Psychophysiological Stress Analyzer
U.S. Patents Granted: 8,264,364; 8,502,691; 8,847,778
The American Polygraph Association wants to bury the TRUTH!
Muscle Tremors…
The most common of all involuntary movements and can affect the hands, arms, head, face, vocal cords, trunk, and legs. Most tremors occur in the hands. A very common kind of tremor is the chattering of teeth, usually induced by cold temperatures or by fear and anxiety. http://ptssa.net/security-screening-brain-emotion/
Sources: http://www.seattleneurology.org/postural-tremor.html and http://en.wikipedia.org/wiki/Tremor
First Proof of Concept Study for the PTSSA Technology
A study was concluded in 2005 to determine whether or not the Psychophysiological Touch Screen Stress Analyzer (PTSSA) is capable of capturing a psychophysiological response to a stimulus. The algorithms utilized in the PTSSA were developed in the 1980’s by Profiles for the Mark II Voice Stress Analyzer. These algorithms were developed in a real world environment with 2000+ examinations.
In this study, a truth verification survey was administered by the PTSSA to 25 different subjects. This survey was adapted for the PTSSA from a psychological preconditioning questionnaire that had been developed for voice stress analysts and polygraph examiners in the 1980’s.
The subject read the adapted questionnaire on the computer touch screen of the PTSSA. The subject answered each of the 65 questions by touching the touch screen “yes” or “no” button at the bottom of the touch screen (the ‘yes’ button was blue and ‘no’ button green). After each touch screen answer button was touched by the subject, the next question was automatically displayed. Only the last 26 questions of the touch screen survey were analyzed to determine emotional reaction patterns (the same procedure followed in voice stress analysis and polygraph).
Immediately after the touch screen survey was completed, a Mark II Voice Analyzer (proven in a blind study to be as accurate at the polygraph by the Florida Polygraph Service, Inc; [see Florida-Polygraph-Service-Blind-Study-On-Voice-Stress]) examination was administered to each subject. The 26 questions asked were the same as the last 26 questions administered by the PTSSA. The PVSA examination was prerecorded and played back through headphones placed over the subject’s ears. The subject’s “yes” and “no” verbal responses to each question were digitally recorded by means of a boom microphone attached to the headphones. The microphone was place in a position just to right of the subject’s mouth, approximately 1 inch. After the PVSA examination was administered, each “yes” and “no” verbal response was analyzed to determine emotional reaction patterns.
CONCLUSION: There was 100% correlation between the PTSSA and PVSA concerning the relevant and control issues. This evidence proves, beyond a reasonable doubt, that when the subject touches the specialized computer touch screen, in response to the stimulus displayed on the touch screen, the subject’s psychophysiological response was captured.
A Second Proof of Concept Study for the PTSSA Technology
In 2009 a second study was conducted. In this study 147 individual were given the 15 question survey used for identifying smugglers and terrorists on the PTSSA. The survey was administered in a non threatening environment, the same as the 2004 proof of concept study. The first 5 questions were used to adapted the person to answering and responding to questions on the touch screen. Questions 6 to 8 concerned weapons; questions 9 to 11 concerned smuggling; questions 12 to 14 concerned terrorism; and question 15 was a non threatening closing question. A factor analysis and standard deviation was completed on the 147 surveys. Results indicated the emotional reaction to each question decreased from the beginning of the survey to the end of the survey. This decrease of 8.97% in emotional reaction was because the subjects relaxed and adapted to being asked and responding to questions on the PTSSA.
Real World Environment Field Acceptance Test (FAT) of the PTSSA Technology
The Known Outcome Test (KOT) was designed to provide additional evidence that the PTSSA system can accurately determine when a person is practicing deception. This KOT was one of the examinations that was administered from November 30 to December 14, 2010 at the Lagos, Nigeria International Airport to a number of adult passengers and security agents without regard for their age, ethnicity, or gender. This testing process was monitored and observed by officials from the Nigerian Civil Aviation Agency (NCAA) and the Federal Aviation Administration of Nigeria (FAAN).
The KOT is a 16 question test, with 4 questions concerning the number 4. The KOT test subject is instructed to intentionally lie to any question concerning the number 4 appearing on the PTSSA computer touch screen. Because of the benign subject matter (no jeopardy or perceived threat), the PTSSA must detect abnormal reaction patterns (deception) in 2 out of 4 times concerning the number 4. The last question, 16, ‘Did you ever lie to escape deserved punishment’, was used in an attempt to induce an emotional reaction from the test subject, even if answered truthfully.
CONCLUSION: The reliability of the KOT examination was 99.163% in detecting deception.
For further details on the Proof of Concept and Field Acceptance Test studies please contact us at info@pvsa.net
3rd Party Testing
A 3rd party evaluation process was conducted by a group of PhD forensic psychologist working with the drug courts. The subjects must submit to Urine Analysis (UA) on a weekly basis. The test subjects are also asked a series of questions on the PTSSA system concerning their use or involvement with mood influencing substances. The subjects must answer ‘Yes’ or ‘No’ to the questions by touching the YES or NO button on the PTSSA screen. This specialize touch screen, and our propitiatory algorithms, measures how the subject emotionally reacted to each question when their finger comes in contact with the screen. The two key questions are “Do you believe your UA will come back positive for alcohol?”, and “Do you believe your UA will come back positive for illegal drugs?” The PTSSA system matched the chemical analysis 92%. See overview of the Clinical Report on this site.
Technology Overview: PTSSA Presentation v20
The Foundation Technology
Voice Stress Analysis and Polygraph
In March 1971, the first production models of the voice stress analyzers, Psychological Stress Analyzer (PSE) was produced and became the center of controversy, unequaled by anything short of nuclear power. The voice stress analyzer was developed to detect levels of significant emotional stress from human or animal voice utterances. The problem with the PSE was that it required the examiner to very skilled at graph interpretation, which was the same problem with the polygraph. Another problem with the PSE was that it could not produce real time results. In 1975 another voice stress analyzer was developed that over came the problems of graph interpretation. The Mark II Voice Analyzer produce a numerical value. This numerical value indicated absolute stress values for each utterance in real time.
It was expected to be useful in psychological and psychiatric evaluations and in truth verification. The voice stress analyzer was immediately compared with the polygraph which has been used in lie detection for years.
There are a number of similarities between the voice stress analyzer and the polygraph. Both are limited to measuring certain physiological manifestations of psychological stress. The polygraph is capable only of displaying relative stress levels and the voice stress analyzer absolute stress levels. In order to achieve accurate lie detection within these limitations, a means is required to differentiate between the stress caused by uttering a significant untruth and the stress from any other source. This distinction is accomplished by establishing control procedures to eliminate or identify non-deception related stresses. Thus, in a controlled test procedure, lie detection is based upon the stress changes displayed by the equipment. The voice stress analyzer controlled testing procedures have borrowed heavily from polygraph procedures which have been evolving since the late 1920’s.
Significant differences also exist between the voice stress analyzer and the polygraph. The voice stress analyzer was developed from technology nearly half century more advanced than that from which the polygraph was developed. Very briefly, these differences are as follows:
The voice stress analyzer processes voice and, therefore, does not require attached sensors. This eliminates the stress caused by the unnatural and sometimes painful physical constraints of polygraph attachments. The use of voice as the source of stress responses has also created some of the controversy that surrounds the voice stress analyzer. Since the voice can be processed regardless of its final source (telephone, television, radio, etc.) it is indeed possible to do stress analysis without the subject being present and, in fact, without his knowledge. On the other hand, the lack of test controls in some of these situations limits the usefulness of these approaches in lie detection.
Stress responses evaluated by the voice stress analyzer essentially occur instantaneously in the utterance; those evaluated by the polygraph are derived from the end of a chain of body chemistry actions and reactions. A delay occurs in polygraph response to the stimulus, and an even greater delay takes place before chemistry returns to normal following a response. To offset this problem, questions must be spaced unnaturally. In addition, the polygraph will not tolerate multi-syllabic responses.
Legal Findings and Case Studies
Florida
Restrictive laws have formally or informally accommodated the voice stress analyzer. In Florida, action in 1973 and 1974 resulted in state sponsored hearings. In spite of a bitter fight by the polygraph sector, the official report found that: “the voice stress analyzer is a voice polygraph; and is a reliable and credible instrument for measuring psychological stress in the hands of an adequately trained operator.” While Florida law was never amended, the hearings resulted in an administrative decision that the law would not affect the use of the voice stress analyzer. Several other states have handled the problem with similar informality.
North Carolina & Arkansas
Two states did change their licensing restrictions. North Carolina created a separate profession of audio stress examiners and promulgated separate licensing requirements, including a reduced training period for the voice stress analyzer. The Arkansas legislature, under Act 342 of 1975, authorized the use of the voice stress analyzer for lie detection by law enforcement agencies. Other progress included the formation of professional societies inspired by the voice stress analyzer. The International Society of Stress Analysts (ISSA) was formed in 1973 to provide a broad professional base, and several state associations were formed as well. ISSA accept all instruments for lie detection and can count a substantial number of polygraph examiners among their members.
Studies and How They Are Conducted
It is somewhat hazardous to accept what “statistics say” and “studies demonstrate” without first examining the validity of a study’s statistical basis and its parameters and techniques. What a study purports to “study” may not be what it studies at all. A study may contain unsubstantiated assumptions and uncontrolled variables that make the results unlikely to deal with the same areas as the study objectives. Usually, but not always, that study’s conclusion will include the alert that, within the limits of “this experimental model”, the results attained could be expected. Obviously, if the same things were done, the same results could be expected. But were these things done faster, and simpler in a less expensive study?
A simple example of both favorable and unfavorable studies concerning the same piece of equipment will help to illustrate this point. If we were to test fire a new model rifle, and a reasonable number of testers were able to place all shots in the bull’s eye, we would probably conclude that the weapon was sufficiently accurate to make bull’s eyes. If, however other testers were unable to hit the target with the same weapon, we would suspect that something invalidated these unsuccessful shootings as a test of the weapon; perhaps the testers did not know how to fire a rifle with accuracy, or there was a bad lot of ammunition, or they were firing at dusk and could not properly see the target. If these variables were not controlled, these shootings would not be a valid test of the rifle’s accuracy. We should note, then, that while the test was for the purpose of validating the accuracy of the weapon, the test itself was affected by these outside variables. Only if they are properly identified and controlled will the test be valid as a test of the rifle’s accuracy.
When we speak of either the voice stress analyzer or the polygraph, we are speaking also of a system of several components, rather than just the instrument involved. In either case, the system must include stress in the examinee, properly working equipment that will convert the stress to a chart indication, a chart reading system that allows the stress to be recognized for what it is, and an examiner capable of applying the chart reading system. The voice stress analyzer must have audio tape recordings of reasonable quality, the polygraph must have ink in its pen reservoirs, and both instruments must have chart paper. When either instrument is used for lie detection, a valid controlled test procedure is required to identify those stresses caused by deception. If any one of these system components is eliminated or modified, the study as an evaluation of the voice stress analyzer or polygraph system is not valid (although it may be valid as an evaluation of the modification).
Frequently, studies performed by members of the academic community are based on an attempt to create an artificial model of the real world, rather than on the real world itself. For example, for a validation study of the polygraph or voice stress analyzer, a number of students pretending they have committed a crime are tested in an attempt to detect deception concerning the pretended crime. This is sometimes an acceptable scientific approach, if a valid model can be accomplished. It has the obvious advantages of being quicker, cheaper, and more standardized as a source of study data than actual, real world lie detection examination. On the other hand, there is little assurance that the stresses produced by the pretenses are reasonably comparable to those produced by an actual jeopardy situation. It is nearly impossible to produce real world stress in the laboratory. For example, a recruit in the U.S. Army was shooting for qualification with the M14 during basic training. This qualification required him to shoot at pop-up targets from a number of different locations at various distances. The targets would only remain visible for about 5 seconds. The recruit was able to shoot a perfect score. After qualifying, the recruit was called into the commander’s office and was questioned regarding how he was able to accomplish such a feat never before witnessed by the command. The recruit indicated that squeezing the trigger was an important part of remaining on target but more importantly, the targets were not shooting back at him.
The voice stress analyzer was designed specifically for the levels of stress encountered in real world criminal, security, and clinical applications. It was never intended to and is not expected to accomplish stress measurement of game situations. In fact, if such low level stresses were allowed to provide significant responses, the voice stress analyzer’s performance would be limited in the real world, as is generally considered to be the case with the galvanic skin response.
Moorhead Committee Hearings
Many early validation studies of the voice stress analyzer were performed by polygraph examiners who wanted to assure themselves of its validity before switching from the polygraph to the voice stress analyzer. Since these studies were for their own purposes, few of them were documented formally. However, in a field survey of 39,000 examinations done for the Moorehead Committee Hearings in 1974, 5,045 cases were reported to involve simultaneous testing with both the voice stress analyzer and the polygraph. Of these, 5,037 produced correlative results. In other words, right or wrong, the voice stress analyzer and the polygraph agreed 99.8% of the time in REAL WORLD testing. As interesting as these figures are, they cannot be accepted definitively because of the lack of detailed documentation. They do, however, indicate the acceptance of the voice stress analyzer by professional polygraph examiners based on a large number of actual cases.
Fortunately, there is no shortage of formal studies of the voice stress analyzer. Exclusive of articles, testimony, and sundry other reports, there are some 60 studies of various applications. Of these, 50 are clearly favorable to the voice stress analyzer and several are partially favorable. While it is obviously impossible to report on or analyze all of these studies in a paper of this length, several are worthy of consideration.
Kubis and Horvath Studies on Truth Verification
First, the two most quoted adverse studies that most polygraph examiners are very quick to point out are studies performed by Kubis and Horvath. The former, in particular, is a study in flaws. Kubis, acting for Fordham University, proposed a contract with the U.S. Army to evaluate a developmental device known as the voice stress analyzer. When the contact was let, the Army supplied what was then the only commercially available voice stress analyzer. According to the Kubis study report the study group’s knowledge of the voice stress analyzer was derived from an advertisement in a police supplier’s catalog. None of the Fordham students who actually conducted the study had any training in any aspect of the voice stress analyzer. For this reason, Kubis arranged to have the voice stress analyzer charts read, through correspondence, by Gordan Barland, then a graduate student at the University of Utah. Barland was subsequently successful with the voice stress analyzer.
Detailed critiques of the Kubis report were accomplished by the manufacture of the voice stress analyzer, Sproston and Kajada Corporation, and will not be repeated here. However, a few points are in order as follows:
The Kubis test used a game type model rather than a real world situation. Thus, at the outset, the study did not evaluate the Voice Analyzer for its design function.
Only 19% of what the contract required for the voice stress analyzer evaluation was actually accomplished, and this was forced in spite of bad tape recordings.
Barland, in his cover letter submission of his findings to Kubis, criticized the structure and conduct of the test. For example, Barland wrote, “…because of the BP (blood pressure) cuff discomfort, the test was sometimes interrupted in the middle of a question sequence. I was usually aware of this only when the E (polygraph examiner) made a comment prior to turning off the recorder. This would account for large response to irrelevant questions (on the first question when the testing was resumed) which could overshadow a genuine response on the following relevant question(s)…”
Further, “…the examiner often lost his or her place in the question sequence on the R?1 test; he or she did not attempt to speak in a monotone when asking the relevant questions; he or she almost never waited for aircraft noises to dissipate before asking the next question. Although it was also bad to interrupt the test when an airplane flew overhead, from the standpoint of voice stress analysis the failure to interrupt often meant that several questions could not be evaluated; if they were relevant questions, then the entire test had to be discarded.” (The test site was apparently located at the end of an airport runway.)
The American Polygraph Association has heralded the Kubis study as proof that the voice stress analyzer does not work. However, it is interesting to note that in the portion of the study where the two polygraph examiners were required to decide from their polygraph charts whether the subject was deceptive or not, one examiner was correct 51% of the time and the other 61%, essentially the flip of a coin.
It is not completely clear why Horvath is cited in opposition to voice stress analysis. Horvath’s study is also a game model and is a comparison between the voice stress analyzer and the galvanic skin response, the device that led the APA to promote laws requiring cardiograph and pneumograph traces. The fact that Horvath has been recognized by the APA (of which he is a member), fortuitously led to the one completely impartial face off between the favorable and ostensibly unfavorable studies concerning voice stress analysis.
Case Study of the Superior Court of Mecklengburg County NC.
On September 18, 1978, Frank E. Milano was convicted in Superior Court for Mecklengburg County, NC, of first degree rape and was sentenced to life imprisonment. The conviction was affirmed, with dissent, by the Superior Court of North Carolina on July 12, 1979. Milano filed a habeas corpus petition to the U.S. District Court for the Western District of North Carolina on October 30, 1979, based upon the fact that unfavorable polygraph testimony was admitted in the original trial and testimony relating to a favorable voice stress analyzer examination was not allowed. At the hearing on December 17, 1979, Horvath appeared as an expert witness for the prosecution and Michael Kradz appeared for Milano. Most of this testimony involved Horvath’s presentation of study data considered unfavorable to the voice stress analyzer, including the Kubis report, his own study, and the defense’s presentation of favorable study data.
As a result of this testimony, the court found: “The Court is satisfied from the evidence that both polygraph and voice stress analysis provided substantially reliable methods of evaluating psychological stress, and that the voice stress analyzer is at least as reliable as the polygraph, and possibly more reliable.” In addition, the Court ruled: “Based upon that evidence and upon a review of the lengthy trial record, I am of the opinion that petitioner was unconstitutionally denied a fair trial when the court admitted evidence of an unfavorable lie detector report but excluded evidence of a favorable lie detector report and that he should have a new trial. The other alleged errors in the case do not appear to be of constitutional stature and will not be further discussed.”
From the standpoint of validating the voice stress analyzer as an effective instrument for lie detection, several outstanding studies exist using real world cases.
Case Study of Howard County, Maryland Police Department
In 1972, Lt. Michael Kradz conducted a study for the Howard County, Maryland, Police Department in which 43 cal suspects took lie detection examinations that were instrumented simultaneously with a polygraph and PSE Voice Analyzer. The test of validity was provided by a comparison of the examiner’s conclusions with the findings of corollary law enforcement investigative techniques. The latter information was available for all but 7 suspects, who were among those cleared of suspicion and for whom no evidence to the contrary was uncovered. The voice stress analyzer proved 100% accurate in the 36 examinations for which complete and concrete corroboration was, or later became, available. The polygraph, in the same examinations, produced two cases of “untestable subjects” and two cases of “inconclusive results.” Comparison with the conclusions of a second independent examiner produced a reliability statistic of 100% for the voice stress analyzer and 93% for the polygraph. It was concluded that the voice stress analyzer is a valid instrument for use in lie detection applications.
Case Study Dr. John Heisse
In 1975 Dr. John Heisse conducted a blind study in which six voice stress analyzer examiners contributed voice stress analysis charts from 53 personally administered real life lie detection examinations. All 53 cases were supported by factual corroborations obtained after the subjects were tested. Each examiner employed a prescribed procedure of test formulation and prescribed chart criteria.
The voice stress analyzer charts (with no other information) were then distributed to the other examiners in the group, who were to act as “blind” evaluators. These evaluators used the same chart interpretation criteria as the original examiners to reach their conclusions. The results of the “blind” evaluations were then submitted to the study administrator. A comparison of the conclusions of the “blind” evaluators with those of the original examiners showed a compliance between examiners, evaluators, and known facts of 96.28%. Of particular interest is the fact that the investigative experience of the original examiners and the evaluators ranged from over 20 years to less than three months, their experience with the voice stress analyzer ranging from over four years to less than three months. Original training in the instrument, with one exception, ranged from three to five days.
Florida Polygraph Service, Inc. A blind study on Voice Stress Analysis. The American Polygraph Association wants to bury the TRUTH!
In the latter part of 1975 and the beginning of 1976, a Florida Polygraph Service concluded 716 pre employment examinations, 323 periodic examinations, 9 specific issue examinations (2 homicides, 3 armed robberies, 1 rape and 3 burglaries). An audio tape recording was made of each examination. The tape recordings were submitted for evaluation to a voice stress analyst who had no knowledge of the evaluations made of the polygraph results with the Mark II Voice Analyzer. The voice stress analyst matched the polygraph evaluations 1045 times out of the 1048 examinations. The polygraph examiners were members of the American Polygraph Association and the Florida Polygraph Association. See Florida-Polygraph-Service-Blind-Study-On-Voice-Stress
Sebastian Sheriff’s Office blind study on Voice Stress Analysis
In 1976 a polygraph examiner submitted 36 audio tape recordings of polygraph examinations to Investigator Marcia Forbus of the Sebastian County Sheriff’s Office in Ft. Smith, Arkansas. She processed the tape through the department’s Mark II Voice Analyzer. She matched the polygraph examiner’s evaluations in every test. The polygraph examiner was a member of the American Polygraph Association.
Study by Stanley Ostrowsky and L. Driscoll
A study was conducted by Mr. Stanley Ostrowsky, a voice stress analyst, and Mr. L. Driscoll, a polygraph examiner in Columbus, Ohio. Of the 21,568 voice response tape records by 5 different polygraph examiners, all but 219 responses were analyzed on a voice stress analyzer due to poor audio quality. At the end of phase IV of the study, the CPA firm retained produced a set of statistics that the voice stress analyzer agreed with 94.6% of the responses with the polygraph. In other words, when the polygraph instruments noted a deceptive response, the voice stress analyzer would agree 94.6% of the time. These statistics were presented to the Criminal Justice Department. The Criminal Justice Department Control Board has accepted the findings as valid and concluded that there is merit of credibility to the voice stress analyzer as a means of detection of deception.
Evaluation of Voice Analyzer in Chanute Kansas Police Department
During the period of April 1, 1978, to March 31, 1979, the Chanute, Kansas, Police Department acted as the executive agency for a federally funded, one year field evaluation of the Voice Analyzer. 159 examinations were conducted during this period at the request of 24 separate law enforcement agencies in the nine county southeast Kansas area. As a result of the year long evaluation, the Chanute Police Department found that “this instrument (voice stress analyzer) is one of the best investigative tools available at any price. We base this judgment on the voice stress analyzer’s versatility, ease of operation, simplicity, accuracy, and relatively short training period…” Leading to these conclusions was the fact that 70 investigators stated the crimes solved would not have been solved without the voice stress analyzer.
Study by Nachshon and Amsel for Israeli Police
In 1979 Nachshon and Amsel conducted a voice stress analysis study using tapes made during polygraph examinations of criminal suspects by Israeli Police. Independent corroborations were not used in this case, rather, the polygraph findings were assumed to be true. Agreement between the voice stress analyzer and the polygraph occurred in 94% of the cases. The Nachshon and Amsel study was carried two steps further. In the first step, blind chart readings were employed. The polygraph examiners read their charts and the voice stress analysis examiner read his without being able to identify the subject or make use of global impressions available with the original polygraph calls. In the second step, the voice stress analyzer and polygraph charts were similarly dissected to remove the control test patterns of responses so calls could be made simply on stress determinations. In both cases the voice stress analyzer was superior to the polygraph in agreeing with the original polygraph examiner findings. As a result, Dr. Nachshon stated, “…I was convinced that the voice stress analyzer is as good as the polygraph instrument to detect lies…” This study is particularly interesting in that Dr. Nachshon had headed a study in 1977 that failed to validate the voice stress analyzer. The question reasonably arises: If the voice stress analyzer was demonstrably successful in a 1979 study, why was it unsuccessful in 1977? An examination of the 1977 study report reveals the flaw. None of the three persons reading the charts knew how to read voice analysis data. The study report found that the three data readers agreed on their reading of the same data only 10% of the time. This means that 90% of the time at least one data reader had to be in error about what the data was telling him. In the 1979 study, Tuvya Amsel, the Voice Analyzer examiner, had received training in reading voice analysis data.
These studies again emphasize the system nature of the Voice Analyzer and the polygraph. If the data reading techniques employed are not valid, then the results of the study are likely to be invalid. Note: The Voice Analyzers used in this report were the Psychological Stress Evaluator (PSE, graph data) and the Mark II Voice Analyzer (PVSA, numerical data).
Aeromedical Laboratory Study, Tokyo Japan
In May of 1976, Aviation, Space and Environmental Medicine published a study conducted by the Aeromedical Laboratory, Japan Air Self Defense Force, Tokyo, Japan. The article was entitled, “Method for Determining Pilot Stress through Analysis of Voice Communications.” The study was conducted by Isao Kuroda, Osamu Fijiwara, Noriko Okamura, and Narisuke Utsuki with acknowledgment made by Dr. Robert F. Thomas, Lt. Col., USAF, for his consistent interest and collaboration in the research. By means of a sound spectrogram, the mean vibration space of a voice can be analyzed if the space between the vertical deflections of the vowel sounds is calculated in micrometers. The VSSR can be divided into three phases: Normal, urgent, and emergency; each with three gauges of 0.5 S.D. apiece. The study concluded that vibrations space shift rate (VSSR) correlated well with the emotional status of the pilot and that the elevation of the pitch of the voice, which varies directly with the tension of the vocal cords, corresponded directly with the increased emotional tension of the pilot. In addition, under stress conditions, the muscle tension on the vocal cord and the wall of the resonating box increase and the resulting pitch, fundamental frequency and dormats also increased. This study indicates that certain characteristics of the voice change during periods of emotional stress.
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