Determination and evaluation of clinically efficient stopping criteria for the multiple auditory steady-state response technique

Background: Although the auditory steady-state response (ASSR) technique utilizes objective statistical detection algorithms to estimate behavioural hearing thresholds, the audiologist still has to decide when to terminate ASSR recordings introducing once more a certain degree of subjectivity. Aims: The present study aimed at establishing clinically efficient stopping criteria for a multiple 80-Hz ASSR system. Methods: In Experiment 1, data of 31 normal hearing subjects were analyzed off-line to propose stopping rules. Consequently, ASSR recordings will be stopped when (1) all 8 responses reach significance and significance can be maintained for 8 consecutive sweeps; (2) the mean noise levels were ≤ 4 nV (if at this “≤ 4-nV” criterion, p-values were between 0.05 and 0.1, measurements were extended only once by 8 sweeps); and (3) a maximum amount of 48 sweeps was attained. In Experiment 2, these stopping criteria were applied on 10 normal hearing and 10 hearing-impaired adults to asses the efficiency. Results: The application of these stopping rules resulted in ASSR threshold values that were comparable to other multiple-ASSR research with normal hearing and hearing-impaired adults. Furthermore, in 80% of the cases, ASSR thresholds could be obtained within a time-frame of 1 hour. Investigating the significant response-amplitudes of the hearing-impaired adults through cumulative curves indicated that probably a higher noise-stop criterion than “≤ 4 nV” can be used. Conclusions: The proposed stopping rules can be used in adults to determine accurate ASSR thresholds within an acceptable time-frame of about 1 hour. However, additional research with infants and adults with varying degrees and configurations of hearing loss is needed to optimize these criteria

North Atlantic Drift Sediments Constrain Eocene Tidal Dissipation and the Evolution of the Earth-Moon System

Cyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High-resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well-suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408–U1410 are highly complex with several hiatuses. Here, we built a two-site composite and constructed a conservative age-depth model to provide a reliable chronology for this rhythmic, highly resolved (<1 kyr) sedimentary archive. Astronomical components (g-terms and precession constant) are extracted from proxy time-series using two different techniques, producing consistent results. We find astronomical frequencies up to 4% lower than reported in astronomical solution La04. This solution, however, was smoothed over 20-Myr intervals, and our results therefore provide constraints on g-term variability on shorter, million-year timescales. We also report first evidence that the g4–g3 “grand eccentricity cycle” may have had a 1.2-Myr period around 41 Ma, contrary to its 2.4-Myr periodicity today. Our median precession constant estimate (51.28 ± 0.56″/year) confirms earlier indicators of a relatively low rate of tidal dissipation in the Paleogene. Newfoundland Ridge drift sediments thus enable a reliable reconstruction of astronomical components at the limit of validity of current astronomical calculations, extracted from geologic data, providing a new target for the next generation of astronomical calculations

The clinical usefulness of the multiple auditory steady-state response technique in adults

The auditory steady-state response (ASSR) is an auditory evoked potential technique which can be used in difficult-to-test populations (infants, individuals with multiple handicaps, subjects who simulate hearing loss) to objectively estimate behavioural thresholds. The ASSR technique is gradually emerging in clinical settings because of some definite advantages over the commonly used click-evoked auditory brainstem response such as frequency-specific assessment of the auditory sensitivity, objective detection algorithms, higher stimulation levels, and multiple frequency stimulation. The main aim of this doctoral thesis is to assess the clinical usefulness of the auditory steady-state technique for an adult population using a commercially available multiple auditory steady-state response or the so-called clinical MASTER system. In particular, this research project focuses on two aspects consisting of optimization of the test efficiency and investigation of the clinical behaviour of the ASSR. The results demonstrate that the multiple ASSR technique accurately estimates pure-tone thresholds in adults with normal hearing and hearing loss using the AM²/FM stimulus. Investigation of the test-retest reliability demonstrates that in normal hearing adults a threshold difference of at least 20 dB is required to be 95% confident that the change in ASSR thresholds represents a true threshold shift instead of measurement error typical to the ASSR technique. Additionally, the impact of degree, type and configurations of hearing loss on ASSR threshold accuracy was assessed. The effect of degree shows that moderate sensorineural hearing loss (SNHL) has lower difference thresholds than normal hearing and that it is very difficult to categorize ASSR thresholds as normal or mild SNHL for 500 Hz and as mild or moderate SNHL for 2000 Hz. The impact of type of hearing loss reveals that air-conduction ASSR thresholds accurately predict the degree of conductive hearing loss, except for 2000 Hz. Furthermore, flat configurations of sensorineural hearing loss results in lower difference thresholds than the sloping SNHL, especially for the lower frequencies. Evaluation of the sensitivity, specificity, positive and negative predictive value reveals that the most appropriate cutoff point to differentiate normal hearing from hearing loss in adults is a 30 dB or lower criterion. The last study attempts to optimize the test efficiency of the ASSR technique by determining stopping criteria that can be used in a clinical setting and efforts are made to provide a framework by which a clinical audiologist can collect significant and non-significant response amplitude data to determine noise stop criteria for specific populations (infants and adults with varying degrees, types and configurations of hearing loss). In conclusion, the present thesis demonstrates that the multiple-ASSR technique accurately determines pure-tone thresholds using the novel proposed AM²/FM stimulus with a clinically acceptable test-retest reliability for normal hearing adults. Furthermore, distinguishing subjects with a mild degree of SNHL from normal hearing will be very difficult and air-conduction ASSR thresholds can be determined quite accurately in conductive hearing impaired patients. Finally, procedures to establish clinically efficient stopping criteria were proposed with a special focus on the framework to construct setting-specific noise-stop criteria. The next step will be investigating infants with varying degrees, types and configurations of hearing loss to establish the clinical usefulness for the ultimate target group of the ASSR technique

Auditory steady-state response in normal hearing adults: a test-retest reliability study

C

Auditory steady-state responses to MM and exponential envelope AM2/FM stimuli in normal-hearing adults

A

Effectiveness of hearing protector devices in impulse noise verified with transiently evoked and distortion product otoacoustic emissions

This study aimed to evaluate the effect of impulse noise on otoacoustic emissions (OAEs) while a passive nonlinear earplug or an active level-dependent earmuff was worn. Since none of the standardized attenuation measurement techniques, REAT (real ear at threshold), ATF (acoustic test fixture), or MIRE (microphone in real ear), is designed to test both types in real-wearing condition, OAEs, suitable for detecting subtle changes in the functional integrity of the cochlear outer hair cells, are used. First, DPOAEs (distortion product) and TEOAEs (transiently evoked) of 24 subjects were compared before, immediately after gunfire practice, and after one hour of non-exposure. Secondly, both types of OAEs were evaluated in 31 subjects before and after exposure during a five-day military practice. Significant differences existed between the ears in most cases; the emissions from the right ear had a tendency to be more robust. There were no significant changes in OAEs either before and after exposure, or in the second experiment over multiple days. These findings suggest that the HPDs are able to prevent cochlear damage

The effect of age on the sinusoidal harmonic acceleration test, pseudorandom rotation test, velocity step test, caloric test, and vestibular-evoked myogenic potential test

OBJECTIVES: Age-related anatomical and morphologic vestibular deterioration has already been elaborated. Demonstrating a corresponding degradation in physiologic function, however, entails a much higher challenge. The objective of this study was to investigate age-related changes using rotational tests, caloric tests, and the vestibular-evoked myogenic potentials (VEMP) test. DESIGN: Eighty healthy human subjects (38 men and 42 women) ranging in age from 18 to 80 yrs participated in this study and were subjected to an extensive vestibular test battery. Function tests included sinusoidal harmonic acceleration tests, a pseudorandom rotation test, velocity step tests, a caloric test, and a VEMP test. RESULTS: No significant age trends were noted for the sinusoidal harmonic acceleration test and velocity step tests response parameters, in contrast to subtle decreasing gain values with advancing age for the pseudorandom rotation test. Increasing slow-component velocity values were measured with the caloric test, whereas the frequency parameter showed no relevant age changes. The largest age trends were detected with the VEMP, with decreasing amplitudes, increasing thresholds, and decreasing N1 latencies. All asymmetry parameters remained stable across the different age categories. CONCLUSIONS: Only subtle age changes could be demonstrated with the rotational and caloric tests, in contrast to more pronounced age trends with the VEMP