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Temporary threshold shifts (TTS) in pure-tone hearing acuity are reported for 15 subjects exposed in separate 15-min periods to taped impact sounds [-played back at 124-to 127-dB peak sound-pressure level (SPL)•, to three levels of filtered (75-to 1200-cps) steady-state noise (90, 100, 110 dB SPL), and to combinations of the recorded impact sounds with each level of the steady-state noise. TTS's from all such exposures were typically small, with the largest shifts occurring in the 1000-to 3000-cps frequency range. When combined with 90-and 100-dB steady-state noise, the impacts caused ]ess threshold shift than when presented alone. Such TTS reductions were believed due to the relatively greater ability of the steady-state noise to arouse and sustain the acoustic reflex with its consequent sound-attenuation effect. The addition of the 110-dB steady-state noise did not induce a similar result quite possibly because this exposure, by itself, caused threshold shifts equal to or exceeding those of the impact sounds. More-effective stimulation of the acoustic reflex was believed responsible for findings showing less TTS for combined impact/steadystate noise than from exposure to just the steady-state component of the combination. Indirect measures of acoustic-reflex response [-contralateral remote masking (CRM)• generally indicated that those ears with a strong reflex response show less noise-induced shift. Correlations between TTS from impact and from steadystate noise for the subject group indicated some degree of positive correspondence limited to frequencies of of 2000 cps and below and strongest for those subjects with a poor reflex response as shown by their CRM data.

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