polygraphs & deception detection Flashcards
how are polygraphs conducted?
Polygraphs are conducted by attaching sensors to a person to measure physiological responses like heart rate, blood pressure, respiration, and skin conductivity. The examiner asks a series of control and relevant questions while monitoring the body’s reactions. Differences in responses may indicate deception
strengths and weaknesses of the polygraph
Strengths:
Can detect physiological signs of stress related to lying
May deter people from lying
Used as a tool in investigations
Weaknesses:
Not 100% accurate
Can produce false positives/negatives
Results can be influenced by anxiety, medical conditions, or countermeasures
Not always admissible in court
how accurate is the polygraph?
Studies suggest it’s about 70–90% accurate, but results can be unreliable due to nervousness, medical conditions, or attempts to cheat the test.
types of questions asked during a polygraph
a mix of relevant (about the issue), control (general truth/lie), and irrelevant (neutral) questions.
The idea is that lies may trigger stress responses (changes in heart rate, breathing, sweating) when answering relevant questions
what does a polygraph measure?
how one responds physiologically (physically) to a series of questions asked by the examiner; meant to detect deception based on physiological response
how many physiological indicators do a polygraph test?
four; Blood pressure, pulse (heart rate), respiration (how fast a person is breathing), and sweating (or what is referred to as Galvanic Skin
Response) – measured by a small electrode placed on the finger which measures how fast electricity passes through the finger. When people lie, they sweat and the GSR indicator goes up)
are polygraphs admissible in court?
no; there are few “exceptions”
if a person confesses during a polygraph, is it admissible in court?
yes; if the person confesses during a polygraph test, the examiner can testify in court that he or she interviewed the suspect and that he or she confessed, and never mention that the “interview” was a polygraph
what are the stereotypes surrounding the indicators of lying? to what extent do they overlap with the actual indicators of lying?
Stereotypes about lying only partially overlap with actual behavioral indicators. Lying is very complex, people don’t know the research on what indicates when a person is lying
Ekman’s classic studies- based on his research, how accurate are people at detecting deception?
Ekman and O’Sullivan 1991 study
- Showed participants videotapes of nursing students lying or telling the truth about
reactions to films (Pleasant or unpleasant) - Participants were: Secret Service Agents, Federal Polygraphers, Judges, Police,
Psychiatrists, and College Students - Secret Service agents did the best with 64% accuracy
- The rest of the participants were no better than chance
Frank and Ekman 1997 study
studied how well people can detect lies by observing facial expressions and body language. They found that some people (called “wizards”) are exceptionally good at spotting lies, but most people perform only slightly better than chance. The study highlighted the importance of microexpressions in detecting deception
what is the central feature of those who can detect deception according to Ekman?
the ability to recognize and interpret micro-level expressions determines whether an individual can accurately detect deception
describe several reasons why people are horrible at detecting deception
- the nature of the lie (high and low stakes lies)
- individuals have unique patterns of lying, especially for low-stakes lies (aka idiosyncratic).
- micro-expressions are difficult to detect by the majority of people
- Most people aren’t exposed to people who tell high-stakes lies, therefore they never learn the cues associated with deception
- It is not just an issue of lying or telling the truth, there is also a false belief, an implanted memory believed by the witness, which is inaccurate and entirely false. (Children and adults come to believe false memories are real).
low stakes lie
(small lies) where people attribute little consequence or regret to
telling a lie. Often people justify low-stakes lies and spend little time planning them or about the possibility of getting caught
high stakes lie
(Big lies with serious consequences):
These include lies about transgressions (ranging from misdeeds such as cheating on
tests to betrayals of intimacy or lying on job applications)
micro-expressions
micro-level changes in the face that involuntarily appear when someone is telling a high-stakes lie. A micro-expression takes less than .25 seconds to occur, but some people can detect them!
what role do micro-expressions play in detecting a lie?
micro-expressions involuntarily reveal that an individual is hiding a high-stakes lie. can be the difference in being able to detect deception or not
is there any one occupation people have been found to be good at detecting deception?
secret service agents (“truth wizards”)
brain fingerprinting method (how it works, what it measures)
recognizing stimuli the brain shows brain patterns. Thus, they use the guilty knowledge test–provide the witness information only known about from the guilty party and see if the brain waves indicate familiarity or not.
In short, it looks for a P-30 wave or Murmur wave that is present when the brain experiences something familiar.
This technology has been used and funded by the FBI, CIA, and NAVY and has been admitted in
criminal court.
cyber lie detection
computers that take Ekman’s Facial Coding System and detect emotional expressions associated with deception. These are being put in
airports in the US and many other countries to fight the war against terrorism
computerized voice detectors
Employ much the same idea as Ekman’s: Machines detect micro-level expressions of emotion associated with lying that is beyond detection by the normal person.
Ekman, O’Sullivan, and Frank 1999 study
tested how well different groups (like law enforcement, judges, and psychologists) could detect lies. They found that most people are only slightly better than chance, but a small group of experts, called “truth wizards,” could detect lies with high accuracy. The study emphasized the role of facial microexpressions in spotting deception
Joe Prewitt case
Charles Bryant was found in a burning car near Jellico, Tennessee. At first, it seemed like an accident, but it was later revealed that Bryant had been murdered, and the car fire was staged to cover up the crime.
It turned out that Joseph Prewitt, Bryant’s acquaintance, had planned the murder. Prewitt had taken out life insurance policies on Bryant worth over $1 million, which provided the motive for the crime
Prewitt was arrested and pleaded guilty to first-degree murder. He was sentenced to life in prison without the possibility of parole until he was at least 100 years old
