The industry of deception detection long relied on the polygraph as the sole tool for uncovering the truth in private and public-sector applications. Particularly, law enforcement found the introduction of the polygraph in the 1920s a useful way to prove their suspicions surrounding a suspect’s criminal actions.

However, since the unveiling of the polygraph, we’ve seen other technologies enter the space of deception detection, notably voice stress analysis (VSA) and computerized voice stress analysis (CVSA). The polygraph, VSA, and CVSA devices cannot tell if a person is lying during an examination.

Instead, they analyze physiological reactions in examinees, looking for signs of stress under questioning that indicate deception. The polygraph monitors several biological markers, including blood pressure, respiration, heart rate, sweat gland, and skin electrical activity.

VSA and CVSA devices only monitor changes in the examinee’s voice. All three tests have a place in deception analysis, but which one is the more effective tool? Experts are divided on the topic, with many biases, depending on who you talk to about it.

This post takes a subjective look at each of these technologies to uncover which is the king of lie detectors.


A Brief History of Polygraph Technology

The modern polygraph is a product of over a century of development involving some of history’s most ingenious psychologists and scientists. The work on polygraph science started in the late 1800s, with four men being standouts in the field.

It starts in Britain with the Scotsman Dr. James McKenzie’s work on the impact of the deceptive activity on the cardiovascular system. McKenzie noted that the act of lying would increase blood pressure and pulse rate, publishing several works on how pulse rate could indicate signs of deception.

Across the pond in the United States, Dr. William Marston noted the impact of deception on blood pressure, developing the “systolic Blood Pressure Test” to measure a suspect’s elevation in blood pressure under questioning.

Marston’s work influenced John A. Larson, a UCLA and Stanford student, to refine his systolic blood pressure test into a more comprehensive device capable of simultaneously measuring heart rate, blood pressure, and respiration rate in a single instrument.

Larson was the first of the three to see his invention used practically in law enforcement investigations, thanks to his ties to the Berkeley Police Department in California. While working on his device, the “Sphyggy,” Larson’s research and methods attracted the attention of Leonard Keeler.

It was Keeler who progressed Larsons designs, improving the efficacy and user-friendly operation of the device while incorporating the ability to measure skin electrical resistance. Keeler went on to launch his “Emotograph” in 1925, but alas, his only prototype was destroyed in a fire at his apartment that year.

Keeler didn’t let this deter his work. He teamed up with a Chicago firm, “Associated Research,” to redevelop it. Keeler passed away in 1949, but Associated Research continued his work, bringing the “Pacesetter Series” to market.

The “Keeler Polygraph” remained the benchmark of polygraph technology up until the advent of computerized technology in the 1990s. From there, the software era took control of polygraph technology. After three decades of advancements in algorithms and hardware, the modern polygraph looks and performs very differently from Keeler’s devices.


A Brief History of Voice Stress Analysis Technology

Compared to the polygraph, the history behind the development of voice stress analysis is far younger. The success of the Keeler polygraph made it the gold standard of deception detection in law enforcement practices around the world. By the 1970s, the Pacesetter model #6338 was the pinnacle of the technology and was used by law enforcement and government agencies across the developed world.

However, it was in 1972 that we saw the introduction of the “Psychological Stress Evaluator” by Allan D. Bell, Jr., Charles R. McQuiston, and Wilson H. Ford. These three individuals were the principles of “Dektor Counterintelligence and Security, Inc.” and the inventors of VSA technology.

All three were retired officers from the US military, heavily involved in interrogations and counterintelligence practices. After their retirement, they entered the private sector, establishing Dektor as a firm specializing in assisting law enforcement with technology and expertise surrounding deception detection and interrogation practices.

The trio patented their invention, the PSE, and it became the first voice stress analyzer device. At the time, it was groundbreaking, but like Larson and Keeler’s devices, it would fall into obscurity as other firms and individuals developed the technology to create devices with better capability and accuracy.

However, like Larson and Keeler, Dektor was the inventor of the technology, forming the foundation of all innovations in this space in the following decades. Eventually, “NITV Federal Services” became the benchmark for the industry, introducing the first “Computer Voice Stress Analyzer” (CVSA) in 1988.

NITV played a similar role to VSA tech as the Stoelting Company and Axiom Systems played to polygraphy, bringing the technology into the digital era of software and hardware. Like the modern polygraph, CVSA tech was a product of decades of refinement.

The original founders of Dektor saw success with the development of the PSE device because, like Keeler and Larson, they all brought independent skills to the table, allowing the trio to thrive off each other’s input during the development phase of their device.

Bell had experience in counterintelligence, Ford was an inventor, and McQuiston was a qualified polygraph examiner. Ford was the first to formulate the idea for the PSE after adopting a discovery made by other inventors, similar to how Larson worked on Marston’s creation.

In 1956, Joe Redfearn and Martin Halliday discovered they could measure muscular tremors as frequencies or oscillations. Olof Lippold progressed their research in 1957, relating physiological stress to these tremors and recording the fluctuations they create.

Lippold used an Electromyograph to evaluate vibrations as muscles stiffened and relaxed. Ford built on Lippold’s work. He recorded a human voice, slowed and filtered it, recording it on an EKG, and highlighting the microtremors.

Ford’s innovation focused on the muscles responsible for regulating the voice. His big discovery was that these microtremors increase in frequency when the body enters the “fight-or-flight” (FoF) mode, activated by the sympathetic nervous system under stress.

Essentially, the technology formed around the same ideas of the Keeler polygraph, being that the activation of the FoF response due to psychological stress results in the manifestation of physiological symptoms.

By analyzing these vocal microtremors, his invention could indicate potential deception, much like the polygraph. The trio named their invention the “Physiological Response Analysis Method and Apparatus,” operating under the governance of the “McQuiston-Ford algorithm,” which works similarly to the “Fast Fourier Transform (FFT) algorithm.”

The algorithm detects vocal microtremors falling between the range of 8 to 12 Hz in unstressed individuals who aren’t stressed or acting deceptively. The FM frequencies aren’t audible, requiring the use of computerized technology to capture them.

The algorithm computes a sequence, converting it into charts. The stress encountered by a deceptive person causes variations in frequency modulation, displaying a flattening effect on the chart. Trained examiners read these charts and determine the examinee’s response concerning the questions they ask during the PSE test. It’s the exact process involved with polygraph examinations.

Dektor was a true innovator and well ahead of its time. However, due to the popularity of the polygraph and its established footprint in the market, Dektor didn’t manage to gain much of a foothold, with Dektor eventually filing for bankruptcy in the late 1990s.

In 1988, NITV Federal Services released the CVSA, its flagship product, based on the original device designed by the Dektor team.


Polygraph Machines and CVSA Devices – How They Work

Both the polygraph and CVSA technology operate under the same principle – detecting the examinee’s response to the “fight-or-flight” (FoF) state. When people undergo a polygraph or CVSA exam, they’re in a subconscious state of stress.

If they’re responsible for the accusations causing the need for the exam, they’ll have to lie during the test to avoid being punished for their actions. This naturally stressed state causes the brain to activate the sympathetic nervous system (SNS).

The SNS is part of the autonomic nervous system (ANS). This part of our physiology processes the autonomous aspects of our body, such as digestion, heart rate, blood pressure regulation, kidney function, and much more.

We don’t have the ability to self-regulate these processes. Think of it as being able to control your pulse when you want to calm down. While you can breathe deeply and think happy thoughts, you must complete these actions to slow your pulse.

Otherwise, it takes the body time to acclimatize to physical stimuli and physiological conditions to achieve this. You can’t just tell your heart to slow subconsciously and have it respond instantaneously. It’s the same thing with the FoF response – we have no control over its activation.

So, when we’re in a stressful environment, like the polygraph exam room, our brain tells the SNS to prime the FoF. When the examiner asks a question and the examinee must lie, the SNS triggers the FoF. The polygraph machine analyzes the feedback from instruments placed on the examinee’s body.

These instruments measure the examinee’s blood pressure, heart rate, sweat gland activity, skin electrical response, respiration, and movement. When the FoF is activated, all these physiological markers elevate naturally. The instruments send this data to a control box linked to a laptop running software.

The software interprets the feedback, presenting the changes to the examiner in chart format on their screen. If the examiner notices these changes, it’s a sign of FoF activation and possible deception by the examinee.

The examiner will repeat the question and notice the physiological feedback with each response. Unlike the polygraph, which relies on up to six parameters for the test, CVSA relies on a microphone, and that’s it. Like the physiological markers activated by the FoF in polygraph exams, the FoF triggers changes in vocal microtremors.

Like the polygraph instrumentation, the microphone hooks into a software program, with the examiner looking for changes in the frequency of the examinee’s voice that are inaudible to the human ear but audible to the software. The examinee can’t control these microtremors, and the examiner can see these changes in chart format on their screen.

The SNS is a powerful part of our physiology, and there’s little the examiner can do to stop it when it activates. According to examinees, when the FoF activates, it sends what’s described as a shockwave through their body, and they can feel the apprehension caused by lying.

The sensitivity of the CVSA and polygraph instrumentation and software make it possible for the examiner to determine the difference between someone nervous and someone experiencing genuine activation of the FoF. As a result, it’s next to impossible to beat the polygraph or CVSA exam.


Which Is More Accurate – Polygraph or Voice Stress Analysis?

According to independent research, the modern polygraph exam, conducted by a trained examiner, has an accuracy rate of up to 97%. The reason why it’s not accurate 100% of the time is that pathological liars make it very hard to detect deception.

The pathological liar doesn’t experience the same FoF response as others when lying. They don’t have remorse or guilt for telling lies and often believe the lies they tell. However, this same scenario applies to CVSA exams since it, too, relies on the activation of the SNS and FoF to analyze data on the changes in the examinee’s vocal response.

Some assume the polygraph inaccuracies come from using “countermeasures” like biting the cheek or taking Xanax before and during the exam. However, that’s not the case. The modern computerized polygraph can see through these countermeasures. CVSA technology has similar success rates, with independent studies showing up to a 95% accuracy rate.

So, it’s challenging to determine which is the better tool for detecting deception. In this case, it comes down to the examiner more than the tech. Trained polygraph examiners undergo six to seven years of study and practical application before conducting exams independently.

CVSA examiners might not have this same level of study and experience. As a result, it might be easier for deceptive individuals to slip through the cracks.