Reliability in warble-tone sound field audiometry

The significance of masking for the poor hearing ear in pure tone audiometry

BACKGROUND

In pure tone audiometry, when the difference of the Average Air Conduction Threshold of pure tone (AACT) between bilateral ears is more than 40 dB HL masking must be performed on the poor side, However, we found that masking also make significance difference when the binaural AACT difference (AACT-d)was less than 40 dB HL in some patients.

AIMS/OBJECTIVE

Assessing the significance of masking for the poor ear in pure tone audiometry in patients with different types of deafness to obtain preoperative accurate hearing.

MATERIAL AND METHODS

A comparative analysis of 163 cases (163 ears) with hearing difference between two ears was conducted, who were divided into three groups: G1 Congenital Malformation of the Middle and Outer Ear (CMMOE)as conductive deafness, 63 ears, G2 sudden deafness as sensorineural deafness, 65 ears, and G3 media otitis as conductive or mixed deafness,35 ears. AACT-d before and after the poor ear masking was analyzed under the following three conditions: (1) 0.125-8 KHz each frequency, (2) 0.5-4 KHz on average, (3) the frequencies of AACT-d ≥ 40 dB HL and <40 dB HL between the two ears before masking. If the sample data did not follow a normal distribution, the Wilcoxon rank sum test was used for comparasion of AACT, and p < 0.05 was considered statistically significant. It is clinically effective for AACT-d ≥ 15 dB HL at 1 frequency or 10 dB HL ≤ AACT-d at 2 frequencies <15 dB HL before and after masking.

RESULTS

Among the three groups, (1) the comparasion of AACT-d before and after the poor ear masking for each frequency of 0.125-8 KHz and 0.5-4 KHz on average with all p < 0.05, and the AACT-d of the G1 group was the largest, with an average 0.5-4KHz of 7.5 dB HL, and the first two were 14.5 dB HL and 13.8 dB HL at 0.125 KHz and 0.25 KHz, respectively. (2) AACT-d ≥ 40 dB HL and <40 dB HL between the two ears before masking were distributed at the full frequency of 0.125-8KHz, the clinically effective rates of ≥40 dB HL groups were G1 (89.3%), G2 (45.5%) and G3 (5.3%), while those of < 40 dB HL groups were G1 (69.7%), G2 (34.4%) and G3 (31.3%), respectively.

CONCLUSION AND SIGNIFICANCE

For all three groups, there was statistically significant in AACT-d before and after the poor ear masking across each frequency of 0.125-8 KHz and on average 0.5-4 KHz. The distribution of AACT-d ≥ 40 dB HL and <40 dB HL between the two ears before masking was observed throughout the full frequency range of 0.125-8 KHz. AACT-d before and after the poor ear masking showed clinical effectiveness in all three groups, with the highest effective rate observed in the G1 group and the highest AACT-d at 0.125 KHz and 0.25 KHz. Therefore, regardless of whether the AACT-d between the two ears before masking is ≥40 dB HL or <40 dB HL, the full frequency masking should be employed in three groups, especially for the G1 group of CMMOE, particularly at 0.125 KHz and 0.25 KHz.

[Significance of deviations in hearing thresholds in pure-tone audiograms]

Variations in tone hearing thresholds can occur with a certain probability at random or due to systematic changes in hearing, the test system or the test methodology. Therefore, a significance analysis is essential for diagnostic statements and expert opinions. The random probability tables published here can be used in a simple way to identify any significant alterations in hearing thresholds with a probability of error of ≤0.05.

Reconsidering the concept of the aided threshold for nonlinear hearing AIDS

The aided threshold (and functional gain) has been discussed in the context of linear hearing aids since the early 1960s. The use of nonlinear hearing aids, however, could change the meaningfulness of this verification tool because of their unique characteristics. The interpretation of the aided threshold (and functional gain) as it pertains to linear and nonlinear hearing aids is reviewed. Also discussed are the ideas of an optimal aided threshold, factors that may affect its magnitude, and a comparison between functional gain and insertion gain measures. Finally, how to improve the accuracy of the aided thresholds (and functional gain) through the use of in-situ unaided threshold measurements is discussed.

Clinical study of Widex Senso on first-time hearing aid users

Using psychoacoustic tests and questionnaires, the aim of this study was to clinically test Widex Senso (WS) versus analogue hearing aids on 200 first-time wearers. Half of the participants were selected at random for fitting with the behind-the-ear model (WS C8) or the in-the-canal model (WS CX). On a group basis, WS was found to provide more benefit than a palette of 29 analogue, modern hearing aid models from 10 manufacturers. Only 3 of 100 subjects changed from WS to another hearing aid. On average, the abbreviated profile of hearing aid benefit (APHAB) (Cox & Alexander, 1995) demonstrated superior performance for WS, i.e. no conflict existed between high comfort and high speech recognition. Median aided frequency-modulated tone thresholds in the sound field were better than 25 dB HL at frequencies up to 4 kHz inclusive. A distinct mean aided improvement of speech threshold in competing speech of 2.5 dB was found in both groups.

Visual reinforcement audiometry. Comparison of loudspeaker arrangements

Two different loudspeaker arrangements are currently used when performing Visual Reinforcement Audiometry (VRA). In the one arrangement, the loudspeakers are mounted on separate movable arms and positioned 15 cm from each ear. In the other, the loudspeakers are rigidly mounted close to their respective picture monitor at a distance of 50-70 cm from the child. In the present study, these two arrangements were compared by measuring real-ear sound pressure levels and actual sound field conditions. It was shown that a predominantly monaural stimulation was best achieved by using the 15-cm position, but also that the measurements were significantly more affected by small head movements when using this close position. When assessing the acoustics as well as practical aspects, it was concluded that loudspeakers mounted beside the picture monitors at a distance of 50-70 cm from the child makes a generally appropriate arrangement for VRA.

Measurement of variability in sound field audiometry due to subject movement

Sound field audiometry is used primarily for hearing assessment in young children and for functional hearing aid evaluation. It is important that measurements are accurate and reliable as they affect the management of patients. Most clinics use a substitution method for calibration and, as a result, if the subject moves from the calibrated test point, the sound pressure level (SPL) at the ears will vary as the sound field is very rarely uniform. This variation can result in inaccurate threshold estimation and increased test-retest variability. A commonly used method for evaluating the potential errors due to subject movement involves measuring the variation in SPL, with respect to the test point, at six points around the test point. This method makes assumptions about the sound field which may not be valid and could lead to an underestimation of the variation present. The aim of this investigation was to assess the accuracy of this method. Measurements of variation were taken with a microphone and repeated with a head and torso simulator (HATS) which was used to represent a test subject. The total degree of variation indicated by these two methods was compared. The microphone measurements indicated less variation than the HATS measurements. The differences were statistically significant but small in clinical terms. Assuming that the HATS is properly representative of the normal population, then this result indicates that simple microphone measurements are acceptable for normal clinical practice but that higher quality measurements are desirable for critical work.

Individual follow-up of hearing aid fitting

Fifty new hearing aid users were summoned to individual follow-up about one year after they had completed their hearing aid fitting. About 30% of the hearing impaired seldom used their hearing aid (< 1 h/day). The hearing aid was mainly used in conversation between two, conversation in groups, listening to TV/radio, etc. The hearing impaired who had a steep hearing loss used the aid to a lesser extent. There is a strong need of follow-up visits. Reliability of the subject's own judgement was good.

Efficiency of speech audiometry and other tests

A formula for expressing the efficiency of audiological tests is proposed: E = (vb/vw - 1)/T where vb is the variance between subjects, vw is the variance within subjects and T is the testing time. This makes it possible to compare various tests even if they require different testing times. The formula has been used on various speech tests and on pure-tone thresholds for a specific group of hearing-impaired subjects, showing that pure-tone threshold tests are much more efficient than speech tests. Some suggestions are given on how to make speech tests in noise more efficient. It is concluded that the proposed formula of test efficiency should be considered when new tests are designed in order to get quick tests which add as much information as possible.

Quantization error in clinical pure-tone audiometry

The current clinical procedure for pure-tone audiometry was analysed for statistical measurement errors. Theoretically, the root-mean-square (RMS) error in a single threshold measurement is always greater than the standard deviation (SD) of measured intra-individual test-retest differences, divided by the square root of two. The RMS error includes an additional quantization component, caused by the finite step size between presented signal levels. In Monte-Carlo simulations with 2-dB and 5-dB steps the quantization error was negligible compared with other errors. Therefore, the single-test RMS error can be estimated with sufficient accuracy from the test-retest SD. The simulated single-test RMS error decreased from about 2.7 dB about 2.3 dB when the audiometric step size was reduced from 5 dB to 2 dB. Hearing thresholds appeared to be about 1.7 dB better with 2-dB steps than with 5-dB steps.

Test-retest variability in audiometric threshold with supraaural and insert earphones among children and adults

The effect of age and earphone condition on test-retest intrasubject variability in audiometric threshold was investigated. Ten subjects in each of the following age groups were investigated: 6-9 years, 10-13 years and young adults. Test-retest audiometric thresholds were collected at six frequencies (250, 500, 1,000, 2,000, 4,000 and 8,000 Hz) under three earphone conditions (Telephonics TDH-50P supraaural and Etymotic Research ER-3A insert earphone coupled to an immittance probe cuff or a foam insert). No statistically significant differences were found in variability of test-retest differences as a function of age, earphone condition or test frequency (p greater than 0.05). The clinical application of the insert earphone is recommended with children and adults as it affords no greater test-retest variability and at the same time provides a solution to a number of limitations incurred with the use of the supraaural earphone.

Reproducibility of hearing threshold measurements. Supplementary data on bone-conduction and speech audiometry

The reproducibility of bone-conduction pure-tone audiometry and speech recognition thresholds has been tested in groups of normal-hearing subjects. Each person was tested twice during the same day, and the test-retest difference was calculated. The reproducibility is presented as the standard deviation of this difference. Bone-conduction threshold measurements have a high degree of test-retest precision, whereas air-bone gaps show a large range of distribution in these normal-hearing subjects. This makes the interpretation of such gaps spurious when values are below 20-30 dB. Speech recognition threshold has the highest degree of test-retest precision of all audiometric tests, and this is probably due to the steep slope of the psychometric function at 50% intelligibility. A more detailed graphic presentation of the 50% point of intersection will bring the reproducibility down to less than 2.5 dB.