Effects of middle-ear pressure on the auditory periphery

Abstract

A series of 52 young adult guinea pigs were used to study the effects of middle-ear pressure on the electrophysiological response of the cochlea. A round window electrode was used to record the cochlear microphonic (CM) and N1 action potential. Pure tones from 80 to 30 000 Hz were used to elicit the CM response; 0.1-msec clicks presented at ten clicks per second were used for N1 response studies. Middle-ear pressures ranging from −300 to +300 mm H20 were examined. Both pressure and frequency were examined in a pseudorandom order. CM response sensitivity (1 μV isopotential contour) and dynamic range of the CM were measured. Greater changes in the cochlear potentials were noted for negative pressures than for positive pressures. Also, it was found that there was a greater falloff of sensitivity of the CM as a function of pressure for small pressure variations than for greater pressure changes. The effects of middle-ear pressure were frequency dependent. Changes in the dynamic range of the CM were found to be consistent with predicted middle-ear transmission changes. [This research was supported by the Office of Naval Research N00014-67-A-0103-0031.]