Audiology : official organ of the International Society of Audiology最新文献

An ideal test for identifying shifts in cochlear function would be highly repeatable and sensitive to minor damage. Three types of otoacoustic emission (OAE) test and pure-tone audiometry were evaluated for this purpose. They were compared in terms of test-retest repeatability within subjects and sensitivity to differences between subjects. The OAE measures were transiently evoked either conventionally (TEOAE) or using maximum length sequences (TEOAE-MLS), or continuously evoked as distortion products (DPOAEs). Several stimulus conditions were evaluated for each type. Thirty eight subjects with normal hearing or mild hearing losses were tested on all measures. Test-retest repeatability was rescaled according to the sensitivity of each measure to differences in hearing threshold level, thus allowing a direct comparison across methods. The most repeatable method thus defined was TEOAE-MLS which gave a rescaled standard deviation of 1.8 dB on replication. This was followed by TEOAE and DPOAE which gave rescaled standard deviations of 2.9 and 3.1 dB, respectively. All were more reliable than pure-tone audiometry which had a standard deviation of 4.9 dB. It is concluded that the various OAE measures have the potential to distinguish small changes in cochlear function from measurement uncertainty, and hence show promise for monitoring cochlear function in ears exposed to noise or other hazards.

It is unlikely that the overall status of a cochlea and middle ear which produces strong otoacoustic emissions (OAEs), i.e. high-level evoked emissions (EOAEs) and spontaneous emissions (SOAEs), has a generalized effect on peripheral auditory processing if the sensitivity is normal. Current data do not support the hypothesis that a weak OAE profile (low-level EOAEs and no SOAEs) is indicative of subclinical damage to the cochlea. Nevertheless, the ability of a subject to perform some psychoacoustical tasks may be influenced by the interaction between OAEs and test signals. The present experiments investigated the influence of strong or weak OAEs on: (1) intensity just-noticeable differences for pure tones; (2) temporal integration in the vicinity of SOAEs; (3) gap detection thresholds for broad-band noise bursts. The results show that OAEs can influence performance on these psychoacoustical tasks, especially for low-level stimuli with spectral components in the vicinity of high-level SOAEs.

Similar patterns of microstructure have been reported in normal ears for Békésy threshold recordings and various forms of otoacoustic emissions (OAE). It has been suggested that they have a common origin associated with the amplifying function of the outer hair cell system and wave interactions occurring within cochlear mechanics. Fine-frequency Békésy audiometry was conducted in ten normal ears and its microstructure was compared with that recorded using two OAq techniques: stimulus frequency (SFOAE) and distortion product (DPOAE). All sweeps encompassed the frequency range from 992 to 2000 Hz in 16-Hz steps. The same probe was used for all Békésy and OAE recordings to eliminate transducer effects. SFOAEs were obtained with stimulus intensities of 0, 3, 6 and 9 dB. DPOAEs were obtained for 2F1-F2 with primary levels (L1/L2) of 40/30, 45/35, 50/40 and 55/45 dB. Reliable microstructure was recorded in all ears. Mean values of microstructure peak spacing ranged from 5.6 to 9.3 per cent amongst methods, consistent with published data. Microstructure was similar within each OAE method for different stimulus intensities for each subject. However, comparisons between Békésy and OAEs, or between OAE methods, did not show the strong correspondence that would be expected if there were a simple common origin to the microstructure. There was weak support for the expected correspondence between Békésy and SFOAE, but no support for any correspondence between Békésy and DPOAE. It is concluded that the various forms of microstructure cannot be explained by a simple common origin.

The subjective recording of the masked threshold of short acoustical stimuli with a loud tone of 30 Hz (phase audiogram) has been used for the clinical diagnosis of endolymphatic hydrops (EH). In normally-hearing subjects, a marked modulation of the threshold was found, depending on the phase of the low-frequency tone. A very small dependence was found in patients with Menière's disease, due to the micromechanical changes in the basilar membrane (BM). The same phase relationship becomes apparent in low-frequency suppression of otoacoustic emissions. The amplitudes of TEOAEs are controlled by the phase-dependent displacement of the BM. The suppressed TEOAEs have to be measured separately in each phase relationship. During recording of suppressed DPOAEs, the low-frequency suppressor is permanently superimposed on the pair of primary tones. After time averaging and a moving short-time FFT, the spectral values of the DPOAEs are obtained depending on the phase of the low-frequency tone. Modulation depends also on the masker level, the levels of the primary tones, and on their frequency range. The method of low-frequency suppressed DPOAEs is an objective method to diagnose EH and could be a useful tool in human inner ear research.

Correspondence between spectral patterns in otoacoustic emissions (OAE) and the fine structure of the pure-tone audiogram has often been noted, but the link is by no means clearly understood nor complete in all subjects. This paper presents part of a broader study focusing on individuals with normal hearing but anomalously weak OAEs, the primary purpose of which was to determine the reasons for the weak OAEs. Subjects were selected from an exhaustive search of some 400 ears of highly co-operative adults, and comprised a test group of subjects with normal hearing thresholds but weak OAEs, and a control group of normals from the same sample. Reported here are data on audiogram fine structure measured in the two groups of subjects. The basic finding is that the subjects with weak OAEs also exhibited significantly less audiogram fine structure than the controls, as evaluated by analysing the periodicity in the respective threshold curves as well as by identifying and quantifying individual peaks in the curves. These findings first provide further evidence of an underlying link between the fine structure of the audiogram and OAEs, as proposed by Kemp in his original work. Second, assuming that the degree of fine structure would be largely unaffected by minor middle ear alterations, our findings suggest that predominantly cochlear rather than middle ear factors are responsible for the low levels of OAEs in the normal subjects of our test group. Finally, the results presented suggest that, like OAEs, audiogram fine structure measurements provide information on the auditory system that is not available in the conventional pure-tone audiogram.

The effectiveness of objective audiometric assessment can be improved by simultaneously recording transient evoked otoacoustic emissions (TEOAE) and auditory brainstem responses (ABR). Using a stimulation paradigm based on sequences of linearly balanced click stimuli (as described by Kemp et al.) acoustical and electrical responses of the auditory system can be obtained in one single run (dual response audiometry, DRA). The click stimuli are presented via an ear canal probe containing a speaker and a miniature microphone. EEG activity is recorded from surface electrodes fixed at the vertex and the mastoid ipsilateral to stimulus presentation. Microphone output and voltage difference between electrodes are fed into a dual-channel data acquisition system, where they are separately amplified and filtered into appropriate frequency ranges. After each stimulus, sweeps of 256 samples within a time window of 17 ms are taken of both signals. They are subject to artefact rejection and averaging of amplitude and polarity. The electrical responses to low and high level clicks within one stimulus sequence are processed separately, whereas the acoustical responses are summated across levels in order to eliminate stimulus-related contamination. As the result of one single run, ABR at two levels and non-linear TEOAEs are obtained within approximately 1 min. The signal quality is estimated by correlation analysis and binomial statistics. Among various features of DRA, the most important advantage is the improvement of the success rate. The influence of perturbations is limited since muscle artefacts due to motor activity affect only the ABR, whereas noise contamination affects only the TEOAE. The accuracy of threshold determination is better than with conventional ABR since the stimulus level is measured in situ. One DRA examination provides complete information about the functional integrity of the cochlea and neural pathways without additional time. It appears ideal for the application as a second stage infant screen.

Researchers have recently reported the effects of age, sex, ear asymmetry, and subject's activity status on transient evoked otoacoustic emissions (TEOAEs). The present study aimed to expand upon such reports by describing the characteristics of TEOAE spectra obtained from a cohort of 607 two-month-old infants in community child health clinics. Results indicated significant sex, ear and activity state effects on the signal:noise ratio, response, whole wave and band reproducibility values. These findings suggest the need for TEOAE normative data to be expressed as a function of sex, ear, and activity state of infants. These characteristics of TEOAE spectra may shape future investigations into appropriate pass fail criteria for two-month-old infants.

The aim of this study was to explore possible differences in the perception of loudness between long-term hearing aid full-time users and non-users. Categorical loudness scaling using pure-tone stimuli was carried out by hearing-impaired subjects. The mean levels of loudness categories at one frequency (hearing threshold: 50-75 dB HL) in a group of 18 hearing aid users (daily use < or = 15 hours per day) were compared with the corresponding levels found in 18 hearing-impaired non-users with the same distribution of hearing thresholds. The results show that, for hearing losses of 50-75 dB HL, the mean level rated as 'loud' by long-term full-time users of hearing aids is 4.5 dB above the mean level of the corresponding category rated by non-users. This difference is statistically significant (P<0.05). No significant differences were found for the lower categories. Among those subjects who had been wearing hearing aids for at least six months, no significant correlation was found between the levels of the 'loud' category and the length of time that hearing aids had been used.

Auditory neuropathy is defined as absent or severely distorted auditory brainstem responses with preserved otoacoustic emissions and cochlear microphonics. This entity can be found in various circumstances including pre-lingual children. An almost universal characteristic reported from adult patients is the ineffectiveness of traditional hearing aids. Adequate management of pre-lingual cases therefore remains an open problem. This paper describes two pre-lingual children whose follow-up data demonstrated a selective loss of the otoacoustic emissions, whereas the cochlear microphonics remained preserved. In one of the patients, hearing aid fitting as soon as she lost her otoacoustic emissions proved successful. These findings have important implications for the operational definition of the condition, since one must be prepared to encounter cases with absent otoacoustic emissions. The present data also demonstrate that conventional amplification can benefit pre-lingual auditory neuropathy cases, at least once they have lost their otoacoustic emissions.

The present study sought to determine whether the duration of white-noise bursts affects their loudness category rating in the same way for hearing-impaired as for normally-hearing subjects. Twelve normally-hearing and 12 hearing-impaired subjects took part. Categorical loudness growth functions were obtained for 16.25 ms, 32.5 ms, 75 ms, 150 ms and 300 ms white noise bursts. Temporal integration of loudness was defined as the intensity difference needed for stimuli of different durations to result in identical category ratings. In normally-hearing subjects, temporal integration of loudness occurred mainly with the short-duration (16.25 ms and 32.5 ms) stimuli, whereas it was found with almost every stimulus duration in hearing-impaired subjects. In other words, temporal integration of loudness between 16.25 ms and 300 ms stimulus duration was greater in hearing-impaired listeners and there was a difference between normal and hearing-impaired subjects regarding change in loudness perception with stimulus duration. Consequently, the use of fixed-duration stimuli hinders loudness normalization.