Loss of auditory sensitivity following exposure to spectrally narrow impulses.

Damage-risk criteria (DRC) for impulse noise do not presently take the spectrum of an impulse into direct account; yet it is clear that the ear is spectrally tuned. In order to establish the sensitivity of various sections of the cochlear duct to trauma from impulses, ears were exposed to 100 spectrally narrow impulses (1.0, 5.0, or 10.0 kHz) delivered in 10 min. Changes in auditory sensitivity were measured by an electrocochleographic technique in 43 cat ears and a threshold of loss established for each type of impulse. Expressed in SPL at the ear drum, the loss threshold rose at 3.2 dB/octave between 1.0 and 10.0 kHz. Expressed in stapes displacements, the loss threshold fell at 5.4 dB/octave in the same region. This curve was used to establish a tentative shape for a DRC for the human ear for impulse noise. The patterns of loss, rates of loss, lack of recovery, and loss thresholds are discussed with respect to their probable physiological basis with conclusion that mechanical displacement rather than metabolic exhaustion is the most reasonable causative factor.