Auditory frequency threshold comparisons of humans and pre-adolescent chimpanzee

Farrer, D. N.

Prim, M. M.

English

NASA Technical Reports Server

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-A PRELIMINARY REPORT ON
AUDITOR Y FREQUENCY TIIRESHOLD COMPARISONS
OF HUMANS AND PRE-AD_LESCENT CHII_PANZEES
Donald N. Farter, Ph.D.
: Merle M. Prim• M, A.
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' 6571st Aeromedica/Research Laboratory ,r
Aerospace Medicad Division
i Air Force Systems Command
, : Holloman Air Force Base, N_w Mexico
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: A PRELIMINARY REPORT ON
$
AUDITORY FREQUENCY THRESHOLD COMPARISCNS
OF HUMANS AND PRF.-ADOLESCENT CHIMPANZEES
$ Donald N. Farrer, Ph.D.
Merle M. Prim, M.A.
2-
L.
1965025503-002
iFOREWORD
This report is based on a study at the 6571st Aeromedical
Research Laboratory, and the authors wish to acknowledge the
assistance in data collection of the following individuals: Ale
Gary T. Barnhart, Mr. Jerry Delich, Mr. Robert Garrett,
Mr. Scott Burr, and Mr. Larry Southard. Also, Mr. Joseph H.
Trujillo and Mr. Leroy C. Shaw calibrated and maintained the
apparatus. This work was completed during March 1965 under
Project 6893, Task 689302.
This Technical report has b_en reviewed and is approved.
Major, USAF, _4C
Chief, Bio-Effects Division
W _
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\-
ABSTRACT
Upper limits of hearing at 80 decibels (db) were establi°_ed
for five chimpanzees (age range: 4 to 6 years) and 90 humans
(age range: 5 to 35 years). It was concluded that pre-adolescent
chimpanzees have the ability to respond to higher frequencies
than pre-adolescent children, and the dim_nntion hl h_naan per-
ception of high f_equencies as a function of age was confirmed.
Statistically significant decrements in hearing were found at
10-year intervals between 5 and 35 years of _ge. Trend analysis
, of these data suggested that the diroinution i:_high frequency per-
ception was linear and the variability appea-:ed Gaussian.
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IINTRODUCTION
Upper limits of hearing were reported for both humans
and chimpanzees by Spector (Ref. i). He reported that the
frequency threshold for humans was Z0 kilocyc]es per second
(kcps), while chimpanzees could hear pure tones as high as 33
kcps. However. this reference is a summary of biological data,
and information concerning age and intensity levels were not
reported. In 1934 and 1935 Elder {Ref. Z and 3) reported upper
i. limits data on three children and three chimpanzees, all of whom
could hear above 20 kcps. The 50 percent response thresholds
for the children ranged from ZZ. 6 kcps to Z3.7 kcps and the two
12 year old children demonstrated inferior abilitywhen compared
: to the 5 year old child. However, the data obtained from the
three chimpanzees indicated an increase in sensitivitywith in-
_, creasing age. The older chimpanzee {approximately 7 years of
I
age) had the highest threshold (33. 3 kcps) while the youngest
,_ animal (approximately 3 years of age) had the lowest threshold
'_ {Z6.0 kcps). Elder concluded that the chimpanzee was superior
i to the hun._.anin the perception of high frequency sounds. Corso
(Ref. 4) did not find human thresholds as .igh as those reported
by Elder (Ref. 3), but the youngest age g_ )up tested by Corso
was 18 to 24 years of age. These highty selected humans were
given complete otological examinations and background investi-
gations {searching for any possible exposure that might have
produced aural damage) prior to testing. Gorso's results indi-
cated an upper limit threshold of approximately Z0.5 kcps.
Behar, Cronholm and Loeb (Ref. 5) reported humans
responded to 20 kcps at intensity levels of 88 db. Their sub-
! _ects {young men 17 to 26 years of age) were tested in a double-
walled sound room, and the sound source was an AR-3 speaker
located 30 inches from the subject. The free-field situatior,was
_: employed without fixing the subject's head in any restraint mecha-
nism; thus, there was variability in the orientation of the ear of
_ the subject to the sound source.
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Obtaining threshold measurements on animals presents
problems in that the experimental situation must provide an
opportunity for an identifiable response from the subject.
El¢=er (Ref, 3) used an auditory cue to teach a chimpanzee to ;!
open a small door to obtain an apple slice. Seminoff and
Young (Ref. 6) obtained aud_ograms from monkeys by establish-
ing a stable classically conditioned galvenic skin response to
pure tones between 125 cycles per second (cps) and 8 kcpso
Their procedure utilized stim_ [i presented to the animal via a
headset while the subject was restrained in a pillory neck plate
chair, _nd failure to respond was rewarded with a forearm
shock. Behar, Cronholm and Loeb (Ref. 5), using rhesus
monkeys in a Lehigh Valley pillory neck plate chair, found
intensity threshold values of 20 db {reference value was . 0002
dynes/era _) at 31.5 kcps with an _R-3 speaker mounted 30
inches from the ear of the subject. These intensity thresholds
were obtained by the shock avoidance technique of Clark and :_
Herman (Ref. 7). (It should be noted that Behar (Ref. 8) _
suggested that the rhesus monkey can hear beyond 31.5 kcps. ) :_
A
The use of headsets and free field sound sources, as well ;_
as behavioral responses and conditioned physiological responses
make direct comparisons of previous findings difficult. The
purpose of t:hepresent study concerns the need for upper limits
data on the chir_panzee using modern sound generating equip-
ment and direct comparison data for humans.
II :_
METHOD <;
• A. Subjects ::
Five chimpanzees and 90 humans were used in this study. :;
The ages of the chimpanzees (by the dental eruption technique) :;
were approximateiy 4 to 6 years. There were 3 humans at each
age level from 5 through 34 years of age. The animals were _,_
selected from the 6571st Aeromedical Research Laboratory :"f
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1965025503-007
colony at Holloman Air Force Base, and the humans were volun-
teers with no knowl_, hearing deficits from the Holloman area of
New Mexico.
B. Apparatus
The apparatus used in this study consisted of the following
unit s:
I. The Instrumentation Roorrt: This room was IZ feet
long by 12 feet wid ,_. and 9 feet high. The walls and ceiling were
covered with acoustic tile, and all electronic programlning and
sound generating equipment was located on the experimenter's
desk. A connection panel in the wall allowed the isolation of all
the test eeuipment from the subject in the test cubicle except the
headset and response lever. The test cubicle (an Industrial
Acoustics Chamber Mode:[ 1204-A with double wall construction
and air conditioning system) was in'stalled in the instrumentation
room so that the subject could be observed th:ough a window
during the testing procedure. The inside_- _timensions of the test
cubi-cle _vere_-g feet by 9 feet b_ 6.5 feet, The average ambient
sound intensity (SPL) inside the test cubicle was 40 decibels
{._ref_rence level = .0002 dynes/cm_}.
2. The Sound Source: This system, described in
detail by Gilbert and Kaplan {Ref. 9) consists of a Hewlett-
Packard audio oscillator, Model 200 AD, a Hewlett-Packard /
vacuum tube voltmeter, Model 400H, and a Grason-Stadler
electronics switch, Model 829D. The pure tones from I0 kcps
to 40 kcps generated by the audio-oscillator were monitored by
the vacuum tube voltmeter and presented to the subject via
standard relay programming equipment (including the electronic
'0
switch) and a one-half inch Bruel and Kjaer speaker mounted in
a Willson sound protector headset.
3. The Response Mechanism: The chimpanzees were
restrained in a chair as shown in Figure I. This figure shews
the relation of the arm rest to the response switch as well as
the head restraint mechanism and headset. The basi_z restraint
chair dascribed by Grunzke (Ref. 10) was modified to include a
chin rest and a posterior cranial cup which immobilized the
animal's head. The human _ubjects wore the sr.l___ headset, but
they sat in a standard office chair and held a microswitch in their
hand,
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1965025503-008
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Figure I. Chimpanzee Seated in the Restraint Chair with the : eadset i
and Response Switch in Place
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1965025503-009
C. Procedure
I. Chimpanzee Data Collectio_
After a chimpanzee had been asymptotically trained
to respond (pre_- _ a button) to auditory cues of various frequen-
cies (1 kcps to.lt; kcps) and intensities (70 tc 25 db), the task was
changed to include aversive reinforcement (Z00 volts, Z0 me.
0.5 seconds duration shock to the foot) for failure to respond to
a tone as well as responses which occurred in the _osence of the
auditory cue. The allowable response interval was established
at 3 seconds, and the frequency rang_ was extended to include
random presentations of pure tones at 80 db between 18.5 kcps
i!_ and 3Z. 5 kcps with aperiodic reinforcement for failure to re- :
spond to the atiditory cues. The test phase included 10 days
testing by the method of limits (14 trials per day) under a modi-
fied extLnction condition. The first failure to re slc Jnd on the
!_ first ascending series of trials was reinforced wi_h the aversive
reinforcement, and that frequency was repeated. If the subject
fai]ed to respond ,_n the second trial, the ascending series was
terminated and all remaining trials for the day were accomplished
without aversive reinforcement. However, if the subject re- |
sponded to the second presentation, the next higher frequency
(.'00 cps -:ncrement_) was attempted, and failure was aversively
rewarded. This procedure was repeated ur:il two successive
failures were obtained for the first ascending series, and all
remaining trials we:re obtained under the standard ps.vcho-
:physical method of limits procedure de,_cribed by Guilford
(Ref. II). The inteztrial intervals for stimulus pre_entaticr_s
were varied randomly between 1 second and 15 seconds so that
response sets were reduced to a minimum while maintair, ing
attention to the task. In all cases the threshold was deff.r.ed as , 'i
the frequency to which the subject responded 50 percent of the L
time.
2. Htnnan Data Collection
The human subjects were brought into the test
cubicle and the appara._ s and purpose of the experiment was
,o explained to them. The exact instruct ions varied with the age
of the subject, but each subjec was told to press the button
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when they heard a tone, but not to Dress it at any oti_er time.
Each subject was asked if he understood, and following an affirma-
tive answer a practice trial was obtained. Then the doors to the
test cubicle were closed, isolating the subject from the experi-
rnenter and apparatus. The standard psychophysical method of
limits (Guilford, Ref. ii) was used to obtain !imens from each
subject during one session.
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I!I
RESULTS
The limens obtained for each chimpanzee were consistently
higher than the limens for humans, but the variability was suffi-
ciently great that overlapping did occur. The means of the upper
limits of hearing by age for chimpanzees and humans arc shown
in Figure Z. The means, standard de,-lations, ranges and medians
for these data are presented in Table I. A visual inspection of
,: the means, standard deviations, ranges and medians suggests
fairly normally distributed variance about the average calcula-
tions for each age group. A simple analysis of variance of the
human data {Table II) yielded an F-ratio of 9. 458 (P< . 01), and
the Duncan's shortest significant range test (Table III) indicated
significant diminutions in ten year st_ps. That is to say, the
5-9 age group did not differ statistically significantly from the
10-14 age group, but the 5-9 group did differ from the 15-19 group.
Also, the !0-14 group was not statistically significantly different
than the 15-19 group, but the 10-14 group did differ from the Z0-Z4
group. The 15-19 group differed, Statistically, fr,ornthe Z5-29
group, and the 20-Z4 group differed statistically from the 30-34
group. The trend analysis suggested a negative linear component
(P< .001) as a function of age. The combined chimpanzee values
were statistically significantly higher than the youngest human
age group (t = 4. 562, P< .01).
6 'K_
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1965025503-011
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16
14
w I 1 v _i i I I 1
4 5 6 5-9 10-14 15-19 20-24, 25-29 _0-34
CHIMPANZEEA_E HUMANAGE GROUPS -_
Figure 2. Mean Upper Limits of Hearing by Age lot Chimpanzees and Humans
7
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1965025503-012

TABLE II. Summary of the Analysis of Variance of the
Human Lira en Data
i
Source of variation ; d< SS MS F
Between human limen
age groups 5 158.442 31.6884 9.458*
Within groups [ 84 [281.440 3. 3505
Total 1891439.882
*P<. 01
TABLE III, Comparison of Ste±isticallySignihcant
, Limens for the Human Age Groups
I
Age groups 5-9 | 10-14 15-19 Z0-Z4 25-29 30-34J_
5-9 - I N.S.S. * * * *
I0-14 - N.S.S. * * *
!
15-19 - N.S.S. * *
20-24 - N.S.S. *
25-29 - N.S.S.
30- 34 [ -
",'1'< . 05
N. S.S. - Not Statistically Significant at the . 05 level.
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IV
DISCUSSION
The consistency of the daily limens and shock avoidance
technique supports the validity of the conclusion that these
measurements represent the upper limits of auditcrv perception
for these chlmpanzee3. It should be noted that complete histories
of the five animals are not known ,_ince they were not born in a
laboratory environment, bu_ none of these _ubjects responded to
tones as high as 30 kcps. The single amrnal of Elder's (Ref. 3)
study which demonstrated a limen of 33. 3 kcps was i year and
8 roonths older than the average age of the five chimpanzees used
in this study, but the age difference in the oldest animal of this
study and Elder's animal wa.s approximately 9 months. The
limited age range data from this study indicates that the percep-
tion of high frequencies diminishes with age in chimpanzees which
is consistent with Corso's (Ref. 4} human data as well as the find-
ings from the humans used in this study. Thus, Elder's older
chimpanzee would not be expected to hear frequencies higher than
these subjects, but the obtained frequency difference was 9. 3 kcps
(approximately 10 standard deviations above the mean obtained in
this study). Perhaps these values represent individual variations,
and the sm_all samples employed tend to magnify the differences
The comparison of the limens of the 4 to 6 year old chimpanzees
and 5 year old children supports Elder's conclusion that chim-
panzees can hear higher frequencies than children. The ce_Dari-
son of the limens of the 5 to IZ year old children of this study with
the iimens obtained by Elder on children in that age range indi-
cated that Elder's values were between the mean of this study and
+I. Z standard deviations.
The Z8 individual human limens above Z0 kcps vet80 db do
not support the average intensity threshold of 88 db reported by
Behar et al (Ref. 5). The difference in the testing situation
(headset versus free field) could account for the variation in
values because the random orientation of the ear away from the
sound source in a free field environment increases the proba-
bility of obtaining higher db threshold values.
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1965025503-0] 5
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Corso's conclusion that presbycusis is greater as a function
of frequencies up to 8 kcps was extended by these data to indicate
that the phenomenon holds for the upper limits of auditory per-
ception. The approximate 10-year time period linear dilrAnution
in the upper limits of hearing also agree with Corso's findings
for the lower frequencies.
V
CONC LUSIONS
i. Pre-adolescent chimpanzees (4-6 years of age) can hear
higher frequencies than humans, but no evidence was found for
an upper limit of frequency perception above 30 kcps=
2. The average human (age 5 to 35) intensity threshold (mea-
sured at the ear) for Z0 kcps is below 80 db.
3. Upper limit frequency perception diminishes linearly as a
function of age within the 5 to 35 human age range. (Statistically
significant diminutions were found at 10-year intervals. )
VI
FUTURE PLANS
The variability in chimpanzee data cannot be isolated without
increasing the size of the sample over a greater age range. Thus,
the next step concerns the determination of upper limits of hearing
for older chimpanzees in this situation. Second, these data will be
more Ineaningful once audiograms are completed on each of the test
subjects. These intensity threshold determinations will cover
frequencies from i00 cps to the upper limits of auditory perception.
Third, the relationship between thresholds obtained by operant
techniques are to be con_pared with thresholds obtained by classi-
cal conditioning techniques.
The high frequency perception of humans will be explored in
more detail also. The threshold of perception at high frequencies
by a snnall percentage of humans suggests anomalies in the slope
of the intensity threshold curves. Audiograms are scheduled to
explore the nature and extent of these anomalies.
II
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!REFERENCES
I. Spector, W. S. (Ed.) Handbook of Biological Data.
W. B. Saunders Co., Philadelphia, 1956.
2. Elder, J. H. "Auditory Acuity of the Chimpanzee. "
J. Comp. Psychoh 17, 157-183 1934.
3. /Elder, J. H. 'The Upper Limits of Hearing in the
Chimpanzee." Amer. J. Physiol. 112, 109-115, 1935.
4. Corso, J. F. "Age and Sex Differences in Pure Tone
Thresholds. " Arch. Otolaryn_zo_l. 77; 385-405, 1963.
5. Behar, I., J. N. Cronholm, and ]91.Loeb. ':Auditory
Sensitivity of the Rhesus Monkey. '_ 5. _5omp. Physiol.
Psychol. _ in press.
6. Seminoff, W. A., and F. A. Young. "Comparison of
the Auditory Acuity of Man and Monkey. _'_J. Com_.
Physioi. Psychol. 57, 89-93, 1964.
7. Clack, T. Do and P. N. Herman. "A Single Lever
Psychophysical Adjustment Procedure for Measuring
Auditory Thresholds in the Monkey. ": J. Aud. Res. 3,
175-183, 1963.
8. Behar, I. Personal communication, March, 1965o
9. Gilbert, G. A. and G. H. Kaplan. A Wide Band
Frequency Auditory Test System for Use with Primates. _!
Aeromedical Research Laboratory Technical Report, I
>
Number ARL-TR-65-5, HollomanAFB, New Mexico. i
I0. Grunzke, M. E. A Restraint Device for Behavioral
Research with the Chimpanzee. AFMDC Technical
Documentary Report Number 61-37, Holloman AFB, i
New Mexico, December, 1961.
II. Guilford, J. P. Psychometric Methods. McGraw-
Hill Co., New York, 1954.
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Auditory frequency threshold comparisons of humans and pre-adolescent chimpanzees

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