Frequency spread of TTS in humans and squirrel monkeys exposed to industrial noises

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.]