*

Fn

i
:
1

tones were generated by Hewlett-Packard
Model 201CR. oscillators fed separately to.two
attenuators, The attennator in the “constant
channel” was a Hewlett-Packard Model 350B;
the attenuator in the “variable channel” was a
Grason-Stadler Model E3262A recording attenn-
ator. From the attenuators, the tones were led
independently to matched TDH 39-3002 ear-

phones motnted in| NAF4S490-1 doughnut .

cushions, The sonnd booth contained only the
subject, the earphones, and a control key for
the recording attenuator, The experimenter,
outside the booth, in addition to determining
settings for the oscillators and for the 350B at-
tenuator, had control of an override switch for
the recording attenuator and a reversing switch
which allowed him to select the ear receiving
signals from the constant channel.

Relative binaural beats. For the production
of relative binaural beats, instrumentation as
shown in Figure 2 was used. Most of the items

ee ee
ee
saree} oS LIU ,
Sere en 4

Ficuns 2. Instrumentation for the luction of relative
Dinaural beats is shown. The “threshold” is plotted as in
Fig. t. On the right is a sketch ing the subject's

intracranial beating images, showing that he hears a beat
whenever the tones are both above threshokd. ]

of apparatus were identical to those red for
the meastrement of absolute binaural beats
with the addition of a Grason-Stadler Model
8295 electronic switch. This switch, set for an
approximate 100 ws rise and decay time, served
to program the stinvalus in the variable chan-
nel (the risedecay time was selected so that
the stimulus in the constant channel appeared
continuous), In the variable channel, during
the “A-on” part of the swicching cycle, the tone
from oscillator Vo was gated on: during the
“B-on" part of the cycle, the tone from oscillator
C (which also fed the constant channel) was on,

The variable tone was then led through the re-
cording attenuator and reversing switch to one
earphone. The constant tone went to its 350B
attenuator, through the reversing switch, and
to the other earphone as hefore. Levels in the
two channels were adjusted so that, with both
attenuators at zero, the two channels were
matched. The electronic switch program was
adjusted so that the earphone receiving the
output of the variable channel received one
second of signal from oscillator V alternating
with one second of signal from oscillator C.

tn both arrangements, line impedances for
the entire system were matched as necessary.

Using the apparatus described for the pro-
duction of absolute binaural beats, one would
expect an ideal listener to hear beats continu-
ously, Using the apparatus described for the
production of relative binaural beats, one would
expect him to hear one second of beating alter-
nating with one second of non-heating.

Subjects. Subjects in the major experiment
were four men, ranging in age from 22 to 44
years, who were experienced in listening to
binaural heats. Twenty-five additional sub-
jects served in pilot experiments.

Method. The technique of plotting a “bin-
aural beat threshold” is simplified considerably
by the use of the recording attenuator which
allows the subject essentially continuous control
over the level of the tone in the variable chan-
nel, As he alters the stimulus magnitude with
this instrument, a graph of his changes in level
with time is produced. For the work reported
here, the recording attenuator was adjusted to
change the leyel_at a rate of 4 dB per second.

Because work preliminary to the present
study showed fairly large individual variation
in the ability to hear binaural beats, subject-
training procedures were improvised to meet
individual problems, As much as_ possible,
listening during training was divided equally
between absolute and relative stimuli, Few
other restrictions were practical, The first
training session began in a standard: fashion,
bat variations were introduced whenever they
became necessary, Typically, the experimenter
fire described the sound of a beating stimulus,
including in this orientation the demonstration
through a loudspeaker system of physical beats

-3-—


ACKNOWLEDGMENTS

Particular thanks are due to Herndon Snyder
who conducted the first: pilot experiment as
part of a classroom project; to Joel Wernick
who served usefully as experimenter, subject,
and critic; to G. von Bekesy who took time to
disctss his own measurements of binaural beat
phenomena; and to E, G, Wever whose help
solved a major bibliographic problem,

210-8 GOVEANWENT FRISTING OFFER | 100.0. THE a1 -8-



*

he

ception of a continuous tone. Remember too
that the decision about this “threshold” is ab-
solute — dependent upon no external reference.

Subjects report a strong beat when the
sound image is near the center of the head;
only with the image centered do they feel very
sure that they are hearing what they are sup-
posed to, If a subject raises the level in the
variable channel until it is approximately 10 dB
higher than in the constant channel, he hears a
beat — sometimes — and he hears it on the
louder side. This lateralized beat is readily
confused with head noises, but when the beat
is reported at all, the record shows an invariant
and reliable 10 dB difference in level between
cars, There is « symmetrical beat on the other
side when the 10 dB favors the constant car,
but it too is very easily lost, One further
nebulous set of beats is heard when the sound
on the softer side is near threshold. A sketch
of the intracranial positions of these various
images is included in Figure 1.

The record in Figure 3 can be easily in-
terpreted in the light of these reported percepts,
(Although this record shows the listener ap-
proaching each new beating image from above,
the traces for ascending trials were similar.)
A tone threshold for the subject's “variable ear”
is shown first (“A"). Following it are beat
thresholds for several values of sensation level
in the “constant car.” When he felf’ that he
had stabilized a particular threshold, the sub-
ject reduced the level in thejvariable ear until
he found another beat or until he had reduced
the level so far that the experimenter recog-
nized that no other beat was forthcomig, In
part “B,” then, the top beat threshold repre-
sents the median plane image; the next one,
the 10-dB-difference image; and the third one,
the “threshold threshold.” In “C,” with a 30 dB

L. in the constant car, the subject found all
four images no€éd in Figure 1, Also, as fre-
quently happened, after the “threshold thresh-
old” he continued to increase the attenuation.
Not finding anything subliminal, he raised the

~ level in the variable channel? until he found a

beat again; note that it matches the beat he

heard before. In part “D,” the first beating
area occurred when the interaural difference
was 10 dB, although some subjects tended

Fe

to search for a beating image in the 10 dB
attenuation vicinity. This process appears in
“E” and in “F.”. From later reports about this
phenomenon, it seems safe to conclude that
the searching occurred because the subject
knew that a beat often appeared a few seconds
after he started increasing the attenuation.
Parts “E” and “F” show the subject’s work at
10 and 0 dB SL in the constant ear, and part
“G” shows another tone threshold, In any
‘presentation of absolute stimuli, subjects felt
confident only when the levels in the two ears
were matched. No subject perceived every
possible image in any single trial.

To avoid misinterpretation of Figure 3, re-
call that the curves were selected to illustrate
a range of responses. Thus, for instance, al-
though it does not appear in the figure, the
0 dB curves frequently showed a beat threshold
region near 10 dB SL, The other curves simi-
larly vary according to which images a subject
did or did not perceive.

Relative binaural beats, The inclusion of a
non-beating reference tone made the subjects’
task strikingly easier and produced completely
different. response patterns, Using relative
rather than absolute stimuli leads to a situation
in which the beat can alteays be heard when
both tones are at or above threshold, As in
the case for absolute beats, the image is in-
variably on the louder side, (Although it is
possible to interpret this fact as the result of
an illusion, it may be considered useful evi-
dence that the beat did not result from phy-
sital mixing of the two tones because of leakage
across the head.)

The sketch of intracranial images for relative
binaural beats shown in Figure 2 illustrates that
listeners find ‘only one beat threshold — when
the tone in the ble channel reaches its”
threshold, The existence of a single limiting
value of stimulus magnitude for the perception
of binaural beats is obvious in Figure 4. This

Froens 4. Cune illustrates consistency of response at any
interaural intensity difference when “relative stimuli are
aed,

5-


Fe

at several beat frequencies, For most subjects,
binaural beats were first’ introduced with a
500 cps tone to one ear and a 503 cps tone to
the other; levels at the two cars were matched.
The selection of 500 eps and matched interaural
levels was based both upon previous reports
of binaural beat perceptions’ and upon ex-
perience gained in preliminary investigations.
That subjects were hearing the beats was most
easily tested by producing changes in the beat
frequency and requiring the listeners to repro-
duce the rate by tapping a finger. When a
subject seemed to be responding to the beat,
he was instructed to press the key (controlling
the recording attenuator) until the beat dis-
appeared, then to release the key until the
beat returned, and so on. A few pilot study
subjects, several days after training, were found
to respond not to the beat but to the difference
in pitch between the ears, An interview in
which the subject was asked to describe just
what he was listening to helped protect against
such responses; more important though, subjects
making judgments on the basis of a pitch dif-
ference produced response curves on the re-
cording attenuator which differed character-
istically in slope and variability from the curves
produced by subjects listening for the beat.

Every tested subject can now hear binaural
beats. The population includes the selected
subjects from the present experiment, the 25
unselected subjects used in prelimilary work,
and 40 more unselected subjects used in an-
other study.

Following a training period of several hours,
subjects were asked to find “binaurgl beat
thresholds” — that is, attenuator tracey around
the variable-channel level at which Keats dis-
appeared — both for absolute and for relative
stimuli, Frequencies ranging from 100 to 2000

s Were investigated with beat frequencies’
varying from [to 10 cps. The similarity of
thresholds from100 to 800 cps and the lack of
reliable beat perception above about 900 eps
led to the collection of most of the data with
one set of stimulus parameters; the tone to one
ear was 500 cps, to the other, 505 eps,

* PCR. Licklider, J. Co Webster, and fo Mo Medlin,
“On the- frequency limite of binaural beat” J. Acoust, Sor
Am, 22, 468-473 (1930),

Since a primary source of error in such studies
is sound leaking across the head,’ care was
taken that the tone in the constant ear never
exceeded a level of 40 dB the threshold in the
variable ear. Thus, the term “sensation level”
(SL) as used here always refers to the thres-
hold on the variable side. A representative trial
would start with a threshold for the tone in the
variable channel. Following that, in random
order, would be binaural beat thresholds with
the constant ear at 40 dB, 30 dB, 20 dB, 10: dB,
and 0 dB SL. Last in a trial was an additional
tone threshold. Trials for absolute and for rel-
ative beats were similar,

RESULTS AND DISCUSSION

Absolute binaural beats. From the hypoth-
esis of a separate time-sensitive system, one
would expect subjects to hear binaural beats
whenever the tone to the ear receiving the
lower-level stimulus was above threshold. Un-
happily, no such clear result occurred for ab-
solute beats. What did happen is shown in
Figure 3, a composite curve illustrating many

AUTCWATIC ATTEWUATOR THAESROLD TRACE
FOR ABSOLUTE BRamOE BEATS

00cm, te

TOME THM.
BEAT THAESOLD (COMMENT Eat AT 048 He
ier eet arise H

Ficus 3. Curve illustrates: several types of response to
absolute binaural beats, Each part of the figure (ie. A,
B, ---, G) is selected from a different trial; thee subjects
are represented. For cave of reading, the traces are cqnated
for sensation level and ordered according to the level at
the constant car,

of the kinds of responses given, Remember
in reading this curve that the subjects were
asked to find the place or places where the
perception of a “wobble” fades inta the per-

“Differences. between “te” oe “subjective” binaural
heats and “leakage” or “objectweTM beats ate de=

tated in CoE. Lane, “Binaural Beaty” Phy
Me (4923).

-4-


see

the percept was extremely difficult to maintain,
The other pertinent study, with one listener,
used a high-level (set by the experimenter at
values from 30 to 90 dB SL) 500 cps tone and
a low-level (independently set at from 0 to
50 dB SL) 505 cps tone added in one ear,
and a 500 eps tone alone in the other ear.
Levels in the second ear were controlled by
the listener, The subject was unable to hear
any beat, Although it might be true that in

such a complex stimulus a beat is somehow -

masked, this finding may well be the result
of a sampling error — the subject was the same
one who had difficulty with the f and (2f + 5)
stimulus.

The relation of these experiments to the
“best beat” studies is straightforward, When a
high level tone is presented to one ear, the
same tone can be present at a 40 or 50 dB lower
level in the other ear as a result of leakage. A
probe tone in the louder ear might possibly pro-
duce a binaural beat with the leakage product
in the contralateral ear. Thus, even with tones
whose difference in level mitigates against the
production of monaural physical beats, one
might hear binaural beats, Depending upon
the experimental procedure and purpose, these
binaural beats would be between f and either
(f+ Af) or (2f+ Af). Subjects often have
trouble hearing a beat in mepsurements of
distortion, and perhaps that trouble could be
accounted for if one considered that they were
really listening for an absolute binaural beat,
Similarly, one must examine any work which
measures cross-hearing with a ¢ontralateral

- probe tone on the basis that responses can te-

sult from binaural beats at or near the “thres-
hold threshold.”

Finally, it is necessary to point out that the
thresholds of those nerve fibers forming timing
cirenits aparently match the thresholds in
audibility circuits,

CONCLUSIONS

From the present data, one can interpret that
there is in the binaural system a timing network
which is separate in function from other chan-
nels which carry only loudness or place-pitch
information, The concept of such functional

separation is certainly not new — it fits th
proposed binaural interaction networks ©
Jeffress? and Licklider"; it is related to wor
on timing processes in the basal tum of th
cochlea"; and it certainly fits Huggins’s prin
ciple of diversity.” Moreover, people studyin
problems of periodicity pitch and the residu
(eg. G. v. Bekesy, E. de Boer, J. Nordmar}
J. F. Schouten, and A. M. Small, Jr.) have nec
essarily held that time-sensitive devices mus
exist in the auditory nervous system. For thes
mechanisms to be functional, they must some
where be essentially separate entities, Thes
new data, then, were collected to test whethe
binaural beat perception conforms to the theor
of an independent timing system. The resul!
add to the evidence confirming the existenc
of that independence.

Anyone attempting similar work should not
that binaural beat thresholds are strongly is
fluenced by the method of stimulus present:
tion. One would properly question the conce}
of departing from matched levels in li
tening for binaural beats if he had data on’
from experiments which used absolute stimu:
consideration of the data gathered using re
ative stimuli, though, leaves no room for douk

*L. A. Jeffress, “A. place theory of sound localization
J. Comp. Physiol. Psychol. 41, 35-59 (1948).

“
(a) J. CR. Licklider, “A duplex theory of pitch pe
ception,” Experientia 7, 128-134 (1981).

(b) J. C. R. Licklider, “Auditory frequency analysi
in C. Cherry (ed.), Information Theory: Third Lond
Symposigm. (Butterworths Scientific Publications, Lond
1955), Chap. 27.

" (a) BL HL Dedtherage, D. H. Eldredge, and H. Dav
“Latency of action potentials in the cochlea of the guin
pig.” J. Acoust. Soc, Am, 31, 479-486 (1959).

(hb) BH. Deatherage and TJ. Minh, “Auditc
localization of clivks,” J. Acoust, Soc, Am. 31, 4564
(1959),

"The principle of diverity states that the nervous 5
tem often hedges Instead of preventing a single tra
form of the peripheral stimulation to the higher crate
the auditory tract may prevent a number of trandort
Given a nuimbee of views of the stimulus, the corteu m
Jook them over and take the most useful one. Or it
acorpt them all and operate upon theca all, trying to pi
together a consistent pictire of the outbsle work” W.
Huggins and PC. BR. Licklider, “Mace mechanisms
andhtory fi analysis” Jo Agnt, Soo Am, 23, 2
(11), (By permivion fran The Journal
ety of America.)

the Acoustical §

-~7-


AOFLS EFF

VL CHeE-63-/7

APPLICATION OF A
“RELATIVE” PROCEDURE
TO A PROBLEM IN
BINAURAL BEAT PERCEPTION

FEDERAL AVIATION AGENCY
AVIATION MEDICAL SERVICE
AEROMEDICAL RESEARCH DIVISION
CIVIL AEROMEDICAL RESEARCH INSTITUTE
ORLMIOMA CITY, ORLATIOMA

AUGUST 1963



figure is plotted from the responses of one
subject during one trial, the only change made
has been to order the curves from highest to
lowest level in the constant ear, The curves
are literally typical; the responses of any subject
during any trial would look the same.

Indicidial differences. Problems of popula-
tion variability were minimized with the selec-
tion of subjects used here, However, the
unsophisticated subjects used in pilot experi-
ments performed similarly, Individual differ-
ences, then, appear to be effectively non-
existent except as was noted in the discussion
of absolute beats and except for the perform-
ance of one subject. The subject in question
was the only one tested who could not hear
binaural beats at all. She was also the only
female in the population, No amount of indoc-
trination and no reasonable amount of listening
experience either to physical beats or to abso-
lute or relative binaural beats helped, After
10 hours of training, an extension of the fre-
quency range from the previously determined
optimum £00 - 600 cps was made, As soon as
the frequency was dropped to 350 cps, she
heard the beats, and the magnitudes of her
beat thresholds were similar to the others.
Apparently, her best range is in the 200 to 300
cps band — a striking variation from the best
range of any of the male subjects. It is not
to be inferred that binaural beat perception
can serve as an adequate screening test for sex.
However, additional work is in progress and
preliminary data indicate a remarkably reliable
sex difference in maximum frequency at which
binaural beats are heard, /

Relations with previous work, The results of
this study raise several questions, Perhaps
foremost is the problem of why previous authors
have insisted on the need for matched levels
in binaural Meat perception, Part of the answer
may be that most of the carly writers were
physicists who recognized that physical beats
are perceptible only when the mixed tones
are fairly closely matched in amplitude. By
extension, they had to conclude that binaural
beats should abso require matched levels, With
one exception, recent writers have not departed
from the physically based concepts, That ex.

re

ception, Wever and his students,’ is interesting
because there too the comment is made that
“the adjustment of the intensity at the two
ears is highly critical.” It now seems obvious
that their critical adjustment resulted from the
use of absolute beats (which, of course, were
quite adequate for measuring the processes they
investigated), and they naturally found only
a highly restricted range of magnitude differ-
ences in which binaural beats could be per-
ceived. In work preceding the present study,
using fixed rather than constantly changing
attenuations, confidence ratings from subjects
indicated that only matched levels (within
plus or minus 3 dB) give any certainty about
the existence of absolute beats. The long his-
tory of notes about the need for matched levels
in binaural beat perception, then, probably can
be laid both. to the interpretation of this bin-
aural neural phenomenon in terms of physical
beating phenomena and to the use of absolute
judgments,

Another question that must be asked per-
tains to studies in which a measurement de-
pends upon the hearing of beats. If binaural
beats can be heard with the softer tone at or
near threshold, can one thrust the results of
experiments in which a probe tone is used to
find “best beats,” for instance, with a distortion
product? Although the answer offered here
is the result of informal listening and not of
systematic investigation, there is some pertin-
ence to the presentation of these data, Two
minor pieces uf work are involved, The first
was a study with two subjects on the hearing
of binaural beats with tones of frequency f
‘and (2f +'5). Either tone was set at 40 dB SL;
the other was adjusted by the listener. In this
experiment, one subject had no difficulty at
all either in hearing beats or in producing a
beat threshold. The second subject found a
nebulous beating image, but reported that

© Particularly J. G. Loesch and BLL. Kapell, “The fires
quency Himit for the perception of binaural beats and for

cytlie’ binaural localization” senior theds, Princeton Unie
verity (1943),

“EG Wever, Theory of Hearing (John Wiley and
Seng Ine, New York, LH), pS” Lane reports rather
that tree binaural beats at SO dB SM, can be heart with
an interaural intenuty difference that approaches 20 dH
(reference @ pp. 402 amd 405-409),

-6—


drawn. In general, people working with bin-
aural beats have designed their experiments as
if they were dealing with phiysical beats. For
the physicist, heats are the result of alternate
reinforcement and cancellation of two added
waveforms that have a constantly changing
phase relation.” For the psychologist, beats
are what a listener hears when presented with
physical heats within a certain range of beat
frequencies. For both the physicist and the
psychologist, the detectability of beats is related
to the relative amplitudes of the two beating
tones. Occasionally, one uses two tones with
unmatched levels for detecting auditory dis-
tortion,” for measuring the size of a difference
threshold,‘ or for noting similar physical or
psychophysical entities. The psychologist who
uses beats for such purposes rapidly discovers
that two tones, although unmatched in mag-
nitude, must still be fairly close together for
subjects to report the preception of beats, If
one approaches the study of binaural beats with
knowledge of the psychological response to
physical beats, he finds considerable logic—and
almost overwhelming evidence—favoring . the
concept that binaural beats also will occur only
when the two tones used are matched in level.
However, if one holds the theoretical bias that
phenomena such as pitch and auditory locali-
zation are based at least partly on temporal
processes, then the older work must be re-
evaluated, A physiological togic must be ap-
plied where reasoning based
previously used.

Consider the possible existence of sepayate
neural pathways for the conduction of place-
pitch information and for the conduction of
timing information, From this viewpoint, bin-

"Beats are perindie variations that result’ from the
superfsition of Ovo simple harmonic quantities of differs
ent frequencies f, and They involve the periodic in-
crease and decrease of amplitude at the beat frequency
C-f,)° American Standart Acuntical Terminolog
(American Standards: Awociation, New York, 1960), SIT,
pect, 1.420 (By permission from the American Standards
‘Avoviation.)

"For example, Mo Lawrence and CL. Blanchard,
“Prediction “a swerphbility to avowtic trama by des
termination of threshokd of distortion.” Ind) Med and
Surgery 23, 194-200 (1934),

SRR, Rie, “Differential intensity senutivity of the
cat for pure tones” Phys. Rev 31, 867-873 (1928),

physics was ~

to

aural beats (which are generally accepted as
being associated with a timing or counting pro-
cess) must be perceptible so long as the tones
to the two ears are both above threshold in the
timing pathways. Working from this concept,
it became necessary to investigate the limits
of dichotic (ie. different at the two ears) in-
tensity which would still allow for the per-
ception of binaural beats.

PROCEDURE

Although a large number of methods for
measuring the limits of dichotic intensity for bi-
naural beats are possible, all of them may be
classified in one of two categories. These two
classes represent basically different (although
noé novel) techniques. In one, termed “relative,”
the subject is asked to make judgments about a
variable stimulus which alternates with a ref-
erence stimulus; in the other, termed “absolute,”
no reference is given. This particular categoriza-
tion is useful not only for differentiating be-
tween species of psyschophysical methods, but
also for showing why no previous work has
reported binaurat beat” perception with un-
matched interaural levels (see Results and Dis-
cussion below).

Absolute binaural beats, For the production
of absolute binaural beats, instrumentation as
illustrated in, Figure 1 was used. The two

nant

oem] Paromre
oat, on

“errearce

commen) [Raat I
eam |e ae

LEE OF vam

STA S38" FOR,
APSCRUTE Damaa eCars

Frcvne 1. Instrumentation for the production of absolute
binaural beats is shown. The subject controls the increase
ot deerme of attenuation in the variable channel and the
automatic attemtator accontingly plots his “threshokl” as a
function of time. A dheteh representing the listener's intra.
ceanial beating images is inclued on the right, showing
& petveived beat when the image iv shifted to the right
wae CRY, when the image is shifted to the left car (1),
when tis evnterat GMD, and when the tone ins the
Natithle channel is near threshokd,


APPLICATION OF A “RELATIVE” PROCEDURE TO A PROBLEM
, IN BINAURAL BEAT PERCEPTION

Jerry V. Tobias

The eritence of binaural beats has long been considered an_ indication of binaural
interaction for timing and for periodicity information. In the past, bilaterally matched sound
presure or sensation levely have been used in the investigation of these beats and the
measuring technique way one which may be termed “abvolute.” “However, the present study,
in investigating with a “relative” technique the limits of dichotic intensity which permit
binaural beats, shows that listeners rexpond to the presence of beats whenever the tones
to both cars are above threshold. It iy suggested that this new result fits more neatly into
current theoretical formulations, The frequencies investigated ranged from 100 to 2000 eps.

As other authors have previ

sly reported, the best performance occurred in the 400-600 cps

range. The prevent findings strengthen the case for an auditory nervous system with timing
channels independent of other transmission lines and, thereby, also have implications for

pitch theory.

’
!

v3

Binaural beats are heard when two sinusoids
of slightly differing frequency are led independ-
ently to the two ears. The subjective effect is
most often described asa fluctuation iyfoudness,
Auditory theory has profited from investigations
of the phenomenon because, in order to be
heard as a beating complex, the tones must be
arought together neurally by a mechanism
which preservgs time or phase relations, That
is, for the Frequencies at which binaural beats
can be heard, auditory tract responses change
in synchrony with the stimulus, Here, then, is
@ perceptual process: whose existence  consti-
tutes good wvidenee for “periodicity following”
of low frequency tones by the auditory nervous
system,

Antecedents of the work reported: here date
hack as far as 1859, and contiue very nearly to

s

‘the present.’ Apparently, each previous in-
vestigator has used a physical approach rather
than a physiological one, even though physio-
logical implications have frequently been

* Detailed historical references (starting with H.W.
Dove, “Nachtrag zu den Combinationstonen,” Reportorium
dL Physik 3, 404-405 (1839) can be found in GW.
Stewart's series of three papery, “Binaural beats" Phys.
Rew, 9, 502.508, 500-513, 514-528 (1917); additional dis.
cusion of the carly work can be found in 1H. Fletcher,
Speech and Heuring (D, Van Nostrand Company, Ine,
New York, 1929), Part TH, Chap, EG. Wever, Theory
of Hearing (John Wiley and York, 1949),
pp. 427-454 and J. CoB J. G. Webster, and
t M. Hledhan, “On the frequency: timity of binaural beats”
Jo Acoust, 463-473 (1950) include further
comments and noes to latee artides not mens
tioned in the preent paper. Lith writing on theoretical
aspects of binant betty has appeared: since, except pees
haps. Belford. “The binaural beat phenomenon, J.
Uarngol and Otol, 69, 645-688 (1955),

-1-


.*

APPLICATION OF A “RELATIVE” PROCEDURE

TO A PROBLEM IN BINAURAL BEAT PERCEPTION

JERRY V. TOBIAS, Ph.D.

Rese-irch Psychologist (Physiological and Experimental)
Psychology Branch °

63-17

FEDERAL AVIATION AGENCY
AVIATION MEDICAL SERVICE
AEROMEDICAL RESEARCH DIVISION
CIVIL AEROMEDICAL RESEARCIU INSTITUTE
OKLANOMA CITY, OKLATOMA
AUGUST 1983