The Polygraph Technique

Vocabulary flashcards covering key terms, concepts, and details from the polygraph lecture notes.

Polygraph examination

An investigative aid used to obtain information about deception by measuring physiological responses; its ultimate objective is to obtain the subject’s admission or confession.

Admission

A statement of fact by the accused that does not necessarily acknowledge guilt in the offense.

Confession

A voluntary declaration stating that the person has committed or participated in the crime.

Tripod Foundations of Polygraph Technique

Three basic premises underlying the polygraph: mechanical, physiological, and psychological.

Mechanical Basic Premise

The polygraph machine can mechanically produce graphical records containing reliable information about physiological changes.

Physiological Basic Premise

Physiological changes occur after stimulation of specific nervous system components and can be reliably diagnosed.

Psychological Basic Premise

Concealment of deception involves involuntary mental/emotional processes that can be diagnosed via stimulation of the nervous system.

Blood Pressure

A physiological measure that increases with deception; part of the physiological signals analyzed in polygraph testing.

Heartbeat Frequency

Heart rate; often increases during deception and is recorded on the polygraph.

Systolic

The high-pressure phase of arterial blood flow measured on the polygraph.

Diastolic

The low-pressure phase of arterial blood flow measured on the polygraph.

Ink Curves

Graphs on moving paper showing beat frequency and systolic/diastolic pressures used to interpret physiological responses.

Pulse

The rhythmic beating of the heart recorded as part of the polygraph data.

Sympathetic Set

Nerve system that accelerates the heartbeat during arousal or deception.

Cranial Autonomic System

Nerves that can retard or influence the heartbeat during the test.

Adrenaline

A hormone that increases heartbeat frequency and arousal.

Breathing

Respiration used in polygraph evaluation; comprises inspiration and expiration.

Inspiration

Inhalation phase of breathing.

Expiration

Exhalation phase of breathing.

Electro-dermal Response

Electrical changes in skin resistance elicited by stimuli; used as a deception indicator.

Normal Response

Typical, non-deceptive changes in electro-dermal activity.

Abnormal Response

Deviations in electro-dermal activity suggesting potential deception; includes specific abnormal patterns.

Machine Fright Response

An abnormal electro-dermal response that appears on early questions but not later in the test.

Physical Movement Response

Muscular activity causing physiological changes that appear as electro-dermal responses.

Outside Interference Response

Responses caused by external noises or irrelevant stimuli (e.g., coughs, sneezes) at the testing location.

Mental Tie-up Response

Also called a guilt complex; a mental state contributing to deceptive responses.

Guilt Complex

A mental tie-up or emotional state associated with deception.

Deception Response

Abnormal physiological responses resulting from telling a lie.

Polygraph Accuracy

Current research reports 95%–98% accuracy for single-issue polygraph tests when properly administered by a competent examiner.

Factors affecting the accuracy

Elements influencing results: the instrument, subject condition, examination room condition, and examiner’s qualification/skill.

The instrument

The polygraph equipment itself; quality and calibration affect accuracy.

Condition of the subject

The physical/mental state of the person being tested affects outcomes.

Condition of the examination room

Environmental factors that can influence test results.

Qualification and skills of the examiner

The examiner’s competence directly impacts interpretation and accuracy.

15% errors of lie detection

Common sources of error include nervousness, physiological/mental abnormalities, unresponsiveness, attempts to beat the machine, and unobserved muscular pressure.

Nervousness

Anxiety or tension in truthful individuals that can produce deceptive-appearing responses.

Physiological Abnormalities

Unusual blood pressure or heart conditions that distort readings.

Mental Abnormalities

Cognitive or developmental differences (e.g., feeblemindedness) that affect results.

Unresponsiveness

Lack of fear or concern in a guilty subject can blunt expected responses.

Beat the machine

Attempt to defeat the test through controlled breathing or muscular actions.

Unobserved application of muscular pressure

Hidden physical actions that can create misleading blood pressure indications.

Limitations of the Polygraph Technique

An investigative aid, not a substitute for investigation; a scientific diagnostic tool, not a definitive lie detector.

Not a substitute for investigation

Polygraph results should not replace thorough investigative work.

Not a lie detector

Polygraphs measure physiological responses, not truth; they do not determine guilt.

Does not determine facts

The test records responses to questions the subject knows to be true, not absolute facts.

As accurate as the examiner

Accuracy depends on the examiner’s competence and judgment.

The test will not be given until enough facts

Tests are only conducted when sufficient prior information and questions are prepared.

Voluntary consent

The subject must willingly agree to take the polygraph test.

No indication of guilt if refused

Refusal to take the test should not be used to infer guilt.

Test explained to the subject

Accused individuals must understand the test and its procedures before proceeding.

No mental/physical evaluation

Polygraphs are not intended to assess mental or physical fitness; they evaluate deception-related responses.

No examination on unfit subject

Subjects who are unfit cannot be tested.

Barriers to the Polygraph Examination

Obstacles or limitations that can hinder conducting a polygraph test.

Pathological Liar

A person who habitually lies, making deception analysis more challenging.

Mental Cases

Individuals with significant mental conditions that complicate polygraph interpretation.