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.(ABSTRACT TRUNCATED AT 250 WORDS)

The study aimed at understanding the loudness memory and especially at testing the hypothesis that the loudness contour of a tone sequence influences differential sensitivity -over a long lapse of time- in the domain of intensity. In the first experiment, the loudness of a first reference tone had to be reproduced after a delay (.5, 2, 10, or 20 s) by adjusting the level of a second tone. Errors of adjustment depended on the initial level of the second tone and on the delay. In the second experiment, subjects compared two tones separated by silences. For delays of .5 and 2s, the best performance was found for comparison levels equal to or lower than the reference. In the third experiment, the tones to be compared were separated by 6 interpolated tones at different levels. For sequences with increasing and decreasing levels, the opposite shifts of sensitivity which were observed could explain the adjustment bias of the first experiment. Moreover, only interpolated contours having components at least 6 dB higher than the reference provide a significant impairment of the performance. These results suggest a “retroactive masking” of the memorized trace by subsequent louder sounds.

Measurements of induced loudness adaptation and temporary threshold shift (TTS) were made on 48 young subjects. Loudness adapatation of a continuous 60-dB test tone was induced in the right ear by an intermittent 1000-Hz inducer tone at 90 dB, presented every 30 s for 20 s. The loudness of a 1000-Hz or 1160-Hz test tone at 60 dB was measured after each occurrence of the inducer by the method of successive magnitude estimations. Induced adaptation caused the loudness of the continuous tone to decrease on the average by 38% (the equivalent of 14 dB) after 120 s. In a separate session, the subject's right ear was exposed for 45 min to a 1000-Hz tone at 90 dB SPL. One minute after exposure, thresholds were measured by Békésy tracking for 4 min. The maximum TTS, averaged across subjects, was 20.4 dB at a mean frequency of 1635 Hz. The correlation between maximum TTS and the amount of induced adaptation was 0.83. Thus ipsilaterally induced adaptation (IIA), which is akin to temporary loudness shift, may stem from cochlear mechanisms just as TTS does. Also, IIA could become the basis for an audiological test to identify those individuals most susceptible to auditory fatigue. [Work supported by Ministère de l'Environnement and NIH.]