THE FUNCTION of the audiologist is twofold (1) to assess the hearing deficit of the individual and (2) to determine, if possible, the locus (or loci) of pathology from which the deficit arises. While bone-conduction audiometry gives a measure of inner ear deficit (or of cochlear reserve), the difference between air-conduction (AC) and bone-conduction (BC) sentitivity gives a measure of middle ear deficit. (An air-conducted signal passes through the outer and middle ear before entering the inner ear. The bone oscillator, on the other hand, stimulates the inner ear directly. Thus, assuming the outer ear is normal, any difference in sensitivity to AC vs BC stimulus is attributed to middle ear loss.) The problem of assessing bone conduction lies in the fact that it is difficult to stimulate one ear without simultaneously stimulating the other. Thus, a measure of bone conduction of the tested ear may be an indirect measure