Residual Effects of Low Noise Levels on the Temporary Threshold Shift

Can a sound level which itself is insufficient to produce a temporary threshold shift (TTS) modify the recovery threshold to a more intense sound? TTS measurements were obtained following two conditions of high‐level noise exposure: (1) a control condition in which a period of silence followed a broad‐band noise exposure; (2) an experimental condition in which the same exposure was followed by noise levels which alone produce no measurable TTS. A 3‐min exposure to a noise level of 120 db SPL was followed: in the control condition, by a 3‐min exposure to silence; and in the experimental condition, by a 3‐min exposure to noise levels of 70 and 80 db SPL, which alone produced no measurable TTS. Threshold measurements were obtained for 16 ears at 4000 cps before and after noise exposure, for post‐exposure durations from 1 to 10 mins. Statistical evaluation demonstrated highly significant differences between the results of the experimental and control conditions. We interpret this finding as answering the initial question affirmatively.