AM-65-.2 

EFFECTS OF SEVERAL MENTAL TASKS 

ON AUDITORY FATIGUE 

Approved by 

STANLEY R. MoHLER, M.D. 

DIRECTOR, CARl 

WILLIAM E. COLLINS, PH. D. 

AND 

MARY JAYNE CAPPS, M.A. 

PSYCHOLOGY LABORATORIES 

FEDERAL AVIATION AGENCY 

Office of Aviation Medicine 

Civil Aeromedical Research Institute 

Oklahoma City, Oklahoma 

January 1965 

Released by . 

»t 4.91'~ 

M. S. WmTE, M.D. 

FEDERAL Am SuRGEON 
EFFECTS OF SEVERAL MENTAL TASKS 

ON AUDITORY FATIGUE1 

WILLIAM E. COLLINS 

AND 

MARY JAYNE CAPPS 

Eight male Ss were exposed for three minutes to a 4000 cps fatigue tone at 40 dB SL. Each S was tested 

under four task-conditions: mental arithmetic (MA), written long division (LD), threshold determination on a 500 cps 

tone (TD), and reverie (REV). Temporary threshold shifts (TTS) were computed by comparing pre- and post-fatigue 

thresholds. MA produced significantly more TTS than any other condition, and LD resulted in greater shifts than 

REV. Amount of auditory fatigue can vary with the type of mental activity performed by the S. 

Recent studies have demonstrated differential 

effects of instructions regarding mental activity 

on responses to sensory stimulation. Thus, for 

example, the effectiveness of a vestibular stimulus in eliciting a nystagmic eye response is 

greater when subjects are engaged in solving 

mental arithmetic problems than when they are 

in "reverie" (Collins, 1962; 1963). Similarly, 

Wernick and Tobias ( 1963) found that the 

temporary threshold shift ( TTS) resulting from 

both low-level and high-level auditory fatigue 

was increased when, during exposure to the 

fatiguing stimulus, subjects performed mental 

arithmetic tasks (silent, continuous division) as 

opposed to relaxing in reverie states. 

Three subsequent reports (Ward & Sweet, 

1963; Bell & Stem, 1964; Riach & Sheposh, 

1964) failed to substantiate the Wernick and 

Tobias ( 1963) data. However, in the former 

two of these reports, different "mental tasks" 

were employed. 

Since not all tasks appear equally potent in 

producing a given sensory effect (Collins, 1962; 

1964), Capps and Collins ( 1965) replicated 

exactly the Wernick and Tobias ( 1963) procedure for low-level fatigue and confirmed the 

finding that the mental arithmetic ( MA) task 

1 Instrumentation assistance rendered by Peter Bergsneider 

is gratefully acknowledged. 

during the fatigue period resulted in statistically 

greater TTS than the reverie ( REV) condition. 

The authors suggested that the task (addition 

of columns of figures) employed by Ward and 

Sweet ( 1963) and those (light tracking and 

pencil-and-paper long division) used by Bell 

and Stem ( 1964) might not have been equivalent to MA. 

The Riach and Sheposh ( 1964) study was 

reported as a non-confirmatory replication of 

Wernick and Tobias ( 1963) conditions. However, Capps and Collins ( 1965) noted that 

the large TTS obtained by Riach and Sheposh 

for the· REV condition under low-level fatigue 

( about 9 dB) was far out of the range of 

values ( 2.3 - 4.1 dB) reported by other investigators for the same condition (Wernick 

and Tobias, 1963; Bell and Stem, 1964; Capps 

and Collins, 1965). 

The present study was designed: ( 1) to provide further evidence concerning the effects 

on TTS of mental arithmetic ( MA) and reverie 

(REV) during periods of low-level auditory 

fa~igue; ( 2) to compare with MA and REV 

the effect on TTS of a different "mental task" 

(written long division); and ( 3) to examine 

the influence on TTS of attending to other 

auditory stimuli during the fatigue period. 

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TEST-TONE 500 CPS 

OSCILLATOR 

TEST-TONE 

OSCILLATOR 

• FATIGUE-TONE 4000 CPS 

OSCILLATOR 1---___;__;____;__~ 

VARIABLE 

ATTENUATOR 

___/·--------~~~ LAMP 

r-~RE~CO~R-DIN-G~-----j_~.__ 

VARIABLE 

ATTENUATOR 

ATTENUATOR RECORDING 

I ATTENUATOR 

CONTROL 

I 

I 

I 

TDH-39 

Figure 1. Block diagram of the apparatus. 

APPARATUS 

Figure 1 shows a block diagram of the instrumentation. The 4000 cps fatigue tone was 

generated by a Hewlett-Packard model200 CD 

oscillator and led through a Hewlett-Packard 

model350 B variable attenuator. The 4000 cps 

and 500 cps test tones were generated respectively, by Hewlett-Packard model 201 C 

and model 200 CD oscillators. Both test tones 

were led through a Grason-Stadler model 839S 

electronic switch, a Hewlett-Packard model 

350 B variable attenuator, and a Grason-Stadler 

model E 326A recording attenuator ( attenuation rate: 4 dB per sec). The fatigue channel and the test tone channel were mixed 

and sent to one Telephonics TDH-39 earphone 

with an MX-41/ AR cushion (a dummy earphone and cushion occluded the opposite ear). 

The instrumentation allowed the experimenter 

to present: ( 1) fatigue tone alone; ( 2) fatigue 

tone and 500 cps test tone together; ( 3) 4000 

cps test tone alone; or ( 4) no tone. The signal 

light in the subject room was also under the 

control of the experimenter. 

SUBJECTS 

The Ss were eight paid, experimentally naive, 

male volunteers ranging in age from 18-29 

years. All had normal hearing. 

PROCEDURE 

All Ss were exposed to the fatiguing stimulus 

at 40 dB SL under each of the four following 

conditions: ( 1) continuous mental division 

( MA); ( 2) written long division ( LD); ( 3) 

threshold determination on 500 cps pulsed tone 

( TD); ( 4) reverie (REV). Four combinations 

of the conditions were selected to obviate order 

effects and two subjects were tested under 

each combination. The conditions were separated by 60-75 min to assure complete recovery from the low-level fatigue tone. The four 

orders of presentation were: ( 1) MA, REV, 

LD, TD; ( 2) REV, LD, TD, MA; ( 3) LD, TD, 

MA, REV; and ( 4) TD, MA, REV, LD. 

Several minutes of practice threshold determinations preceded the first condition for 

each S. Mter a brief rest period, instructions 

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for the test condition were given. Each condition then began with a two min threshold 

determination for the 4000 cps pulsed tone, and 

was followed by a three min period of silence 

and rest. At the end of the rest period, the 

fatigue tone and the light in the subject room 

were turned on; the S then performed as previously instructed until the light and tone were 

turned off. At this time, a three min postfatigue threshold was taken on the 4000 cps 

pulsed test tone. 

The following instructions were given for the 

four conditions: 

( 1) Mental arithmetic (MA) - "In a moment 

I'll ask you to take your threshold again and 

after a few minutes 111 tell you to stop. Then 

relax. Mter a while the light in your room 

will go on and you11 hear a tone in your earphones. When the light goes on tum this 

card over. There are two numbers on it. 

Divide the larger number by the smaller number. Take that answer and divide it by the 

smaller number from the card. Keep dividing 

your answers by the smaller number from the 

card, not writing anything down at all. Do 

it all in your head. In a few minutes the 

light in your room will go off again. The 

instant the light goes off, write down your last 

answer on the bottom of the card. Don't 

worry if it's a fraction or a decimal. Immediately start taking your threshold. Work as 

fast and as accurately as you can because your 

performance will be graded. If you get mixed 

up and forget an answer, you may start over 

again, but be sure to stop wherever you are 

when the light goes off, because the tone will 

start very quickly, and I want you to be ready 

for it. Remember . . . take your threshold . . . 

when the light goes on, you tum over the 

card and start dividing . . . and when the light 

goes out, you immediately write down your 

last answer and start taking your threshold. 

Do you have any questions?" 

( 2) Threshold determination ( TD) - "In 

a moment I'll ask you to take your threshold 

again and after a few minutes 111 tell you to 

stop. Then relax. Mter a while the light in 

your room will go on and you11 hear two 

tones in your earphones. The higher tone 

will be continuous while the lower tone will 

be pulsed. When the light goes on, I want you 

to start taking a threshold on the lower, pulsed 

tone in the same way as you did before. Continue to take your threshold until the light 

goes off. When the light goes off the first 

pulsed tone will reappear and you will begin 

to take a threshold on it. Remember . . . 

take your threshold . . . when the light goes 

on take a threshold on the lower tone. When 

the light goes off start taking your threshold 

on the next pulsed tone. Do you have any 

questions?" 

( 3) Long Division ( LD) - "In a moment 

111 ask you to take your threshold again and 

after a few minutes 111 tell you to stop. Then 

relax. Mter a while the light in your room 

will go on and you'll hear a tone in your earphones. There are division problems on this 

paper. As soon as the light goes on, tum the 

paper over and begin to work the problems. 

All of the answers come out even. In a few 

minutes the light in your room will go off 

again. The instant the light goes off stop 

wherever you are and immediately start taking 

your threshold. Work on the problems as fast 

and as accurately as you can because your performance will be graded, but be sure to stop 

wherever you are when the light goes off, because the tone will start very quickly, and I 

want you to be ready for it. Remember . . . 

take your threshold . . . and when the light 

goes on, you· tum over the paper and start dividing . . . and when the light goes off, you 

immediately start taking your threshold. Do 

you have any questions?" 

( 4) Reverie ( REV) - "In a moment 111 ask 

you to take your threshold again, and after a 

few minutes 111 tell you to stop. Then relax. 

Mter a littl~ while, the light in your room will 

go on and you'll hear a tone in your earphones. 

Just continue to relax and try not to follow any 

train of thoi.Ight. . In a few minutes the light 

will go off again. The instant the light goes 

off, start taking your threshold. Remember ... 

take your threshold · ... when the light goes on, 

just relax completely and try not to follow any 

train of thought . . . and as soon as the light 

goes out, start taking your threshold. Do you 

have any questions?" 

-3-
RESULTS 

Means and standard deviations of the TTS 

data at the 10-second post-fatigue point are 

presented in Table 1. The greatest mean shift 

occurred for MA and the smallest for REV. 

For seven of the eight Ss the shift under MA 

was greater than that under any of the other 

conditions. The single exception was an 

equally great shift for both MA and LD. 

A time-course comparison of recovery from 

auditory fatigue under the MA and REV conditions appears in Figure 2. In addition to 

greater initial TTS differences, the recovery 

time appears longer for MA than for REV. 

Further comparisons are plotted in Figure 3. 

Again the MA data show greater evidences of 

fatigue and an apparently longer recovery time 

than do those of the LD and TD conditions. 

The latter two appear to differ little from the 

REV data with the exception of the 10-sec 

point. 

Analysis of variance of the 10-sec TTS data 

indicated significant differences among the 

conditions ( Fa,21 = 10.01, p < .001). Orthogonal comparisons showed that the MA TTS 

scores were significantly higher than those of 

the other three conditions ( F1,21 = 25.09, 

p < .001), that LD scores were significantly 

higher than those of REV (F1,21 = 4.93, p < .05), 

and that no statistically reliable difference occurred when TD scores were compared with 

those of LD and REV (F1,21 = .005, p > .05). 

DISCUSSION 

The striking differences between the TTS 

data for the MA and REV conditions clearly 

support the studies of Wernick and Tobias 

( 1963) and Capps and Collins ( 1965). The 

data indicate that performance of mental arithmetic during a low-level auditory fatigue period results in statistically greater TTS and an 

apparently longer recovery time than does a 

state of reverie. 

The data also point to differences among 

attention-demanding tasks in their contribution 

to auditory fatigue. Thus, the MA task resulted in greater TTS than did either LD or, 

perhaps most surprisingly, TD. In both cases, 

the difference persisted in favor of MA for 

60 sec or more. The LD task produced statistically greater TIS than REV at the 10-sec 

point, but differences among those tasks became negligible within the next five sec. 

The REV data obtained in this study lend 

further support to the proposed explanation 

(Capps & Collins, 1965) that the failure of 

Riach and Sheposh ( 1964) to obtain MA-REV 

differences in TTS was due primarily to an ineffective REV condition. Differences obtained with the three attention - demanding 

tasks used here also support the position that 

the tasks employed by Ward and Sweet ( 1963) 

and Bell and Stem ( 1964) may not have been 

so effective in producing whatever central 

changes occur as a result of MA. 

TABLE I 

Temporary threshold shift (TIS) means and standard deviations for 

data obtained 10 seconds after exposure to a 4000 cps fatiguing tone. 

During the fatigue period, subjects were either in reverie (REV) or 

engaged in mental arithmetic ( MA), long division ( LD), or threshold 

determination ( TD) tasks. ( N = 8) 

TIS (dB) 

Task M SD 

- MA 9.6 5.6 

LD 6.6 3.1 

TD 5.4 1.7 

REV 4.3 2.3 

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Figure 2. 

CCI 

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.... 

0 

::c 

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c.=: 

::c 

.... 

9 

8 

7 

6 

5 

4 

3 

2 

..... MENTAL ARITHMETIC 

o-oREVERIE 

10 15 20 30 45 60 90 120 180 

TIME IN SECONDS 

{log scale) 

Recovery from auditory fatigue: comparison of mental arithmetic and reverie 

conditions. Each point is a mean for 8 Ss. 

10 10 

10 15 20 30 45 60 90 120 180 

o--o REVERJE 

10 15 20 30 -45 60 90 120 180 

TIME IN SECONDS 

(log scale) 

- MENTAL ARITHMEJIC 

~ THRESHOW DETERMINATION 

10 15 20 30 45 60 90 120 180 

o--o REVERIE 

"-"' THRESHOW DETB>MINATION 

10 15 20 30 45 60 90 120 110 

Figure 3. Time-course comparisons of the temporary threshold shifts to a 4000 cps 

fatiguing tone. Each point is a mean for 8 Ss. 

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The mean LD-REV data reported in this 

study are very similar to those noted by Bell 

and Stem ( 1964) for their first trials, although 

variability in the present study was less. That 

the LD-REV differences in the Bell ~d Stem 

( 1964) study were not maintained with repeated exposure to the conditions might result 

from rapid habituation to the test and/or test 

situation. That such habituation can occur 

(although perhaps not so rapidly) has been 

noted elsewhere with regard to other phenomena (Collins, 1963, 1964; Galambos, 1956). 

In addition, Bell and Stem ( 1964) used female 

s"':lbjects and there is the possibility that a female's approach to a given type of mental task 

may differ from that of a male. 

Two other points seem worthy of mention. 

If too much time (more than 10 sec) is allowed to elapse from the end of the fatigue period to the start of the post -exposure threshold 

determination, some tasks may show no difference in TIS from the REV condition. The 

LD task in the present study is a case in point. 

Second, it is of interest that the TD trials 

proved relatively ineffective in contributing to 

auditory fatigue. Although the TD task may 

simply not require the same central components or amount of attention as MA, there is 

a possibility that considerable selectivity may 

exist, such that attention to a tone of the same, 

or nearly the same, frequency may be required 

during the fatigue period if the tone is to exert 

aninfluence on TIS. 

REFERENCES 

1. Bell, D. W., & Stem, H. W. Effects of extraneous 

tasks on auditory fatigue. ]. Acoust. Soc. Amer., 1964, 

36, 1162-1166. 

2. Capps, M. J., & Collins, W. E. Auditory fatigue: 

Influence of mental factors. ]. Acoust. Soc. Amer., 

1965, (in press). 

3. Collins, W. E. Effects of mental set upon vestibular 

nystagmus. ]. exp. Psychol., 1962, 63, 191-197. 

4. Collins, W. E. Manipulation of arousal and its effects 

upon human vestibular nystagmus induced by caloric 

irrigation and angular accelerations. Aerospace Med., 

1963, 34, 124-129. 

5. Collins, W. E. Task-control of arousal and the effects 

of repeated unidirectional angular acceleration on human vestibular responses. Acta Otolaryngol., 1964, 

Supplement 190, 34 pp. 

6. Galambos, R. Suppression of auditory nerve activity 

by stimulation of efferent fibers to cochlea. ]. Neurophysiol., 1956, 19, 424-437. 

7. Riach, W. D., & Sheposh, J. Further observations on 

the central factor in auditory fatigue. ]. Acoust. Soc. 

Amer., 1964, 19, 967-968. 

8. Ward, W. D., & Sweet, D. F. Absence of central factors in auditory fatigue. ]. Acoust. Soc. Amer., 1963, 

35, 1880-1881 (A). 

9. Wernick, J. S., & Tobias, J. V. Central factor in puretone auditory fatigue. ]. Acoust. Soc. Amer., 1963, 35, 

1967-1971. 

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