Sound-field hearing tests.
Facilities for sound-field testing of hearing and calibration procedures are described.
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Facilities for sound-field testing of hearing and calibration procedures are described.
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Forty employees received pure-tone baseline hearing tests at the time they began employment as LSM operators for the U.S. Postal Services; the workplace eight-hour average sound level (TWA) was 85 dBA. Nineteen operators from the original group had their hearing retested three years later. None of the retested subjects showed large or systematic changes in hearing sensitivity over the three-year period. For the audiometric frequencies most susceptible to noise exposure (3000, 4000, 6000 Hz), only 5 percent of the operators showed a bilateral change in threshold greater than 5 dB at any frequency, and none of them showed more than a 10 dB threshold change in both ears. None of the operators displayed a Standard Threshold Shift as described by OSHA. The data further suggested that many workers began their LSM work assignment with a pre-existing hearing loss and, based upon audiometric and history information, the impairment probably resulted from prior occupational and/or nonoccupational noise exposure. The importance of hearing-conservation programs for employees is emphasized.
Thirty difficult-to-test children have been tested with transtympanic ECoG. When possible, informal hearing tests and/or free-field testing were performed. Children in whom no action potential (AP) could be recorded were submitted to conventional radiography of the inner ear, and vestibular tests. The correlation between free-field test thresholds and AP "thresholds" was good, especially in subjects with relatively good hearing. Response amplitude increased, and latency decreased, with increasing frequency of the stimulus implying that different parts of the basilar membrane are stimulated according to the frequency of the stimulus. Input-output curves of response amplitude and latency were plotted, and three different types were distinguished. ECoG can contribute to the evaluation of peripheral hearing in difficult-to-test children, and vestibular tests should always be performed on a child with suspected deafness or sensorineural hearing loss. Conventional radiography of the inner ear, however, seems to be of little value.
A new method of hearing testing has been evaluated on a trial basis in the Baby Health Centres of the Sydney Inner Metropolitan and Illawarra Health Regions, of New South Wales. This consists of earlier and more frequent testing with a newly devised range of auditory stimuli presented in front of the child, rather than behind the child. The reason for the change is that earlier detection leads to earlier treatment and improved speech. The new method will assess whether there is adequate hearing for speech development.
As greater numbers of workers come under industrial hearing conservation programs, the problem of nonorganic hearing loss is become critical. The potential malingerer can be identified by behavioral observations both before and during the testing of hearing and by an analysis of test results. Manual, self-recording, and microprocessor audiometry all incorporate validity and reliability checks which assist in detecting the malingerer. Methods of documenting inaccurate hearing tests are detailed, along with ways of obtaining accurate follow-up tests. The key to alleviating the problem of malingering is early detection and immediate resolution of the problem.
The brain-stem electroencephalograph (EEG)-evoked response (BSER) constitutes a reliable and objective method of testing hearing in infants, and in uncooperative, or retarded patients. The procedure is harmless and painless, and involves recording the EEG brain-stem responses to clicks presented by headphones. The patient may be sedated, or even anaesthetized, if necessary. Because of the equipment and time involved, the procedure is not recommended as a routine screening procedure, but constitutes a valuable adjunct to conventional audiological testing, especially in doubtful cases.
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