AM-65-1 

AUDITORY FATIGUE: INFLUENCE OF MENTAL FACTORS 

Approved by 

STANLEY R. MoHLER, M.D. 

DIRECTOR, CARl 

MARY JAYNE CAPPS, M.A. 

AND 

WILLIAM E. COLLINS, PH.D. 

PSYCHOLOGY LABORATORIES 

FEDERAL AVIATION AGENCY 

Office of Aviation Medicine 

Civil Aeromedical Research Institute 

Oklahoma City, Oklahoma 

,January 1965 

Released by 

»t 41r~ 

M. S. WHITE, M.D. 

FEDERAL ~ SURGEON 
R c 16 5 ~ 

UsiJi 

J?&F:!-1'/ 

AUDITORY FATIGUE: INFLUENCE OF MENTAL FACTORS 

MARY JAYNE CAPPS AND WILLIAM E. COLLINS 

Conflicting reports regarding the influence of mental tasks on auditory fatigue have recently appeared in the 

literature. In the present study, 10 male subjects were exposed to a 4000 cps fatigue tone at 40 dB SL for 3 min 

nnder conditions of mental arithmetic and reverie. Temporary threshold shifts, as indicated by comparing pre- and 

post-fatigue thresholds, were consistently greater when subjects worked mental arithmetic during exposure to the 

fatigue tone than when they engaged in reverie. 

Wernick and Tobias1 recently reported that 

the amount of temporary threshold shift (TIS) 

induced by a fatigue tone varied with instructions designed to influence the subject's level 

of mental activity. Shifts were greater for both 

low-level ( 40 dB SL) and high-level (90 dB SL) 

fatigue when subjects performed mental arithmetic than when they simply relaxed in a 

"reverie" state. Subsequent studies have failed 

to confirm this finding~ 2-4 In two of these 

studies,''4 tasks different from those used by 

Wernick and Tobias were employed. Experience with the manipulation of sensory responses by instructions concerning mental activity indicates that all tasks are not equal in 

producing a given effect.'·" Consequently, the 

present authors replicated the low-level fatigue 

condition of the Wernick and Tobias study in 

order to explore the possibility that differences 

in task or procedure might account for the failure of the subsequent experiments to detect 

differences in fatigue as a function of mental 

activity during the fatigue period. 

APPARATUS 

Figure 1 shows a block diagram of the instrumentation which, as with Wernick and Tobias, comprised three basic parts: a fatigue 

channel, a test channel, and a light signal for 

the ·subject. The fatigue tone was generated 

by a Hewlett-Packard model 200 CD oscillator 

and led through a Hewlett-Packard model 

350 B variable attenuator. The test tone, generated by a Hewlett-Packard model 201 C oscillator was led through a Grason - Stadler 

model 829S electronic switch, a HewlettPackard model 350 B variable attenuator, and 

a Grason-Stadler model E-3262A recording attenuator (attenuation rate - 4 dB per sec). 

Test tone, fatigue tone, or no tone (as selected 

by the experimenter) was transmitted. to one 

ear by a set of Telephonics TDH-39 earphones 

with MX-41/ AR cushions. The signal light in 

the subject room was controlled by the 

experimenter. 

SUBJECTS 

Subjects were 10 paid volunteers, experimentally naive males between the ages of 19 

arid 29 years. All had normal hearing. All 

subjects received fatigue stimulation under conditions of mental arithmetic ( MA) and "reverie" (REV). 

PROCEDURE 

The procedure replicated exactly that of the 

low-level group of Wernick and Tobias, omitting the control conditions in which no fatigue 

stimulus was presented during the task. Half 

of the subjects received MA first and the remainder received REV first. The two trials 

-1-

433 
4000 CPS. 

SOURCE 

CONTROL 

Figure 1. Block diagram of the apparatus. 

were separated by 48 hours, and the first trial 

was preceded by several practice threshold 

determinations. A 3 min rest period followed 

a 2 min Bekesy-type threshold determination 

for the test tone, after which the fatiguing 

stimulus was presented for 3 min. A 3 min 

continuous threshold determination at the fatigue tone frequency was made immediately 

following the cessation of the fatigue tone. 

The test tone was a 4000 cps pulsed tone 

( 0.2 sec on, 0.2 sec off); the fatigue tone was 

a 4000 cps continuous tone presented at a sensation level of 40 dB. 

The instructions given in the original study1 

were used here and comprised directions for 

activity during the fatigue stimulus. A subject was instructed either ( 1) to relax and follow no train of thought, or ( 2) to work a 

mental arithmetic problem involving continuous division with a constant divisor. A light 

in the subject-room provided the signal for 

the beginning of the fatigue period during 

which· the subject performed as previously instructed. The experimenter turned off the 

light to signal the subject to start establishing 

his post-fatigue threshold. 

RESULTS 

Figure 2 shows the course of recovery from 

auditory fatigue for each of the two conditions. 

It is clear that exposure to the fatigue tone 

while the subjects were doing MA consistently 

produced greater TIS than exposure to the 

tone during REV. The mean TIS 10 sec after 

cessation of the fatigue tone was 6.25 dB 

(standard deviation = 3.14) for MA and 

2.15 dB (standard deviation = 2.73) for REV, 

giving a difference of 4.10 dB favoring MA. 

A t test for correlated observations7 conducted 

on the individual differences in TIS between 

MA and REV at the 10 sec point, yielded a t 

value of 6.16 with 9 degrees of freedom, significant at the .001 level. All of the subjects 

tested, including seven who did not .participate in the formal experiment but only in pilot 

studies and such, shoWed a greater shift for 

the MA condition. 

In addition to the difference in TIS between the two conditions, a longer recovery 

time for MA seems to be indicated by the 

curves of Figure 2. 

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7 

.:a 6 -a ...-. MENTAL ARITHMETIC 

z 5 - o-o REVERIE .... 

..... 4 -:c 

~ 3 

Q 

.... 2 0 

:c 

~ 1 ..... 

c.:: 

:c 0 .... -1 

10 15 20 30 45 60 90 120 180 

TIME IN SECONDS 

(log scale) 

Figure 2. Mean temporary threshold shift for 10 subjects as a function of instructions 

regarding mental activity. Subjects were either in "reverie" or performing 

continuous mental division during exposure to the fatiguing tone. 

DISCUSSION 

Some possible explanations may be offered 

to account for the failure of other investigators 

to obtain these results. Ward and Sweee used 

a task involving the adding of columns of figures and failed to obtain a "mental task - reverie" difference under high-level ( 100 dB SPL) 

fatigue conditions. Barring the influence of 

some unknown procedural differences, it is 

possible that the task employed by Ward and 

Sweet was simply not so effective as the mental 

arithmetic condition used here and in the ·Wernick and Tobias study. Work in progress indicates that written computational tasks may 

not have the same effect on auditory fatigue 

that continuous mental division does. 

Similarly, Bell and Stem4 used written arith'-

metic problems (long division) instead of the 

continuous division task, and added a light 

tracking task as an additional condition. They 

compared the TTS obtained with these two 

tasks to that obtained under reverie with both 

a high-level ( 100 dB SPL) and a low-level 

(50 dB SPL) fatiguing tone and reported no 

simificant differences between the task and 

reverie conditions. Their data do show, however, that the TTS was greater for the long 

division task than for reverie at both low and 

high levels in the first trials. That the differences obtained on the first set of trials were 

not greater and that they were not maintained 

with repeated trials might result from: ( 1) 

differences in the effectiveness of written long 

division and mental arithmetic, and ( 2) the 

fact that some tasks may lose their arousal 

value with repeated use.8 

The Riach and Sheposh3 study reported a 

replication of the Wernick and Tobias procedure but failed to obtain MA-REV differences 

in TTS with either high- or low-level fatigue. 

If the mean TTS obtained under the REV condition in the present study and in those of 

-3-
Wernick and Tobias and of Bell and Stem may 

be used as a criterion, it would appear that 

Riach and Sheposh did not have appropriate 

REV conditions. They report a mean 10-sec 

TTS of about 9 dB for both MA and REV with 

low-level fatigue. The range of meari REV 

TTS values at similar levels in the other three 

studies was 2.1-4.3 dB. 

CONCLUSIONS 

The possibility of a central influence on 

auditory fatigue cannot be discounted on the 

grounds that the data result from chance variation. The choice of "mental task" and the 

instructions for "reverie" appear to be primary 

considerations in experiments designed to study 

differences in TIS as a function of mental 

activity. 

REFERENCES 

1. J. S. Wernick and J, V. Tobias, "Central Factor in 

Pure-Tone Auditory Fatigue," J. Acoust. Soc. Am. 35, 

1967-1971 (1963). 

2. W. D. Ward and D. F. Sweet, "Absence of Central 

Factors in Auditory Fatigue," J. Acoust. Soc. Am. 35, 

1880-1881 (A) (1963). 

3. W. D. Riach and J. Sheposh, "Further Observations 

on the Central Factor in Auditory Fatigue," J. Acoust. 

Soc. Am. 36, 967-968 (1964). 

4. D. W. Bell and H. W. Stem, "Effects of Extraneous 

Tasks on Auditory Fatigue," J. Acoust. Soc. Am. 36, 

1162-1166 (1964). 

5. W. E. Collins, "Effects of Mental Set Upon Vestibular 

Nystagmus," J, exp. Psycho!. 63, 191-197 (1962). 

6. W. E. Collins, "Manipulation of Arousal and its Effects 

on Human Vestibular Nystagmus Induced by Caloric 

Irrigation and Angular Accelerations," Aerospace Med. 

34, 124-129 (1963). 

7. B. J. Winer, Statistical Principles in Experimental Design (McGraw-Hill Book Co., Inc., New York, 1962), 

Chap. 2, pp. 39-43. 

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