Variations in bone-conduction responses with contact area (further experiments)

Abstract

Bone-conduction (BC) thresholds measured in terms of acceleration had shown large systematic variations, mainly with contact area [J. Acoust. Soc. Am. 55, S62 (1974)]. Sound pressures generated in the occluded ear canal by BC signals of threshold strength were now found to be independent of contact area and, below 2 kHz, equal to those required for AC thresholds. Air/bone cancellation experiments revealed that, below 2 kHz and with the ear canal occluded, the BC stimulus is really given by the sound pressure generated in the ear canal, i.e., one measures the response to an air signal instead of that to a bone signal. [Essentially the same conclusion was reached for the cat; cf. Acta Otolaryng. Suppl. 132 (1966).] The cancellation experiments permitted the assessment of BC components unaffected by the sound pressure in the ear canal. These true inner-ear BC responses also varied with the contact area, demonstrating once more that acceleration is a poor indicator of BC responses. Experiments now in progress will determine if the above findings apply also to the unoccluded ear canal. [Supported by NIH and DRF grants.]