Though the reliability of brain scanning for lie detection is still under question, these tests are fast becoming popular with the crime investigating teams. Here’s how they work
DR S.S. VERMA
Police use lie detectors to crack criminal cases. Based on the signals caught from the criminals, they can decide to proceed the investigation further or not.
Various scientific tools of interrogation are in use, like the psychological tests, narco tests and polygraphic tests. But, their reliability in courtrooms is still an issue. These tests generally don’t have legal validity in court and they can only assist police investigations. At the same time, these lie detection tests prove to be a futile exercise in the case of mastermind criminals.
New technologies are being developed so as to replace the traditional lie detection methods. Here we discuss some of the prevailing and upcoming methods of lie detection.
Psychological tests are usually administered and interpreted by a psychologist. These tests assess and evaluate the information that is given by the criminal to the examiner. The information is taken either in the form of answers to interview questions or as answers on paper—or on a computer—to specific questions.
Ultimately, the accuracy of a physiological test depends on how carefully and seriously the answers are given. Hence, no psychological test is ever completely valid or reliable because the human psyche is just too complicated to know anything about it with full confidence. That’s why there can be uncertainty about a case even after extensive testing.
The term ‘narco-analysis’ is derived from the Greek word ‘nark’ (meaning ‘anesthesia’ or ‘torpor’). It is a diagnostic and psychotherapeutic technique that uses psychotropic drugs, particularly barbiturates, to induce a stupor in which mental elements with strong associated affects come to the surface, where they can be exploited by the therapist.
The narco analysis test lowers a subject’s inhibitions by interfering with his nervous system at the molecular level, in the hope that the subject will more freely share information and feelings. In this state, it becomes difficult though not impossible for him to lie. The subject is not in a position to speak up on his own but can answer specific but simple questions.
The answers are believed to be spontaneous as a semi-conscious person is unable to manipulate the answers. However, crime branch
officials have found that key suspects took anaesthetic drugs (like Catamine, Propofol, Pentothal and Fortwin) to cheat narco tests, in case they were arrested. Regular use of the drugs made them immune to narco tests. This effectively puts a question mark on all ‘revelations’ made during narco tests so far.
Polygraph examination is based on the assumption that there is an interaction between the mind and body. It is conducted by various components or the sensors of a polygraph machine, which are attached to the body of the person who is interrogated by the expert.
Polygraph machines are essentially biofeedback devices. The machine records the blood pressure, pulse rate, respiration, muscle movements and electrical resistance of the skin. Polygraph test is conducted in three phases: a pretest interview, chart recording and diagnosis.
Even with a trained and skillful administrator, polygraph technology is not altogether perfect at detecting lies. There is a lot of variability in how different people react when lying first of all. The act of being measured tends to produce anxiety, which creates the possibility of false positives. The worst part is that there are people out there who are so good at lying that they believe their own lies (or at least are in large part non-reactive) and thus don’t perturb the polygraph.
In the brain mapping method (P300), also called ‘brain-wave fingerprinting,’ the accused is first interviewed and interrogated to find out whether he is concealing any information. Then sensors are attached to his head and he is made to sit before a computer monitor. The accused is then shown certain images or made to hear certain sounds. The sensors monitor electrical activity in his brain and register P300 waves, which are generated only if the subject has connection with the stimulus, i.e., picture or sound. The subject is not asked any question here.
Functional magnetic resonance imaging
In functional magnetic resonance imaging (fMRI) experiments, the subject usually alternates between performing a mental task and resting (or undertaking an alternative task) while repeated images of his brain are rapidly captured. Areas of the brain in which there are strong correlations between the performance of the task and the MRI signal time course are then identified as having been involved in that task.
When the subject starts to perform the task, neuronal activity increases in the required parts of the brain. These areas require additional energy, which is provided by an increase in the regional blood supply. This increase in blood flow leads to an increase in the blood oxygenation level, which, in turn, changes the magnetic properties of the blood and hence the MRI signal.
Unfortunately, fMRI, as it is used today, has a major drawback: It measures blood flow, or haemodynamics, which is an indirect measure of neural cell activity. It turns out that haemodynamics basically introduces a delay of five seconds. So fMRI is not able to detect fast variation.
Since neurons typically fire at an interval of the order of milliseconds, current fMRI techniques provide only a rough estimate of what the brain is doing at any given moment. fMRI scans also have a relatively low spatial resolution, measuring activity in areas of 100 microns—a volume that typically contains 10,000 neurons, each with varying activation patterns. Efforts to fine-tune fMRI have focused on developing stronger magnets.
Researchers have found that tracking calcium—a key messenger in the brain—may be a more precise way of measuring neural activity than current imaging techniques (viz, fMRI). When a neuron sends an electrical impulse to another neuron, calcium-specific channels in the neuron’s membrane instantaneously open up, letting calcium flow into the cell. It’s a very dramatic signal change.
Fluorescent calcium sensors are already used in superficial optical imaging, but these haven’t yet been applied to the deeper brain tissues that are accessible via the powerful magnets of fMRI machines.
The human brain emits electrical signals called ‘event-related potentials,’ which can be tracked with a high-density electroencephalogram machine and sensors attached to the face and scalp. Telling the truth and then a lie can take from 40 to 60 milliseconds longer than telling two truths in a row, because the brain must shift its data-assembly strategies. Psychologists working on the technology believe it is 86 per cent accurate.
The stress that creates the clues picked up by polygraphs also boosts blood flow in capillaries around the eye. A new application of thermal-imaging technology, called ‘periorbital thermography,’ uses a high-resolution camera to detect temperature changes as small as 0.025°C.
Scientists are also developing technology to track and interpret the motion of the eyes. When the eye takes in a series of images of faces, objects or scenes, it spends less time on familiar elements because the brain needs less processing to interpret them.
Scientists agree that the face tells tales about the person. Psychologists are busy codifying facial movements into micro expressions called the ‘facial action coding system’ (FACS). FACS is the most promising lie detection technology which is the least technologically dependent. It costs much less than other ‘device-oriented’ techniques, and is much easier to train people to use it. It is also the only technique that can be easily used in a natural setting.
A new non-invasive diagnostic technology could give the single-most important sign of brain health: oxygen saturation. A standard pulse oximeter is clipped onto a finger or earlobe of the subject to measure oxygen levels under the skin. It works by transmitting a beam of light through blood vessels in order to measure the absorption of light by oxygenated and deoxygenated haemoglobin. The information allows physicians to know immediately if oxygen levels in the subject’s blood are rising or falling.
The new device uses a technique called ‘ultrasonic light tagging’ to isolate and monitor an area of tissue the size of a sugar cube located between 1 and 2.5 centimetres under the skin. The probe, which rests on the scalp, contains three laser light sources of different wavelengths, a light detector and an ultrasonic emitter. The laser light diffuses through the skull and illuminates the tissue underneath it. The ultrasonic emitter sends highly directional pulses into the tissue. The pulses change the optical properties of the tissue in such a way that they modulate the laser light traveling through the tissue. In effect, the ultrasonic pulses ‘tag’ a specific portion of the tissue to be observed by the detector. Since the speed of the ultrasonic pulses is known, a specific depth can be selected for monitoring. The modulated laser light is picked up by the detector and used to calculate the tissue’s colour. Since colour is directly related to blood oxygen saturation, it can be used to deduce the tissue’s oxygen saturation.
The measurement is absolute rather than relative, because colour is an indicator of the spectral absorption of haemoglobin and is unaffected by the scalp. Deeper areas could be illuminated with stronger laser beams, but light intensity has to be kept at levels that will not injure the skin.
Given the technology’s current practical depth of 2.5 cm, it is best suited for monitoring the upper layers of the brain. While the technology is designed to monitor a specific area, it could also be used to monitor an entire hemisphere of the brain. Measuring any area within the brain could yield better information about whole-brain oxygen saturation than a pulse oximeter elsewhere on the body.
The author is from Department of Physics, S.L.I.E.T. (Deemed to be University), Longowal, District Sangrur (Punjab)