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Written by Bhavya Anand and Lalima Das of Delhi Metropolitan Education


Within this era of modern technology, everything has levelled into more advanced form. Technical establishment in Neuroscience has also been observed in the field of law. One such being the use of DDTs (Deception Detection Tests) for evidentiary purposes to confirm suspicion and an accused’s conviction. These methods have been considered as treading on dangerous waters during the initial phase but soon its acceptance has brought great convenience for the courts. Nevertheless, such tests cannot be relied on like “Pinochhio’s Nose” and still used only in crucial cases.


Deception detection tests (DDTs) such as polygraph, narco-analysis and mind mapping have significant health, science, moral and legal implications. DDTs are beneficial to understand the secret information relevant to the offence. This knowledge, which is accessible only to oneself, is often vital to a criminal case. These have been extensively used by the enforcement agencies. However, the enforcement agencies know that the information gathered cannot be used as testimony in the trial phase. They denied that it was better than the ‘third-degree approaches’ used by other inspectors. In this case, the argument is that by employing these ‘research techniques’ in fact-finding would actually enable the investigation authorities to collect evidence. Thus raising the rate of conviction of the accused and the rate of acquittement of the innocent. Recently, these approaches have been marketed to be much more reliable and not to avail, without conclusive evidence.[1]


  • Narco-Analysis:

This test requires intravenous administration of a substance (such as sodium pentothal, scopolamine and sodium amytal) that causes an individual to enter different stages of anaesthesia. At the hypnotic level, the subject is less anxious and more prone to disclose information that would not necessarily be shared in state of consciousness. It’s a part of the criminal psychology and forensic science. It is used as identification, classification, personalisation and development of physical proof by applying the tools and processes of natural science for the purposes of the criminal justice system.

There are mainly four stage of Narco-Analysis Tests:[2]

  1. Pre-Test Interview: In this phase, the person has carried out all the tests and procedures of the test and then the permission have been obtained.
  2. Narcotic-State: Anaesthetic fuelled medication and preserve pre-narcotic status throughout the entire episode.
  3. Semi-Narcotic State: After the required situation has been established, the people tend to get-
  4. Red
  5. Low and muddled voice
  6. Reasonable detection of Nystagamus by inspection of the examinee’s eye, muscles, and finger.
  7. At the conclusion of the interview is encouraged.
  8. Interviewer allow the person to sleep off and allow him to wake up.
  9. Links anaesthetic inspection of the body.
  10. Post-State Interview: This is the phase where the person is released from the interrogation; discomfort free level.

While this methodology has been recognized since the Second World War, it has not been backed by evidence based research to validate its argument.[3]

  • Polygraph evidence:

This is often referred to as a lie detector test, but this term is a bit misleading. The hypothesis behind lie detector tests is that the convicted individual is more likely to be involved with misleading about the actual information of the incident, which in turn creates a neurotic-arousal condition that is scooped up by a person skilled in interpreting lie detector test findings. The assessment of neurotic-arousal status is based on a variety of variables such as heart rate, blood pressure, breathing rate, skin conductivity and electromyography. The theory behind these tests is unclear because the calculated shifts in the equilibrium condition are not necessarily caused by exaggeration or deceit. Rather, they may be caused by uneasiness, anxiety, fear, uncertainty, hypoglycaemia, paranoia, depression, mediated drug (nicotine, stimulants), drug detox (alcohol separation) or other impulses. This state was also due to the manner in which the investigative agents asked the questions. At the same point, it is not tough to match lie detector tests by a capable professional who can monitor or inhibit his / her arousal symptoms by progressive muscle relaxation, yoga, meditation, etc. The accuracy of the lie detector test was also frequently challenged in academic research.

  • Brain-Mapping:

It analyses the changes in the electrical wave potential created by the amount of the synaptic processes in the brain by ways of electrodes mounted on the skin’s surface surrounding the head and the face. Modifications specifically linked to particular behavioral or cognitive experiences are referred to as event-based prospects.[4]

Simply put, it is supported by the finding that the brain produces a specific brain-wave signal when an individual experiences a recognizable signal.[5] Commonly employed tool in India is called the Brain Electrical Activation Profile Test. During the study, subjects are introduced to visual or auditory signals (photographs, clips and sounds) that are important to the evidence being tested, along with other unrelated words and images. Such signals may be commonly categorised as material ‘probes’ and neutral ‘probes.’ The basic principle is that, in the situation of convicted offenders, proximity to substance probes would result in the exposure of P300 signal properties to be adequately reported by the devices.

By analysing the records of these pulse elements, the investigator can draw assumptions about the individual’s experience of the crime-related details. However, it just tests the recollection or awareness of the crime scene and nothing else. For example, a person who endured a murder may theoretically be charged as a suspect if the examination shows that the individual in question was aware of the details relevant to the same.

Similarly, nothing is known about the effect of watching the depiction of the murder scene in the media, such as television, film and publication, on brain mapping.

Therefore, this method cannot be employed to convict an accused, but can be viewed as a ‘alibi’ for a honest person to show that he/she has no recollection of the incident on this test.[6]


Considering the most essential purpose of judicial proceedings is to render justice by extracting the truth from the shrouded lies, it is important to adapt valid instruments to seek out the truth. Lie detection techniques have been considered as a way to skim off the necessary indications which points towards an accused’s wrongdoing. Even after its successful outcomes, there are legal implications of their application which raises questions like intrusion in an individual’s privacy, mental health and psychological effect.

One of the DDTs like Polygraph was first created in 1921 and is considered efficient to deduce the information required.[7] Despite the results, courts felt the need to use it with restrictions as it was observed that inconsistencies prevailed. This may lead to undesired influence on the decision-making of the courts.

In the 20th century, the introduction of Polygraph test in courts like evidence was challenged in a case[8]. The main concern was that the technique brings possibility for inaccurate results because the persons undergoing the test can be easily deceptive. This led to usage of this method in rarest of rare cases.

Seeing this, want for more developed methodologies arose which paved the way for Brain-mapping test, otherwise known as Brain-wave analysis. Problems still persisted regarding its application, utility by the authorities and related approaches regardless its more accuracy than polygraph test. The procedure runs deep into a person’s brain mechanism and a single discrepancy can cause misleading results.

Another problem was that the results obtained from brain-mapping test was so general in a case determining a criminal’s knowing of a crime scene[9] that the entire purpose of the evaluation was considered futile. Admissibility of such evidences procured from these DDTs were questioned and laid out by the U.S. Supreme court in another case[10] in which standards of “reliability” was required in such scientific evidences. Litigants have a way of interpreting the authenticity by worthiness of a courtroom evidence and the same has been identified by apex court of U.S.

The U.S. Supreme court stated –

“To qualify as ‘scientific knowledge,’ an inference or assertion must be derived by the scientific method. Proposed testimony must be supported by appropriate validation—i.e., ‘good grounds,’ based on what is known. In short, the requirement that an expert’s testimony pertain to ‘scientific knowledge’ establishes a standard of evidentiary reliability.”

Such interpretations help to curb inadmissible evidence or information which may adversely affect the decision-making in a court.


In a leading case[11], the High Court of Madras stated that the investigative authority is expected to conclude the inquiry within a reasonable time frame, if not, the benefit of the delay being provided to the accused. If the suspect fails to comply with the disciplinary process conducted during the custody interview in order to solve the ambiguity surrounding the case, the techniques of empirical analysis would have to be used to discover the facts.

Keeping the very same principle in another judgement, the court held that the narco-analysis test was a phase in the inquiry. It forms an essential basis for the further examination as it can contribute to the gathering of additional evidence. With regard to the dissemination of offences against community, it is also important to recognise the need for society overall. The need for a comprehensive and fair examination as against individual rights, while at the same time acknowledging that constitutional rights are not violated.

Resultantly, in the case in question, the narco-analysis test doesn’t really suffer from any constitutional incapacity as it is a phase in the inquiry. Any consciousness-incriminatory argument, if rendered by the suspect, cannot be used or considered by the court. The court ordered the suspect to undergo a narco-analysis examination within a prescribed period of time. These decisions strongly supported the use of DDTs in proceedings.[12]


It is natural that complexities in today’s world can be head-on challenged with well-equipped methods. All over the world the legal field tries its best to dispense justice with maximum veracity in decision-making. No doubt, the Deception Detection Tests have assisted the courts majorly and has helped in deciphering the toughest of cases. But it cannot be ignored that these tests have been abused by authorities and provided inaccurate results leading to mislead convictions.

The constitutionality of DDTs was questioned due to the probability of crossing the silver-lining of privacy of an individual. One can never determine when an investigation ends and turns into violation of a person’s privacy. The discrepancies have led the acceptance of these tests in a limited manner in the courts. In fact, the evidentiary value of such outcomes are not considered high as there is always a chance that the person administered such procedure may have deceived or was wrongly alleged. With the above problems prevailing, it can be only hoped that legitimate use of DDTs are administered and authentic results are achieved.

[1] Math, S. B. (2011). Supreme Court judgment on polygraph, narco-analysis & brain-mapping: A boon or a bane. The Indian journal of medical research134(1), 4.

[2] Inamdar, S. (2020). Narco Analysis

[3] Naples M, Hackett T. The Amytal interview: history and current uses. Psychosomatic. 1978;1998–105

[4] Lefebvre CD, Marchand Y, Smith SM, Connolly JF. Use of event-related brain potentials (ERPs) to assess eyewitness accuracy and deception. Int J Psychophysiol. 2009;73:218–25

[5] Appelbaum PS. Law & psychiatry: the new lie detectors: neuroscience, deception, and the courts. Psychiatr Serv. 2007;58:460–2

[6] New Delhi: Directorate of Forensic Science, Ministry of Home Affairs, Government of India; 2005. Laboratory procedure manual. Brain electrical activation profile

[7] Synnott, J., Dietzel, D., & Ioannou, M. (2015). A review of the polygraph: history, methodology and current status. Crime Psychology Review1(1), 59-83.

[8] Frye v. United States, 293 F 1013 (DC Cir 1923)

[9] Harrington v Iowa, 659 NW 2d 509 (Iowa 2003)

[10] Daubert v Merrell Dow Pharmaceuticals, 516 US 869 (1993)

[11] Dinesh Dalmia v. State, Crl. R.C. No. 259 of 2006

[12] Sh. Shailender Sharma v. State, Crl. WP No. 532 of 2008

Image courtesy: The National Academics Press

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