TTS growth and frequency spread to a 500 Hz octave band of noise

Abstract

Six squirrel monkeys were exposed to an octave band of noise centered at 500 Hz and presented at 95 dB SPL for up to 96 hours. TTS4.5 was measured either during a 5-min interruption in the exposure or at the end of continuous exposures of various lengths. Growth of TTS4.5 measured under interrupted and continuous exposures showed no differences. After 16 hours, both growth functions showed plateaus which were followed by a continuation of the growth of TTS4.5 through 96 hours of exposure. As with our previous reports of TTS in this primate, no asymptotic threshold shift was observed. Spread of frequency effects were measured to 24 hour exposures to the same noise. TTS4.5 showed a broad shift of about 14 dB in the 125 Hz–1.5 kHz range. Second TTS4.5 maxima of 10 dB were measured at 4.5 and 7.5 kHz. While the squirrel monkey growth functions parallel published human data, the frequency spread data appears to show a broader primary effect in the low frequencies for the squirrel monkey. [This study was supported in part by Henry Ford Hospital Institutional Grant from the Ford Foundation, The Deafness Research Foundation, and an NIH Biomedical Research Grant.]