[Elimination of hearing by way of air conduction in threshold studies of bone conduction].
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The aim of this study was to provide more knowledge about the influence of various factors on the reliability of speech audiometric measurements. On the basis of these data, new material on speech has also been developed for measurements of the speech reception threshold in noise. In a theoretical and a clinical investigation it has been shown that the reliability of speech discrimination scores may be predicted by using the binomial distribution. The reliability mainly depends on the score obtained and on the length of the word list. Curves with confidence intervals as well as diagrams which indicate when two different discrimination results deviate significantly from each other are presented. On the whole, the reliability is surprisingly poor. The reliability of speech reception threshold (SRT) measurements was studied by computer simulations and clinical studies. The SRT results of "subjects" who had poor speech discrimination were unreliable and were greatly affected by the level at which the test started. Some new methods were also simulated, one of which (the 2x4-word method) was 8% faster and also somewhat more reliable in the clinical studies than the ordinary 10-word method. It was also less affected by the patient's speech discrimination. Several speech lists with exactly the same content of sound, but with new sentences, were obtained by editing a list of ten spoken Swedish sentences in a computer. A noise was synthesized from the speech material by the computer to obtain the exact same spectrum of the speech and the noise. This material was tested monaurally on normal-hearing subjects and hearing-impaired subjects. A very steep intelligibility curve was obtained in noise (25%/dB), which gave a standard deviation of only 0.44 dB at repeated threshold measurements in noise for the normal-hearing subjects when the learning effect was outbalanced. This figure increased to 1.1 dB for those with severely impaired hearing. The learning effect between the first and the second thresholds did not exceed 1 dB. The threshold values ranged from -8 to -5 dB signal-to-noise ratio for those with normal hearing and from -7 to +7 dB for those with impaired hearing. The new sentence and noise material developed is well suited for clinical measurements of the speech reception threshold in noise.
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A retrospective study was conducted to assess results of hearing in patients who underwent resections of acoustic neuromas via the middle fossa approach. A statistical correlation of results with preoperative clinical and audiological data determined if any prognostic indicators could be associated with successful preservation of hearing. Of 93 patients included in the study, useful hearing was preserved in 54 (58%), while hearing was preserved within 10 dB of preoperative levels in 42 patients (45%). The possibility for hearing preservation appeared to be inversely related to the size of the acoustic tumor, with hearing preserved in 39 of 65 patients (60%) with tumors less than or equal to 0.5 cm. Preoperative hearing levels and electronystagmography seemed to have no prognostic value. However, auditory brain stem responses showed that a wave V latency of less than 6.8 msec was associated with an increased chance of hearing preservation. Additionally, the presence of vertigo as a pre-operative complaint appeared to be a good prognostic indicator for successful hearing preservation.