NEW DATA ON THE SHORT-TERM EFFECTS OF TONE EXPOSURE

Three experiments studied the short-term effects of moderate- and high-level tone exposures on threshold and loudness. Experiment 1 measured temporary threshold and loudness shifts (TTS and TLS) due to a 1000-Hz exposure at a moderate level (65 dB SPL) as a function of exposure duration. Whereas there was no significant TTS, TLS was as high as 11 dB and recovered rapidly. TLS was significantly larger for the highest test levels. TTS and TLS were practically independent of exposure duration. Experiment 2 measured TTS and TLS as a function of test frequency following exposures to 500-, 1000-, or 3000-Hz tones at 65 dB SPL. The frequency patterns of TLS were established at test levels of 20-60 phons. TLS and TTS had similar frequency patterns with a maximum at the exposure frequency, but TLS patterns were higher and more extended than those of TTS. In experiment 3, subjects were exposed to a 1000-Hz tone at a high level (90 dB SPL). Frequency patterns for TTS or TLS at a 60-dB test level were measured repeatedly during 5 1/2 min after the end of exposure. Two short-term effects were observed immediately after the exposure: (1) a slight TTS (4.5 dB) at the exposure frequency which disappeared 2 to 3 min later; and (2) a large TLS (9 dB) which extended over the whole range of test frequencies, recovered rapidly, and had disappeared by 330 s after exposure. Concomitant with these short-term effects, an additional long-term TTS affected the test frequencies above the exposure frequency and reached a maximum of 17 dB at 150-s post-exposure, after which it began to recover relatively slowly. Thus, as well as causing ''classical'' long-term fatigue, high-level exposure also results in marked short-term effects that strongly reduce loudness over a wide frequency range.