Terms Relating to Lie Detectors Explained – Letter S
Sacrifice Relevant Question
Question introduced by Cleve Backster and used in most forms of the
ZCT as well as other types of tests. The sacrifice relevant is a question that
asks the examinee if he intends to answer truthfully to every question related
to the relevant issue. Its putative role is to dissipate the responses of innocent
persons who frequently react to the first relevant question. The sacrifice
relevant question is not numerically scored. Its value has been disputed in
independent research. See: Capps, (1991); Horvath (1994).
The state or quality of standing out relative to other stimuli. It is a vital
unconscious process that helps an organism efficiently use limited attentional
resources, and facilitates survival. In learning theory, salience refers to the
strength of the relationship between a response and a reinforcer or outcome.
In general, as the intensity of the outcome increases, the intensity of the
response increases. In the framework of PDD testing, the intensity of arousal
will increase commensurate with perceived salience of stimuli as they relate to
the subject’s goals, standards and attitudes.
Scale of data
Data come in four levels. Nominal data are those that are name or
designations only. Social Security Numbers are nominal data. They have
meaning, but cannot be mathematically manipulated beyond being tabulated.
The next level is ordinal data. Ordinal data allow meaningful interpretations of
the order, but not the distances between the measurements. For example,
scores in an Olympic event of 8, 9, and 10 mean that 10 is better than 9, which
is better than 8. They do not mean the athlete who received the 9 was 90% as
good as the one who received the 10, nor the one who received the 8 only 80%
as good. There are not equal intervals between the units. The next level,
interval data, does have this property. Both Fahrenheit and Celsius
temperature scales are interval. The units are equally spaced. In order to
satisfy the requirements for the last scale of data, ratio, there must be a true
zero. The zero point in Fahrenheit and Celsius scales is not a true zero in the
sense of an absolute lack of heat, though the Kelvin temperature scale has as
its zero point (absolute zero), making it a ratio scale. Other ratio scales include
measures such as distance, weight, and speed. The scale of data will set the
type of statistical test that can be performed. For example, polygraph decisions
are nominal, either deceptive, truthful, or inconclusive (though if these
outcomes are based on scores, some have argued that they are ordinal scale).
Precise measurements of response amplitudes, latency, and recovery time are
ratio data and allow sophisticated statistical treatments and automated
algorithms that render probability statements.
Device built by Angelo Mosso (1896) to record respiratory and
cardiovascular responses to fear. It consisted of a fulcrum base onto which
was placed a platform for his subject to lie upon. Using counterweights to
bring the platform into balance, the device recorded on a smoked drum the
changing balance of the platform that accompanied the undulations of
breathing and the shifting concentration of blood in the body.
A polygraph examination conducted in the absence of a reported issue or
allegation to investigate whether an examinee has withheld information
regarding engagement in behaviors encompassed by the relevant questions
that cover specified periods of time. Screening examinations may be designed
to investigate both multiple and single types of behavior. The strength of
screening examinations is in their utility to develop significant information that
is most often not obtainable from any other source. Its weakness is that it is
not as powerful an examination as is the specific issue test in terms of validity
and reliability. See: Krapohl & Stern (2003).
Searching (or Probing) Peak of Tension (SPOT)
Peak of Tension test in which the testing examiner does not know the
critical item, and it is used to determine information concealed by a guilty
examinee. Applications of this format include determining the location of
stolen goods or the bodies of murder victims, the amount of cash stolen, or the
name of an accomplice. In practice, SPOT tests are not often used alone, but
rather are a post hoc procedure once deception has been established with
comparison question or relevant/irrelevant tests. Called a Type B by Keeler
graduates, and a Probing Peak of Tension by Backster. There is no published
research to support the SPOT.
One of four tracks in the Quadri-Track Zone Comparison Technique,
which includes the primary, outside, and inside tracks. The secondary track
contains a relevant question, and a non-current exclusive probable-lie
comparison question against which the relevant question is compared. See:
Feature included with the electronic cardiograph of the Lafayette
polygraph in 1979 that allowed for manual setting of the high-pass filter via the
“response control” knob, and low-pass filter with the “notch control” knob.
Ability of a test to detect specific features at all levels of magnitude or
prevalence. Mathematically, sensitivity can be calculated by dividing the
number of true positives by the sum of true positives and false negatives. In
PDD testing this term is used to describe how well a test identifies a person
engaging in deception to the issue under investigation. It is a measure of “true
positive” results generally expressed as a decimal (for example a sensitivity of
0.90 would indicate a particular test identified 90% of the liars.)
See afferent nerves.
Also called two-stage rules, Senter Rules are used for single-issue
testing. The Senter Rules begin by basing a decision on the total score for the
case. If a decision would be inconclusive from the total score rule, the second
stage is used in which the spot scores are considered. The net effect of the
Senter Rules is to decrease the proportion of inconclusive results while not
affecting the proportion of correct decisions. See: Senter & Dollins (2002).
Serrated Respiration Pattern
Respiration tracing that also includes the examinees pulse due to the
proximity of the respiration sensors to the heart. In some schools the sudden
onset or disappearance of the serrated pattern is taught to be noteworthy for
diagnosing deception, while in others it is an artifact. Empirical research is
Sexual History Examination
A form of Post-Conviction Sex Offender Testing (PCSOT) which entails an
in-depth look at the entire life cycle of an offender and his or her sexual
behaviors up to the date of criminal conviction. Sometimes referred to as a
disclosure examination. See: Cooley-Towel, Pasini-Hill, & Patrick (2000);
Dutton, (2000); English, Pullen, & Jones (1996); Heil, Ahlmeyer, McCullar, &
Sexual Offender Monitoring
Use of the polygraph to verify that sexual offenders on parole or
probation are in compliance with the conditions of their release from
Signal Detection Theory (SDT)
One approach used to quantify the capacity of a test or method to
discriminate between signal and noise. Its greatest value has been in the field
of diagnostics, including polygraphy. Using SDT, optimal cutting scores can be
calculated that correspond with the costs and benefits of errors. See Swets
(1995) and Green & Swets (1988).
The perceived significance of a stimulus to an organism, and is related to
the concept of salience. Significant stimuli (those with signal value) can elicit
physiological responses, and greater signal value corresponds with greater
response magnitude. External significance is assigned to a stimulus when it
appears to differ from others based on appearance. In polygraphy, this could
be when a test question is much longer or is read in a louder tone of voice.
Internal significance is assigned to a stimulus due to its meaning. An objective
of a CQT examination is to make the external significance of relevant and
comparison questions appear equal, and for their internal significance to vary.
An innocent examinee would be expected to find higher internal significance in
the comparison questions, whereas the relevant questions would hold higher
internal significance for the deceptive. See Handler & Honts (2007).
Significant Physiological Responses (SPR or SR)
Accepted verbiage in the US polygraph screening programs, and is
equivalent to Deception Indicated in specific-issue tests. This alternate
language comes from an acceptance that screening examinations do not
produce the high validity of specific-issue tests and, therefore, the results are
better reported as the presence of physiologic arousals rather than inferring
deceptive intent on the part of the examinee.
Silent Answer Test (SAT)
Specialized procedure in which the examinee is directed to answer to
himself instead of making a verbal response. The use of the SAT is prescribed
by some PDD experts to help avoid distortions to the pneumograph tracings
attributable to speech disorders, or to uncover certain countermeasures. To
ensure examinees are attending to the content of the test questions, some PDD
examiners instruct the examinees to indicate their responses by slightly
nodding or shaking their heads. When the SAT is used with head movements,
it is called an SAT Nod. See: Horvath (1972).
An event specific or a screening polygraph examination conducted in
response to a single known or alleged incident for which the examinee is
suspected of involvement or to investigate the examinee’s possible involvement
in a single behavioral concern for which there is no known or alleged incident.
When used in screening, a single-issue examination typically follows a multiple
or mixed issue screening examination in the successive hurdles model.
Situational Comparison Question
Question used for comparison in the Modified Relevant/Irrelevant (MRI)
technique that elicits physiologic responses for comparison against those of the
relevant question. Situational comparison questions are a departure from their
conventional counterparts in that the examinee is not faced with a question to
which he is deceiving or uncertain. Rather, this type of comparison question
addresses how the examinee is linked to the crime, such as having legitimate
access to money that later disappeared or being the last person to see a murder
victim alive. The truthful examinee is allowed to respond to a question related
to the crime that is not a relevant question, but one for which the examinee
may feel uncomfortable because it put him on the list of suspects.
Skin Conductance (SC)
Broad term for two exosomatic electrodermal phenomena, skin
conductance level and skin conductance response. See Handler et al (2010).
Skin Conductance Level (SCL)
Basal conductance of the skin. SCL is the tonic measure of SC.
Skin Conductance Response (SCR)
A change in the electrical conductance of the skin elicited by a stimulus.
SCR is a phasic response.
Skin Potential (SP)
General term for the endosomatic electrodermal properties of the skin.
Though not currently used in PDD, preliminary laboratory research has shown
SP to be as diagnostic as the exosomatic measures. See Handler (2010);
Kircher & Raskin (1988).
Skin Potential Level (SPL)
Basal electropotential of the skin. SPL is the tonic level.
Skin Potential Response (SPR):
An endosomatically produced electrodermal response, and of interest as
a parameter in PDD. It is frequently measured between the forearm and the
hypothenar eminence. (Special note: In the Japanese PDD literature the term
skin potential was sometimes reported in the English translation when skin
resistance was actually used. Caution is advised.)
Skin Resistance (SR)
General term for the phenomena of skin resistance level and skin
resistance response. SR is recorded exosomatically and was the primary
means of detecting electrodermal activity throughout much of PDD history
until the introduction of computerized instrumentation with SC. See Handler
Skin Resistance Level (SRL)
Tonic level of electrical resistance of the skin.
Skin Resistance Response (SRR)
Phasic response measured by electrical resistance of the skin.
Abbreviation for Suspect, Know, You. A standardized Zone Comparison
Technique test format that is included under the umbrella of the Backster Zone
Comparison Technique. In a structured format, the S-K-Y allows for
broadening of the scope of a single-issue test to include questions relating to
secondary involvement and knowledge. Along with the questions addressing
direct involvement, such as “Did you shoot Henry Jones?”, other moderate
strength relevant questions could be used, such as “Do you know for sure who
shot Henry Jones?” or tertiary issues such as those that place the examinee at
the crime scene, address his alibi, or tests prior knowledge. As with the
exploratory test, the mixing of different relevant questions allows for only
vertical scoring when applying the 7-position scoring method.
Smoked Drum Recording
An antecedent to the continuous strip chart. A cylinder was wrapped
with paper that had been covered with soot produced by a yellow flame. The
paper-covered cylinder was rotated against a stylus at a selected rate to
produce a graphic recording of physiologic and other events. The recording was
preserved by a coat of shellac varnish.
All of the involuntary nonstriated muscles involved in autonomic
functions, except the heart. Smooth muscles are located in the bladder,
intestines, and blood vessels. Also called unstriated muscles.
Spearman Rank Correlation
Statistical technique for testing the correlation between ordinal-level
data (see scale of data). This method can be used to assess interrater reliability
for rankings to questions assigned by different evaluators.
A term most used in the scientific literature to describe the selectivity of
a test. It is the proportion of true negatives a test can produce.
Mathematically, specificity is the number of true negatives divided by the sum
of true negatives and false positives. The specificity of a test will determine its
efficiency. If a PDD test can detect deception 100% of the time, but has a high
false positive rate, it does not have good specificity and would have lower
validity. Specificity and sensitivity are dimensions that characterize the validity
of a test.
Specific Issue Polygraph Examination
A single-issue PDD examination, almost always administered in
conjunction with a criminal investigation, and usually addresses a single issue.
Sometimes called a specific by PDD practitioners to differentiate from
preemployment or periodic testing.
Specific Physiological Response (SPR)
Accepted verbiage in the Federal Government for polygraph screening
examination outcomes equivalent to Deception Indicated in single-issue tests.
The alternate language comes from an acceptance that screening examinations
do not produce the high validity of single-issue tests, and, therefore, the results
are better reported as the presence of physiologic arousals rather than inferring
deceptive intent on the part of the examinee. See Deception Indicated.
Specific Point Countermeasures
Attempts to defeat a polygraph examination by the self-induction of
physiological responses to particular questions. Typical strategies include
targeting comparison questions with manipulated respiration, self-inflicted
pain, covert tensing of muscles, and sometimes mental imagery. See: Honts &
An instrument for graphically recording arterial pulse and blood
pressure. A more precise term for the cardiograph channel in PDD.
Aneroid gauge used to register air pressure in the polygraph
cardiovascular sensor system. Changes in a closed sphygmomanometer
system signal changes in relative blood volume at the recording site on the
Efforts used to interfere with PDD testing for which the examinee has
not prepared in advance. These types of countermeasures have been shown in
laboratory studies to be ineffective. See: Honts & Amato (2002).
Any reaction not associated with an identifiable stimulus. A high
incidence of spontaneous responses can be used as an index of general
arousal. Also known as a non-specific response.
A permanently assigned location of a relevant question in a CQT
The numerical evaluation of a relevant question by comparing it to a
comparison question no further than one position to the left or right of that
spot location. A “spot” represents the location of a relevant question in a
question series; the physiological data at the relevant question (spot) are
compared with those of an adjacent comparison question.
An as-yet unproven concept wherein an examinee has a propensity to
physiologically respond to a question by virtue of its position in a sequence of
questions rather than the content of the question. Some techniques rotate the
serial position of relevant questions because of the concern of spot responses.
Computer polygraph manufactured in the Peoples Republic of China.
The Chinese used “SPS” to stand for “Super Polygraph System” in English.
Resistant to change. Opposed to labile.
Expression for a pattern of respiration in which the tops of the
inhalation cycles move higher or lower with each subsequent cycle, forming the
characteristic “staircase” appearance. The increase in respiratory amplitude is
called an ascending suppression, while the opposite pattern is a descending
suppression. These patterns are considered diagnostic features in some
Statistical term for a standardized unit of dispersion of scores. When
scores are clustered closely together, the standard deviation is small, whereas a
wide spread would have a larger standard deviation. Mathematically, the
standard deviation is the square root of the variance. Conceptually, the
standard deviation is the square root of the average squared deviation from the
A measurement of a sample. There are several ways to measure
samples, including the mean, standard deviation, and variance. When these
measurements are taken from an entire population they are referred to as
Phrase to describe an experimental result that is unlikely to have
occurred by chance. In PDD, conventional thresholds of statistical significance
are 0.05 and 0.01.
See event marker.
Procedure used by many PDD examiners before or between the regular
tests. One of its purposes is to demonstrate to examinees that the polygraph
works with them, and in doing so, reassure the innocent while heightening the
guilty person’s concern about the relevant questions. Other purposes include
allowing the testing examiner set the gains properly, to verify that the sensors
are properly placed and functioning correctly, and to acquaint the examinee
with the examination procedures. Virtually all stimulation tests use a question
set of very similar items in which is embedded a single item that the subject is
directed to lie about. There are several types of stimulation tests. The more
common are the card test, known numbers acquaintance test, blind numbers
test, control test, and true blue control test. Tests of this nature were used by
early polygraph examiners for the purpose of comparing the reactions on the
stimulation test with those from the relevant questions on the R/I test.
Stimulation tests were sometimes referred to in general as stim tests.
Stimulus Irrelevant Question
Question used in some RI screening formats to determine whether the
examinee is capable of responding physiologically and is employed when
significant responses have not occurred to relevant questions. It may take the
form of a simple mathematics question, a regular irrelevant question read
incorrectly, or other types.
C.H. Stoelting of Chicago, Illinois. An American manufacturer of analog
and computer polygraphs.
Straight-Through Test (ST)
A Reid polygraph test with a standard sequence of questions, usually
conducted before other sequences are used. In contrast to Reid’s Mixed
Question Test (MQT). See Reid & Inbau (1977).
Generally, any sensor for registering changes occurring in the
dimensions of a solid or body. In PDD, respiration is sometimes recorded with
pneumatic strain gauges placed about the thorax or abdomen, or both.
Includes all skeletal muscles that perform voluntary contractions, as
well as cardiac muscle responsible for the involuntary muscular activity of the
heart. Also called striped muscles.
Stroke Volume (SV)
Measure of the amount of blood ejected from the heart in each beat.
Strong Relevant Question
PDD question that goes directly to the heart of the matter under
investigation, as compared to knowledge or complicity questions.
Subjective lie/truth question
In the Positive Control Technique, examinees are presented with each
question two times in succession as a set. Examinees are instructed to admit
committing the offense under investigation after the first presentation of each
question, and deny it after the second reading of the same question. The first
time the question is read, it is called the subjective lie question, while the
second presentation is called the subjective truth question. See: Driscoll,
Honts & Jones (1987); Gordon & Cochetti (1982); Howland (1981); Reali (1978).
Successive Hurdles Approach
In screening, it is a method to maximize accuracy when base rates are
unbalanced or very low. For example, an agency may have a vital interest in
uncovering past activities of applicants before hiring them, behaviors that are
very difficult to investigate effectively with any method except the polygraph.
The agency may choose to conduct a single-issue polygraph for each of the
subject areas. If there only two or three areas, this approach may be effective,
however, if the number is greater, it would tax the agency’s resources in terms
of polygraph examiners and processing time. Alternatively, in the successive
hurdles approach, each applicant would begin with a multiple-issue
examination. Though multiple-issue examinations have a higher false positive
rate (incorrect decision of deception) than do single-issue examinations, they
have a very small rate of false negatives. If no significant responses were noted
during the multiple-issue examination, the polygraph session would be over.
However, if there were significant responses during the multiple-issue
examination, the polygraph session would continue. Next, a single-issue
examination would be administered in the area the examiner observed
significant responses during the multiple-issue examination. The single-issue
examination has much better discrimination power, and would help to
elucidate physiological arousal more specifically. In this way, the more
resource-intensive single-issue examinations would be reserved for the smaller
subset of applicants who did not pass the multiple-issue examination. The net
effect of the two-stage screening process is a better accuracy without increased
resources. See: Krapohl & Stern (2003); Meehl & Rosen (1955).
Early researcher of deception testing who used an electrodermal device
and a structured test series to verify truthfulness and deception. Summers
reported the use of what he called emotional standards, which are similar in
many respects to present day comparison questions. See: Summers (1939).
Concept forwarded by Cleve Backster which holds that there will be a
suppression of general reactivity to relevant and comparison questions when
the examinee is more concerned that the examiner will ask an unreviewed
question about another issue outside the scope of the current examination
questions. Though once widely accepted, the available evidence suggests that
the effect is negligible or nonexistent. See: Backster, (1964); Capps, Knill, &
Evans (1993); Honts, Amato, & Gordon (2000); Krapohl (2001); Matte (2001).
One respiratory response pattern indicative of orienting and arousal,
characterized by breathing that is shallower and slower than tracing average.
The PDD respiration tracing of suppression will manifest in a decrease in
amplitude, a slower rate, or a temporary increase in the baseline of the
waveform. Suppression has been found to be a reliable indicator of salience
since the first part of this century, and it is a primary reaction criterion for
Surreptitious Respiration Tracing
Recording of the respiration cycles of an examinee during a portion of
the polygraph session when the examinee is not aware of it. Frequently,
though not always, this is done just before or immediately after a test is
conducted. Surreptitious respiration recordings are useful to help assess
whether an examinee has altered his breathing during testing. Differences can
indicate countermeasures. The motives of the examinee may be discerned with
a Yes Test or other specialized techniques that help assess the examinee’s level
of cooperation. A related but less precise method is the counting of the
examinee’s respiration cycles during the pretest interview while he is otherwise
occupied, such as during his reading of the consent form or while the examiner
is readjusting the electrodermal sensors.
Suspicion-Knowledge-Guilt Test (SKG)
Technique used to tentatively identify suspects who may have had direct
or indirect participation in the crime under investigation, or concealed
knowledge relating to the crime. It is used before a CQT as a screening tool
when there are multiple suspects and possibly different levels of criminal
involvement. The SKG also includes some of the comparison questions used in
the Quadri-Track Zone Comparison Technique. Developed by James Matte.
See: Matte (1996).
Sympathetic Nervous System
Thoracolumbar portion of the autonomic nervous system centrally
involved in responding to arousing stimuli. Most sympathetic nerves are
adrenergic and prepare the body to respond to increased demands.
Sympathetic nervous activation increases blood flow from the heart, triggers
the release of glucose and epinephrine, dilates the pupils, and initiates other
responses in preparation for action. Unlike most of the sympathetic nervous
system, sympathetic nerves to the eccrine sweat glands are cholinergic.
A system of 21 to 22 pairs of ganglia located in the thoracic and
abdominal areas and is the site of synapse between pre- and postganglionic
sympathetic neurons. There is one notable exception—there is no
postganglionic sympathetic nerve to adrenal medulla.
Drugs that mimic the action of sympathetic postganglionic nerves or
A question type developed by Cleve Backster that was once thought to
identify whether an examinee is fearful the examiner will ask an unreviewed
question about an outside issue. In this construct, the examinee’s mistrust
would dampen his responses to other test questions, and the symptomatic
question could determine whether the lack of responsivity was attributable to
the outside issue. Symptomatic questions are widely used, though the trend in
the research finds they have no meaningful effect. See: Backster (2001a);
Honts, Amato, & Gordon (2000); Krapohl & Ryan (2001); Matte (2001).
Junction between neurons. Site where the nervous impulse is
transferred from one neuron to another. Neurotransmitters reside in vesicles of
one neuron and are released by the axon into the synapse to chemically induce
the next neuron or organ to respond.
Contraction of the cardiac muscles. Left ventricular systole results in
movement of blood out of the heart into the aorta. Systoles can be subdivided
into three primary components: preejection, ejection, and relaxation periods.
The left ventricular systolic peak is represented on a conventional polygraph as
the highest vertical point in the pulse wave of the cardiovascular tracing.
Systolic Blood Pressure
Force exerted by blood against the wall of the arteries at the height of
ventricular contraction. Also called maximum pressure and expressed in
millimeters of mercury (mmHg).