Reference

Polygraph & Forensic Psychophysiology Glossary

A plain-English reference covering polygraph examinations, credibility assessment, forensic psychophysiology, scoring methods, question design, and UK risk-management terminology. Written by Dr Keith Ashcroft.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Acquaintance Test: A preliminary or demonstration test used to familiarise an examinee with the polygraph process, question timing, and recording procedures. It may also be used to show that physiological reactions can be recorded.

Actigraphy: Measurement of movement, usually through wearable sensors. In credibility assessment contexts, movement can be relevant as an artefact source or as part of broader behavioural monitoring, but it is not a direct deception measure.

Activity Sensor: An activity sensor records movement or muscular activity during a polygraph examination. It may be built into a seat pad, foot pad, armrest, or other accessory, and is used to identify movement that could distort physiological recordings or indicate a possible physical countermeasure. Activity data are not a separate deception measure. They help the examiner assess chart quality, distinguish artefact from question-related physiology, and decide whether a response can be scored. In contemporary practice, activity sensors support quality control by documenting movements that might otherwise be missed during visual observation.

Adjudication: The administrative, investigative, or legal decision-making process that may consider polygraph results alongside other evidence. Polygraph outcomes should not be treated as standalone proof.

Admissibility: Admissibility refers to whether evidence may be received and considered by a court or tribunal. In the context of polygraph and forensic psychophysiology, admissibility depends on the jurisdiction, the purpose for which the evidence is offered, procedural rules, relevance, reliability, expert competence, and judicial discretion. Standards such as the Frye Standard and Daubert Standard are historically important in the United States, but they are not the governing test in England and Wales. A polygraph report may still have investigative, clinical, employment, safeguarding, or risk-management value even where it is not treated as determinative court evidence.

Algorithmic Scoring: Use of statistical or computer-based models to evaluate physiological response patterns. Examples include automated numerical scoring systems and probabilistic classification tools.

Amplitude: The size or magnitude of a physiological response, such as the height of an electrodermal response or change in cardiovascular tracing.

Arousal: A general state of physiological activation involving systems such as sympathetic nervous activity, cardiovascular activity, respiration, and electrodermal activity. Polygraph methods infer diagnostic value from differential arousal to different question types, not from arousal alone.

Artefact: Distortion in recorded physiological data caused by non-relevant factors such as movement, coughing, sensor slippage, talking, poor contact, deep breathing, or equipment noise.

Atypical Physiology: Physiological patterns that differ from expected norms because of medical, psychological, pharmacological, developmental, or situational factors. These may complicate interpretation.

Automated Polygraph Scoring: Computer-assisted scoring of physiological recordings using predefined rules or statistical models. It may support, but does not replace, examiner judgement in many protocols.

Autonomic Nervous System (ANS): The autonomic nervous system is the part of the peripheral nervous system that regulates largely involuntary functions such as sweating, breathing rhythm, blood-vessel tone, heart rate, and digestive activity. It has two main divisions: the sympathetic nervous system, associated with mobilisation, vigilance, and threat-related activation, and the parasympathetic nervous system, associated with recovery, regulation, and conservation of energy. The ANS is central to psychophysiological credibility assessment because contemporary polygraph instruments record peripheral autonomic activity, including electrodermal activity, respiration, and cardiovascular activity. Examiners interpret patterned changes across these channels in relation to the test format and question sequence, rather than treating any single autonomic response as proof of deception.

B

Base Rate: The base rate is the underlying frequency of a condition or behaviour in the population or case group being assessed. It matters because even an accurate test can produce misleading practical results when the target behaviour is very rare or very common. In polygraph screening, for example, the base rate of undisclosed behaviour affects the meaning of positive and negative outcomes, predictive value, and the consequences of false-positive and false-negative classifications. Base rate thinking is therefore important for solicitors, investigators, employers, and psychologists when interpreting test results as part of wider evidence or risk assessment.

Baseline: A reference level of physiological activity against which later responses are compared. Baselines may be informal, pre-question, or built into chart interpretation.

Behavioural Analysis Interview: An interview method that evaluates verbal, non-verbal, and contextual indicators of credibility. It is distinct from instrumented polygraph testing and is more vulnerable to subjectivity.

Behavioural Cue: An observable action, facial expression, posture, speech pattern, or gesture sometimes interpreted as relevant to credibility. No single behavioural cue reliably indicates deception.

Beta Blockers: A class of medication (beta-adrenergic antagonists) prescribed for conditions such as hypertension, anxiety, and cardiac arrhythmias. Beta blockers reduce sympathetic nervous system activation and may attenuate cardiovascular and, to a lesser extent, electrodermal responses, potentially affecting the interpretability of polygraph recordings.

Biofeedback (as Countermeasure): The deliberate use of real-time physiological monitoring techniques to learn voluntary control over autonomic responses such as heart rate, respiration, or skin conductance. In a polygraph context, prior biofeedback training is considered a potential countermeasure because it may enable an examinee to suppress or alter phasic responses during testing.

Biometric Sensor: A device that measures biological or physiological signals, such as skin conductance, blood pressure, respiration, heart rate, eye movement, voice, or brain activity.

Blood Pressure Cuff: A cardiovascular sensor commonly used in polygraph instrumentation to record relative changes in blood pressure and pulse activity.

Bracketing: Placement of question types in a structured sequence so that responses can be compared across relevant, comparison, and neutral questions.

C

Calibration: Procedures used to confirm that equipment is functioning properly and recording signals accurately or consistently.

Calibration Verification of Sensitivity Test (CVOS): A structured demonstration or verification procedure used before or during a polygraph examination to confirm that the instrument is recording physiological responses of sufficient quality and that the examinee’s physiology is suitable for testing. It may also serve to orient the examinee to the testing process.

Cancelled Examination: A cancelled examination is an examination that does not proceed to meaningful testing. It may be cancelled because the referral is withdrawn, the examinee does not attend, informed consent is not obtained, the case is unsuitable, required information is unavailable, or a safeguarding, legal, medical, or procedural issue prevents testing. A cancelled examination differs from an incomplete examination, which begins but cannot be finished, and from an inconclusive result, where testing is completed but the data do not support a definitive classification. Clear reporting of cancellation protects against misunderstanding and prevents the absence of a result being treated as evidence of deception or truthfulness.

Cardiograph: The polygraph component or channel that records cardiovascular activity.

Cardiovascular Activity: Cardiovascular activity refers to heart and blood-vessel changes recorded during a polygraph examination, commonly including pulse amplitude, relative blood pressure, pulse rate, and vasomotor change. Traditional instruments often used a blood pressure cuff, while modern systems may also use a photoplethysmograph to record peripheral blood-volume pulse. Cardiovascular recordings are interpreted alongside electrodermal activity and respiration because autonomic responses can vary across channels. In a valid test format, the examiner looks for consistent, question-related patterns across the polygram, not an isolated increase in heart rate or blood pressure.

Case Facts: Known details about an investigation that inform question formulation, issue selection, and test design.

Central Nervous System (CNS): The brain and spinal cord. Some credibility technologies, such as EEG and fMRI, attempt to measure CNS activity rather than peripheral autonomic responses.

Chart: A recorded segment of physiological data collected during a question sequence. Traditional terminology refers to each run as a chart, even when recorded digitally.

Chart Collection: Chart collection is the data-gathering phase of a polygraph examination in which reviewed test questions are presented in a structured sequence while physiological channels are recorded. Several charts or repetitions are usually collected so that response patterns can be evaluated for consistency rather than relying on a single presentation. The examiner monitors signal quality, question timing, artefacts, breathing, movement, and examinee compliance throughout this phase. Chart collection is distinct from the pretest interview, question review, scoring, and post-test discussion, although all phases affect the reliability and interpretability of the final opinion.

Chart Interpretation: The process of evaluating physiological recordings to determine whether response patterns are more consistent with deception, non-deception, recognition, or inconclusive outcomes depending on the test format.

Comparison Question: A comparison question is a test question designed to create a meaningful physiological comparison with a relevant question. In comparison question techniques, the examiner evaluates whether the examinee reacts more strongly to the issue under investigation or to carefully constructed comparison material. Comparison questions may be probable lie comparison questions, where the examinee is expected to be concerned about the truthfulness or completeness of an answer, or directed lie comparison questions, where the examinee is instructed to answer falsely. Their purpose is to support within-subject comparison and reduce reliance on general nervousness or arousal.

Comparison Question Test (CQT): A comparison question test is a validated polygraph format in which physiological responses to relevant questions are compared with responses to comparison questions. The central issue is not whether the examinee shows arousal, but where the strongest and most consistent responses occur within the question sequence. Modern CQT formats include probable-lie and directed-lie approaches, structured question review, repeated charts, numerical or empirical scoring, and quality-control procedures. CQT methods differ from the older Relevant/Irrelevant Technique, which did not provide the same diagnostic comparison between relevant and comparison questions.

Computerised Polygraph: A digital polygraph system that records, displays, stores, and may assist in scoring physiological data.

Concealed Information: Knowledge that an examinee may possess but deny or withhold. Recognition of concealed information can be assessed through methods such as the CIT.

Concealed Information Test (CIT): A recognition-based test format designed to determine whether an examinee recognises crime-relevant or otherwise concealed information. It does not directly test lying; it tests differential recognition.

Confession: An admission of involvement or culpability. In polygraph practice, confessions or admissions may occur before, during, or after testing, but should be documented separately from physiological outcomes.

Confirmation Bias: The tendency to interpret information in a way that confirms prior beliefs. It is a major concern in investigative interviewing and credibility assessment.

Countermeasure: A deliberate physical, mental, or behavioural strategy used by an examinee to alter physiological responses or interfere with test interpretation.

Credibility Assessment: The broad evaluation of whether a person’s statements, denials, memories, or claims are reliable, truthful, complete, or internally and externally consistent. Polygraph testing is one form of credibility assessment.

Criterion Validity: The degree to which a test result corresponds to an external truth criterion, such as verified facts, independent evidence, or known ground truth.

Cut-Off Score: A cut-off score is the numerical threshold used to convert chart scores into an outcome classification such as deception indicated, no deception indicated, significant response, no significant response, or inconclusive. Cut-offs vary according to the test format, scoring system, number of relevant questions, and decision rule. Their purpose is to reduce subjectivity and provide consistent interpretation of physiological data. A score close to a cut-off should be understood with caution because small changes in artefact handling, channel quality, or scoring judgement may affect the classification.

D

Data Acquisition: The process by which sensors collect physiological signals and convert them into digital or analogue records.

Daubert Standard: The Daubert Standard is a United States legal standard for assessing the admissibility of expert scientific evidence, derived from Daubert v. Merrell Dow Pharmaceuticals (1993). It asks courts to consider reliability factors such as testability, peer review, known or potential error rates, standards controlling the technique, and general acceptance. It is historically important in debates about polygraph evidence and scientific validity, particularly in the United States. It is not the legal standard used within England and Wales, where expert evidence is assessed under domestic rules on relevance, reliability, expertise, and the duties of expert witnesses. Daubert nevertheless remains influential in international discussions about forensic science.

Deception: Deliberate communication intended to mislead another person. Polygraph instruments do not directly detect deception; they record physiological activity interpreted in relation to test structure.

Deception Indicated (DI): A traditional polygraph outcome indicating that recorded responses support deception under the scoring rules used.

Decision Rule: A predefined rule for converting scores or response patterns into classifications such as deception indicated, no deception indicated, significant response, no significant response, or inconclusive.

Detection of Deception: A general term for methods intended to identify deception through physiological, behavioural, linguistic, cognitive, or technological measures.

Diagnostic Examination: A polygraph examination focused on a known event or specific allegation, often with a clearly defined issue.

Differential Reactivity: The pattern of stronger physiological response to one category of questions than another. It is central to many polygraph scoring methods.

Directed Lie Comparison Question (DLC): A directed lie comparison question is a comparison question that the examinee is instructed to answer falsely, usually after acknowledging that the answer will be deliberately untrue. It differs from a probable lie comparison question, which relies on the examinee’s concern about past behaviour, moral fault, or incomplete disclosure. Directed lie questions provide a more controlled comparison stimulus because the examiner defines the expected false answer rather than depending on an unverified personal history issue. DLC procedures are used in validated comparison question test formats to create differential salience, improve standardisation, and reduce some ethical or practical difficulties associated with probable-lie questioning.

Disclosure Test: A test or interview procedure aimed at eliciting previously undisclosed information. In some contexts, this may be used in monitoring or supervision settings.

Discriminant Validity: The degree to which a test measures the construct it claims to measure and not unrelated constructs such as anxiety, fear, confusion, or anger.

E

Electrodermal Activity (EDA): Electrical activity of the skin associated with sweat gland activity and sympathetic nervous system activation. It is one of the principal channels in polygraph recording.

Electrodermal Response (EDR): A measurable change in skin conductance or resistance following a stimulus, such as a test question.

Electroencephalography (EEG): Measurement of electrical activity of the brain via scalp electrodes. Some deception and concealed-information research uses EEG components such as the P300.

Electromyography (EMG): Measurement of muscle activity. EMG may be used in psychophysiology and can also help identify movement artefacts.

Empirical Scoring System: A scoring approach developed and validated using data and statistical analysis rather than only tradition or examiner intuition.

Empirical Scoring System – Multinomial (ESS-M): A validated, rule-based scoring method for polygraph chart evaluation that uses multinomial probability models to classify physiological response patterns. ESS-M is designed to reduce subjectivity and improve inter-rater reliability by applying empirically derived decision rules to multi-channel data.

Examinee: The person undergoing the polygraph examination or credibility assessment.

Examinee Suitability: Examinee suitability refers to whether a person can fairly and meaningfully undergo a polygraph examination. Suitability may be affected by age, language comprehension, cognitive ability, mental health, medication, acute distress, intoxication, fatigue, medical conditions, pain, respiratory or cardiovascular problems, and the ability to understand and answer the questions. It also includes procedural matters such as informed consent, legal advice where appropriate, and the absence of coercion. A suitable examinee is not simply someone who is willing to be tested; they must be able to participate in a way that allows interpretable physiological recordings and ethically defensible conclusions.

Examiner: The trained professional who conducts the examination, formulates questions, records physiological data, interprets results, and reports findings.

Exclusive Comparison Question: An exclusive comparison question is a comparison question whose scope is intended to be separate from the specific matter addressed by the relevant question. For example, in a test about one defined allegation, the comparison question may refer to a different class of behaviour, a different time period, or a broader honesty issue that excludes the event under investigation. The purpose is to prevent overlap between the comparison material and the relevant issue, so that responses can be interpreted as separate sources of psychological salience. Exclusive comparison questions are used when clear separation improves fairness, question clarity, and the logic of within-subject comparison.

Expert Evidence (England and Wales): Expert evidence in England and Wales is opinion evidence provided by a person with relevant expertise to assist a court on matters outside ordinary knowledge. The expert’s overriding duty is to the court, not to the party instructing them. Scientific and technical evidence must be relevant, reliable, and within the expert’s competence, and it is governed by procedural rules and case law rather than by the US Frye or Daubert standards. In polygraph-related matters, this distinction is important because scientific validity, examiner qualifications, test format, limitations, and the purpose of the report all affect how the evidence may be understood.

External Validity: The extent to which research findings generalise to real-world field conditions.

F

False Negative: A result that incorrectly classifies a deceptive or knowledgeable person as non-deceptive or not knowledgeable.

False Positive: A result that incorrectly classifies a truthful or non-knowledgeable person as deceptive or knowledgeable.

Field Study: Research conducted using real cases or operational settings rather than laboratory simulations.

Forensic Psychophysiology: Forensic psychophysiology is the application of psychophysiological science to legal, investigative, regulatory, and forensic questions. It examines how psychological processes such as attention, recognition, threat appraisal, memory, and response inhibition are reflected in measurable physiological activity. Polygraph examinations sit within this discipline because they use structured questioning and instrumentation to record autonomic nervous system activity, including electrodermal activity, cardiovascular activity, and respiration. The discipline is broader than polygraph practice alone and also includes research on concealed information, stress physiology, neurophysiology, measurement validity, and the proper interpretation of physiological data in forensic contexts.

Frye Standard: The Frye Standard is a United States legal test for the admissibility of scientific evidence, originating in Frye v. United States (1923). It asks whether a scientific principle or technique has gained general acceptance in the relevant scientific community. Frye is historically important to polygraph evidence because early admissibility debates often centred on whether polygraph methods had achieved sufficient scientific acceptance. It is not the legal standard used within England and Wales, where courts apply domestic rules concerning relevance, reliability, expertise, and the duties of expert witnesses. Frye remains influential as a historical reference point in international discussions of forensic validity and expert evidence.

Functional Magnetic Resonance Imaging (fMRI): A neuroimaging method measuring blood-oxygen-level-dependent changes in the brain. It has been studied for deception detection but is not equivalent to conventional polygraph testing.

G

Galvanic Skin Response (GSR): Older term for electrodermal response. It refers to changes in the electrical properties of the skin.

Ground Truth: Independently verified information about what actually happened or whether an examinee is truthful, deceptive, knowledgeable, or not knowledgeable. Ground truth is essential for validity research.

Guilty Knowledge Test (GKT): An older term often associated with recognition-based testing similar to the Concealed Information Test. The term can be misleading because recognition does not necessarily prove guilt.

H

Habituation: A reduction in physiological response after repeated exposure to the same or similar stimulus.

Heart Rate Variability (HRV): Variation in time intervals between heartbeats. It reflects autonomic regulation and may be relevant in broader psychophysiological research.

Homeostasis: The body’s regulation of internal stability. Polygraph recordings reflect changes in systems that maintain or respond to disruptions in homeostasis.

Hyperventilation: Rapid or deep breathing that can alter respiratory and cardiovascular tracings. It may occur naturally or as a countermeasure.

I

Incomplete Examination: An incomplete examination is a polygraph examination that begins but cannot be finished to the point required for a valid professional opinion. This may occur because of illness, equipment failure, unsuitable physiology, withdrawal of consent, inadequate question review, interruption, or insufficient usable data. It is different from an inconclusive outcome, where the examination is completed but the physiological data do not meet decision criteria for a clear classification. It is also different from a cancelled examination, which is stopped before meaningful testing begins, for example because the referral is withdrawn or the case is found to be unsuitable during pretest screening. Reports should distinguish these categories clearly because they have different procedural and evidential meanings.

Inconclusive Result: A result that does not meet criteria for a definitive classification. Causes may include weak differential response, artefacts, poor recordings, inconsistent data, or scoring thresholds.

Independent Review: Review of polygraph charts, scoring, or procedures by another qualified examiner or quality-control reviewer.

Instrumentation: The equipment used to collect physiological data, including sensors, amplifiers, software, computers, and recording devices.

Inter-Rater Reliability: The degree to which different examiners or scorers reach the same result when evaluating the same data.

Interview Phase: The portion of the examination involving explanation of procedures, background information, issue review, question formulation, and post-test discussion.

Irrelevant Question: A question not directly related to the issue under investigation and generally not used for diagnostic comparison in the same way as relevant or comparison questions.

K

Knowledge-Based Detection: Assessment focused on whether a person recognises specific information, rather than whether they are lying about an allegation.

Known-Solution Test: A research or training test in which the true status of examinees is known, allowing accuracy assessment.

L

Lafayette Instrument: A well-known manufacturer of polygraph and psychophysiological recording equipment. Mentioned here as a technology term, not as an endorsement.

Latency: The time between presentation of a stimulus, such as a question, and the onset of a physiological response.

Lykken Scoring / CIT Tradition: A research tradition associated with recognition-based concealed information approaches, emphasising memory and recognition rather than broad emotional arousal.

M

Maintenance Polygraph: A recurring or monitoring-focused examination sometimes used in supervision programmes, security contexts, or compliance settings.

Mental Countermeasure: A covert cognitive strategy, such as mental arithmetic or emotionally arousing imagery, intended to change response patterns.

Motion Artefact: Distortion caused by body movement, muscle tension, sensor displacement, or posture changes.

Movement Sensor: A movement sensor is an accessory used to record physical movement during testing, often through a seat pad, foot pad, or limb sensor. Its purpose is to document activity that may affect the polygram, such as shifting posture, muscle tensing, pressing the toes, controlled breathing movements, or other possible physical countermeasures. Movement sensor data are interpreted cautiously and in context. A movement trace may explain an artefact, support a decision not to score a response, or prompt further review, but it is not by itself a measure of deception.

Multichannel Recording: Simultaneous recording of multiple physiological channels, commonly respiration, cardiovascular activity, and electrodermal activity.

N

Negative Control: A comparison condition expected not to produce issue-relevant responses. In polygraph terminology, neutral or irrelevant questions sometimes function informally in this role.

Neutral Question: A question designed to be emotionally non-threatening and unrelated to the issue under investigation.

No Deception Indicated (NDI): A traditional polygraph outcome indicating that the recorded responses do not support deception under the scoring rules used.

No Significant Response (NSR): A result often used in screening or relevant/irrelevant contexts indicating that no diagnostically significant physiological response was observed to a target issue.

Non-Exclusive Comparison Question: A non-exclusive comparison question is a comparison question that is not fully separated from the time period, behavioural category, or general subject matter of the relevant issue. It may address a broader area that could include conduct similar to, or connected with, the allegation under investigation. This contrasts with an exclusive comparison question, which is deliberately scoped away from the relevant matter. Non-exclusive comparison questions can be useful in some validated formats because they may increase personal salience, but they require careful wording, explanation, and review to avoid confusion, perceived unfairness, or overlap that weakens the logic of the comparison.

Numerical Scoring: Assignment of numerical values to physiological responses, usually comparing relevant and comparison questions across recording channels.

O

Objective Scoring System (OSS): A structured scoring method intended to reduce subjectivity by using explicit measurement and decision rules.

Orienting Response: Physiological response to a novel, meaningful, or significant stimulus. It is particularly relevant to recognition-based tests such as the CIT.

Outcome Classification: The final category assigned after scoring and interpretation, such as DI, NDI, SR, NSR, inconclusive, or no opinion.

P

P300: An event-related brain potential associated with attention and recognition of meaningful stimuli. It has been studied in concealed-information research.

Parasympathetic Nervous System: The parasympathetic nervous system is the division of the autonomic nervous system associated with recovery, conservation of energy, digestion, and homeostatic regulation after activation. It is often described as supporting “rest and digest” functions, although real physiology is more complex than a simple on/off switch. Polygraph recordings reflect the balance between parasympathetic and sympathetic nervous system influences. For example, heart rate, blood pressure, breathing pattern, and peripheral blood flow can change because of shifting autonomic control. Examiners therefore interpret responses across the whole polygram and in context, recognising that measured signals are products of dynamic regulation rather than isolated signs of truthfulness or deception.

Peak of Tension Test (POT): A test format in which a sequence of alternatives is presented, one of which is expected to be most salient to a knowledgeable examinee.

Peripheral Nervous System (PNS): The nerves outside the brain and spinal cord. Conventional polygraph testing mainly records peripheral autonomic responses.

Photoplethysmograph (PPG): A photoplethysmograph is an optical sensor that estimates changes in peripheral blood volume by shining light into the skin and detecting variation in reflected or transmitted light. In polygraph instrumentation it is usually attached to a finger or thumb and records blood-volume pulse, pulse amplitude, and vasomotor change. The PPG is non-invasive and can provide useful cardiovascular information alongside a blood pressure cuff or other cardiograph channel. It does not measure deception directly. Its value lies in showing how peripheral circulation changes during question presentation, when interpreted with respiration, electrodermal activity, and the wider polygram.

Plethysmograph: A plethysmograph is an instrument used to measure changes in volume within an organ, limb, or body part, often by detecting changes in blood volume. Traditional plethysmography may use air displacement, strain gauges, or pressure changes to record vascular or respiratory volume shifts. A photoplethysmograph is a specific optical form of plethysmography that estimates blood-volume pulse by measuring light absorption or reflection in tissue. In contemporary polygraph practice, plethysmographic methods are relevant mainly to cardiovascular recording, especially peripheral blood flow and pulse amplitude. They provide one channel of autonomic information and must be interpreted with other physiological channels.

Pneumograph: A sensor placed around the chest or abdomen to record respiration patterns.

Polygram: A polygram is the complete recorded display of physiological activity collected during a polygraph chart or examination. It typically includes respiration tracings, cardiovascular activity, electrodermal activity, movement or activity sensors, and sometimes a photoplethysmograph channel. Examiners do not rely on a single response, one question, or one physiological measure. They evaluate patterns across repeated charts, question types, response windows, artefacts, baseline changes, and scoring rules. The polygram is therefore the evidential record of the physiological data, while the professional opinion depends on validated test format, chart quality, and interpretation.

Polygraph: An instrument that records multiple physiological channels simultaneously, commonly respiration, cardiovascular activity, and electrodermal activity. The instrument records physiology; interpretation depends on test design and scoring.

Polygraph Examination: A structured process involving pretest procedures, question review, physiological data collection, chart interpretation, and reporting.

Polygraph Instrument: The hardware and software system used to collect and display physiological data.

Polygraph Suite: The physical environment in which testing occurs, ideally controlled to reduce distractions, interruptions, and environmental artefacts.

Post-Test Interview: Discussion after chart collection and scoring. It may include clarification, review of reactions, or opportunity for explanation or admissions.

Pre-Employment Screening: Credibility assessment used before hiring or appointment, often in security-sensitive occupations. Legal limits vary by jurisdiction.

Predictive Value: Predictive value describes the practical probability that a test classification corresponds to the examinee’s true status in a particular setting. Positive predictive value concerns how often positive or significant outcomes are correct; negative predictive value concerns how often negative or no significant response outcomes are correct. Predictive value depends not only on test accuracy, sensitivity, and specificity, but also on the base rate of the target behaviour in the tested population. This is important in polygraph screening and risk-management contexts because a technically valid method can have different practical meaning in low-prevalence and high-prevalence settings.

Premature Ventricular Contractions (PVCs): Irregular heartbeats originating from the ventricles that appear as characteristic anomalies in cardiovascular polygraph tracings. PVCs may occur spontaneously or be associated with stress, caffeine intake, fatigue, or cardiac conditions, and can interfere with accurate chart interpretation.

Pretest Interview: The phase before physiological data collection in which the examiner explains the process, obtains consent, reviews relevant facts, and formulates or reviews questions.

Probable Lie Comparison Question (PLC): A probable lie comparison question is a comparison question about a broad behavioural or moral issue for which the examinee is expected to be uncertain, concerned, or less than fully confident about a completely truthful answer. The rationale developed historically from comparison question testing: a truthful person may react more strongly to the comparison question, while a deceptive person may react more strongly to the relevant question about the allegation. PLCs are used in validated comparison question techniques when carefully introduced, reviewed, and scored across repeated charts. They differ from directed lie comparison questions, because the examiner does not instruct the examinee to lie; instead, the question relies on probable concern about truthfulness or disclosure.

Psychological Set: The cognitive and emotional focus an examinee brings to a polygraph examination, particularly which questions are perceived as most threatening or significant. In comparison-question formats, differential psychological set between relevant and comparison questions is considered central to producing diagnostically meaningful physiological responses.

Psychophysiological Detection of Deception (PDD): A formal term for polygraph-based methods that infer deception or truthfulness from physiological responses under structured questioning.

Psychophysiology: The scientific study of relationships between psychological processes and physiological responses.

Q

Quality Assurance: Quality assurance is the wider system used to maintain professional standards before, during, and after polygraph testing. It includes examiner training, validated test formats, equipment checks, suitability screening, informed consent, question review, chart quality, scoring rules, report review, data retention, and independent quality control where appropriate. Quality assurance differs from a single quality-control review because it covers the whole service process, not just the final chart analysis. For legal, clinical, corporate, and safeguarding users, quality assurance is central to deciding whether a polygraph opinion is procedurally sound and proportionate to the decision being made.

Quality Control (QC): Review procedures intended to ensure that examinations meet professional, technical, and procedural standards.

Question Formulation: The construction of test questions with precise wording, clear scope, appropriate time frame, and suitability for the test format.

Question Sequence: The ordered presentation of relevant, comparison, neutral, and other questions during a chart.

R

Relevant Question: A relevant question directly addresses the issue under investigation, allegation, or target behaviour. In a specific-issue polygraph examination it is the question category most closely tied to the matter being assessed, such as whether the examinee carried out, concealed, or knew about a defined act. Relevant questions must be clear, behaviourally specific, time-limited where appropriate, and reviewed before testing so the examinee understands their meaning. In a comparison question test, responses to relevant questions are evaluated against responses to comparison questions. A strong response to a relevant question is not interpreted in isolation; it is assessed across charts, channels, and scoring rules.

Relevant/Irrelevant Technique (RIT): The Relevant/Irrelevant Technique is an early polygraph format in which responses to issue-related questions were compared mainly with neutral or irrelevant questions. Historically it was important in the development of polygraph practice and was sometimes called the R/I test. It is no longer generally regarded as a validated diagnostic format for determining deception in the way modern comparison question techniques are used. The main limitation is that irrelevant questions do not provide a psychologically meaningful diagnostic comparison with relevant questions; they are usually expected to be low-salience. Contemporary practice therefore distinguishes RIT from validated comparison question formats that use comparison questions, repeated charts, structured scoring, and quality control.

Reliability: Consistency of measurement or interpretation, such as whether the same data produce the same result across time, instruments, or examiners.

Respiration: Respiration refers to breathing activity recorded during a polygraph examination, usually by pneumograph sensors placed around the chest and abdomen. The resulting traces show changes in breathing rate, depth, rhythm, suppression, and other patterns that may occur after question presentation. Respiration is influenced by voluntary control, emotion, attention, speech, posture, medical conditions, and the balance of sympathetic and parasympathetic activity. For that reason, breathing patterns are not interpreted as standalone indicators. They are evaluated with electrodermal activity, cardiovascular activity, artefact review, and the structure of the question sequence.

Respiration Line: The tracing produced by pneumograph sensors that record respiration patterns.

Response Onset: The point at which a physiological response begins after a question or stimulus.

Response Window: The defined time period after a question during which physiological responses are evaluated.

Risk Assessment: Structured estimation of future risk, often used in corrections, supervision, employment, or security contexts. It may incorporate but should not rely solely on polygraph information.

S

Sacrifice Relevant Question: A question related to the general topic of concern but not usually scored as a primary relevant question. It may be used to absorb initial reactivity.

Salience: The psychological significance or importance of a question or stimulus to an examinee. Polygraph methods depend heavily on assumptions about relative salience.

Salience Theory: A theoretical framework proposing that physiological responses during polygraph testing reflect the relative psychological significance, or salience, of stimuli rather than deception per se. Salience may arise from recognition, emotional relevance, consequence awareness, or novelty.

Screening Examination: An examination used to assess possible risk or undisclosed behaviour when no single known incident may be under investigation.

Sensitivity: The ability of a test to correctly identify deceptive, knowledgeable, or otherwise target-positive individuals.

Sensor: A device that detects a physiological signal, such as skin conductance electrodes, pneumograph tubes, or cardiovascular cuffs.

Sexual History Disclosure Examination (SHDE): A structured polygraph examination used in therapeutic or supervision contexts to assess the completeness of an individual’s disclosed sexual history. SHDEs are typically administered as part of a treatment programme and are distinct from event-specific diagnostic examinations.

Signal Detection Theory / ROC Analysis: A statistical framework used to evaluate the discriminative accuracy of a diagnostic test by plotting sensitivity against the false-positive rate across varying decision thresholds. Receiver operating characteristic (ROC) analysis provides a threshold-independent measure of test performance, expressed as area under the curve (AUC).

Signal Processing: Computational handling of physiological data, including filtering, smoothing, sampling, artefact detection, and feature extraction.

Significant Response (SR): A result indicating that physiological responses to a relevant issue meet criteria for concern under a given scoring system.

Silent Answer Test (SAT): A silent answer test is a procedure in which the examinee listens to each reviewed test question and answers silently rather than speaking aloud. The method may be considered when overt verbal responses are likely to disturb recordings, increase artefacts, create respiratory disruption, or when a specific protocol calls for silent responding after the questions have been fully reviewed. It is not a shortcut around consent, comprehension, or proper question formulation. Silent answering may be appropriate only when the examiner has confirmed that the examinee understands the required answer, can follow the procedure, and remains suitable for testing. The examiner must distinguish genuine question-related physiology from movement, breath holding, counting, or other artefacts.

Specific-Issue Examination: A diagnostic examination focused on a particular event, allegation, or incident.

Specificity: The ability of a test to correctly identify truthful, non-knowledgeable, or target-negative individuals.

Spontaneous Response: A spontaneous response is a physiological change that occurs independently of question presentation or outside the expected response window. It may arise from discomfort, memory, pain, intrusive thoughts, movement, environmental noise, anticipation, or normal autonomic fluctuation. Spontaneous responses are important because they can resemble question-related changes in electrodermal activity, respiration, or cardiovascular activity. During chart interpretation, examiners distinguish spontaneous activity from responses that begin after a test question and fall within the defined scoring window. This protects against over-interpreting random physiology and helps preserve the validity of the polygram.

Spot: A location in the question sequence where a relevant question and associated comparison question are evaluated.

Statement Verification Test: A polygraph format in which the examinee’s own written or verbal statement is used as the basis for test questions, typically to assess whether the account given is consistent with the examinee’s physiological responses. It differs from standard diagnostic formats in its emphasis on verifying a specific narrative.

Stimulus: Any event that can evoke a physiological response, including a test question, sound, image, word, or memory cue.

Stimulus Presentation: The controlled delivery of questions or other stimuli to an examinee during testing.

Sympathetic Nervous System: The sympathetic nervous system is the division of the autonomic nervous system most associated with mobilisation, vigilance, and preparation for action. It influences sweat gland activity, heart rate, blood-vessel tone, blood pressure, and aspects of breathing during threat, effort, novelty, or emotional significance. In polygraph examinations, sympathetic activity is especially relevant to electrodermal activity, because palmar sweat glands are strongly sympathetically innervated. It also contributes to cardiovascular and respiratory change. The sympathetic system does not operate alone; recorded physiology reflects its balance with the parasympathetic nervous system, the examinee’s state, medication, health, and the psychological meaning of each question.

T

Test Data Analysis (TDA): The evaluation of physiological recordings using scoring rules, measurements, or algorithms applied to the polygram.

Test Format: The structured design of a polygraph examination, including the type of questions, sequence, number of charts, and scoring method.

Test Question: A question presented during data collection. Its diagnostic meaning depends on its role as relevant, comparison, neutral, sacrifice relevant, or other category.

Threat-of-Punishment Model: A theoretical explanation suggesting that deceptive individuals may react more strongly to relevant questions because of perceived consequences.

Tonic Activity: Slow-changing background physiological level, such as general skin conductance level.

Tonic vs. Phasic Activity: Tonic activity refers to the slow-changing baseline level of a physiological signal, such as overall skin conductance level. Phasic activity refers to short-duration, stimulus-linked responses superimposed on the tonic level, such as an electrodermal response following a test question. Polygraph scoring methods primarily evaluate phasic responses.

Truth Verification: A term sometimes used for credibility assessment or polygraph testing. It should be used cautiously because polygraph methods estimate response patterns, not truth itself.

U

Utility: Practical value of a test in a particular setting, including accuracy, deterrence, investigative leads, costs, fairness, and consequences of errors.

Utterance Analysis: Evaluation of spoken or written statements for consistency, plausibility, detail, and linguistic patterns. It is separate from instrumented psychophysiology.

V

Validated Technique: A validated technique is a test format, scoring method, or procedure that has been evaluated through empirical research and shown to support the interpretation for which it is used. In polygraph practice, validation is not a general label that applies equally to every question format or operational setting. The examiner must consider whether the technique is appropriate for the referral question, whether the examinee is suitable, whether the scoring rules match the format, and whether the available evidence supports the intended conclusion. This distinction is especially important when comparing modern comparison question techniques with older or non-diagnostic procedures.

Validity: The degree to which a method measures what it claims to measure and supports the interpretation made from its results.

Voice Stress Analysis (VSA): A technology that claims to assess credibility through vocal features associated with stress. It is distinct from polygraph testing and has been scientifically controversial.

W

Within-Subject Comparison: Comparing an examinee’s physiological responses to different question types within the same examination, rather than comparing the examinee to population norms. It is central to comparison question test interpretation.

Z

Zone Comparison Test (ZCT): A comparison-question polygraph format using zones or groups of relevant and comparison questions. It is one of the best-known specific-issue formats.

Related Concepts & Abbreviations

ANS — Autonomic Nervous System

CIT — Concealed Information Test

CQT — Comparison Question Test

DLC — Directed Lie Comparison

DI — Deception Indicated

EDA — Electrodermal Activity

EDR — Electrodermal Response

EEG — Electroencephalography

EMG — Electromyography

fMRI — Functional Magnetic Resonance Imaging

GKT — Guilty Knowledge Test

GSR — Galvanic Skin Response

NDI — No Deception Indicated

NSR — No Significant Response

OSS — Objective Scoring System

PDD — Psychophysiological Detection of Deception

POT — Peak of Tension Test

PPG — Photoplethysmograph

PLC — Probable Lie Comparison

SAT — Silent Answer Test

QC — Quality Control

RIT — Relevant/Irrelevant Technique

SR — Significant Response

TDA — Test Data Analysis

VSA — Voice Stress Analysis

ZCT — Zone Comparison Test

Cautionary Note

Polygraph and related credibility-assessment methods are best understood as structured procedures for recording and interpreting physiological, behavioural, cognitive, or technological indicators under defined conditions. The polygraph does not literally detect lies. Its conclusions depend on examinee suitability, question design, examiner competence, instrumentation, scoring rules, quality control, base rates, and the consequences of false-positive and false-negative errors.