The 2 f1-f2 distortion product otoacoustic emission (DP) was measured in 20 normal hearing subjects and 15 patients with moderate cochlear hearing loss and compared to the pure-tone hearing threshold, measured with the same probe system at the f2 frequencies. DPs were elicited over a wide primary tone level range between L2 = 20 and 65 dB SPL. With decreasing L2, the L1-L2 primary tone level difference was continuously increased according to L1 = 0.4L2 + 39 dB, to account for differences of the primary tone responses at the f2 place. Above 1.5 kHz, DPs were measurable with that paradigm on average within 10 dB of the average hearing threshold in both subject groups. The growth of the DP was compressive in normal hearing subjects, with strong saturation at moderate primary tone levels. In cases of cochlear impairment, reductions of the DP level were greatest at lowest, but smallest at highest stimulus levels, such that the growth of the DP became linearized. The correlation of the DP level to the hearing threshold was found to depend on the stimulus level. Maximal correlations were found in impaired ears at moderate primary tone levels around L2 = 45 dB SPL, but at lowest stimulus levels in normal hearing (L2 = 25 dB SPL). At these levels, 17/20 impaired ears and 14/15 normally hearing ears showed statistically significant correlations. It is concluded that for a clinical application and prediction of the hearing threshold, DPs should be measured not only at high, but also at lower primary tone levels.

A new method for direct pure-tone threshold estimation from input/output functions of distortion product otoacoustic emissions (DPOAEs) in humans is presented. Previous methods use statistical models relating DPOAE level to hearing threshold including additional parameters e.g., age or slope of DPOAE I/O-function. Here we derive a DPOAE threshold from extrapolated DPOAE I/O-functions directly. Cubic 2 f1-f2 distortion products and pure-tone threshold at f2 were measured at 51 frequencies between f2=500 Hz and 8 kHz at up to ten primary tone levels between L2=65 and 20 dB SPL in 30 normally hearing and 119 sensorineural hearing loss ears. Using an optimized primary tone level setting (L1 = 0.4L2 + 39 dB) that accounts for the nonlinear interaction of the two primaries at the DPOAE generation site at f2, the pressure of the 2 f1-f2 distortion product pDP is a linear function of the primary tone level L2. Linear regression yields correlation coefficients higher than 0.8 in the majority of the DPOAE I/O-functions. The linear behavior is sufficiently fulfilled for all frequencies in normal and impaired hearing. This suggests that the observed linear functional dependency is quite general. Extrapolating towards pDP=0 yields the DPOAE threshold for L2. There is a significant correlation between DPOAE threshold and pure-tone threshold (r=0.65, p<0.001). Thus, the DPOAEs that reflect the functioning of an essential element of peripheral sound processing enable a reliable estimation of cochlear hearing threshold up to hearing losses of 50 dBHL without any statistical data.

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The suppression tuning properties of the 2 f1-f2 distortion-product otoacoustic emission (DPOAE) were measured in 16 ears of normally hearing human subjects. DPOAE were elicited by fixed, low-level primary tones in four frequency regions with the second primary tone frequency f2 at 1, 2, 4, and 6 kHz. For various suppressor frequencies, suppression of the DPOAE was measured as a function of the suppressor tone level, enabling the assessment of the threshold and the growth of suppression. Depending on the distance of the suppressor tone to f2, there were marked differences in the suppression behavior of different suppressor frequencies. The threshold of suppression was minimal slightly above f2 and hardly increased with increasing frequency, but increased continuously with decreasing suppressor frequency. The growth of suppression, however, did not systematically change below f2, but decreased rapidly above f2. Both changes resulted in asymmetrical, V-shaped suppression tuning curves. They were sharply tuned to a frequency slightly above f2, with Q10 dB values up to 7.87. This is consistent with the assumption that the main source of the DPOAE is at the f2 site. In some cases, the DPOAE was particularly sensitive to suppressor tones near the DPOAE frequency. In one individual case, facilitation was found for corresponding frequency-level ranges of the suppressor tone. This may suggest a secondary emission source at the distortion product place.

The present multicentric clinical study involves 19 centres, 16 of them in German-speaking countries, 1 British, 1 Polish and 1 Hungarian. 60 postlingually deafened adults with a mean age of 47.5 years (20–70) and a mean duration of deafness of 5.3 years (0.5–20) have been evaluated with the MED-EL COMBI 40 cochlear implant which implements a high-rate continuous-interleaved-sampling strategy with 8 channels. Safety and effectiveness data have been collected. Speech perception tests include a 16-consonant, an 8-vowel, a sentence and a monosyllabic-word test in all languages and a 2-digit figure test in all languages but English. Test intervals are 1,3,6 months and 1 year after first fitting. 41 of the 60 postlingually deafened adult study patients have completed their 6-month evaluation. While their pre-operative monosyllabic-word score was 0%, their mean monosyllabic-word score 6 months after first fitting was 48% (8–90) with a median of 50%. The mean sentence understanding was 84% (24–100) with a median of 90%. The respective values for the 1-year evaluations with 25 patients are a mean of 50% (5–85), with a median of 60%, for the monosyllables and a mean of 89% (30–100), with a median of 97%, for the sentences.

High-resolution hearing threshold and 2 f1-f2 distortion product otoacoustic emission (DP) were measured with the same in-the-ear sound probe and same calibration at 51 frequencies between 500 and 8000 Hz in 39 sensorineural hearing loss ears associated with tinnitus. Using a primary tone setting L1 = 0.4L2 + 39 that accounts for the nonlinear interaction of the two primary tones at the DP generation site at f2, DPs were elicited in a wide range from L2 = 65 to 20 dB SPL. We failed to find a uniform DP behavior in the 39 tinnitus ears tested. Seventeen of them behaved like impaired ears without tinnitus. In these ears a linearized DP growth was observed where the DP level decreased and the slope of the DP I/O functions steepened with increasing hearing loss and as a result both the DP level and the DP slope strongly correlated with hearing threshold. The other population, 22 tinnitus ears, exhibited a poor or even inverse relationship between DP level and hearing threshold, i.e., displayed an increase of DP level with increasing hearing loss. Despite the severe hearing loss but due to the high level, DPs could be recorded well in the frequency range that corresponded to the appearance of the tinnitus. The DP slope, however, increased with increasing hearing loss and, therefore, did still correlate with hearing threshold revealing pathological alteration. The data suggest that the DP level alone is hardly capable of assessing hearing impairment in tinnitus ears and may even be misleading. Thus just the DP slope seems to be the only reliable indicator of cochlear malfunction around the tinnitus frequency. The observed nonuniform DP behavior suggests different cochlear impairments in tinnitus ears. In those ears where the DP level decreases and the slope of the I/O functions increases with hearing loss, cochlear sensitivity and tuning are supposed to be diminished. In those ears where the DP level increases with increasing hearing loss, a reinforced mechanical distortion is hypothetized to be generated by cochlear hyperactivity that can be the source of both the abnormally high DP level and the tinnitus.

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.

Practical location estimation is never ideal, and each location estimate is burdened with a certain level of error. In many use-case scenarios, knowing the magnitude of these errors can significantly improve the usability of the location estimates. The localization errors for different localization approaches are currently assessed using static performance benchmarks. These benchmarks typically provide aggregate metrics that statistically characterize the localization errors across the entire deployment environment. Due to the potentially dynamic nature and spatial heterogeneity of the environment, this characterization can be too generic to be really useful from the point of view of an individual location estimate. To address this issue for fingerprinting-based localization, we propose a regression-based procedure for estimating the individual (i.e., per-location estimate) localization errors. We use the received signal strength (RSS) values from various locations in an environment, as well as the observed localization errors in case the location estimates are generated using these RSS values, for training a number of contemporary regression models. Using the trained models, we are able to estimate the localization error of a location estimate at a new location using only RSS values collected at that location. Both by simulation and experimentally, we demonstrate the feasibility of the proposed procedure for Wi-Fi-based indoor and LoRa-and SigFoxbased outdoor fingerprinting approaches. We do that by showing that the proposed procedure can, in the best-case scenario, yield more than 50% more accurate estimation than the reference procedure based on the average localization errors derived from the static performance benchmarks.