknown. Different studies showed contradictory results. We demonstrate a secondary generator by successive suppression of the SFOAE with a sine wave close to the frequency 2f1−f2. Suppression growth functions (SGF) showed a three-step behavior. For low suppressor levels, the emission either decreased or increased when increasing the suppressor. For intermediate suppressor levels, DP amplitude was constant and independant of suppressor level. For high suppressor levels, the emission always decreased with further increase of the suppressor. The behavior of the SGF in the first section depends on the fine structure of the DP-gram, which shows minima and maxima. Emissions at a maximum decreased while emissions at a minimum increased in the first section of the SGF. We conclude that the fine structure of the DP-gram is produced by alternate constructive and destructive interference of the two generators. By adding a third tone near 2f1−f2 the SFOAE and thus the interference are suppressed. The fine structure of the DP-gram vanishes and the resulting DP-gram should be more closely related to the cochlear status near f2.

Comparing behavioral and physiological measures of combination tones: Sex and race differences

“…This dissociation presumably is attributable in part to the fact that, while the DPOAE recorded in the ear canal is a sum of sounds of the same frequency originating from multiple sites in the cochlea (e.g., Kim, 1980;Shera and Guinan, 1999;Konrad-Martin et al, 2001;Martin et al, 2009), the listener has access to ("hears") only the component originating from that frequency's characteristic place on the basilar membrane. Also, both auditory sensitivity and the strength of DPOAEs can show microstructure (marked and reliable variation across small changes in frequency) that differs across individual ears (Gaskill and Brown, 1990;Heitmann et al, 1998;Talmadge et al, 1999). That microstructure has the potential to affect any estimates of the relationship between behavior and physiology in the present context.…”

Level dependence of the nonlinear-distortion component of distortion-product otoacoustic emissions in humans

“…Heitmann et al (1998) showed that a third tone with a frequency close to f DP can suppress the coherent-reflection component yielding reduction of the interference effects, evident as loss of DPOAE fine structure. However, the suppressor level for sufficient suppression has been shown to be frequency-dependent and highly variable across subjects (Dhar and Shaffer, 2004;Johnson et al, 2006b).…”

“…A major limiting factor when measuring DPOAEs with continuous primary tones is error associated with wave interference between the nonlinear-distortion and coherentreflection components. Interference causes the fine structure in plots of DPOAE amplitude versus f 2 (Heitmann et al, 1998;Mauermann et al, 1999;Talmadge et al, 1999); that is, these so-called DP-grams contain amplitude maxima and minima at stimulus frequencies of constructive and destructive interference, respectively (Kemp and Brown, 1983;Gaskill and Brown, 1990). The pattern of the DPOAE fine structure was reported to shift along the f 2 -axis with changing primary-tone levels (He and Schmiedt, 1993;Whitehead et al, 1995a), inducing large deviations in the shape and slope of I/O-functions in L 1 ,L 2 space, as also reported later by others (Mauermann and Kollmeier, 2004;Dalhoff et al, 2013).…”

Otoacoustic Emission Theories and Behavioral Estimates of Human Basilar Membrane Motion Are Mutually Consistent

“…The fine structure is thought to occur by vector summation of two DPOAE contributions: one that originates at the BM region of maximum overlap between the cochlear excitation patterns evoked by the two primaries (i.e., the f 2 region), and one that originates at the cochlear site with characteristic frequency (CF)∼2f 1 −f 2 , where the first contribution reflects back to the ear canal. The varying phases of these two contributions give rise to constructive and destructive interference, thus to peaks and valleys in the DP gram (Heitmann et al 1998;Shera and Guinan 1999).…”