(ESTIMATED PUB DATE) RESEARCH ON SIDED-TONE DELAY AS AN INTERROGATION DEVICE - MAY, 1953

• Document Type: SPECIALCOLLECTION
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): 00184417
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 48
• Document Creation Date: January 21, 2025
• Document Release Date: January 15, 1983
• Publication Date: May 1, 1953

RESEARCH ON SIDE-TONE DELAY
AS AN INTERROGATION DEVICE
By
May, 1953
Final Report
RESEARCH ON SIDE-TONE DELAY AS AN INTERROGATION DEVICE
by
May, 1953
Contract Period: June 1, 1952 to May 31, 1953
INDEX
Page
I. Aims and Purpose of this Research 1
How the Side-Tone Delay Was Produced 2
III. Effect of the Side-Tone Delay on a Subject
IV. The Gaining of Confessions Dependent Upon Two Factors
V. Procedures
VI. Side-Tone Delay Instrument Is Not a Lie-Detector
VII. The Testing of Criminal Suspects
VIII. Examples of Experimental Cases
IX. Instrumentation
X. Conclusions
3
4
5
14
15
19
28
34
XI. Bibliography 39
RESEARCH ON SIDE-TONE DELAY AS AN INTERROGATION DEVICE
I. Aims and Purpose of this Research.
The primary aim and purpose of this project was to obtain a successful
interrogation device from the effects of side-tone delay, together with an
appropriate procedure for its use with a minimum number of attachments.'
The secondary aim, developed in this laboratory, was to obtain more
easily interpreted polygraph records by use of side-tone delay in con-
junction with the polygraph.2
1 Throughout the report this phenomenon is termed "Side-Tone Delay" and
for brevity the initials STD are used. Previous investigators in this field have
used other terms to denote this same phenomenon. For example, Professor
John W. Black, Ohio State University, terms it "Delayed Side-Tone," while
Professor Grant Fairbanks, University of Illinois, has referred to it as
"Delayed Auditory Feedback."
1/ 2 The.
)
Polygraph was utilized for these experiments. It provides for
the recording of five different responses -- blood pressure-pulse, respiration,
galvanic skin reflex, arm movements, and thigh-leg movements. This poly-
graph is the only instrument equipped with arm and leg movement recorders.
1
II. How the Side-Tone Delay Was Produced.
Basically the side-tone delay phenomenon was produced in this
laboratory by the following method:
The subject's speech was picked up by a microphone, which
was connected to a tape recorder. At the recording head of
this instrument the speech was recorded on a moving tape, and
then this speech was reproduced when that part of the tape
reached the playback head of the instrument. This. reproduced
speech was then amplified by the amplifier which, in turn, was
connected to the subject's earphones.
Thus, the subject hears through his earphones what he has previously
said. How later he hears his speech is dependent upon two equally im-
portant factors: first, the distance the recording tape must travel from
the recording head to the playback head, and second, the speed at which
the recording tape is traveling.
That is, the amount of delay depends upon the time it takes for the
moving tape to go from the recording head to the playback head. If this
interval of time is .20 seconds, the delay is .20 seconds. Naturally, if
either the distance between these two heads is varied or if the speed of
the tape is changed, the amount of delay will also correspondingly change.
2
III. Effect of the Side-Tone Delay on a Subject.
It was first believed that the general effect of delaying the side-tone
on a subject was to retard his speech and cause a variance in his vocal
intensity. This belief was based upon the findings of previous experimenters.
It was found at the laboratory that this phenomenon only occasionally
occurred. It is thought by the investigators that the amount of difficulty
experienced by the subject might be based upon his education, intelligence,
social consciousness, or a combination of these three factors. In most
cases it appeared that the more education and higher intelligence a sub-
ject had, the greater difficulty he experienced with the side-tone delay.
3 For example, Black, John W., "The Effect of Delayed Side-Tone upon
Vocal Rate and Intensity," THE JOURNAL OF SPEECH AND HEARING DIS-
ORDERS, 16, 1951, 56-60; Lee, B. S., "Some Effects of Side-Tone Delay, "
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 22, 1950, 639-640;
and Lee, B. S., "Effects of Delayed Speech Feedback," JOURNAL OF THE
ACOUSTICAL SOCIETY OF AMERICA, 22, 1950, 824-826. �
3
IV. The Gaining of Confessions Dependent upon Two Factors.
The use of the STD instrument in obtaining confessions, the primary
aim of this project, is mainly dependent upon two things -- the interrogator
and his procedure. No instrument or device can even partially fulfill the
basic requirement of having a good interrogator, and he must have suitable
procedures to use with the STD instrument.
The interrogator is the man in charge of the situation, and how he
performs will determine whether the interrogation is a success or a failure.
From this, one can logically conclude that the interrogator who is better
qualified and trained will gain more confessions and information than the
interrogator who is unqualified or who is untrained. This is true regardless
of whether the STD instrument is or is not utilized during an interrogation.
Therefore, the better interrogator will obtain more confessions with
the STD instrument than the poor interrogator. The STD instrument is
certainly no panacea for the poor interrogator. In fact, the poor interrogator
will not only obtain little information through the use of the instrument, he
possibly will hinder the investigation.
-4
V. Procedures.
Because the interrogator must have suitable procedures to use with the
STD instrument, the investigators devoted the first five months of this
project to developing and preliminarily experimenting with various interro-
gational procedures and techniques. A great number of criminal suspects
were experimented with during these months in order to determine which
procedures might be the most effective. Conclusions were reached as to
their practicability, and the following procedures were deemed worthy for
further experimentation. These are now listed and explained along with a
statement as to their value.
It was decided that regardless of the type of procedure used, the subject
should be instructed before the use of the STD as to what he would experience
if he was not telling the truth. The actual wording of this instruction, of course,
was based upon the subject's intelligence, but the following is a sample
instruction:
"This instrument is a very sensitive device, and when you lie about
a fact you have mental conflicts regarding that lie. These conflicts are
indicated in your voice, and this instrument amplifies these conflicts
and they are heard as actual stuttering and hesitations. "4
4 When the subject asked why he even stuttered on the irrelevant questions
(those questions not pertaining to the crime and to which the subject is telling the
truth, e. g. , "Where were you born?"), the examiner replied:
"You are not really thinking about where you were born and about
those other meaningless questions. You are waiting for the crime
questions to be asked, and you are worried about whether the instrument
will show you are telling the truth or show that you are lying. That's
why you stutter on these meaningless questions."
5
A. Use of the Polygraph and Then the Side-Tone Delay Instrument.
1. The polygraph is used first to determine actual points
of deception. Then during the oral interrogation the side-tone
delay instrument is used at these points of deception. The STD
switch is turned on at points of deception and is turned off when
the subject is telling the truth.
This procedure was found to be of great value for several reasons.
First, the interrogator knew before the use of the STD on which questions
the subject was not telling the truth. Second, the STD is introduced after
the polygraph, therefore, the interrogator's psychological position is
greatly strengthened just as the interrogation begins.
However, the objection to this procedure is that an additional instru-
ment, the polygraph, must be used as well as the services of a competent
polygraph examiner.
B. Joint Use of Side-Tone Delay and Polygraph Instruments.
1. Manually manipulating STD switch at points of possible
deception while the polygraph is in actual operation.
This method was found to be of value only when used for its psychological
effect because the resulting polygraph records were too distorted for a
correct interpretation. Naturally, no dependable comparison of polygraph
responses could be made between the irrelevant and relevant (crime)
6
questions because of the switching on of the STD at the relevant questions.
This introduced a strong stimulus that was not present during the irrelevant
questions.
This procedure was found to be of some value in those cases where it
could be assumed before the examination that the subject would be lying
about the matter under investigation. This assumption can only be made
in those cases where the subject has been implicated in a trustworthy
confession by one of his co-conspirators, or when the subject is a prisoner-
of-war. In the latter case, the subject is probably withholding information
about his equipment, deployment of his fellow troops, and other information
that is of great value to an intelligence unit.
2. Side-tone delay in operation throughout the polygraph tests.
In the majority of the cases with this procedure the STD did not
materially distort the polygraph recordings so as to prevent a correct
interpretation from being made, since the stimulus of the STD was constant
throughout the polygraph test.
The secondary aim of this project, developed by this laboratory, was
to determine if more easily interpreted polygraph records could be ob-
tained by the joint use of the STD and the polygraph. This procedure,
that is, 'the STD in operation throughout the polygraph tests, appeared to
be the only procedure feasible to determine the value of this aim. After
completely reviewing all the records obtained by this procedure it was
determined that many times the polygraph records were probably much
7
harder to interpret, because of the use of the STD, than they would have
been without its use. Sometimes the records were completely uninterpre-
table because of the use of the STD. Many times the subject's attention and
interest were focused on the STD and its effect, rather than to whether or
not he was telling the truth on the questions being asked. In fact, the STD
caused two subjects, later verified as innocent, to respond during the
polygraph test as guilty. These guilty responses were in contrast to their
innocent responses on the polygraph tests when questioned without the use
of the STD.
This last procedure appeared to be the most desirable of the two
possibilities listed under this category, Joint Use of Side-Tone Delay and
Polygraph Instruments. The investigators originally thought that while the
STD was operating there might be more difficulty on the part of the subject
to answer his question smoothly when he attempted deception. Since the
polygraph is believed to record mental conflicts and the fear of detection,
it was thought that with the STD these conflicts might be translated into a
speech impediment at the points of deception. In ordinary polygraph tests
it has been found that some verified guilty subjects experience mental blocks
at points of deception.
But it was found during this experiment that when an STD subject ex-
perienced mental blocks it had nothing to do with his truth telling. Rather,
it was the effect of the STD which caused the subject to have these mental
blocks, since they appeared on the irrelevant questions as well as the relevant
8
(crime) questions of both the guilty and the innocent. At no time during this
experiment did mental blocks occur only on the relevant questions.
The following are the types of questions and answers that can be utilized
when the STD and polygraph are used jointly:
a. Direct, unambiguous questions requiring "yes" or
"no" answers., This is the most commonly used type
of polygraph question and answer.
b. Direct, unambiguous questions with previous instruction
given to the subject to use short-term answers. These
answers also require the usual "yes" or "no" reply,
followed by a very short sentence. Examples of this
type answer are "Yes, I do," or "No, I did not".
c. Direct, unambiguous questions with previous instruc-
tion given to the subject to use long-term answers.
These answers also require the usual "yes" or "no"
reply, but then a statement follows which repeats the
essential points of the test question. For example,
if the question was "Did you steal that $1,000 last
Saturday night?", the answer would be, "No, I did
not steal that $1,000 last Saturday night."
d. Searching-type questions with narrative answers
required, e.g. , "Where were you last night at ten
o'clock?"; "I was at Kelly's tavern drinking beer
with the boys."
9
Of these four types of questions and answers, B, the question requiring
a "yes" or "no" answer followed by a short sentence, appeared to be the
most effective when both the polygraph and STD instruments were used at
the same time. It was effective because the polygraph records were usually
not too distorted to prevent a diagnosis of guilt or innocence while the sub-
ject experienced the STD effect. However, in some cases with this type
question and answer, the polygraph records were too distorted because of
the STD for an interpretation to be made.
When the subjects answered "yes" or "no" (type A answer), there was
no apparent evidence that the STD affected them. Consequently, this type
answer with the STD did not help to improve the interpretability of the poly-
graph records.
The long-term answer (type C answer) was objectionable in those cases
involving subjects who experienced difficulty in speaking with the STD,
because their resulting polygraph records were too distorted for a correct
interpretation. This distortion was caused by several factors. First, the
subject's polygraph respiration recording was drawn-out and thereby dis-
torted because the time required to answer the question was more than
usual. Second, the blood pressure-pulse recording was often distorted
because the subject, in experiencing speech difficulty due to the STD,
attempted to express his thoughts by moving his arms and hands. When
these movements occurred, the blood pressure-pulse recorder indicated
movements instead of natural responses.
- 10 -
The narrative answer (type D answer) has the same disadvantages as
the long-term answer, that is, the resulting polygraph records are often too
distorted because of the STD. In addition to this, the polygraph examiner
experienced difficulty in having the subject follow instructions, which were
to respond with a full and complete answer to the question. Usually the
subject's answer consisted of one or two words. For example, if the subject
was asked where he was last Saturday night, he would reply, "Home",
instead of the answer the subject gave before the test, "I was home with my
wife and kids watching television."
C. Use of Only the Side-Tone Delay Instrument.
1. Manual manipulation of STD switch during the interrogation
at the points of possible deception.
Because there is no utilization of the polygraph with this procedure,
the interrogator must assume beforehand that the subject is guilty. For
this procedure to be most effective, the interrogator must have the STD on
whenever he believes the subject to be lying. This necessitates guessing on
the part of the interrogator as to when the subject will lie. Obviously, the
effectiveness of the procedure is greatly diminished as soon as the interro-
gator makes an erroneous guess. Probably no confession will result from
a guilty subject if many such wrong guesses occur.
Moreover, with this procedure the interrogator does not know before
the interrogation if the subject is guilty or innocent. In the great majority
of cases the interrogator will still not know even after the interrogation.
2. The STD operating continuously and purely as an interroga-
tional device.
a. During the interrogation, while the STD is con-
tinuously operating, the subject is allowed to
interrupt in order to make his denials. The
examiner may then call the subject to task for
his failure to express himself without stuttering
and/or hesitation.
Again, the guilt or innocence of a subject cannot be reliably determined
if this procedure is used unless the subject fully confesses or makes serious
admissions against his interest.
b. While the STD is continuously operating, the
interrogator uses the technique of immediately
stopping the subject from fully discussing the
case while an appeal for the truth is made by
the interrogator. When this appeal appears to
change the tenor of the subject's denials, he is
then allowed to make any explanation regarding
his position in the case. In doing so he will ex-
perience difficulty due to the effects of the STD.
When this difficulty is brought to the subject's
attention it might materially aid in obtaining a
confession.
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Of the three possible techniques listed under this category, Use of
Only the Side-Tone Delay Instrument, this last technique, 2b. , appears
to be most effective, providing the interrogator has mastered the art of
inoffensively stopping the subject from registering his denials until the
interrogator invites his comments. Using this technique the interrogator
must also be familiar with the changes that occur in the subject's facial
expressions, physical actions, and verbal comments which will acquaint
the interrogator as to the proper time to invite these comments.
The obvious objection to this procedure is that unless the subject
confesses, the interrogator does not know whether the subject is innocent
or guilty. This particular drawback, not being able to establish the guilt
or innocence of a subject, applies to all procedures in which there is no
utilization of the polygraph. In a great majority of cases guilt or innocence
can be readily determined by a competently conducted polygraph examina-
tion.4
4 As a matter of fact, all of the procedures proposed in this project fall far
short of the effectiveness of the ordinary polygraph techniques. With a compe-
tently conducted polygraph examination, the guilt or innocence of a subject can
be determined in over 95 per cent of the cases, and over 60 per cent of those
reported guilty confessed to the examiner. (These statistics are based upon
those of the
laboratory in during a five-year period ending
December 31, 1952.)
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VI. Side-Tone Delay Instrument Is Not a Lie-Detector.
During these experiments the investigators never considered the STD
instrument to be a lie-detector or an instrument to be used in place of
the lie-detector. The investigators never found any significant correlation
whatsoever between the results of the STD tests and the subject's guilt or
innocence. Therefore, the STD instrument should not be considered as a
type of lie-detector.
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VII. The Testing of Criminal Suspects.
After developing and preliminarily experimenting with these various
procedures for five months, in November, 1952, a more suitable arrange-
ment was made with the Judge of the
Municipal Court The Judge agreed to steadily supply this
laboratory with criminal defendants who appeared to be guilty, yet who
claimed innocence. Before this time criminal-case subjects were only
irregularly submitted to this laboratory by various judges of the Municipal
Court
.5
was in charge of Boys Court, and this court was believed
by the investigators to be the most representative for this laboratory's
purposes since it handles criminal preliminary hearings for boys ranging in
age from 16 to 21. Also under this court's jurisdiction are adults who have
been implicated in crimes with boys in this age group. Most of the cases
referred to this laboratory by Boys Court were of a felonious nature, how-
ever, misdemeanors were sometimes included.
5 Throughout the entire contract period many other subjects, besides those
arrested for felonies and misdemeanors, were experimented with on the STD in-
strument. Mainly in this group were applicants for trusted positions in various
companies. These subjects were questioned concerning their general honesty,
honesty at former places of employment, previous arrests, and bad habits such
as excessive indebtedness, gambling, and drunkenness. Also included in these
experiments were those people involved in quasi-criminal matters, such as
bastardy cases from the Municipal Court.
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The first of these subjects arrived on November 12, 1952. From that
time until January 19, 1953, appointments were made for the examining of
51 of these subjects, of whom 26 appeared and agreed to be tested. During
this period the investigators' main effort, besides determining the guilt or
innocence of a subject, was in having the subject experience speech difficulty
because of the STD. The results of these examinations follow:
Table One. Outcome of the Examinations*
White Colored
Innocent 6 12
Guilty 1(1 con- 6 (3 con-
fession) fe ssion.$)
Indefinite 0 1
*As determined by the
Polygraph and/or full confessions.
Table Two. Speech Difficulty While STD Operating**
Innocent
Guilty
Indefinite
** Scale of Speech Difficulty
White Colored
2 Fours, 3 Twos, 2 Fours, 3 Threes,
1 One 3 Twos, 4 Ones
1 Two (cora.)
1 Four (conf. ),
1 Three,
1 Two (conf.),
3 Ones, (1 conf. )
None 1 Two
Five -- Great difficulty
Four Some difficulty
Three Little difficulty
Two -- Very little difficulty
One No apparent difficulty
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From January 19 to February 11, 1953, 17 additional Boys Court subjects
as well as other subjects were experimented with in this laboratory. During
this period the investigators' main attention was directed towards obtaining
confessions from the subjects by use of procedures with the STD rather than
having the subjects experience speech difficulty because of the STD. The
results of these experiments with the Boys Court subjects were:
Table Three. Outcome of the Examinations*
White Colored
Innocent
Guilty
Indefinite
6 5
3 (2 con- 3 (1 con-
fessions) fession)
*As determined by the Polygraph and/or full confessions.
Table Four. Speech Difficulty While STD Operating**
White Colored
Innocent 3 Fours, I Three, 1 Four, 3 Twos,
2 Twos 1 One
Guilty 2 Fours, (lconf.) 2 Twos (1 conf. )
1 Three (conf.) 1 Two
Indefinite None None
**Scale of Speech Difficulty
Five Great difficulty
Four Some difficulty
Three Little difficulty
Two Very little difficulty
One No apparent difficulty
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As shown by Table Two and Table Four, very few subjects stuttered or
hesitated to any extent when the STD was operating. This is especially
significant in Table Two, since with these subjects the investigators con-
centrated on having the full effect of the STD occur. It was originally thought
that the more difficulty a guilty subject had in speaking because of the STD
effect, the more likely he was to confess. However, Table Four indicates
that about the same percentage of confessions was gained when the interro-
gator concentrated on the interrogation procedures rather than having the
STD effect occur.
Therefore, since January the investigators were not too concerned about
the effect of the side-tone delay per se, but they concentrated on the pro-
cedures to be used with the STD instrument so that confessions could be
more easily and readily obtained. These and the other experiments since
then have proven that most guilty subjects confess, even though their speech
was unaffected by the STD device.
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VIII. Examples of Experimental Cases.
The following ten cases were selected as representative examples upon
which various conclusions were based as to the value of the STD. In these
ten cases the subjects were males of varying intelligence and education.
With the STD all these subjects were interrogated as guilty, even when the
interrogator believed them to be innocent. Opinions are expressed at the
end of each case concerning the value of the STD in that particular case.
These expressed opinions were found to be duplicated in other cases.
1. The subject, a 17 year old with a 10th grade education, was
arrested for attempted burglary. A store window was broken, and the
burglar was frightened away because the breaking attracted the attention
of several persons. One of these later identified the subject as the perpe-
trator. The subject denied the accusation.
Test 1: Polygraph, no STD, short-term answers. The records
indicated he was guilty.
Test 2: Polygraph and STD operating simultaneously with short-term
answers. Again the polygraph records indicated he was
guilty. Subject had very little speech difficulty because of
the STD.
Interrogation with STD: Subject made no admissions, and after 30 minutes
STD turned off and subject's earphones removed.
Interrogation without STD: Within 30 seconds the subject fully confessed to
the crime and also confessed another attempted burglary. When
- 19 -
asked why he hadn't confessed earlier, he stated, "I wanted to wait
until this thing (pointed to the STD earphones) was taken off."
Opinions: The STD did not help to improve the polygraph responses, and
it greatly hindered the interrogation.
2. C. S., J. K., & P. H. were accused of assault and battery upon a
young couple, as well as threatening them with a knife and promising to
"blast them" with a gun if they made an outcry. All three subjects denied
any knowledge concerning this occurrence.
C. S., 18 years old, high school student:
Tests 1, 2, & 3: The STD and polygraph operated simultaneously with
short-term answers. No speech difficulty. Records indi-
cated he was guilty.
Interrogation with STD: Subject made no admissions.
J. K., 21 years old, high school graduate:
Tests 1 & 2: STD and polygraph operated simultaneously with short-
term answers. No speech difficulty. Records indicated he
was guilty.
Interrogation with STD: Subject made no admissions.
P. H., 20 years old, high school graduate:
Tests 1 & 2: Polygraph, no STD, short-term answers. Both tests
indicated he was telling the truth on the questions pertaining
to actual participation, but indicated he had guilty knowledge.
- 20 -
Test 3: STD and polygraph used with short-term answers. Subject had
no speech difficulty due to the STD. This record was similar
to his first two records.
Interrogation with STD: The subject readily admitted that he saw C. S. and
3. K. accost the couple, that he heard J. K. threaten to shoot them, and
that he knew C. S. had a knife.
Opinions: In this case the STD did not help to obtain a confession from the
two verified guilty subjects, nor did it help the examiner in his
interpretation of the polygraph records. The interrogator believed
that P. H. would have confessed without the use of the STD.
3. The subject, a 17 year old with a 10th grade education, was arrested
for armed robbery of a newspaper boy. The subject claimed that he was
"being framed" by the newspaper boy and the one witness.
Polygraph tests: The subject was given four tests with yes and no
answers, and no STD. His polygraph responses were ambiguous
and inconsistent.
Interrogation with STD: Within 30 seconds the subject started to cry, however,
he still maintained his innocence. Subject experienced some speech
difficulty because of the STD.
Re-examination two days later: Again the subject was given four polygraph
tests without any STD. This time the records indicated he was
telling the truth.
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The innocence of the subject was later definitely verified.
Opinions: The use of the STD may cause an innocent person to break down
emotionally, but if it is properly used no false confession will result.
4. The subject, an AWOL Air Force Corporal, was accused of assault
and battery and also armed robbery. He was arrested with a friend, but
both denied being the perpetrator.
Tests 1 & 2: Polygraph and STD used together on both tests with short-
term answers. Both polygraph records indicated that the
corporal was guilty. The subject had little speech difficulty
because of the STD.
Interrogation with STD: After six minutes the subject fully confessed and
implicated his co-defendant as well.
Opinions: This subject's polygraph records were not too distorted to prevent
interpretation, even though he did experience some speech difficulty.
The interrogator believed that the subject would have confessed to
the crime even without the use of the STD.
5. The subject, an 18 year old with a 9th grade education, was arrested
for stealing a wallet from a man's pocket. The wallet was not found on the
subject, although he was immediately arrested and searched. Subject denied
the charge.
Test 1: Polygraph used by itself with yes and no answers. Records
indicated that he stole the wallet.
- 22 -
Test 2: Polygraph and STD used jointly with short-term answers.
The subject experienced no speech difficulty. There was no
significant difference in the subject's two test records.
Interrogation with STD: Subject made no admissions.
Opinions: The STD did not help to improve the polygraph records, nor did
it help to gain a confession.
6. The subject, a 20 year old with a 2nd grade education, was arrested
for attempted murder and assault with a deadly weapon. It was alleged that
the subject stabbed the victim several times in the chest and throat. The
subject denied the accusation.
Test 1: Polygraph, no STD, yes and no answers. Records clearly
indicated that the subject was guilty.
Test 2: Polygraph and STD operating simultaneously with yes and no
answers. Again the subject's record indicated he was guilty,
but this time the polygraph records were much harder to
interpret since distortion occurred in the record due to the
slight speech difficulty induced by the STD.
Interrogation with STD: Although questioned for a long period of time, the
subject made no admissions.
Opinions: The STD did not improve the polygraph records, nor did it help
to obtain a confession.
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7. The subject, a 17 year old Marine with an 11th grade education, was
accused of attempted rape and assault with a deadly weapon. The subject
claimed this was a case of mistaken identity.
Tests 1 & 2: Polygraph, no STD, yes and no answers. Records clearly
indicated he was telling the truth.
Test 3: Polygraph and STD used together with long-term answers. The
subject experienced speech difficulty and his polygraph records
were distorted throughout because of the STD.
Interrogation with STD: Subject made no admissions against interest.
Later it was proven that the subject's alibi was the truth and that he was
not the guilty person.
Opinions: The use of the STD definitely helped to distort the polygraph records
when long-term answers were required. Interrogation with the STD
instrument did not induce a false confession.
8. Two high school students, G. H. and C. B., both 17 years old, were
examined in regard to an alleged breaking and entering, assault and battery,
and assault with a deadly weapon. Both subjects denied doing what the com-
plainants alleged, and both said that they were innocent bystanders.
G. H.:
Test 1: Polygraph used, no STD, yes and no answers. Records in-
dicated he was telling the truth.
- 24 -
Tests 2 & 3: Polygraph and STD used together with long-term answers.
No speech difficulty because of the STD, although these records
were distorted in comparison to the first test record.
Interrogation with STD: Subject maintained his innocence.
C. B . :
Test 1: Polygraph, no STD, yes and no answers. Record indicated
truth-telling on all questions but one, a minor issue under
investigation.
Test 2: Polygraph and STD used together, with yes and no answers.
The record was similar in its indications to test 1. The sub-
ject experienced little speech difficulty.
Interrogation with STD: Readily admitted doing the act which the polygraph
had indicated that he had done, but vehemently denied doing what the
polygraph had indicated he had not done.
Opinions: The use of the STD with the polygraph did not help to improve the
polygraph records, in fact, it distorted G. H. 's records. The use
of the STD did not induce any false admissions from either of these
subjects. The interrogator believed that C. B. would have admitted
the minor issue without the use of the STD.
9. The subject, 37 years old with 2 years of college education, was
arrested for drunken driving. The subject claimed he was merely a passenger
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in the car, and that another man was the actual driver.
Tests 1 & 2: Polygraph, no STD, yes and no answers. Both records
indicated that he was the driver.
Test 3: Polygraph and STD operated simultaneously with yes and
no answers. Subject's polygraph responses were similar
to those of the first two tests.
Interrogation with STD: No speech difficulty noticed. During the interro-
gation the subject laughed at the interrogator and said, "Stop trying to
fool me with this ... (STD)."
Opinions: The STD did not improve the interpretability of the polygraph
records, nor did it help to gain a confession. In fact, it hindered
the interrogation because the subject knew something was amiss
and believed that he was being tricked.
10. T. W. was arrested for assault and battery on the complaint of the
victim, G. F. In court, T. W. claimed that both G. F. and G. C. severely
beat him when he did not permit them to "crash" a New Year's dance. T. W.
also stated that later that night his mother was "cussed out" by G. F., and so
he and several of his friends did assault G. F. G. F. and G. C. both deny
being at the dance or assaulting T. W. G. F. also denies swearing at
T. W. '5 mother.
G. F., a 19 year old high school graduate:
Test 1: Polygraph, no STD, yes and no answers. The polygraph
- 26 -
record indicated he was telling the truth.
Test 2: STD and polygraph used jointly with yes and no answers. Sub-
ject had very little speech difficulty. Record similar to test 1.
Interrogated with STD: Made no admissions against interest.
G. C., an 18 year old high school student:
Test 1: Polygraph, no STD, yes and no answers. Polygraph record
clearly indicated he was telling the truth.
Test 2: Polygraph with STD, yes and no answers. Subject had no
apparent speech difficulty. This time the polygraph records
indicated that he was lying!
Interrogated with STD: Made no admissions against interest.
T. W., an 18 year old high school student:
Before his first test the subject confessed that G. F. and G. C. were
not at the dance, that they did not strike him at any time, and that he made
up the story about G. F. "cussing out" his mother.
In order to make sure this was the truth and not a statement givenbecause
of previous threats on the part of G. F. or G. C., T. W. was given two poly-
graph tests. The first test was of the regular type -- no STD, yes and no
answers. The second polygraph test included the STD with short-term answers.
On both polygraph records the responses clearly indicated that he was telling
the truth. This proved that his confession was trustworthy and that G. F.
and G. C. were verified innocent.
Opinions: When the STD was used during G. C. 's second polygraph test, it
caused him to respond as guilty although he is verified innocent.
However, the use of the STD did not induce either G. F. or G. C.
to make a false confession.
- 27 -
IX. Instrumentation.
During the first five months of the contract period, while the investigators
developed and preliminarily experimented with various procedures and tech-
2Iniques,
(instrument specialists employed
by the investigators) were developing various side-tone delay instruments.
Their aim was to design and construct an instrument that would prove prac-
tical from an interrogator's standpoint.
The first instrument built was designed on the principle of a constant
tape speed of about 40 inches per second along with a variable-distance
between the recording and playback heads. The recording head was fixed
in position and the playback head was movable on a track, which was designed
to preserve the alignment. The tape, in the form of an endless loop, was
carried over two light low-inertia pulleys, one of which was fixed, the other
having a spring mounting which maintained a constant tension on the tape.
The sound quality was fair. The loop of tape, of overall length about 2 feet,
appeared to give adequate results for periods up to one-half hour.
The overall quality of this instrument, however, was not by any means
equal to the Magnecord equipment. Although lower quality amplifiers
(Pentron) were used in this work, the main difference in quality was the
noise inherent in the tape and in the head system.
Consequently, a variable-speed constant head-separation device was
designed and built. The heads were fixed in position at the minimum distance
- 28 -
(1 inch). The endless loop of tape was driven by a variable-speed DC motor,
using a 6-volt storage battery. Since an overall speed range of at least 10-1
was desired with good torque over the range, the use of a resistance in the
field was found to be inadequate. The desired conditions were made by
varying the armature resistance and the field resistance simultaneously, but
in opposite directions. In this way, a 25-1 speed range was obtained with
good torque. The range of delay with this equipment was from about .02 to
.40 seconds. However, the noise level of the machine was fairly high,
apparently due to inadequate alignment and tracking of the tape.
It became apparent that construction of a higher order of accuracy was
necessary. It was decided to modify the Magnecord recording unit by keeping
a fixed relationship between the heads, and a constant tape speed by including
means for varying the length of tape between the fixed record and playback
heads. This was done by an arrangement of small pulleys, the middle one of
which was varied in distance from the heads. In using this method, the
amount of tape between the heads is twice the separation of the middle roller
from the heads. When this apparatus was constructed and tested, it was
found that the introduction of the auxiliary equipment in the neighborhood of
the heads upset the shielding system and resulted in the introduction of a
fair amount of noise. Consequently, the position of the heads was modified
to the extent that they were turned at 1800 so that the gaps faced each other
and were about 1/4" apart. A shield was inserted between the heads and a
small pulley mounted on a shaft running in micro ball-bearings was used to
- 29 -
Figure 1.
VARIABLE-DELAY, MODIFIED TRIPLE-HEAD UNIT
(Front View)
(1) Guide rollers.
(2) Erase head.
(3) Record head.
(4) Tape guides.
(5) Adjustable guide with
pointer and variable-
delay scale.
0111�111111101W
4=11111.0
(6) Magnetic shield between heads.
(7) Playback head.
(8) Tape drive capistan.
(9) Pressure roller.
(10) Recording tape.
position the tape. The separation of this pulley from the heads was controlled
by a dial which operated the carriage. The dial was calibrated directly in
ij delay in seconds. This device was extensively tested in the labora-
tory and found to give, with 15 inches per second tape speed, delay which
could be varied between . 07 seconds and .50 seconds. The overall sound
quality of this instrument approximately equalled that of the original Magne-
cord unit. The apparatus was tested by means of a steady thousand cycle
input from an audio frequency oscillator. The sound from the playback head
was examined and found to be of adequate quality from the standpoint of wow,
flutter, and noise. (See Figure 1.)
tf"),
The instrument described in the preceding paragraph was installed in the
laboratory on December 4, 1952, and was tested extensively with actual
criminal-case subjects. The quality of reproduction steadily and rapidly
deteriorated and after several weeks use it became completely inadequate.
Upon examination it was discovered that the recording tape was not
properly tracking over the heads because of a major mechanical flaw.
Apparently the mechanical ruggedness of the equipment was inadequate for
the conditions of use. Thus, the effectiveness of this instrument was greatly
limited. In an attempt to correct this flaw a number of minor adjustments
were made, which somewhat rectified the problem at first, but did not fully
correct the flaw.
A small drive pulley was then constructed for use with the standard
Magnecord equipment. This attachment permitted a delay of .30 seconds
- 30 -
Figure' VARIABLE-SPEED DRIVE, UNMODIFIED TRIPLE-HEAD UNIT
(Top View)
ii
(1) Motor rails.
(2) Delay control handle.
(3) Motor.
(4) Shaft extension and
"0" ring drive.
(5) Main drive disc.
(6) Idler drive disc.
(7) Idler drive rollers with
"0" ring tires.
(8) Main bearing.
(9) Outer bearing.
(10) Self aligning ball bearing.
(11) Spring tension nut and lock nut.
(12) Pressure spring.
(13) Tape guide rollers.
(14) Triple head unit.
(15) Tape drive capistan.
(16) Pressure roller.
Not shown:-
Oscillator unit and required
electrical connections.
with the 7-1/2 inch per second tape speed. This instrument was used while
a new instrument was being constructed.
On January 15, 1953, the investigators requested the construction of a
more refined variable-delay instrument, since it was believed that its re-
finements would eliminate some of the difficulties encountered in previous
instruments. The refinement by the laboratory consisted of a variable
tape speed which was incorporated with the erase, record, and playback head
assembly of the standard Magnecord. In order to accomplish this, a standard
Magnecord recording unit was completely dismantled and then rebuilt with a
variable tape speed. Also, the standard Magnecord synchronous motor was
adjusted so as to drive a disc at variable distances from the axis. The newly
constructed drive was free from wow and had a 1-10 speed range, which
meant the tape speed was 3" to 30" per second. This provided an easily
adjustable variable in the side-tone delay from . 041 to .416 seconds. The
standard Magnecord endless-loop tape device was utilized in place of the
standard two-reel device. This instrument was delivered in March, 1953.
(See Figure Z.)
This variable-delay instrument proved to be the most durable so far
tested because of its improved design and better construction. It provided
the interrogator with an instrument which did not have disturbing wow,
flutter, or noise. The investigators thought that this improved instrument
would provide a better evaluation of the variable side-tone delay because
of these refinements. It was believed that more subjects would be affected
- 31 -
by the side-tone delay phenomenon with this improved instrument and that
more confessions might result. However, in actual criminal cases it was
found that the subjects, who were not affected by a preadjusted .20 seconds
delay, were usually not affected when the variable-delay device was used.
This was true even though the entire range from .041 to .416 seconds was
utilized. Furthermore, the subjects who were affected to any extent by
the preadjusted delay of .20 seconds were seldom affected to any greater
extent when the delay was increased or decreased. Also, the percentage
of confessions did not increase with the use of this improved instrument.
In February, 1953, the investigators decided that possibly better re-
sults could be obtained if the subject was not required to wear earphones.
On May 12, 1953, additional apparatus was added to this variable-delay
equipment so that it would be unnecessary for the subject to wear earphones.
The elimination of the subject's earphones was accomplished by adding two
throat microphones, an auxiliary amplifier, and two external speakers.
The microphones are of the crystal-contact type and were adapted as
throat microphones since no commercial ones were available. The subject's
microphone is connected to the standard Magnecord amplifier, and the
amplifier's meter switch becomes the STD off-and-on switch. The Magne-
cord's monitoring jack is the outlet from this instrument and it is connected
directly to the auxiliary amplifier. The subject's speech goes through this
auxiliary amplifier to the two external speakers. The second throat micro-
phone is used by the interrogator, but this microphone is connected directly
- 32 -
Figure 3. VARIABLE-DELAY, EXTERNAL SPEAKERS:
Pictorial and Schematic Diagrams
(1) Subject's microphone and cord.
(2) Magnecorder amplifier and special recording panel.
(3) Interconnection cable.
(4) Auxiliary amplifier.
(5A & B) Speakers and speaker cords.
(6) Interrogator's microphone and cord.
(7) Power input (117 V., 60 cy. AC.)
(8) Power cord from Magnecorder amplifier (Plugs into
auxiliary amplifier)
to the auxiliary amplifier, thence to the two external speakers. (See Figure 3.)
Thus, the subject's speech can be delayed any desired time by means of
the variable-speed constant head-separation device, while the interrogator's
speech can never be delayed. Since the interrogator's and subject's voices
are heard through the same auxiliary amplifier and speakers, they both
sound alike. Therefore, it was thought that the subject would be less likely
to suspect that his voice was being delayed since both voices sounded alike.
Through experimentation at the laboratory it was found that two
external speakers were much more effective in inducing the STD effect than
one speaker. With only one speaker the subject can turn his head and focus
his attention away from the source of his delayed speech. The best results
were obtained when the two speakers were placed equidistant from each side
of the subject.
However, in testing this laboratory's personnel with the external-speaker
system, it was their opinion that it was very noticeable that the instrument
itself was causing the STD effect. With the earphones, the subjects believed
that they were at fault since their voices seemed directed at them without
delay. Because the external-speaker system so obviously delays the voice,
it is believed that this arrangement will not help to obtain confessions; in
fact, it will hinder the interrogator.
- 33 -
X. Conclusions.
1. Experiments in this laboratory indicated that the .20 second
delay was much more effective in producing the STD phenomenon than
any other delay ranging from .02 to .50 seconds. The conclusion,
that the . 20 second delay was the most effective, was in agreement
with the findings of other experimentors in this field. 6
2. The difficulty in speaking encountered by the subjects at this
laboratory was far less than expected, even with the .20 second delay.
In fact, the investigators were greatly surprised at the little difficulty
the subjects had in speaking with the STD. The reports of other
experimentors seemed to indicate that most subjects would automatically
experience great difficulty in speaking. 7
6 Guttman, Newman, "An Analysis of Articulation as a Function of Delayed
Auditory Feedback," M. A. Thesis, University of Illinois, 1951.
7 Included in the Summary of N. Guttman's thesis, ibid, was the following:
"Each of 16 male subjects read the same passage aloud under the
following conditions of time delay: Unamplified, zero delay, no headset;
amplified, zero delay; amplified . 10, .20, .40, and .80 sec. delays;
amplified, zero delay. Data were obtained from phonetic transcriptions
of the readings.
In almost all measures the peak of disturbance was at .20 sec. In
comparison to zero delay total articulatory errors at the peak were
approximately 400% more numerous, articulatory rate decreased 30 to
40%, phonetic output increased 8%, and error rate increased 300%.
Rate of error increased from one error every three seconds for
zero delay to more than one per second at .20 sec. Each of the
(continue at bottom of next page)
- 34 -
These results indicated to the investigators that possibly the amount of
difficulty the subject experienced due to the STD might be related to his
educational background, intelligence, social consciousness, or a combination
of these three factors. This hypothesis was based upon the fact that previous
experimentors apparently only used college students as their subjects, while
many of the subjects at this laboratory were uneducated, and their lack of
social responsibility was often demonstrated by their numerous arrests.
Their examinations at this laboratory was something very serious to
these subjects since their liberty depended on the results of the examinations.
No explanation as to the how and the why of the STD could be given to them,
since the psychological value would then be completely destroyed. Also,
because so much was at stake for the subjects, the investigators could not
expect complete mental or physical co-operation from them, especially from
those who were guilty.
3. Since it was found that the . 20 second delay was the most effec-
tive in producing the STD phenomenon, an unmodified Magnecord unit
(PT63-J Amplifier and PT63-AH Recorder) which affords a delay of . 20
seconds, is sufficient as a STD instrument. Any further instrumentation
beyond this is unnecessary if future experiments are to be conducted
individual types of error, substitution, omission, addition, and
miscellaneous, also peaked at . 20 sec.
Rate of articulation, similar in pattern for each of the three
measures of output, varied significantly with delay and was slowest
at . 20 sec."
- 35 -
in using the STD as an interrogation device.
4. During this experiment almost every criminal-case subject,
considered innocent by the investigators, was interrogated with the
STD to determine if its use would induce a false confession. Not one
of these innocent subjects made any admissions against interest, how-
ever slight, when interrogated as guilty. Therefore, it is believed that
no false confessions or admissions will result from innocent subjects
when the STD instrument is properly used.
5. It was found that approximately the same percentage of guilty
subjects confessed when the variable-delay instruments were used for
the interrogation as when the one fixed-delay instruments were used.
The total percentage of confessions from interrogated guilty STD
subjects amounted to approximately 56 per cent. This figure of 56
per cent can be contrasted to the percentage of criminal confessions
gained at the. _ laboratory between January 1, 1948 and December
31, 1952. During this five-year period, when no side-tone delay
instruments were used on the subjects, approximately 62 per cent
of the interrogated subjects did confess to the crimes under investigation.
Thus, when one reviews the past year in its entirety, it appears
that the side-tone delay did not increase the percentage of confessions.
When a confession was gained by the use of the STD instrument, it did
not materially reduce the time required for obtaining the confession,
nor did it make the interrogation any easier. Furthermore, the
- 36 -
investigators believe that the great majority of those who did confess
would have confessed anyhow without the use of the STD instrument!
In fact, there is a good possibility that the use of the STD actually
stopped a number of subjects from confessing their crimes. This was
definitely proven to be true in two cases when, after fully confessing,
the subjects stated that they did not confess earlier because of the
STD and that they waited until the STD instrument was turned off before
doing so. Also, it is believed that during many other interrogations
the guilty subjects were so confused or bewildered by the STD effect
that they were no longer concerned about their crimes and were not
listening to what the interrogator said. When the subject is actually
distracted by the effects of the STD, the interrogator's persuasiveness
is lost and there is very little likelihood of obtaining the confession.
6. It is the opinion of the investigators that the future holds very
little hope for the side-tone delay instrument as an effective interro-
gation device.
7. Also extensively tested in this laboratory was the hypothesis
that the use of the STD would produce more easily interpreted poly-
graph records. The investigators considered this so important that
they added it to the project as its secondary aim. Various types of
answers (yes or no, short-term, long-term, and narrative type
answers) were experimented with during polygraph tests when the
STD instrument was also being operated.
- 37 -
In the great majority of instances the STD was ineffective in
producing the desired results, and in many instances the STD affected
polygraph records so that they were more difficult to interpret. In
fact, on two occasions the use of the STD actually defeated the
purpose of the polygraph tests. On these occasions the side-tone
delay caused two verified innocent subjects to respond as if they were
actually guilty.
For these reasons the investigators believe that the STD instru-
ment should not be used in conjunction with the polygraph.
XI. BIBLIOGRAPHY
1. Black, John W., "The Effect of the Consonant on the Vowel,??
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, X, 1939,
203-205.
2. Black, J. W., "Timed Phrases," ONR Technical Report,
SDC 411-1-5, 1949.
3. Black, J. W., "Exploratory Studies: The Relation between
Uncertainty and Vocal Intensity," ONR Technical Report,
SDC 411-1-6, 1949.
4. Black, J. W., "The Intensity of Oral Responses to Stimulus Words,"
THE JOURNAL OF SPEECH AND HEARING DISORDERS, XIV,
March 1949.
5. Black, J. W., "Loudness of Speaking: The Effect of Heard Stimuli
of Low Intensity," JOURNAL OF EXPERIMENTAL PSYCHOLOGY,
XI, June 1949.
6. Black, J. W., "Natural Frequency Duration and Intensity of Vowels
in Reading," THE JOURNAL OF SPEECH AND HEARING DISORDERS,
XIV, 3, September 1949, 216-221.
7. Black, J. W., "The Effect of Room Characteristics upon Vocal
Intensity and Rate," JOURNAL OF THE ACOUSTICAL SOCIETY OF
AMERICA, 21, 1950, 174-176.
8. Black, J. W., "Some Effects upon Voice of Hearing Tones of
Varying Frequency and Intensity while Reading," BuMed Research
Project Report No. NM 001064. 01. 01, U. S. Naval School of
Aviation Medicine, Pensacola Florida, January 1950.1
1. Other reports from this same project include:
A. Accompaniments of Word Intelligibility.
B. Adaptation to Delayed Side-Tone.
C. The Effect of Delayed Side-Tone upon Vocal Rate and Intensity.
D. The Effect of Noise-Induced Temporary Deafness upon Vocal
Intensity.
E. Formal Spoken Vocabulary of College Students.
F. The Intrinsic Intensity of Oral Phrases.
(continue at top of next page)
- 39 -
G. Intelligibility of Speech Heard at High Altitude and Sea Level.
H. The Pressure in the Oral Cavity in the Production of
Consonants.
I. Some Influences of Delayed Side-Tone upon Intelligibility.
J. Some Physiological Accompaniments of Speaking.
K. A Study of Vocal Responses during Controlled Aural
Stimulation.
9. Black, J. W., "A Compensatory Effect in Vocal Responses to Stimuli
of Low Intensity," JOURNAL OF EXPERIMENTAL PSYCHOLOGY,
XI, June 1950, 396-397.
10. Black, J. W., "The Effect of Delayed Side-Tone upon Vocal Rate
and Intensity," THE JOURNAL OF SPEECH AND HEARING DISORDERS,
16, March 1951, 56-60.
11. Brubaker, R. S., "An Experimental Investigation of Speech
Disturbance as a Function of the Intensity of Delayed Auditory
Feedback," Ph. D. Thesis, University of Illinois, 1952.
12. Davis, Hallowell, et al., HEARING AND DEAFNESS, New York,
Murray Hill Books, Inc., 1947.
13. Draegert, G. L., "Relationships between Voice Variables and
Speech Intelligibility in High Level Voice, SPEECH MONOGRAPHS,
November 1951, 272-278.
14. Dunn, H. K. and White, S. D., "Statistical Measurements on
Conversational Speech," THE JOURNAL OF THE ACOUSTICAL
SOCIETY OF AMERICA, II, January 1940, 278-288.
15. Egan, J. P., "Articulation Testing Methods II," OSRD Report
3802, 1944. (Office of Technical Services Report PBL 22848)
16. Fairbanks, Grant, "VOICE AND ARTICULATION DRILLBOOK,
New York, Harper and Brothers, 1940.
17. Fairbanks, G. and Hoaglin, M. W., "An Experimental Study of the
Durational Characteristics of the Voice during the Expression of
Emotion," SPEECH MONOGRAPHS, VIII, 85-90, 1941.
18. Fairbanks, G., House, A. S., and Stevaas, E. L.; "Experimental
Study of Vowel Intensities," JOURNAL OF THE ACOUSTICAL
SOCIETY OF AMERICA, XXII, 4, July 1950, 457-459.
19. Fairbanks, G. and Jaeger, R. P.. "A Device for Continuous
Variable Time Delay of Headset Monitoring during Magnetic
Recording of Speech," THE JOURNAL OF SPEECH AND HEARING
DISORDERS, 16, 1951, 162-164.
- 40 -
20. Fletcher, Harvey, SPEECH AND HEARING, New York, D. Van
Nostrand, 1929.
21. Fletcher, H. and Munson, W. A., "Loudness: Its Definition,
Measurement and Calculation, "JOURNAL OF THE ACOUSTICAL
SOCIETY OF AMERICA, VI, 1933, 82-108.
22. Fletcher, H. and Galt, R. H., "The Perception of Speech and
Its Relation to Telephony," JOURNAL OF THE ACOUSTICAL
SOCIETY OF AMERICA, 22, 1950, 89-151.
23. French, N. R. and Steinberg, J. C., "Factors Governing the
Intelligibility of Speech Sounds," JOURNAL OF THE ACOUSTICAL
SOCIETY OF AMERICA, 1947, 19, 90-119.
24. Guttman, N., "An Analysis of Articulation as a Function of
Delayed Auditory Feedback," M. A. Thesis, University of
Illinois, 1951.
25. Hall, M., "Auditory Factors in Functional Articulatory Speech
Defects," JOURNAL OF EXPERIMENTAL EDUCATION, 7, 1938,
110-132.
26. Hull, F. M., "An Experimental Investigation of Speech Disturbance
as a Function of Frequency Distortion of Delayed Auditory Feedback,"
Ph. D. Thesis, University of Illinois, 1952.
27. Huntington, D. A., "An Experimental Investigation of the Relation-
ships between Auditory Abilities and the Speech Disturbances
Produced by Delayed Auditory Feedback," Ph. D. Thesis, University
of Illinois, 1952.
28. Inbau, Fred E., LIE DETECTION AND CRIMINAL INTERROGATION,
Baltimore Maryland, The Williams & Wilkins Co., 1948.
29. Inbau, F. E., SELF-INCRIMINATION: WHAT CAN AN ACCUSED
PERSON BE COMPELLED TO DO, Springfield Illinois, Charles
C Thomas, 1950.
30. Jordan, E. P., "A Comparative Investigation of Impromptu Speaking
and Oral Reading under Conditions of Delayed Auditory Feedback,"
M. A. Thesis, University of Illinois, 1952.
31. Kryter, K. D., "The Effects of Noise on Man," THE JOURNAL OF
SPEECH AND HEARING DISORDERS, Mon. Supp. 1, 1950.
- 41 -
32. Lee, B. S., "Some Effects of Side-Tone Delay, " JOURNAL OF
THE ACOUSTICAL SOCIETY OF AMERICA, 22, 1950, 639-640.
33. Lee, B. S., "Effects of Delayed Speech Feedback," JOURNAL
OF THE ACOUSTICAL SOCIETY OF AMERICA, 22, 1950,
824-826.
34. Lewis, D. and Tiffin, J., "A Psychophysical Study of Individual
Differences in Speaking Ability," ARCHIVES OF SPEECH,
Vol. I, No. 1, January 1934, 43-60.
35. Lightfoot, C. M., "Rate of Speaking: I. Relationship between
Original and Repeated Phrases," ONR Technical Report SDC
411-1-1, 1948.
36. Lightfoot, C. and Morril, S., "Loudness of Speaking: The
Effect of the Intensity of the Side-Tone upon the Intensity of the
Speaker," Joint Report No. 4, BuMed Research Project No.
NM 001 053, U. S. Naval School of Aviation Medicine, Pensacola
Florida, September 1949.
37. Marple, N. B. IV, and Morril S. N., "A Device for the
Production of Delayed Side-Tone," U. S. Naval School of
Aviation Medicine, Joint Report No. 8, Bulsvied Research
Project No. NM 001064.01, August 1951.
38. Snidecor, J. C., "Comparative Study of Pitch and Duration
Characteristics of Impromptu Speaking and Oral Reading,"
SPEECH MONOGRAPHS, 10, 1943, 50-55.
39. Stevans, S. S. and Davis, H., HEARING, New York, John Wiley
and Sons, Inc., 1938.
40. Tiffany, W. R. and Hanley, C. N., "Delayed Speech Feedback
as a Test for Auditory Malingering," SCIENCE, 115, 1952, 59-60.
41. Terman, L. A. and Merrill, M. A., MEASURING INTELLIGENCE,
New York, Houghton-Mifflin Co., 1937.
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