Hearing by Bone Conduction and the Use of Bone-Conduction Hearing Aids

Abstract

THE exact nature of the communication of sound to the inner ear by bone conduction is somewhat obscure although the experimental work of Bekesy (1932), Barany (1938) and others offers suggestions of possible explanations of this means of stimulation. The relationship of the "occlusion" effect as observed when the meatus is plugged externally and internally and the effect of restriction of the conductive mechanism is discussed. It is suggested that in normal subjects and patients with perceptive deafness hearing by bone-conductor stimulation occurs virtually by means of the normal air-conduction mechanism due to the inertia of the free ossicular chain. In conductive deafness stimulation may be by direct excitation of the bony structure of the cochlea with the inertia of the cochlear fluid operative if the round window is unobstructed. In advanced stages of otosclerosis the obstruction of both windows would be expected to indicate an apparent perceptive element, i.e. a lowered bone-conduction audiogram. An account is given of experiments relating to the communication of sound from one ear to the other. When sound from a telephone receiver is applied to one ear the level of sound communicated to the other ear known as "cross-hearing" depends on the mode of application and the type of receiver. For a bone-conduction receiver applied to the mastoid there is in general very little difference in the level of sound reaching the two ears over the frequency range 250 to 2000 c/s. In the case of sound applied by an air-conduction receiver the communication of sound by "cross-hearing" suffers a reduction of 45 to 50 db. for an external receiver and 75 to 80 db. for an insert receiver. The importance of masking when making bone-conduction tests is emphasized and it is suggested that the application of the masking noise is accomplished most efficiently by means of an insert form of receiver. The usefulness of bone-conduction hearing aids and the conditions under which their application is superior or preferable to air-conduction types is discussed. Now let us consider the state of motion of the head when under the influence of a source of alter-Nov.-OTOL. AND LARYNG. 1

The floating mass transducer at the round window: Direct transmission or bone conduction?

“…Bone conduction (BC) is a complex physical phenomenon that different researchers have attempted to explain (Littler et al, 1952;Tonndorf, 1968). Recent investigations show (Stenfelt and Goode, 2005a) that inertial motion of the cochlear fluid and compression and expansion of the cochlear surrounding bones contribute to BC hearing.…”

The principles and practice of bone conduction audiometry: A review of the present position

“…Thus, the smaller the area the greater the attenuation, and in the limiting case when an insert receiver is used, thus presenting the smallest possible surface to the skull, the inter-aural attenuation increases to a figure as high is 90 db. As Littler et al (1952) so ably pointed out, the practical importance of this finding is considerable, making possible as it does the accurate determination of bone-conduction thresholds in the presence of conductive deafness well beyond the limit of 50 db. This is illustrated in Fig.…”

The Principles and Practice of Bone Conduction Audiometry: A Review of the Present Position

“…As Littler et al (1952) so ably pointed out, the practical importance of this finding is considerable, making possible as it does the accurate determination of bone-conduction thresholds in the presence of conductive deafness well beyond the limit of 50 db. This is illustrated in Fig.…”