No abstract

Few investigators have studied the appropriateness of an animal model for the effects of noise on hearing in the human. The goal of our research is to provide such data for the squirrel monkey. Our approach was to reproduce industrial working conditions by using exposures of work-day length and recorded factory noises, in addition to octave-band and pink noises for both humans and monkeys. The results enable us to compare the effects of commonly used laboratory noises with those of recorded factory noises on man and monkey. We exposed 20 humans and 12 squirrel monkeys twice to each of five different noises (pink noise, two octave bands centered at 500 Hz and 4 kHz, stamping plant noise, and stall wrench noise) for 8 h at each of two levels. Auditory thresholds were determined after 1, 2, 4, and 8 h of noise exposure. TTS growth to each noise demonstrates that the squirrel monkey is similar to the human in the manner in which auditory thresholds shift as a function of time for these various noises. Presumably, the physiological changes underlying TTS are also similar for the two species. [Work supported by NIOSH.]

We have been investigating the squirrel monkey (Saimiri sciureus) as a suitable animal model for testing the effects of noise on hearing. Our previous research has shown a similarity between human and squirrel monkey temporary threshold shift (TTS) growth with time in the noise. The goal of this study was to measure the frequency spread of TTS to five different industrial noises for both humans and squirrel monkeys and to compare the results. Fifteen human subjects and six squirrel monkeys were exposed to each of the five noises for 8 h, and TTS was measured at ten different frequencies ranging from 250 Hz to 8 kHz. In the experiments with humans, five frequencies were tested twice (counterbalanced) after each 8-h session. In the squirrel monkey experiments, a complete 8-h exposure was required for each frequency tested, since only one frequency could be measured each time the monkeys were removed from the noise. The results indicate that in predicting human TTS from the squirrel monkey TTS for these exposures, TTS would be overestimated at 750 Hz and 1 kHz and underestimated at 5.6 kHz, whereas the TTS at other frequencies would correspond closely. [Work supported by NIOSH.]