Terms Relating to Lie Detectors Explained – Letter L
Labile
Unstable, inconsistent, or dynamic. PDD tracings that display a high
degree of responsibility or broad amplitude changes are referred to as labile.
Laboratory Research
Scientific investigation in which experimental procedures are designed to
mimic real-world circumstances, but in which there is direct control over the
independent variables.
Lafayette Instrument Company
An American manufacturer of polygraphs, both analog and
computerized, founded by Max Wastl. Headquarters is located in Lafayette,
Indiana.
Lantern
A voice stress device. The Diogenes Company produces the Lantern,
first introduced in 1998. Examiner certification is required. The Lantern
testing format is dissimilar to PDD formats. See voice stress analysis.
Larson, John
One of the first modern researchers in PDD, Dr. Larson first used
continuous recordings of respiratory and vasomotor activity with a test format
using relevant and irrelevant questions. Dr. Larson’s 1932 book, Lying and Its
Detection, provided the best scientific evaluation of PDD up to that time.
Latency
The delay between stimulus presentation and some aspect of the
response. Onset latency relates to the delay between the stimulus presentation
and the beginning of the response, while the peak latency uses the time of the
maximum amplitude of the response as the second point. Latencies of specific
physiologic responses vary. The latency of an electrodermal response, for
example, from stimulus onset is about one to three seconds for the average
person, while hormonal influences on blood pressure require several seconds
more. A significant departure from typical latencies can indicate that a given
response is unrelated to the stimulus, that there are problems in attention for
the subject, or that countermeasures are being engaged. Because of individual
differences, within-subject analyses are warranted.
Law of Initial Values (LIV)
The magnitude of a given physiologic response will be constrained by the
level of arousal present when the response begins. If a response occurs when
arousal is already high, the amplitude of the response measured from onset to
maximum expression will be less than if the same response occurred during a
median level. While there are differing opinions regarding this
psychophysiologic principle, it can certainly be said that all biological systems
do have upper limits in their potential for response, and ceiling effects can
come into play. This is because compensatory systems mediated via the
sympathetic and parasympathetic nervous systems work to limit response
intensities. Additionally, concrete limitations may exist, such as the finite
number of sweat glands establishes the maximum electrodermal response.
Layered Voice Analysis (LVA)
A voice-based technology sold as a means of detecting emotions and
deceit. LVA was developed in Israel by Amir Liberman, owner of Nemesysco,
Ltd, and is sold in the US through Voice Analysis Technologies in Madison,
Wisconsin. The LVA software operates on a laptop computer, and applies
numerous algorithms to the voice signal to assess a wide range of factors. The
company has a very assertive promotional campaign. The company also
attempts to distance this technology from the Computer Voice Stress Analyzer
(CVSA) in part because of reports of poor validity for the CVSA, and the
different approach to analysis of voice data. Research on the LVA has found its
validity to be poor to none. See: Damphousse, Pointon, Upchurch & Moore
(2007); Harnsberger, Hollien, Martin & Hollien (2009); Hollien & Harnsberger
(2006).
Law of Intensity
Within limits, response magnitudes and stimulus intensities share a loglinear
relationship; the stronger the stimulus, the greater the magnitude of the
response. Response magnitudes are used in PDD to infer the type of question
the examinee considers most salient or threatening.
Lens Model
Model for studying the decision rules used by human decision-makers,
first proposed by E. Brunswik in the early 1950s. Conceptually, the model
characterizes the decision process as the selection and evaluation of cues in
the assessing of reality. Which cues are used and how they are weighted are
central to this model. The term lens model springs from the sense that subjects
view reality through the lens of these cues. This approach has been applied in
the study of PDD decisions at the University of Utah. The lens model is useful
to assess the diagnosticity of physiological responses, in identifying how
examiners use the physiological information, and to determine the combination
and weights of the cues that will maximize decision accuracy. See: Kircher &
Raskin (1983); Kircher, J.C., Raskin, D.C., Honts, C.R., & Horowitz, S.W.
(1995).
Law Enforcement Pre-Employment Test (LEPET)
A form of the Air Force Modified General Question Test (AFMGQT) which
uses specific relevant questions, and is used for police candidate screening.
lie detector
A common but inaccurate term for the polygraph.
Lie Question
Rarely used terminology for probable lie comparison question.
Likelihood Ratio
The Likelihood Ratio (LR) provides an index of how much a test result will
change the probability or odds of having a condition after a known or assumed
prior incidence rate (base rate). In the case of polygraph testing, the condition
of interest is involvement in the issue under investigation. The LR+ tells us how
much more likely it is that a person is lying than not, after failing a polygraph
test, compared with the likelihood before he or she sat in the chair and
completed the test. If a person produces a truthful test result, the LR- tells us
how much more likely are a person is to be telling the truth than before the
test. LRs may also be used to compare the efficacy of two or more scoring and
decision models, for a given or assumed base rate. The advantage of the LR,
compared with traditional Bayesian metrics such as positive predictive value
(PPV) and negative predictive value (NPV) is that the LR is inclusive of
inconclusive results, and will provide information that more accurately
generalizes to field settings.
Limestone Technologies
A Canadian manufacturer of computerized polygraph instruments.
Headquartered in Odessa, Ontario, Canada.
Lombroso, Cesare
Italian physician biologist who first employed instrumentation in an
effort to detect deception in suspects in live criminal investigations. He
reported in 1885 in the second edition of his book, L’Homme Criminel the use of
the “hydrosphygmograph,” a mechanical arrangement invented for medical
purposes, to detect blood pressure changes during interrogation. One of his
students, Angelo Mosso, also went on to perform instrumental deception
detection experiments.
Loyalty Examination
See Counterintelligence-Scope Polygraph.
Luria, Aleksandr
Russian researcher and originator of the conflict theory, one of the
theories proffered to explain the psychophysiological mechanisms underlying
PDD. Luria did deception detection experiments with a tremograph. See: Luria
(1930); Runkel (1936).
Lykken, David T.
Psychologist and ardent critic of the CQT who passed away in 2006. Dr.
Lykken produced numerous writings for the scientific and general press,
including a book, A Tremor in the Blood, in which he argued strongly that the
CQT is fatally flawed, that it resulted in wrongful criminal convictions, and it
was vulnerable to countermeasures by the guilty. Dr. Lykken did not publish
any research of his own on the CQT, but used anecdotal histories and
interpretations of other research to form his arguments. Lykken endorsed the
Guilty Knowledge Test (GKT, now known as the Concealed Information Test),
an alternate PDD testing format. The GKT has not been widely used outside of
Japan. See: Lykken (1998).
Lykken scoring
System of scoring electrodermal responses in the Concealed Information
Test (formerly the Guilty Knowledge Test) and establishing the threshold for
decisions. The Lykken scoring system compares the responses of the critical
test items in a rank order method against those of the neutral items. One
variant uses averaged ranks. See: Lykken (1998).
