Polygraph – An Effective Tool For Detecting Deception

Detecting deception plays a crucial role in criminal investigations and has an important role in detection of untrue testimonies. Detection of deception is very important at interviewing the suspects, but also at the eyewitnesses and victims of a crime. Eyewitness testimonies are concerned with their credibility. There have been many different techniques of detection deception in history. These include famous witch-hunts in which women alleged of witchcraft had a choice to either confess or undergo a torture test, for instance, women had heavy stones tied up to their bodies and were thrown into water, if they washed-up, they were considered as witches and eventually killed. With the evolution of our civilization and enforcement of humanistic thoughts, it was necessary to find a more credible and safer method of detecting deception. Probably the most notorious technique used is a polygraph. 

Polygraph is a scientific measuring device, which displays the values of different body activities with the aid of ink pens or computer screens. It is capable to detect even small differences thanks to the sensors adherent to different body parts. The foundations of polygraph testing are that lying and increased autonomic arousal that cannot be suppressed are associated, and that control questions can be designed to make subject produce lies. Although the polygraph is still being used, for example as a part of a job interview, it has not gain credibility among scientists and researchers. Moreover, even courts do not want to admit tests on polygraph as evidence in trials. This reluctance has got roots in the fact that polygraphs cannot reliably determine when someone is lying or telling the truth. The reason for the polygraph being inadmissible in trials is that it has not gain a general acceptance in the community of scientist and researchers. 

Thanks to the modernization and the development of technology, new techniques for detecting deception and lies have been introduced, for example EEG (electroencephalography) and fMRI (functional magnetic resonance imaging), or voice stress analysis. EEG measures the brain waves. In reaction to personally significant stimuli, P300 brainwaves appear (P300 refers to 300 to 1000 miliseconds since the stimulation), and these waves can be considered as orientation reflexes and can be used at lie detection. Vrij (2008) claims that these P300 waves are helpful at correct classification of guilty subjects (51-100%). Merzagora et al. (2006) conducted a study in which they examined the likelihood of detecting deception based on EEG. Participants were measured on EEG while they were doing an altered Guilty Knowledge Test (GKT). The EEG results showed that true and deceptive responses differed significantly and these differences were found in features that correspond with P300, concluding that this method seems to be more reliable in detecting deception that a standard event-related potential (ERP refers to the electrophysiological response to stimuli). 

Structural magnetic resonance was used by Raine et al. (2005) to test whether individuals who are lying have different volumes of prefrontal white and grey matter. They tested twelve participants (volunteers) with a history of lying, twenty-one normal controls, and sixteen antisocial controls. To be classified as a liar in this study, participants had to meet certain criteria, for instance criteria for malingering, deceitfulness criteria in DSM-IV, criteria for manipulative behaviours, and finally criteria for pathological lying. The results showed higher volumes of white matter and slightly reduced volume of grey matter in the prefrontal cortex in the liars. The first study conducted by the researchers showed abnormalities in the brains of people who cheat, lie and tend to manipulate with other people. Liars had similar brain differences when compared with the antisocial controls. This approach needs more investigation, but it is suggested that higher volumes of white matter in prefrontal cortex provide lying individuals with the capacity to do so. Further, the slight reduction of grey matter in prefrontal cortex may predispose individuals to antisocial tendencies, which when taken together with high volumes of white matter in PFC can product disproportionate lying. This study not only shows that pathological liars have brain abnormalities that “help” them lie, but also it suggests that using fMRIs is a good way to detect deception and lies. 

To this date, most fMRI studies, including studies of deception using fMRI scanners, have got their results by averaging all subjects together, and thus getting a group data. The first study that tested deception on individual level using fMRI scanners has been conducted by Kozel et al. (2005). The intention of the study was to show that certain regions in the brain are activated when individuals deceive. Participants in the study took a part in a mock crime in which they stole a valuable item and were further put in the fMRI scanner where they answered visual questions regarding the crime. The researchers found that this technique allowed them correctly detect when participants were telling the truth or lied. 

In conclusion, studies that have used technology such as EEG and fMRI to detect deception have been successful. The fMRIs seem to be most effective in this matter, however they have got many issues associated with further practical applications and use at the courts. Kozel et al. (2005) argue that in order to detect deception and obtain needed results, the person being tested needs to cooperate. If the person refuses to enter the fMRI scanner, refuses to answer questions, or intentionally moves his/her head, this person cannot be tested. This raises a question regarding suspects of serious crimes being scanned. Although fMRIs are effective tools, results can be easily altered by, as mentioned above, moving the heads or refusing to answer questions.