Test-retest repeatability of distortion product otoacoustic emissions.

OBJECTIVES: Distortion product otoacoustic emissions (DPOAE) have become part of routine audiological diagnostics. The large scale of clinical DPOAE applications, such as screening of hearing in infants, objective estimation of hearing status, distinction between cochlear and retrocochlear origin of sensorineural hearing loss, exclusion of psychogenic hearing loss, monitoring of hearing during administration of ototoxic drugs, and others illustrates the significance of this audiological tool. In all diagnostic tests, knowledge about the procedure's test-retest repeatability is of crucial importance, to allow for distinction between measurement deviations and true physiological or pathological changes in monitoring over time. DESIGN: Measurements of DPOAE were performed in triplicate in 80 normally hearing ears of 40 subjects. Both immediate remeasurements with the ear probe left in place [single-fit mode (SF-mode)] and remeasurements after approximately 5 to 10 days [multiple-fit mode (MF-mode)] were included. DPOAE primary tone levels were varied in 5 dB steps from L2 = 60 to 20 dB SPL (L1 = L2 x 0.4 + 39 dB SPL) and within the frequency range f2 = 1 to 6 kHz. Repeatability of DPOAE was evaluated by the standard error of measurement (Sm), reliability (Cronbach alpha), absolute differences between measurements, 95% confidence intervals, and repeatability standard deviations. RESULTS: Sm averaged 0.67 dB over all frequencies and primary tone levels in the SF-mode, and 1.44 dB in the MF-mode, respectively. As expected, test-retest repeatability declined with decreasing primary tone levels; however, repeatability values were still mostly satisfactory with the lower primary tone levels. For the exemplary primary tone level combination of L1/L2 = 63/60 dB SPL, which is close to common clinical paradigms, the difference between two DPOAE measurements under the reported test conditions could be considered statistically significant (p = 0.05) if it exceeded 0.7 to 1.3 dB in the range 1 to 5 kHz and 2.3 dB for 6 kHz in the SF-mode, when compared with 1.8 to 2.7 dB for 1 to 5 kHz and 3.7 dB for 6 kHz in the MF-mode. Signal to noise ratio (SNR) did not seem to have a large influence on repeatability, as long as SNR was within 6 to 35 dB, which covers the range of most clinical DPOAE measurements. CONCLUSIONS: The DPOAE-test-retest study presented here is to our knowledge the first, which combines variation of primary tone levels, assessment of both SF- and MF-modes, and comparison of the two modalities within the same subjects. Although the measurements were conducted under practical conditions resembling the clinical setting, repeatability was generally good. The widely used minimum SNR of 6 dB seems to be a recommendable criterion when considering both practicability and measurement quality under clinical conditions. The current findings underline the suitability of DPOAE as a monitoring tool of cochlear status over time. The data are intended to assist the clinician and the scientist in the correct interpretation of DPOAE level changes in the test-retest situation.

Speech-in-noise intelligibility does not correlate with efferent olivocochlear reflex in humans with normal hearing.

CONCLUSION: According to the presented data, speech-in-noise intelligibility (SI) does not correlate with olivocochlear efferent activity - as measured by contralateral suppression (CS) of distortion product otoacoustic emissions (DPOAE) in humans with normal auditory threshold. OBJECTIVES: Literature data indicate a possible role of the medial olivocochlear efferents in speech intelligibility, especially in background noise. The objective of this study was to investigate this relationship. MATERIALS AND METHODS: SI was evaluated in three independent sessions by determining the ratio speech level/noise level, at which 50% of the words are understood (i.e. speech reception threshold, SRT). Efferent activity was inferred measuring CS of DPOAE, using two different paradigms with extensive variation of stimulus parameters and duplicate measurements. RESULTS: For optimum measurement of CS, the study was restricted to subjects (n =49) with valid DPOAE down to primary tone levels L1=47/L2 =20 dB SPL. Average SRT was -6.66 dB (-4.50 to -7.65 dB, SD 0.63 dB). CS increased with decreasing primary tone levels, with mean absolute CS values in the range of 0.6-6 dB SPL. Test-retest repeatability was good. Statistical evaluation revealed no significant relationship between SI and CS of DPOAE.

Evidence for a bipolar change in distortion product otoacoustic emissions during contralateral acoustic stimulation in humans.

The aim of this study was to investigate the activity of the medial olivocochlear (MOC) efferents during contralateral (CAS) and ipsilateral acoustic stimulation (IAS) by recording distortion product otoacoustic emission (DPOAE) suppression and DPOAE adaptation in humans. The main question was: do large bipolar changes in DPOAE level (transition from enhancement to suppression) also occur in humans when changing the primary tone level within a small range as described by Maison and Liberman for guinea pigs [J. Neurosci. 20, 4701-4707 (2000)]? In the present study, large bipolar changes in DPOAE level (14 dB on average across subjects) were found during CAS predominantly at frequencies where dips in the DPOAE fine structure occurred. Thus, effects of the second DPOAE source might be responsible for the observed bipolar effect. In contrast, comparable effects were not found during IAS as was reported in guinea pigs. Reproducibility of CAS DPOAEs was better than that for IAS DPOAEs. Thus, contralateral DPOAE suppression is suggested to be superior to ipsilateral DPOAE adaptation with regard to measuring the MOC reflex strength and for evaluating the vulnerability of the cochlea to acoustic overexposure in a clinical context.