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The Problems With Lie Detection Methods

by | May 11, 2024 | Criminal Defense | 0 comments

Accurate Lie Detection Could Be a Scientific White Whale

Police officers and prosecutors have long yearned for a reliable way to tell whether or not a suspect or defendant is telling the truth. The search for an accurate lie-detection device or technique has ushered in many false dawns, but science has yet to crack the problem. Many scientists believe that efforts to detect deception will never yield consistent results because all human beings are different. A successful system would have to provide consistent results, but that may not be possible because people have individual traits and unique life experiences. With that in mind, let’s take a look at some of the methods that have been used to separate truth from deception.

Polygraph Machines

If you ever apply for a government job that requires a security clearance, you will probably be asked to take a polygraph test. The federal government conducts about 70,000 polygraph tests each year, but a large and growing body of scientific evidence suggests that they do not work. Polygraph machines measure physiological factors like respiration, perspiration, heart rate and blood pressure, but there is no credible scientific evidence linking changes in these factors to deception. Scientists have concluded that polygraph machines can reliably measure fear and anxiety, but not every fearful or anxious person is lying.

A study of the scientific validity of polygraph machines was submitted to Congress in 1983. When lawmakers read the report, they passed legislation that prohibited private employers from requiring polygraph tests. In 1998, the U.S. Supreme Court ruled that polygraph test results may not be used in federal courts because the science supporting them is unreliable. Polygraph machines are still the most common lie-detection tool, but they are not accurate enough to be used in court.

Reading Nonverbal Behavior

Reading nonverbal cues, micro-expressions and body language is another popular lie-detection method. Police officers began using this technique when it became clear that polygraph machines were unreliable. The problem with this approach is that not all people behave in the same way when they are placed in stressful situations. The evidence supporting this approach has been largely debunked by scientists, but law enforcement agencies around the world still use it. The results of nonverbal behavior analysis may guide police investigations, but they have little evidentiary value.

Reality Monitoring

Reality monitoring and criterion-based content analysis are lie-detection methods that examine the statements people make rather than their physiological responses to questions. The theory is that true statements based on a lived experience are more complex and vivid than lies. Researchers have concluded that such methods can separate fabricated statements from experience-based statements, but only about 70% of the time. That margin of error is large enough to prevent these techniques from providing prosecutors with evidence reliable enough to be used in court.

MRI Tests

Magnetic resonance imaging machines use a magnetic field and radio waves to create detailed images of organs like the brain. They can also show how hard the brain is working. Telling a lie and trying to keep a story straight are more cognitively challenging than answering a question truthfully, so MRI machines should be able to identify false statements. Scientists have explored this approach, but they have run into the same problems that have plagued polygraph machines. People react to stress differently, which means MRI scans of their brains do not reveal very much. This is why most experts have concluded that neurological lie detection is a scientific dead end.

Voice Pattern Analysis

Voice pattern analysis identifies false statements by examining how people respond to questions. Police officers trained in this technique analyze speech patterns and look for guilt indicators like pauses and tonal changes. The voice pattern analysis approach was pioneered by a retired police chief with no scientific credentials who never investigated a homicide. The technique was originally used to analyze recordings of 911 calls, and the Federal Bureau of Investigation even created a training curriculum that was used by law enforcement agencies around the country.

Scientists were less convinced. When they listened to 911 calls, they could not find any evidence to show that voice pattern analysis is a reliable way to identify guilt or false statements. The FBI succumbed to scientific pressure and advised police departments to stop using voice pattern analysis in 2020. In 2022, an FBI study concluded that voice pattern analysis could actually increase bias.

Police Interview Techniques

The questions police officers ask when they interview suspects remain the most reliable way to identify false statements in a criminal investigation. People who lie to the police tend to keep their stories as simple as possible to avoid being caught out, and they may make mistakes when they are pressed to provide details. Police officers press suspects by confronting them with facts or evidence that contradicts their accounts. When suspects respond to this pressure by concocting more elaborate lies, their deception usually becomes apparent. This is one of the reasons why experienced Pennsylvania criminal defense attorneys advise their clients to never talk to the police unless a lawyer is present.

Artificial Intelligence

Some scientists believe that machine learning and artificial intelligence could one day provide a reliable way to detect lies. AI can analyze data and identify patterns far more quickly and thoroughly than human beings, which means it may be able to identify signs of deception that have so far escaped detection. In 2021, a team of Dutch researchers compared how human judges and AI algorithms performed when evaluating accounts that included lies. The technology did better than the human experts, but it was only accurate about 69% of the time. AI is still in its nascent stages, so a more effective machine learning approach to lie detecting could be developed in the future.

Junk Science

Juries find scientific evidence compelling, which is why prosecutors love to introduce it. The problem is that scientific breakthroughs are not always as groundbreaking as they seem. “Junk science” is a term used to describe theories or methods that cannot withstand rigorous scrutiny and are not supported by evidence, and it can be used to describe just about all of the techniques used in the criminal justice system to identify false statements. Police officers rely on their training and their instincts when they have to decide whether or not a suspect or witness is telling the truth, and that is unlikely to change in the years ahead.

Legal Help in Criminal Defense Matters

If you are ever accused of committing a crime, questionable lie-detection methods are something that you may worry less about if you speak with a Pennsylvania criminal defense attorney before you answer police questions. Bauer, Scanlon & Wigginton is a law firm with extensive criminal defense experience, and our attorneys are standing by to help you and answer your questions. If you would like to learn more about your legal options, you can schedule a meeting at our Media office by calling us at (610) 590-5092 or by filling out and submitting our online contact form.