Cochlear damage following interrupted exposure to high-frequency noise.

Four groups of chinchillas were exposed to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 80 or 86 dB SPL on interrupted schedules with 18, 42 or 162 h of rest between successive 6-h exposures. Damage in these ears was compared to that in ears receiving continuous exposures which were equal in total energy. The same pattern of cell loss was found in ears damaged by continuous and interrupted exposures. However, both the incidence and average size of the lesion in the basal turn were reduced in all ears receiving interrupted exposures. Eighteen hours of rest between successive 6-h, high-frequency noise exposures was found to provide significant protection from damage for the basal turn of the chinchilla cochlea.