Interruption of recovery during intermittent stimulation produces greater loss in sensitivity

Abstract

Recent work on hearing loss to intermittent stimulation [G. R. Price, J. Acoust. Soc. Am. 56 (1974)] has documented an early recovery process (ERP) in the cochlear microphonic (CM) and led to the hypothesis that if the ERP is interrupted by subsequent exposures, loss in CM sensitivity would be greater than the loss to an equivalent amount of continuous stimulation or to an equal amount of intermittent stimulation timed to avoid interrupting it. This hypothesis .was tested by exposing anesthetized cat ears to 5.0-kHz pure-tone stimulation at an intensity 30 dB above that producing a maximum in CM output at the round window. Stimuli were on for 1 min and off for an appropriate period until a total of 30 rain of stimulation had been delivered. In one experimental group (N = 10), the exposure schedule interrupted the ERP when it had 5 dB left to run and for a second group (N = 10), the inte rexposure interval was 9 min, a period allowing the ERP to run to completion. Interrupting the ERP did result in significantly more loss than continuous stimulation. Allowing the ERP to go to completion resulted in less loss, although the difference was not statistically significant. Data from studies using human ears indicate that similar processes may also be acting in the human ear as well.