CUMULATIVE AUDITORY EFFECTS RESULTING FROM MULTIPLE EXPOSURE TO INTENSE ACOUSTIC STIMULATION. PART 1. DEAFENING EFFECTS OF NOISE ON THE CAT
INDIANA UNIV AT BLOOMINGTON
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Aural effects of exposure to intense noise were investigated by measurements of the auditory sensitivity of cats, as determined by their behavior, before and after exposures and by histological examination of their cochleas. Exposures to 115 db for 18 hour or 105 db for 14 hour result in temporary threshold shift TTS with the same general features and course of recovery as for man. However, 14-hour expsures require 18 db less sound to produce the same magnitude of shift in the cat. Noise of 115 db for 14, 12, 2, or 8 hours without interruption produced permanent threshold shift PTS in which magnitude depended on the duration of the exposure, the test-tone frequency, and the susceptibility of the individual cat. When the 2-hour exposure was divided into 16 doses of 18 hour each and four different inter-exposure intervals of 0, 1, 6, and 24 hours were used, PTS declined as inter-exposure interval in creased. The pattern of injury ratings along the basilar membrane is highly similar to the pattern of the behavioral audiograms, if both are on anatomical-frequency scale.
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