Time and Frequency Characteristics of Temporary Threshold Shifts Caused by Pure Tone Exposures

The time-frequency characteristics of Temporary Threshold Shifts (TTS) caused by pure tones were determined using the Békésy audiometric method with narrow-band noise of short duration as the probe stimuli. Two experiments were done using exposures of 3 min at 100 dB above threshold. In the first experiment, the frequency dependent characteristics of TTS produced by a 500-Hz tone were assessed. Thresholds were determined from 0.25 to 2 kHz in 1/ ₂-octave steps for up to 20 min after the exposure. The results showed that the maximum affected frequency was 1/ ₂ octave above the exposure frequency. In the second experiment, the TTS recovery curve produced by a 1-kHz pure tone exposure was assessed at 1.5 kHz, at approximately 15 s intervals for the first 5 min and at regularly increasing intervals up to 45 min after the exposure. The results showed a maximum in the recovery around 2 min after the exposure. The data gathered in these experiments were used to construct a mathematical model of TTS recovery. The model describes both the 1/ ₂-octave shift and the 2-min bounce and it can be used in the comparison of temporary changes in the auditory function, assessed at different times and frequencies.