LIE DETECTION: EKMAN'S THEORY 

Paul Ekman is one of the most important figures in the psychological study of deception.  His theory suggests that while people try to hide the truth, their bodies and faces often reveal small signs of hidden emotions. These signs are not always obvious, but they can be seen in quick facial expressions, small changes in voice, or body movements. Ekman emphasized that effective lie detection depends not on obvious nervous gestures, but on careful attention to micro-expressions, emotional leakage, and facial muscle movements.

 


1. MICRO-EXPRESSIONS

Definition: Micro-expressions are extremely brief, involuntary facial expressions that show hidden emotions.

Explanation: When lying, people may try to hide feelings like fear, anger, or guilt. However, before they can control their expressions, the real emotion may quickly appear on their face.

Example: A suspect who says they are innocent may briefly show fear or contempt when asked about the crime scene.

Application: To study this, Ekman created the Facial Action Coding System (FACS), which analyzes facial muscle movements. This system has been used by police and intelligence agencies for training.


2. Emotional Leakage

Definition: Emotional leakage happens when real emotions “leak out” despite efforts to hide them.

Explanation: This conflict between true feelings and controlled behavior can show in tone of voice, hesitation, eye movements, or body language.

Example: A witness may say they are calm, but their trembling voice and lack of eye contact reveal hidden anxiety.

Key Point: Ekman argued that mismatches between spoken words and non-verbal cues are strong indicators of lying.


3. Universality of Facial Expressions

Finding: Ekman discovered that basic emotions—happiness, sadness, anger, fear, surprise, disgust, and contempt—are universal. His studies with isolated tribes in Papua New Guinea proved that these expressions are biological and not learned. Because these expressions are natural, liars cannot fully suppress them.

Example: A fraud suspect may smile to appear friendly, but a quick flash of disgust might appear when asked about the victim.

 

 

FACIAL ACTION CODING SYSTEM (FACS)

    The Facial Action Coding System (FACS)was developed by Paul Ekman and Wallace Friesen in the 1970s. It is a comprehensive, anatomically based system for analyzing facial movements to detect emotions and possible deception. Instead of simply labeling expressions (e.g., "smile" = happy), FACS breaks down facial behavior into the smallest measurable units of movement, called Action Units (AUs). Each AU corresponds to the contraction of a specific facial muscle or group of muscles.

ACTION UNITS (AUS)

    Every visible facial movement is coded as an AU. These AUs are the building blocks of expressions. For example:

AU 1: Inner brow raiser – controlled by the frontalis muscle.

AU 4: Brow lowerer – controlled by the corrugator supercilii muscle.

AU 12: Lip corner puller – controlled by the zygomaticus major muscle.

AU 14: Dimpler – caused by the buccinator muscle pulling the corners of the lips sideways.

By combining different AUs, people show complex emotions on their face.

UNIVERSAL EMOTIONS AND THEIR AUS

    Ekman discovered that certain combinations of AUs represent universal emotions. These expressions are the same across all cultures and are biologically based.

Happiness: AU 6 (cheek raiser) + AU 12 (lip corner puller). Example: A genuine smile, also called a Duchenne smile, shows raised cheeks and lifted lip corners.

Sadness: AU 1 (inner brow raiser) + AU 4 (brow lowerer) + AU 15 (lip corner depressor). Example: When recalling a sad memory, the mouth droops and brows furrow.

Anger: AU 4 (brow lowerer) + AU 5 (upper lid raiser) + AU 7 (lid tightener) + AU 23 (lip tightener). Example: During an argument, lips tighten and brows lower.

These universal emotions show that facial expressions are hardwired into human biology and not learned.

 

FACS IN LIE DETECTION

    FACS is very useful in detecting lies because it can reveal micro-expressions—tiny, brief flashes of facial movements that show hidden feelings. The spoken words and the facial expression do not match, which signals possible deception.

 

PRACTICAL EXAMPLE OF FACS IN ACTION

    Imagine a police interrogation: Question: “Were you at the victim’s house last night?” Suspect’s response: “No, I wasn’t.” (spoken confidently, with a smile). Observation: While smiling, a brief AU 9 (nose wrinkler) flashes on the suspect’s face. Interpretation: This could indicate disgust, possibly linked to guilt or discomfort about the question.

 

BEHAVIORAL AND PHYSIOLOGICAL INDICATORS

    Unlike the polygraph, which measures body arousal, Ekman focused on visible behavior. Some common signs of visible behavior are:

  • Increased blinking
  • Speech errors
  • Nervous mannerisms
  • Longer response times

These signs alone are not enough to prove lying. They must be combined with micro-expressions and emotional consistency.

 

PRACTICAL APPLICATIONS

Ekman’s work has been used in many real-world situations:

  • Police interrogations.
  • Airport security
  • Counter-terrorism
  • Courtroom settings


LIMITATIONS AND CRITICISMS

  • Emotions ≠ Lies: Micro-expressions may reveal feelings but not always deception.
    For example, someone can show fear just because they are being questioned, even if they are telling the truth.
  • For example, someone can show fear just because they are being questioned, even if they are telling the truth.
  • Accuracy Issues: Success rates are often lower in real-world conditions.
  • Training Required: Detecting lies using Ekman’s method needs a lot of practice and expertise.
  • Risk of Misinterpretation: Over-reliance can lead to mistakes.

 

LIE DETECTION: POLYGRAPH TEST

The polygraph, often called the “lie detector,” is one of the most widely known but also most controversial techniques in lie detection. It is based on the assumption that lying produces physiological changes, that can be measured and distinguished from truth-telling.

 

THE BASIS OF THE POLYGRAPH

The polygraph measures autonomic nervous system responses—the body’s automatic reactions with emotional arousal. Key physiological changes recorded are:

  • Blood pressure
  • Heart rate
  • Respiration
  • Galvanic skin response (sweating / skin conductivity)

The assumption is that lying produces stress and anxiety, which trigger measurable physiological reactions.

 

TECHNIQUES USED IN POLYGRAPH TESTING

The following techniques are used in polygraph testing:

1. CONTROL QUESTION TEST (CQT):

It is the Most commonly used method. It involves two types of questions:

  • Relevant questions – directly linked to the crime (Did you steal the money?).
  • Control questions – unrelated but emotionally arousing (Have you ever lied to get out of trouble).

Logic is that: Truth-tellers are usually more nervous about control questions. Liars show stronger reactions to relevant questions.

 

2. GUILTY KNOWLEDGE TEST (GKT) / CONCEALED INFORMATION TEST (CIT)

It is based on the idea that guilty people know details of the crime that innocent people do not.

Procedure: The examiner asks multiple-choice questions where only one answer is correct. Example: “Was the stolen item a watch, a wallet, or a ring?”

Logic: If the suspect shows stronger physical reactions to the correct answer, it suggests they have secret knowledge. The GKT is considered more scientifically reliable than the CQT.

 

APPLICATIONS IN FORENSIC SETTINGS

The polygraph is used in different fields: Criminal investigations, Employment screening & Court proceedings  Example: In a theft case, if a suspect shows strong reactions to relevant questions, investigators may treat it as a possible sign of lying.

 

STRENGTHS OF THE POLYGRAPH

Provides a structured and systematic method for checking truthfulness. Sometimes encourages suspects to confess, because they believe the test is very accurate. The GKT method has stronger scientific support than the CQT, especially in lab studies

 

WEAKNESSES AND CRITICISMS

It measures arousal, but arousal can come from many sources like fear, anger, or embarrassment—not just lying. Some people can cheat the test by controlling breathing, tensing muscles, or creating extra stress during control questions. False results: Innocent people may look guilty because of nervousness.