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A RAPID MEASURE OF THE SUSCEPTIBILITY TO AUDITORY FATIGUE
S. Mönikheim, M.-C. Botte, C. Baruch
To cite this version:
S. Mönikheim, M.-C. Botte, C. Baruch. A RAPID MEASURE OF THE SUSCEPTIBILITY TO AUDITORY FATIGUE. Journal de Physique Colloques, 1990, 51 (C2), pp.C2-151-C2-154.
�10.1051/jphyscol:1990236�. �jpa-00230656�
COLLOQUE DE PHYSIQUE
Colloque C2, suppl6ment au n02, Tome 51, Fgvrier 1990 ler Congres Fran~ais d'Acoustique 1990
A RAPID MEASURE OF THE SUSCEPTIBILITY TO AUDITORY FATIGUE
S. M ~ N I K H E I M , M. -C. BOTTE and C. BARUCH
Laboratoire de Psychologie Exp&rimentale, CNRS URA 316, Universite Paris V, 28 rue Serpente, F-75006 Paris, France
PM
-
Une premiere experience a compare deux mkthodes de mesure de la sensibilite B la fatigue auditive. Quinze sujets ont Btd exposhs h un son de 1000 Hz B 90 dB SPL pendant 60 S. La diminution temporaire de la sonie (TLS) d'un son test de 1000 Hz h 55 dB Btait mesurge B partir de l'estimation de la sonie au moyen de nombres ainsi que par 1-ajustement du niveau du son test de facon B rdtablir sa sonie initiale (pr6-exposition). La corr6lation entre les deux valeurs de TLS atteint 0,85, mais le TLS obtenu par la mdthode d'ajustement est inf6rieur de 8 dB en moyenne B celui ddduit des estimations numeriques. Une seconde experience a examin6 la precision de la memorisation de la sonie par la methode d'ajustement du niveau avec le meme paradigme experimental que dans la premihre experience, mais en l'absence de son fatigant. Dans certaines conditions, une sous-estimation (d'environ 4 dB) de la sonie mBmorisQe se manifeste.Abstract - A first experiment compared two methods for measuring the susceptibility to auditory fatigue. Fifteen subjects were exposed to a 1000-Hz, 90-dB SPL tone for 60 sec. The temporary loudness shift (TLS) of a 1000-Hz, 55-dB test tone w a s established by estimates of loudness (numbers), and also by adjustments of the teat-tone level in order to reproduce the initial (pre-exposure) loudness. The correlation between the two values of TLS reaches 0.85, however the TLS provided by the adjustment method is lesser (by an average of 8 dB) than the TLS deduced from the numerical estimates. A second experiment investigated the accuracy of loudness memorization by the method of level adjustment in the same paradigm as in the first experiment, but without the fatiguing tone. In some conditions, the memorized loudness is under-estimated
(by about 4 dB)
.
The individual susceptibility to auditory fatigue has been traditionally assessed by the measurement of the temporary threshold shift (TTS) which follows a long-duration exposure to an intense sound.
A very high correlation exists between this kind of TTS and the loudness reduction provided by an intermittent exposure for a short duration /l/.
This temporary loudness shift (TLS) has been called ipsilaterally induced adaptation /2/ and was recently shown to be a supra-liminal manifestation of auditory fatigue that has a cochlear origin /3/. The measurement of individual TLS by a few minutes testing would then give information about individual susceptibility. The method of direct loudness estimation, by means of numbers proportional to the perceived loudness, apparently provides an easy measurement of the rapidly changing TLS. Nevertheless, the nature of the task (production of numbers) led to interindividual differences which are not due to the suceptibility to auditory fatigue. One way to avoid these shortcomings is to transform the decreases in numerical estimates into equivalent decreases in level derived from individual loudness functions. But, the loudness functions also depend on the subject's use of numbers.
The present experiments sought to establish the validity of a
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990236
COLLOQUE DE PHYSIQUE
different method for TLS measurement : the adjustment of the test-tone level in order to compensate for TLS.
'
15 subjects with normal 1000-Hz thresholds participated in the experiment. After the measurement of the loudness function, one experimental session was devoted to the two different TLS measuremente.Loudneee function. A 1000-Hz, 2-sec tone was randomly set to one of 7 levels (15-75 dB SPL) and presented to the right ear every 8 sec. The subject had to numerically estimate the loudness of the tone, without any imposed scale. After 3 presentations of the 7 levels, a loudness function was caculated by averaging the last two estimates for each level.
TLS measurements. A 1000-Hz tone was presented to the right ear at 55 dB (the tested level for TLS) during 10 sec and the subject was asked to estimate and to memorize its loudness. After the first 10 sec, the tone level was intermittently increased to 90 dB for 10 sec every 20 sec. The 55-dB tone followed each of the six occurrences of this increment.
Subject had then to judge the loudness and to adjust immediately afterwards (by means of a potentiometer) the tone level to reproduce the loudness perceived during the first 10 sec of the trial (pre-exposure).
RESULTS
Whatever the method, the TLS increases as a function of time during the session as seen previously for loudness estimates /2,3,4/. The maximum amounts of TLS which occur during the last 10 sec have been compared for the two methods.
Table I lists the maximum TLSs from estimates ( % and equivalent dB) and the maximum TLSs from adjustment (dB).
Table I
-
Maximum TLS measured by the methods of loudness estimation and level adjustment. Individual values of 15 subjects and correlations (r) are presented.Subject ! Loudness- ! Ad.lustment
! !
! % ! equivalent dB ! dB
...
l ! 0 I 0 I 0.25
2 ! 50 ! 8.75 I 8
3 ! 7 3 ! 38.67 ! 15.75
4 ! 86 ! 40 ! 12.5
5 ! 50 ! 17.14 ! 5.75
6 ! 50 ! 8.33 ! 5.75
7 1 75 I 27.75 ! 22
8 ! 0 ! 0 I 1
9 ! 20 ! 2.61 ! 5.75
10 ! 23 ! 4.27 I 7.25
11 ! 64 ! 20.13 I 16.5
12 ! 94 ! 36.8 ! 18.75
13 ! 66 ! 31.5 ! 13.25
14 ! 70 ! 18.78 I 8.75
15 ! 70 ! 27.6 ! 14.5
...
M I 52.7 ! 18.82 ! 10.38
________-__________---
SD I 29.5 I 14.35 ! 6.40
The correlations between TLSs from loudness estimation and TLS from level adjustment are fairly high (r = 0.82; p < 0.001 and r = 0.85; p <
0.001). However, the mean TLS in dB for level adjustment (10.4 dB) is significantly lower than that for numerical estimation (18.8 dB) (t
=
3.33; p < 0.01). Therefore, while adjustment and loudness estimation similarly classify the subjects with respect to their TLSs, the two methods result in a mean difference of more than 8 dB.
The 53% mean reduction of loudness estimates is noteworthy because it corresponds to a 10 dB decrease of level in the standard loudness function, and the adjustment method also shows a 10-dB decrease suggesting that the TLS from numerical judgements could be overestimated. Actually, the conversion into equivalent dBs leads to systematically larger TLSs because a majority of subjects used a relatively small scale of numbers in the loudness function measurement;
thereafter, a small change in numbers during the TLS measurement corresponds to an exceedingly large decrease in equivalent level.
This experiment sought to assess the accuracy of the memorized loudness in a paradigm similar to that of Experiment 1.
14 subjects with normal 1000-Hz thresholds participated in two experimental conditions. In condition 1 (C l), a 1000-Hz, 55-dB tone was presented first to the right-ear for 10 sec; the subject's task was to memorize its loudness. During the following 120 sec, six 10-sec pauses alternated with six 1000-Hz tone presentations. At each presentation the level of the tone was set randomly at 37, 40, 43, 46, 49, or 52 dB SPL and the eubject had to modify this level to reproduce the loudness of the first 10-sec presentation. The level of presentation of the tone to be adjusted was never set above 55 dB to avoid the underestimation of the loudness of decreasing tones /4/. In condition 2 (C 2), the paradigm was the same as in condition 1 but the silent pauses were replaced by 1000-Hz tones at 40 dB. Half of the subjects completed 3 trials (P l-P 3) in condition 1 then 3 trials (P l-P 3) in condition 2; the order was inverted for the other half.
RESULTS
The adjusted levels were not different from the first to the sixth adjustments in a trial as shown by an analysis of variance (VAREDI) [F (5,65) = 1,721. But the level fixed for the adjustment to begin with, strongly influences the error of adjustment (Fig. 1).
EREOR OF ADJUSTMENT (dB)
"
34 37 40 43 44 49 52 55
LEVEL OF PRESEN-ON (dB)
Fig. 1
-
Error in adjusted level of a memorized 55-dB, 1000-Hz tone as a function of the presentation level for adjustment. See text for inset.COLLOQUE DE PHYSIQUE
The presentation level has a highly significant effect on the error of adjustment : The adjusted level decreases progressively as the presentation level moves from 55 dB towards lower levels [F (5,60) = 35.88; P < 0.00051. This effect is more marked in the condition with silent pauses (C 1) for which the errors are significantly larger than in the condition with the "40-dB" pauses (C 2) [F (1.12) = 4.86; p <
0.051. However, the adjusted level remains rather close to 55 dB; the mean error does not exceed 4-5 dB. Moreover the repetition does not affect the results [F (2,241 = 0.95; not significant].
All the features of the loudness memorization in this experiment (independence of time, independence of interference by the 40-dB tone, dependence on the range of intensities to be processed) suggest that loudness was coded according to the "context-coding mode" in which the accuracy of the memorized loudness is independent of time and deteriorates as a function of the width of the intensity range of the stimuli /5/. However, the reason for the direction of the error in adjustments (overestimation of the adjusted level, or underestimation of the memorized loudness) is not clear; since a 55-dB level is relatively moderate, a possible explanation is the tendency of small stimulus values to become underestimated after a retention interval /6/.
The measures of TLS by the method of adjustment are highly correlated with those from loudness estimates even if the first method yields considerably lower values. Difficulties in using a numerical scale probably explains a large part of this difference. The role of memorization might also explain a slight disparity in the TLS values:
for level adjustments, an underestimation of a few decibels is found without any fatiguing sound when the adjustable level is 18 dB lower than the memorized level; this effect could provide a slight underestimation of the TLS measured by level adjustment, especially for the most susceptible subjects insofar as the level of the adjustable test tone is lowest for those subjects. Whether a similar underestimation of TLS due to loudness memorization also affects the TLS obtained with numerical estimates remains questionable. Finally, the adjustment method proves reliable enough to be preferred to the estimation method, especially for setting up an audiological test.
This research was funded, in part, by the Ministbre de 1'Environnement (Grant No. 88091).
/l/ Botte, M.C., Charron, S., M6nikheim, S. and Scharf, B., Predicting susceptibility to auditory fatigue on the basis of loudness adaptation, In Noise as a Public Health Problem, B. Berglund, U.
Berglund, J. Karlsson and T. Lindall, Eds, Stockholm, Sweden (1988) 39.
/2/ Canevet, G., Scharf, B. and Botte, M.C., Loudness adaptation, when induced, is real, Br. J. Audiol. 3 2 (1983) 49.
/3/ Charron, S. and Botte, M.C., Frequency selectivity in loudness adaptation and auditory fatigue, J. Acoust. Soc. Am. (1988) 178.
/4/ Botte, M.C., Charron, S. and Canhet, G., On the measurement of loudness adaptation, In Fechner Day-86, B. Berglund, U. Berglund and R. Teghtsoonian, Eds, Stockholm, Sweden (1986) 53.
/5/ Durlach, N.I. and Braida, L.D., Intensity perception. I. Preliminary theory of intensity resolution, J. Acoust. Soc. Am. 46 (1969) 372.
/6/ Moyer, R.S., Bradley, D.R., Sorensen, M.H., Whiting J.C., and Mansfield, D.P., Psychophysical functions for perceived and remembered size, Science ZQQ (1978) 330.
