Legal System, Forensic Psychology, and Lie Detection Techniques

Adversarial system

The US legal system where two opposing sides (prosecution vs defense) argue their cases, and a neutral judge/jury decides who wins.

Brief

A written legal argument submitted to a court explaining why one side should win using laws and past cases.

Amicus curiae brief

(friend of the court) A brief written by someone not directly involved in the case (like a psychology organization) to give the court extra information or expertise.

Brandeis Brief

A special type of brief that relies heavily on social science research and data (psychology, sociology) instead of just legal cases.

Trier of fact

The person who decides what actually happened in a case, usually the jury or sometimes the judge.

Gatekeepers

Judges acting as filters who decide which expert testimony is allowed into court.

Precedents

Past court decisions that help guide how current cases should be decided.

Stare decisis

(let the decision stand) Courts should follow precedents unless there's a strong reason not to.

Legal realism

The idea that judges' decisions are influenced by real-world factors (beliefs, values, social context, not just strict legal rules).

Daubert trilogy

Three supreme cases that set rules for when scientific expert testimony is allowed.

Code of professional responsibility

Ethical rules that guide lawyers' behavior, including honesty, competence, and loyalty to clients.

Suborning perjury

Knowingly encouraging or allowing someone to lie under oath (illegal and unethical).

Forensic Psychology

An application of psychological science to legal issues, including courtroom decision-making, criminal investigations, jury behavior, eyewitness memory, competency & insanity evaluations, and risk assessment.

Roles of Forensic Psychologists

Clinical competency evaluations, insanity assessments, risk assessment, treatment, experimental research on memory, false confessions, jury decision-making, and consulting trial consulting, jury selection, witness preparation.

Law vs. Psychology

Psychology and law work together, but the relationship is uneasy because they operate with different goals, methods, and assumptions.

Burden of proof

Criminal (beyond a reasonable doubt), civil (preponderance of evidence).

Polygraph tests

How they work (measuring heart rate, skin conductance) and why they're controversial.

Control Question Test (CQT)

A technique that has a high false-positive rate; innocent people look guilty by comparing responses to crime-relevant vs. 'control' questions.

Guilty Knowledge Test (GKT)

A more accurate technique that tests recognition of crime details only the perpetrator should know.

Accuracy Problems

Countermeasures (biting tongue, toe pressing, mental arithmetic), anxiety doesn't mean guilt, and some guilty people show little arousal.

Legal Status of Polygraph

Many courts exclude polygraph evidence; federal employees may still undergo polygraph screening.

Newer Approaches to Lie Detection

Brain-based lie detection (fMRI, EEG/P300) is promising but not courtroom-ready due to issues like countermeasures, ecological validity, and ethics.

Cognitive load

How much mental effort is your brain using at one time; lying usually increases cognitive load because it's harder than telling the truth.

Cognitive privacy

The idea that your thoughts should stay private and not be accessed by technology (like brain scans used to detect lies).

Polygraph

A machine that measures body reactions (heart rate, sweating, breathing) that might be linked to lying, but does NOT detect lies directly.

Comparison questions

Broad questions about past behavior used to create a baseline reaction.

Positive comparison test (PCT)

A polygraph test where comparison questions are phrased so most people will answer 'yes,' increasing emotional response.

Electroencephalography (EEG)

Measures brain electrical activity using sensors on the scalp.

Functional magnetic resonance imaging (fMRI)

A brain-imaging method that shows which parts of the brain are active during tasks like lying.

Eye movement memory assessment

Detects lying by tracking eye movements linked to memory recognition.

High definition infrared thermal imaging

Detects heat changes in the face, which may increase during stress or deception.

Laser Doppler vibrometry

Uses lasers to detect tiny vibrations (like vocal cord movement) that may change when someone lies.

Mock crimes

Fake crimes used in experiments so researchers can study lying in a controlled, ethical way.

Criteria-based content analysis

A method that evaluates what a statement contains (details, logic, emotion) to judge whether it sounds truthful.

Reality monitoring (RM)

A technique that checks whether a memory sounds like it came from a real experience or was made up.

Confirmation Bias

The tendency to look for information that confirms what you already believe.

Liar's stereotype

Common but often wrong beliefs about how liars behave (avoiding eye contact).

Wizards

Rare individuals who are exceptionally good at detecting lies, far better than ordinary people.

Interrogation strategies

Psychological tactics used in questioning suspects (pressure, themes, minimization).

False Confessions

Admitting to a crime you didn't commit.

Voluntary false confession

No pressure; desire for attention or to protect someone.

Coerced-compliant false confession

Confess to escape interrogation & avoid punishment.

Coerced-internalized false confession

Suspect comes to believe they did it.

Reid Technique

A widely used interrogation method that assumes guilt and uses psychological pressure.

Camera-perspective bias

Suspect-focused camera makes confession seem more voluntary.

PEACE model

A non-accusatory, information-gathering technique used in the UK.

Fundamental attribution error

The tendency to blame someone's behavior on their character, not the situation.

Good cop-bad cop approach

One officer is harsh, the other is friendly, to make the suspect think resistance is useless.

Evidence ploy

Police claim they have evidence (real or fake) to make the suspect think resistance is useless.

Totality of circumstances

Courts judge whether a confession is voluntary by looking at all factors together.

Equal-focus camera perspective

Video recording that shows both the suspect and interrogator equally.

Types of physical evidence

DNA, fingerprints, trace evidence.

Estimator vs. System variables

Estimator variables cannot be controlled; system variables can be controlled.

Cross-race effect

People are worse at identifying faces of other races.

Misinformation effect

Post-event information alters memory; leading questions distort recall.

Unconscious transference

Witness misidentifies a familiar but innocent person.

DNA

Your genetic blueprint; used in forensics to identify people.

Alleles

Different versions of a gene.

Random match probabilities

The chance that a random, unrelated person would have the same DNA profile.

Blind testing

Analysts don't know case details, reducing bias.

CSI effect

When jurors expect perfect, high-tech forensic evidence because of crime TV shows.