Cognitive psychology: Case study 1: High stake liars

Cognitive psychology

Case study 1: Suspects, lies and videotapes: an Analysis of authentic high-stake liars

Author: Mann et al. (Samantha Mann, Aldert Vrij, Ray Bull) (2002)

Key term: Lying

Approach: Cognitive psychology

Authentic high stake liar is someone who has to tell a real lie, when they have too much to lose by telling the truth.

Aim/hypothesis: To conduct a study observing the behaviour and body language of liars in high stake situations - in this situation, real criminals being interviewed by police officers, who are telling real lies (and some truths) without knowing that they are going to be analysed in an experiment.

The aim is to use this research to prove that:

1. Liars will make fewer movements (e.g hand movements)
2. Liars will have more speech disturbances, with longer pauses between sentences or words
3. Liars will blink less

Method: Natural experiment - Participants do not know the videos of their interview will be observed and analysed, so their lies will be genuine. If this experiment was done as a laboratory experiment, with actors, who knew they were being watched, the results would be invalid.

Variables: 

• Independent variable: Truth or lie. The IV was not able to be manipulated by the researches because the criminals could choose whether or not to lie.
• Dependent variable: The behaviour of the suspects when they lied or didn't on the tape, 

Design: Repeated measures - The participants told both truths and lies in the tape.

Observation coding/response categories: The two observers were told to code the video footage of the interview. They were not told what the study was about or that truths and lies were involved. This was so their observations would be unbiased; if they knew they were watching people lie, the results may be different as the observers could exaggerate observations.

The participants had to code (mark on a sheet when a behaviour happened) eight different behaviours:

1. Gaze aversion
2. Blinking
3. Head movement
4. Self-manipulations (head scratching, scratching the wrist, etc)
5. Illustrators (supplements to speech - gestures)
6. Hand/finger movement
7. Speech disturbances
8. Pauses

The observations would be coded and then the tape would be replayed so the researcher could analyse which behaviours happened the most and whether they were during a lie or truth. (The experimenters knew whether the suspect was lying or not in each video clip, but the observers didn't.)

Participants: 16 police suspects (13 male, 3 female), aged between 13 and 65. Suspected of crimes such as murder, arson, attempted rape and theft.

Sampling technique: Interviews were recorded by the Kent police, which were then used in the study. The sample was self selecting because suspects made both truth and lies in the statement. Lies were known because the suspects later confessed to lying.

Apparatus:

• 1 hour video tape with 65 clips of the 16 suspects. 27 of those clips were lies, 38 were truths.
• Record of the behaviour the observers recorded during each clip/

Controls:

• The observers who recorded the results were unaware of what the experiment was about or whether the suspect lied or told the truth. If the researchers did the coding themselves the results could be biased - "seen what they wanted to see"
• The lies and truths were confirmed by the police because the criminals confessed later and admitted they lied.

Procedure

1. Video tapes of authentic liars were broken down so there was at least 1 truth and 1 lie per participant (suspect). 
2. Observer 1 watched all the clips coding the 8 behaviours he saw in each clip. He was told just to "code the video".
3. Observer 2 watched a random sample of 36 clips (at least one of each suspect) instead of all.
4. Codings were checked to see if both observers recorded similar results.

Inter-rater reliability is the correlation between the results of two observations of the same experiment. The inter-rater reliability of the two observers in this experiment were very good, On the correlation test (Pearson product-moment test), with 0 being no agreement and 1 being perfect agreement, the observers scored:

• Gaze aversion: 0.86
• Blinking: 0.99
• Head movements: 0.95
• Self manipulations: 0.99
• Illustrators; 0.99
• Hand/finger movements: 0.99
• Speech disturbances: 0.97
• Pauses: 0.55

Data: Quantitative data was gathered and placed on tally chart. Illustrators, self-manipulations and finger/hand movements were merged into one hand/arm category. The mean number of times each behaviour was recorded and put in a table.

Behaviour                                                 Truthful                                  Deceptive                                  

Gaze aversion                                           27.82                                      27.78                                         Blinks                                                       23.56                                      18.50                                         Head movements                                     26.57                                       27.53                                         Hand/arm movements                             15.13                                       10.80                                         Pauses                                                      3.73                                         5.31                                           Speech disturbances                                 5.22                                        5.34                                           

Findings

• There was no behaviour that all liars exhibited. This means there are many individual differences so generalization would be inaccurate.
• No differences were found for speech disturbances and head movements. 50% of participants showed an increase in each behaviour when lying and 50% showed a decrease. 
• 69%  of participants showed an increase in hand/arm movements when lying.
• 81% of participants blinked less and paused longer while lying. This was the most reliable finding and showed significant difference between lying and truth telling.

Conclusion: Mann et al can confirm that the most reliable indication of a liar are longer pauses and blinking less, which is two out of three of their hypotheses. It also contradicts the popular belief that liars act nervous, which actors might do when pretending to lie. 

Evaluation of experiment and study

Strength: 

Suspects did not know they were going to be analysed, so they were telling genuine lies and their behaviour was natural. If the participants knew they were being recorded, they might not lie and there behaviour could be different.                                                                                                                    

Strength:
The results were recorded quantitatively, so results were more objective, clear and scientific. The inter-reliability confirmed the results were more clear and objective.                                                      
Weakness:
The results may be different if the experiment was repeated so this could be unreliable. The experiment environment is hard to duplicate, and if police know the tapes will be analysed, they might act differently and unnaturally when interviewing the suspects.