Limitations in the use of distortion product otoacoustic emissions in objective audiometry as the result of fine structure

Abstract

There is strong evidence for a link between intact cochlear function and otoacoustic emissions (OAE). However, all attempts to find a close correlation between auditory thresholds and amplitudes of distortion product otoacoustic emissions (DPOAE) have failed. As an explanation for these findings, we have studied DPOAE fine structure and its dependence on increasing primary sound levels. Errors due to different calibrations of equipment for measuring DPOAE and auditory thresholds were also investigated. DPOAE were measured in 16 subjects using a frequency range of 500-1000 Hz. Frequencies were changed in 12.5 Hz steps at primary levels of 55, 60, 65 and 70 dB SPL. DPOAE amplitudes were found to vary by up to 20 dB for a frequency step of 50 Hz. Some fine structures showed narrow dips that shifted in frequency and diminished in amplitude with increasing primary levels. These findings demonstrated that sampling DPOAE amplitudes at widely spaced frequencies gave incomplete information about true course. DPOAE growth functions measured close to a dip in the DPOAE fine structure were rendered useless by interference with either the frequency shift or amplitude variations of the dip at different primary levels.

Considering distortion product otoacoustic emission fine structure in measurements of the medial olivocochlear reflex

“…Additionally, the swept tone recording paradigm has much greater frequency resolution than those used in past studies and, therefore, this approach may have been able to define spacing intervals with greater accuracy. As expected, larger spacing intervals with increased DPOAE frequency were observed in the present study, consistent with past reports ͑Reuter and Hammershøi, 2006;He and Schmiedt, 1993;Engdahl and Kemp, 1996;Heitmann et al, 1996͒. Changes in the spacing ratio index as a function of frequency were also observed and are somewhat surprising considering the presumed scaling symmetry along the basilar membrane.…”

Distortion product otoacoustic emissions: Cochlear-source contributions and clinical test performance

“…These differing patterns of fine structure might lead to the erroneous conclusion that the normal-hearing ear producing a minimum at 2 kHz is impaired. Additionally, the frequencies at which maxima and minima occur within an individual ear may shift as level is increased (e.g., Schmiedt, 1993, 1997;Heitmann et al, 1996;Johnson et al, 2006b). This shift will influence the slope of the DPOAE I/O function and, therefore, may not only affect predictions of auditory status (i.e., normal versus impaired), but also may affect the accuracy with which behavioral thresholds can be predicted from DPOAE I/O functions (e.g., Boege and Janssen, 2002;Gorga et al, 2003;Oswald and Janssen, 2003).…”

?Single-generator- Distorsionsprodukte? (sgDPOAE)

“…Die Frequenzverschiebung der Feinstruktur mit ansteigendem Stimuluspegel kann bei der Bestimmung der DP-Wachstumsfunktion sogar zu paradoxen Ergebnissen führen, indem mit steigendem Primärpegel die Antwort kleiner wird [6]. Daher ist der diagnostische Einsatz der konventionellen Wachstumsfunktion ohne Kenntnis der zugrundeliegenden Feinstruktur zweifelhaft.…”

“…DPOAE kön-nen auch subjektiv wahrgenommen werden, wie schon 1754 der italienische Musiker Guiseppe Tartini beschrieb [10]. Folglich kommt es auch zu einer Erregung der Kochlea in dem Bereich mit der charakteristischen Frequenz druck am Trommelfell zuverlässig bestimmt werden [6]. Die Frequenzgänge wurden anschließend während der eigentlichen Messungen zur Einstellung der Lautsprecherpegel herangezogen.…”