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.
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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.