Frequency and Intensity Effects on Noise-Induced Auditory Threshold Shift in the Squirrel Monkey
Nelson, Nancy A.
MetadataShow full item record
Six squirrel monkeys (Saimiri sciureus) were exposed for 96 hours to noise of 83 and 89 decibels centered at 500 hertz and to 80 and 90 dB noise centered at 4000 hertz. The exposure duration was interrupted by temporary threshold shifts (TTS) testing done at 2, 4, 8, 12, 16, 24, 36, 48, 60, 72, 84, and 96 hours of exposure. The TTS growth curves for the 500 Hz exposures indicated small threshold shifts and a reasonably uniform increase in TTS as exposure intensity increased. TTs did not exhibit asymptotic behavior at this frequency. TTS growth curves for the 4000 Hz exposures also indicated increasing shifts as exposure intensity increased, but in a manner much less uniform than observed at 500 HZ. TTS curves for the 4000 Hz exposures also did not exhibit asymptotic behavior. For all exposures but the 90 dB intensity, the mean thresholds of the six monkeys had returned within 5 dB of the pre-exposure mean by 8 hours after exposure. Results form this experiment suggested that in using the squirrel monkey as an animal model, TTS curves demonstrate somewhat different manifestations at differing frequencies. This may occur because of absolute sensitivity effects on auditory function in the monkey ear.