Recording Distortion Product Otoacoustic Emissions using the Adaptive Noise Cancelling Algorithm

Background: A DPOAE signal must be detected in the presence of ambient acoustic noise and physiological noise arising from the patient. For testing in an unquiet environment, e.g., clinic offices or schools, attaining an advisable signal-to-noise ratio (S/N) is challenging. An effective noise reduction approach to detect DPOAEs uses weighted averaging by accepting quiet frames and applying a high weight to them while discarding frames with noise artifacts treated with low weight. A DPOAE probe of the QScreen system features two microphones to capture noise inside and outside the ear canal. An adaptive noise cancellation (ANC) algorithm includes filtering out environmental noise that passes the seal of the ear tip, resulting in an improved S/N and a reduced testing time. The study aimed to collect DPOAEs with the QScreen system under simulated noisy environment conditions to evaluate whether applying the ANC decreases the number of false positives and reduces testing time significantly. Methods: DPOAEs were recorded in 26 ears of normal-hearing young adults with a subject seated in a reclining chair outside the audiometric booth. The tests were performed with the ANC turned off and on under three conditions: 1. without presenting any signals from loudspeakers of an audio system (ambient noise level ≈35 dBA); 2. with a cafeteria noise presented at 60 and 70 dBA, and 3. with Fastl noise [1] presented at 50, 60, and 70 dBA. The volume of the sound system was adjusted to reach the target level of the noise signal with a sound level meter placed close to the entrance of the ear canal. DP-grams were recorded for the f2 frequency of 1, 1.5, 2, 3, 4, and 6 kHz with the primaries L1=61/L2=55 dB SPL. Minimum and maximum recording time per frequency was set at 2.1 and 15.2 sec. If S/N\u3e9dB was not reached after the maximum averaging time, the data point was considered a “refer”. The overall pass criterion required at least 4 “pass” results out of 6 frequencies tested. Results: The ANC benefit increased with increasing noise level for both Fastl and cafeteria noise, with a minimal benefit in the ambient noise condition. Applying the ANC reduced testing time by up to a quarter, i.e., the median time benefit was up to 35 sec. For Fastl noise presented at 70 dBA, \u3e70% of initial overall “refer” changed to “pass” results after applying the ANC. The highest rate of “refer” to “pass” change, as well as the greatest decrease of testing time, occurred for f2 = 1, 1.5, and 2 kHz with the ANC turned on. Conclusions: The ANC algorithm using the second microphone pointing outwards for capturing ambient noise and the primary microphone for capturing the DPOAE response in the ear canal decreases the impact of the environmental noise without influencing the DPOAE response. The benefits include: 1. reduced number of false positives, i.e., an improvement of specificity; 2. shorter testing time, and 3. a possibility of performing the screening of cochlea function based on DPOAE tests in adverse environmental conditions

Effects of Age, Age-Related Hearing Loss, and Contralateral Cafeteria Noise on the Discrimination of Small Frequency Changes: Psychoacoustic and Electrophysiological Measures

The aim of the study was to examine central auditory processes compromised by age, age-related hearing loss, and the presentation of a distracting cafeteria noise using auditory event-related potentials (ERPs). In addition, the relation of ERPs to behavioral measures of discrimination was investigated. Three groups of subjects participated: young normal hearing, elderly subjects with normal hearing for their age, and elderly hearing-impaired subjects. Psychoacoustic frequency discrimination thresholds for a 1000-Hz pure tone were determined in quiet and in the presence of a contralateral cafeteria noise. To elicit ERPs, small frequency contrasts were presented with and without noise under unattended and attended conditions. In the attended condition, behavioral measures of d′ detectability and reaction times were also obtained. Noise affected all measures of behavioral frequency discrimination significantly. Except N1, all ERP components in the standard and difference waveforms decreased significantly in amplitude and increased in latency to the same degree in all three subject groups, arguing against a specific age-related sensitivity to the effects of contralateral background noise. For N1 amplitude, the effect of noise was different in the three subject groups, with a complex interaction of age, hearing loss, and attention. Behavioral frequency discrimination was not affected by age but deteriorated significantly in the elderly subjects with hearing loss. In the electrophysiological test, age-related changes occurred at various levels. The most prominent finding in the response to the standard stimuli was a sustained negativity (N2) following P2 in the young subjects that was absent in the elderly, possibly indicating a deficit in the inhibition of irrelevant information processing. In the attended difference waveform, significantly larger N2b and smaller P3b amplitudes and longer N2b and P3b latencies were observed in the elderly indicating different processing strategies. The pronounced age-related changes in the later cognitive components suggest that the discrimination of difficult contrasts, although behaviorally maintained, becomes more effortful in the elderl

Evaluation of Pure-Tone Thresholds and Distortion Product Otoacoustic Emissions Measured in the Extended High Frequency Region

When the cochlea is stimulated with two primary tones (f1 and f2) some of the energy is reflected back and propagates via the middle ear into the outer ear. Due to cochlear nonlinearities, distortion product otoacoustic emissions (DPOAEs), may be detected by a probe microphone sealed in the ear canal. Reduced DPOAEs may indicate subclinical cochlear lesions. The relationship between hearing sensitivity and the strength of DPOAEs is debatable, especially in the extended high frequency (EHF) region (≥8 kHz). Monitoring cochlea function corresponding to the EHF range is important for detecting early stages of hearing loss, which typically begins above 8 kHz. Complex interactions of high-frequency pure-tones in the ear canal result in standing waves that increases test-retest variability of DPOAEs measured for f2≥6 kHz. The aim of the project was to evaluate reliability of DPOAEs measured up to 12 kHz with a system used routinely in audiology clinics. Thirty-one adults (age, 18-30 yrs) with normal middle-ear function and normal hearing thresholds in the conventional region (≤8 kHz) participated. The EHF audiometry was performed for frequencies up to 16 kHz. The DPOAE data were collected for the f2 frequency varied from 1.5 to 12 kHz, twice for each ear with the probe removed and then repositioned after the first test. The EHF audiometric data of four participants showed elevated thresholds. Their DPOAEs were reduced or absent for f2≥9 kHz, i.e., supporting the sensitivity of DPOAEs for cochlear hearing loss above the conventional audiometry frequency range. Mean and standard deviations of DPOAE levels were calculated separately for the left and the right ears of subjects with normal EHF thresholds. There were no differences between mean DPOAE values in the left and the right ears. The intersubject variability of the DPOAE levels was moderate (SD≈6 dB or lower) but it increased significantly in the 12-kHz region, per the F-test for variances, possibly due to 1. effects of standing waves on the high-frequency DPOAE reliability and/or 2. subclinical pathology in the most basal portion (i.e., high-frequency region) of the cochlea. For each ear, absolute values of differences between test/retest levels of detectable DPOAEs were calculated. ANOVA showed the main effect of frequency for the data collected in the left and the right ears. Post-hoc analyses indicated that test/retest variability of DPOAEs was rather constant for f2 frequencies up to 10 kHz, but a statistically significant increase of test/retest variability for f2 of 11 and 12 kHz was found. This aspect needs to be considered when using DPOAE tests for longitudinal monitoring of cochlear function in the basal portion. Nevertheless, combining behavioral thresholds with DPOAEs collected for the EHF range is vital for detecting the initial stage of the cochlear pathology corresponding to the high-frequency region, e.g., due to ototoxicity or aging of the cochlea

Musical Training Influences Auditory Temporal Processing

Background: A link between musical expertise and auditory temporal processing abilities was examined. Material and methods: Trained musicians (n=13) and non-musicians (n=12) were tested on speech tasks (phonetic identification, speech recognition in noise) and non-speech tasks (temporal gap detection). Results: Results indicated musicians had shorter between-channel gap detection thresholds and sharper phonetic identification functions, suggesting that perceptual reorganization following musical training assists basic temporal auditory processes. Conclusions: In general, our results provide a conceptual advance in understanding how musical training influences speech processing, an ability which, when impaired, can affect speech and reading competency

Hearing Loss in the Dental Office: The Effects of High Speed Dental Drills on Dentists\u27 Hearing

Hearing test results of 23 dentists obtained before and after working hours are compared to determine if dentists experience any temporary hearing loss. The aim of the project is to determine whether dental drills cause hearing loss and to document the consequences of the loss. Hearing evaluations include pure-tone audiometry, middle-ear testing, and measurements of otoacoustic emissions. The results are expected to convince dentists of the danger of noise exposure and the need for hearing protectio