Eine Verbesserte Vertäubungsmethode Für Die Audiometrie

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Abstract
Masking may be brought about by noise, by pure tone, or with a water or air jet. There is no intensity of noise which would in any case of deafness provide sufficient masking of the ear which is to be excluded, without elevating the auditory threshold of the ear under examination. The usual masking noise with a frequency spectrum over the whole audible range is in itself disadvantageous. This is manifested (a) in a poor degree of efficiency, i.e., an unfavorable relationship of the masking obtained to the loudness, (b) in the difficulty of adaptation to the various curves of hearing loss, and (c) in the associated excessive claims made on hearing at low frequencies which show a relatively small difference in intensity between the auditory threshold and the threshold of pain. In addition auditory fatigue can not always be avoided. To eliminate the disadvantages of masking by noise which is now in use, it is suggested that a masking noise with a narrow frequency band confined to the neighboring frequencies of the test tone should be used. Such a frequency band has practically the same masking effect as a broad band noise but provides significantly less loudness. To prevent undesirable summation effects the frequency of the test tone must be eliminated from the noise by a suitable electrical circuit, so that only 2 side-bands remain. These side-bands surround the test tone irrespective of its frequency, and mask it effectively. The narrow band noise has practically the same threshold as the test tone and can be calibrated similarly for each frequency individually. Thanks to the automatic adjustment it is adapted to every hearing loss, it does not produce unnecessary high-sound intensity at any frequency, and it provides in practically every case of deafness a sufficient masking without elevating the auditory threshold of the ear under investigation. When tuning the masking noise for the investigation of the bone conduction, the difference between the hearing losses for air and bone conduction in the ear under masking must be taken into consideration. This difference weakens the noise intensity relative to the bone conduction. A compensation of the loss in noise intensity must be provided by a supplementary attenuator calibrated accordingly. A method of control of masking is described which is based on the fact that the masking noise affects the threshold of a tone only in the ear to which it is conducted. If the test tone is perceived in the masked ear due to insufficient masking, its threshold varies with the intensity of the masking noise; if the test tone is heard in the tested ear, its threshold is irrespective of the masking noise. This no longer holds good when the masking noise reaches the tested ear to such a degree that it masks the test tone in this ear. The occurrence of this effect can be demonstrated by occluding the ear under investigation.

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