Psychophysiological Basis of Polygraph

Polygraph

Polygraph is one of the oldest techniques for detecting deception. Many people contributed to its development, and it is still used in many countries. A polygraph examination is a psychophysiological phenomenon. While the person administering the test need not be a physiologist or a psychologist to be a good examiner, they must understand the science behind polygraph to conduct it efficiently.

History of Polygraph

Introduction

Our human body is made up of cells that form tissues. These tissues form organs, and when they work together, they form different systems in our body. One such system is the central nervous system which is comprised of the brain and spinal cord. The brain is the source of all behaviour and contains a complex set of structures, the limbic system, which is responsible for emotion, motivation, etc. Another important structure in the brain is the hypothalamus, which is responsible for certain metabolic processes and other autonomic nervous system activities. The autonomic system is a part of our peripheral nervous system that connects our central nervous system to the rest of our body. The peripheral nervous system is divided into the somatic and autonomic nervous systems. The somatic nervous system deals with voluntary actions, whereas the autonomic nervous system deals with involuntary actions such as beating the heart. The autonomic nervous system is divided into the sympathetic and parasympathetic systems. The brain controls every involuntary function in the body with the help of these two systems. If it wants your heartbeat to slow down, it sends a parasympathetic message; if it wants to speed up your heartbeat, it sends a sympathetic message.

The parasympathetic system is considered the “housekeeper”, whereas the sympathetic system is the emergency system, often called the “fight or flight” system. The parasympathetic system slows down heartbeat, lowers blood pressure, and increases the speed of abdominal activity. On the other hand, the sympathetic nervous system increases the activity to ensure that the body is properly oxygenated for any emergency while slowing down the abdominal activity. Other systems that come into play during the polygraph testing are the respiration, circulatory, exocrine, etc. It is important to understand the normal functioning of these systems.

Deception Detection Tests (DDT) and It’s Evidentiary Value

The basis of polygraph testing is that deception and truth elicit different responses. It is assumed that the psychological and physiological responses when the person engages in deceptive behaviour differ greatly from when the person is telling the truth. These responses can be measured and compared. Marston and Larson found that when a person is engaged in deceptive behaviour, the blood pressure increases. However, the important question is, ‘Why do these physiological changes occur when the person is engaging in deceptive behavior?’ Psychology gives us the answer to that.

The study of psychology involves understanding our thoughts and feelings and the influence of these on our behaviour. Marston believed that the underlying cause of the changes was fear, whereas others believed that physiological changes occurred due to excitement or arousal. This idea of fear or arousal as the basis of the physiological changes in the body served as the basis for the relevant-irrelevant question technique. The other questioning technique, the comparison question technique, is based on the assumption that the innocents will give more responses to the comparison question than the relevant question. These assumptions for different questioning techniques are based on theoretical frameworks.

Conflict theory

Many researchers have concluded that lying is complex and requires more effort than speaking the truth. Whenever a person is asked a question, there is a tendency to opt for a more relaxed and effortless answer, i.e., telling the truth. However, if the consequences of that answer are not suitable for the person in question, they would make the situation favourable to them by opting for an effortful answer. This tendency to speak the truth but then suppress that tendency to give a deceptive one creates a conflict in the person. This conflict leads to stress or fear that, in turn, leads to physiological changes, which are measured using Polygraph. These physiological changes are believed to be caused due to the activation of the autonomic nervous system and different brain structures.

Conditioned Response Theory

This theory has its roots in operant conditioning. In this type of conditioning, the individual first responds, and then based on the feedback they get, either a reward or a punishment, they will have a future expectation of receiving the same outcome. If a person has received punishment for engaging in deceptive behaviour, they will have an expectation of the oncoming punishment whenever they engage in the deceptive behaviour again. With this expectation, their brain prepares them for the upcoming emergency by heightening their emergency system.

Backster’s psychological set

Cleve Backster introduces many theories to help us understand the workings of the polygraph. Backster’s concept of psychological set deals with the mind focusing on those questions in the polygraph examination that hold the greatest threat to the immediate well-being of the individual in question. This will create heightened responses to the relevant questions for the guilty and the comparison questions for the innocent. Dr. Senter and his associates redefined this theory as ‘salience’.

Relevant Issue Gravity

This psychological theory was developed by Dr Avital Ginton. His theory is based on attention. He proposes that due to the gravity of the situation, the suspect’s attention will be automatically drawn towards the relevant question for a guilty individual. In contrast, the attention will be more on the comparison question for the innocent suspect. This theory is similar to the salience theory, where the focus is more on the individual’s attention to the relevant questions or the comparison questions rather than the fear of detecting the individual.

The polygraph test uses different theories to explain the physiological changes seen in the examinee. Understanding the psychophysiological basis of behaviour is important for better understanding these theories and making informed decisions.

References

1. https://nap.nationalacademies.org/read/10420/chapter/5#80
2. Essentials of Polygraph and Polygraph Testing Nathan J. Gordon

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