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.

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.

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 change, 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.

B

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.

Cardio Activity: Cardiovascular information recorded during a polygraph examination, commonly including pulse amplitude, relative blood pressure, and heart rate changes.

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

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 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 question designed to elicit a physiological response that can be compared with responses to relevant questions. Comparison questions may be probable-lie or directed-lie questions.

Comparison Question Test (CQT): A common polygraph format in which reactions to relevant questions are compared with reactions to 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.

D

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

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: A comparison question in which the examinee is instructed to answer falsely. The directed lie provides a controlled comparison stimulus.

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.

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

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: The application of psychophysiological principles, methods, and measurements to legal, investigative, or forensic questions.

Frye / Daubert Standards (Admissibility of Expert Evidence): US legal tests governing the admissibility of expert and scientific evidence. The Frye standard (1923) requires general acceptance within the relevant scientific community; Daubert v. Merrell Dow Pharmaceuticals (1993) applies a broader reliability analysis including testability, peer review, error rates, and standards. While Frye/Daubert apply in US federal and state courts, UK courts assess expert evidence under the common-law test of reliability and relevance, as articulated in R v. Dlugosz [2013] EWCA Crim 2, the Criminal Procedure Rules Part 33, and the duty of an expert witness under the Civil Procedure Rules.

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

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.

Informed Consent: The examinee’s voluntary agreement to participate after being informed about the nature, purpose, limits, and possible consequences of the examination.

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.

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

Multi-Facet Screening: Screening that covers multiple possible issue areas in one examination, such as security, criminal history, drug use, or policy violations.

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.

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.

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.

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

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.

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: A comparison question about a broad behaviour or moral issue for which the examinee is expected to be concerned 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 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 question directly addressing the issue under investigation, allegation, or target behaviour.

Relevant/Irrelevant Test (R/I Test): A format comparing responses to relevant questions with responses to irrelevant or neutral questions. It is generally considered less robust than comparison-question formats for many diagnostic uses.

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

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

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.

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 branch of the autonomic nervous system involved in arousal, threat response, and activation of sweat glands, heart, and vascular systems.

T

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

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

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.

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

QC — Quality Control

R/I — Relevant/Irrelevant

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.