Even the best poker face can’t hide certain physiological signs of stress.

Even the best poker face can’t hide certain physiological signs of stress. Image Source: Flickr user Daniel Morrison.

Putting on your poker face doesn’t work when you are taking a truth verification exam; there are always other indications that someone is “bluffing” or telling a lie. And unlike classic “tells,” these signs of deception are often subtle physiological changes that can’t always be seen by the savvy person sitting across the table.

In the police interview room, the stakes are much higher than in a game of poker. Every person who walks into that room will be feeling a certain level of stress, which will manifest itself in the voice and body in various ways. However, it’s up to law enforcement officials to sort through the normal stress and the stress that indicates deception or involvement in a crime. The best way to do this is by using proper interview techniques combined with proven truth verification technology which can reliably determine if a suspect or witness is being truthful based on physiological signs of stress.  

How Stress Affects the Body

Stress causes a lot of temporary changes in the body. It first registers in the brain, which goes into fight-or-flight mode when we feel fear or anxiety. The sympathetic nervous system (SNS) becomes engaged and stress hormones such as cortisol and adrenaline are released to give the body more energy. Our muscles tense up—the body’s way of protecting us. We also breathe differently; some forget to take a breath, hold our breath, or breathe faster in order to bring more oxygen to the brain. The heart starts to beat faster, and your body produces more glucose, providing the spark of energy needed for a dash away from danger. Our digestive system can also be affected, causing the sensation of butterflies in the stomach or even diarrhea.

While the fight-or-flight response is an evolutionary reaction meant to protect us in times of danger and can still be effective in a crisis, sometimes we can’t run. When a person is taken in for police questioning, all they can do is either put their proverbial cards on the table or try to bluff their way out of it. It’s important for investigators to realize that just being in that police interview room will trigger the fight-or-flight response, and how you differentiate that from the stress caused by deception is what truth verification is all about.

Measuring Stress to Detect Deception

Truth verification systems don’t actually detect lies; they measure the stress caused by those lies, according to CVSA Examiner and Senior Instructor Bill Endler.  Right now, there are two main truth verification devices used by law enforcement—the polygraph and the Computer Voice Stress Analyzer (CVSA®). However, they measure stress in different ways.

The polygraph measures delayed or “downstream” physiological stress by monitoring heart rate, blood pressure, breathing, and galvanic skin response (GSR) through sensors placed on the body. These include a blood pressure cuff, pneumograph tubes around the chest to measure respiration, and galvanometers attached to the fingertips to measure perspiration. The subject is asked a series of questions and the results appear on a graph.

On the other hand, the CVSA measures one physiological change in response to questions. Remember how, when stressed, our muscles tense up? This also applies to the muscles that control the human voice, and this is what the CVSA focuses on. While stress doesn’t affect the pitch or the volume of our voice in a way that is apparent to the naked ear, it does cause vibrations in these tense muscles to change the FM frequencies in the voice. This response can only be measured by voice stress analysis software. The CVSA gathers this data through a microphone and the results are instantaneously charted on a graph.

Comparing the CVSA vs. the Polygraph

While the polygraph and CVSA both measure stress caused by answering questions, it is possible for an individual to control certain symptoms or responses. There are countermeasures that will allow an individual to affect responses during control questions, which will cause incorrect or inconclusive results. People have tried everything from a thumbtack in the shoe to tightening their sphincter muscles to biting their tongue. All these methods cause pain or physical stress during control questions which are unrelated to the criminal activity. This way, when the important questions relating to the crime are asked, their responses don’t indicate a higher level of stress compared to the control questions. In fact, it was well publicized that some federal law enforcement agencies trained their undercover operatives to beat the polygraph using countermeasures.

In contrast, the muscles that affect the FM frequency measured by the CVSA cannot be controlled voluntarily. While a person can change the pitch or volume of their voice, it won’t affect the outcome of a CVSA examination because they can’t control how those muscles vibrate when tensed. And even if someone did try to alter their voice, it would be easy for the examiner to catch them trying to cheat.

There is another major difference between the polygraph and the CVSA—the person who is giving the examination. Remember that the individual is already in fight-or-flight mode just by being in that room. Typically, polygraph examiners use the Reid Technique, which is an accusatory questioning method that actually causes more stress. This makes it more difficult to discern when stress is ramped up by questioning, especially when the subject is already constricted by the polygraph’s many sensors.

Instead, the CVSA Examiner is taught to use the Defense Barrier Removal (DBR®) interview method, where the goal is to reduce stress at the outset by building rapport and making the interviewee feel comfortable. This reduces situational stress caused by the suspect’s anxiety and allows the examiner to focus on the important causes of stress—questions about innocence or guilt.

The CVSA doesn’t rely on physical indicators that may be caused by other factors, such as situational stress, heat, exhaustion, illness, or high blood pressure. Instead, it takes the quickest route to the truth by zeroing in on stress signals which can’t be hidden by countermeasures. The moment of truth comes when you show the interview subject a CVSA chart that indicates where they were being deceptive. That chart proves that lying further is futile. They may be perspiring; their heart is racing—but that is because they are finally admitting the truth.

Please reach out to us at NITV Federal Services to learn more about our CVSA systems and training programs.