One of the most misunderstood stages of a professional polygraph examination is the stimulation test. Critics sometimes describe it as inherently deceptive — a trick designed to intimidate examinees into believing that the instrument is infallible. Experienced examiners, by contrast, often regard it as an educational and familiarisation exercise that helps examinees understand what will happen during the examination and how the equipment records physiological activity. The truth, as with most things in forensic practice, depends on how it is conducted.
The important question is not whether a stimulation test exists as a procedure. It is whether it is presented honestly, with informed consent, and without exaggerated claims about accuracy. This article examines the legitimate purposes of the stimulation test, the ethical criticisms that have been directed at certain implementations of it, and the approach used in professional practice at The Centre for Forensic Neuroscience.
What Is a Stimulation Test?
The stimulation test — also known as the acquaintance test or demonstration test — is a brief procedure conducted during the pre-test phase of a polygraph examination. It takes place before any relevant questions are asked and before the evidential portion of the examination begins. It is not part of the formal testing sequence and its results do not form part of the examination outcome.
During the stimulation test, the examinee is typically asked to respond to a simple task — often involving a number or a card — while connected to the polygraph instrument. The examiner then reviews the physiological recordings with the examinee.
The legitimate purposes of the stimulation test include:
- Familiarising the examinee with the equipment — many examinees have never been connected to a polygraph instrument before. The stimulation test provides a low-stakes opportunity to experience the sensors, the recording process, and the physical environment of the examination
- Explaining physiological recording — the stimulation test allows the examiner to show the examinee, in real time, how cardiovascular activity, respiratory patterns, and electrodermal responses are recorded and displayed
- Demonstrating how the procedure works — rather than relying solely on verbal explanation, the stimulation test provides a practical demonstration that many examinees find helpful
- Ensuring instructions are understood — the stimulation test provides an opportunity to confirm that the examinee understands how to respond during the examination, including the requirement to remain still and to answer questions with a simple yes or no
- Checking recording quality — the stimulation test allows the examiner to verify that all sensors are functioning correctly, that recordings are clean, and that the equipment is properly calibrated before formal testing begins
- Identifying misunderstandings before formal testing — if the examinee has misunderstood any aspect of the process, the stimulation test provides an opportunity to address this before the evidential examination commences
It is essential to understand that the stimulation test is not designed to prove deception. It is a preparatory procedure. Its purpose is educational and operational, not evidential.
Key Point: The stimulation test is not part of the evidential examination. It is a pre-test familiarisation exercise. Its purpose is to educate the examinee and prepare them for the examination process.
The Ethical Criticism
The most frequently cited academic criticism of the stimulation test comes from the British Psychological Society (BPS) Working Party report on polygraph examination, chaired by Professor Ray Bull. This report has been influential in shaping professional and public discussion about polygraph practice in the United Kingdom.
It is important to represent the BPS report accurately. The report did not state that every stimulation test is unethical. It did not recommend that the procedure be abolished in all circumstances. What the report criticised was a specific misuse of the stimulation test: the practice of using it to persuade examinees that the polygraph is effectively infallible — that it cannot be beaten and that any attempt at deception will inevitably be detected.
The report stated:
“Anybody who attempts to persuade others that polygraphic lie detection is an error-free procedure … by, for example, using a stimulation procedure … will be attempting to deceive.”
This is an important and legitimate concern. If an examiner uses the stimulation test to create the impression that the polygraph is infallible, the examiner is being dishonest. No polygraph examination is error-free. No diagnostic procedure in any field of science achieves perfect accuracy. An examiner who suggests otherwise — whether through explicit claims or through the theatrical presentation of a stimulation test designed to overawe the examinee — is engaging in deception.
However, the ethical concern identified by the BPS report is deception by the examiner, not the existence of the procedure itself. The criticism is directed at how some examiners have presented the stimulation test, not at the concept of familiarising examinees with the examination process.
This is a distinction that is frequently overlooked in popular commentary. The stimulation test is not inherently unethical. It becomes unethical when it is used to mislead.
Myth: The British Psychological Society stated that stimulation tests are always unethical.
Reality: The BPS report criticised examiners who use stimulation procedures to create the false impression that the polygraph is infallible. The ethical issue is deception by the examiner, not the existence of the procedure itself.
Why Some Examiners Still Use a Stimulation Test
Given the criticism, it is reasonable to ask why experienced examiners continue to include a stimulation test as part of their pre-test process. The answer lies in the practical benefits of the procedure when it is conducted transparently and honestly.
- Reducing uncertainty — many examinees arrive for a polygraph examination with significant anxiety about the unknown. A stimulation test reduces uncertainty by showing them exactly what will happen, how the equipment works, and what the physiological recordings look like
- Helping examinees understand the process — verbal explanations, however thorough, are not always sufficient. Some examinees benefit from a practical demonstration. The stimulation test bridges the gap between explanation and experience
- Reducing unnecessary anxiety — anxiety about the examination process itself — as distinct from anxiety related to the issues being examined — can affect physiological recordings. The stimulation test can help reduce process-related anxiety by demystifying the procedure
- Reinforcing careful listening — the stimulation test requires the examinee to listen to instructions, follow directions, and respond in a structured way. This practice run reinforces the importance of careful listening during the formal examination
- Allowing questions before testing begins — the stimulation test creates a natural opportunity for examinees to ask questions about the process. Questions asked after a practical demonstration are often more specific and more useful than those asked in the abstract
- Equipment familiarisation — the physical experience of wearing the sensors, sitting in the examination chair, and hearing questions delivered through the examination format is qualitatively different from having these things described verbally. The stimulation test provides this experience in a low-pressure context
These purposes can be achieved ethically, provided the examiner does not overstate the capabilities of the instrument and does not use the demonstration to create a false impression of infallibility.
How I Conduct the Stimulation Test
My approach to the stimulation test differs from the practices criticised by the British Psychological Society. I regard transparency as more important than persuasion, and I take specific steps to ensure that the stimulation test serves its educational purpose without misleading the examinee.
Before any demonstration takes place, I explain clearly that:
- A polygraph does not detect lies directly — it records physiological responses associated with psychological processes
- No polygraph examination is 100% accurate — like all diagnostic procedures, it is subject to error
- The demonstration is not evidence that the instrument is infallible — it is an opportunity to familiarise the examinee with the recording process
- The purpose of the stimulation test is simply to help the examinee understand how the examination works in practice
- The stimulation test is not part of the formal examination and does not contribute to the examination outcome
Examinees are encouraged to ask questions at any point during the stimulation test. If they have concerns about the process, I address them before proceeding to the formal examination. If an examinee indicates that they do not wish to participate in the stimulation test, this preference is respected.
The stimulation test should increase the examinee's understanding of what is about to happen. It should not increase their fear or create an impression that resistance is futile. Transparency, in my experience, produces better examinations than theatricality.
The Stimulation Test and Countermeasures
I also use the pre-test phase — including the stimulation test — as an opportunity to educate examinees about deliberate attempts to manipulate polygraph examinations.
Before the formal examination begins, I show a short instructional video demonstrating common physical and mental countermeasure techniques that have circulated on the internet and in various publications. These include deliberate breathing alterations, muscular contractions, mental arithmetic, and other methods that individuals have been advised to use in order to influence their physiological recordings.
The purpose of this is educational rather than accusatory. I do not present the video as an accusation that the examinee intends to use countermeasures. Instead, I explain that these techniques exist, that some people encounter them before their examination, and that I want to discuss them openly before the examination begins.
I invite examinees to tell me whether they have encountered any of these methods — whether through internet research, advice from others, or personal curiosity. This conversation is conducted in a non-judgemental manner. The goal is transparency and informed consent, not intimidation.
This approach supports several important principles:
- Transparency — rather than treating countermeasures as a secret concern that the examiner watches for covertly, I discuss them openly. This is consistent with the broader principle of conducting the examination transparently
- Informed consent — the examinee is made aware that countermeasure activity, if detected, could compromise the validity of the examination. This allows them to make an informed decision about how they participate
- Procedural fairness — discussing countermeasures before the examination begins ensures that the examinee cannot later claim that they were unaware that such activity was monitored or that it could affect the examination outcome
- Protecting examination validity — an examinee who has been fully informed about countermeasures and who has had the opportunity to discuss them is less likely to attempt manipulations during the examination
- Reducing misunderstandings — examinees who have researched polygraph examinations online may have encountered misleading advice about countermeasures. Discussing these methods openly allows the examiner to address misconceptions and correct inaccurate information before testing begins
Discussing countermeasures openly is consistent with modern professional practice. It encourages honesty and removes the misconception that countermeasures are either necessary or likely to remain undetected. In my experience, examinees appreciate this transparency and often report that it reduces their anxiety about the process.
Key Point: Discussing countermeasures openly before the examination supports transparency, informed consent, and procedural fairness. It is an educational conversation, not an accusation.
Why Transparency Matters
The broader principle underlying both the stimulation test and the countermeasures discussion is transparency. A professional polygraph examination should be conducted openly, with the examinee fully informed about the process, its capabilities, and its limitations.
Transparency matters for several reasons:
- Informed consent — an examinee who understands what will happen during the examination, how the instrument works, and what the results mean is in a position to provide genuine informed consent. An examinee who has been misled about the capabilities of the instrument has not given informed consent in any meaningful sense
- Professional credibility — examiners who overstate the accuracy of their instrument undermine the credibility of their profession. When exaggerated claims are exposed — as they inevitably are — the resulting scepticism affects all practitioners, including those who conduct their examinations responsibly
- Realistic expectations — examinees and instructing parties should understand what a polygraph examination can and cannot deliver. It provides structured physiological information that contributes to investigative decision-making. It does not provide absolute proof of truth or deception
- Scientific integrity — the scientific literature on polygraph examinations is clear that the technique has both strengths and limitations. An examiner who presents only the strengths and conceals the limitations is not practising in accordance with the scientific evidence
Confidence in the examination should come from the quality of the process — from careful question formulation, validated testing procedures, standardised administration, thorough pre-examination screening, quality assurance, and proper interpretation — not from exaggerated claims made during a stimulation test.
What the Science Actually Says
No responsible examiner should claim that a polygraph examination achieves perfect accuracy. No responsible examiner should claim infallibility. No responsible examiner should suggest that a single physiological recording provides certainty about whether an examinee is telling the truth.
The scientific literature on polygraph accuracy supports the following general conclusions:
- Validated polygraph techniques achieve accuracy rates that are significantly above chance but fall short of perfection
- All polygraph techniques are subject to both false positive errors (indicating deception when the examinee is truthful) and false negative errors (failing to detect deception when the examinee is deceptive)
- The accuracy of a polygraph examination depends substantially on the competence, training, and professionalism of the examiner
- The quality of question formulation is one of the most important determinants of examination validity
- Results should be interpreted probabilistically, within the context of the wider investigation, and with appropriate professional caution
- The complete examination — including the pre-test interview, the testing phase, and the post-test interview — contributes to the overall assessment, not any single component in isolation
A stimulation test that accurately represents these realities is consistent with the scientific evidence. A stimulation test that overstates accuracy, implies infallibility, or creates the impression that the polygraph cannot be beaten is not.
The standard against which the stimulation test should be judged is the same standard against which every other aspect of the examination should be judged: does it reflect what the science actually says?
Conclusion
The ethical issue with the stimulation test is not whether the procedure is performed. It is whether it is presented honestly.
A stimulation test that is used to persuade an examinee that the polygraph is infallible is deceptive. This is the practice that the British Psychological Society correctly criticised. An examiner who uses the stimulation test in this way is misleading the examinee and compromising the integrity of the examination.
A stimulation test that is used to educate the examinee, to familiarise them with the equipment, to explain how physiological recording works, and to provide an opportunity for questions is consistent with ethical professional practice. It serves the interests of the examinee, the examiner, and the integrity of the examination process.
The same principle applies to the discussion of countermeasures. An examiner who ignores the existence of countermeasures and hopes that examinees will not have encountered them is being naïve. An examiner who discusses them openly, explains their implications, and invites honest conversation is acting in accordance with the principles of transparency, informed consent, and procedural fairness.
This is the approach used by Dr Keith Ashcroft at The Centre for Forensic Neuroscience. It reflects a commitment to conducting polygraph examinations in a manner that is scientifically informed, professionally responsible, and transparently honest. The stimulation test, when conducted properly, is not a trick. It is a professional tool that should educate rather than deceive, and increase understanding rather than exaggerate accuracy.
The ethical question is not whether a stimulation test is performed. It is whether the examiner tells the truth about what the instrument can and cannot do.
Frequently Asked Questions
What is a stimulation test in a polygraph examination?
A stimulation test — also called an acquaintance test or demonstration test — is a brief procedure conducted during the pre-test phase of a polygraph examination. It familiarises the examinee with the polygraph equipment, demonstrates how physiological responses are recorded, and provides an opportunity to ask questions before the formal examination begins. It is not part of the evidential examination and does not contribute to the examination outcome.
Is a stimulation test compulsory?
No. The stimulation test is a preparatory exercise, not a mandatory component of every polygraph examination. If an examinee indicates that they do not wish to participate in a stimulation test, a responsible examiner will respect that preference. However, most examinees find the demonstration helpful in reducing uncertainty and anxiety about the process.
Does the stimulation test prove the polygraph works?
No. The stimulation test does not prove that the polygraph is accurate or infallible. It is a familiarisation exercise that demonstrates how physiological responses are recorded. Any examiner who presents the stimulation test as proof that the polygraph cannot be beaten is misrepresenting the capabilities of the instrument. No polygraph examination achieves perfect accuracy.
Why do some examiners use a stimulation test?
Examiners use the stimulation test to familiarise examinees with the equipment, explain how physiological recording works, reduce process-related anxiety, check that all sensors are functioning correctly, and provide an opportunity for questions before the formal examination begins. When conducted transparently, it serves a legitimate educational purpose.
Why has the stimulation test been criticised?
The British Psychological Society Working Party, chaired by Professor Ray Bull, criticised examiners who use the stimulation test to create the false impression that the polygraph is infallible. The ethical concern is deception by the examiner — specifically, attempts to persuade examinees that the instrument cannot make errors. The criticism is directed at how the procedure has sometimes been presented, not at the procedure itself.
How does The Centre for Forensic Neuroscience conduct the stimulation test?
Dr Keith Ashcroft conducts the stimulation test with full transparency. Before any demonstration, examinees are informed that the polygraph does not detect lies directly, that no examination is 100% accurate, and that the demonstration is not evidence of infallibility. Examinees are encouraged to ask questions and are given the opportunity to decline the stimulation test. Additionally, common countermeasure techniques are discussed openly to support informed consent and procedural fairness.
Can countermeasures be discussed before the examination?
Yes. At The Centre for Forensic Neuroscience, countermeasure techniques are discussed openly during the pre-test phase. Examinees are shown examples of common countermeasure methods and invited to discuss whether they have encountered them. This educational approach supports transparency, informed consent, and procedural fairness, and is consistent with modern professional practice.
Important Disclaimer
This article is provided for general educational and professional information only. It does not constitute legal advice or clinical advice. Polygraph examinations are not proof of guilt or innocence and do not achieve perfect accuracy. The discussion of the British Psychological Society Working Party report reflects publicly available information and should be verified independently by readers with access to the original publication. Professional practice standards may vary between jurisdictions and organisations. No solicitor-client relationship is created by this publication.
Dr Keith Ashcroft is an Investigative Psychologist and Principal Forensic Polygraph Examiner at the Centre for Forensic Neuroscience, with over two decades of investigative experience and advanced international training. For professional enquiries concerning polygraph examinations, or to discuss how the pre-test process is conducted, contact Dr Keith Ashcroft at the Centre for Forensic Neuroscience.