Encyclopedia of Psychology and Law

See alsoPolice Decision Making; Police Psychology; Police

Selection; Police Training and Evaluation

Further Readings

Geller, W. A., & Toch, H. (Eds.). (1995). And justice for all:

Understanding and controlling police abuse of force.

Washington, DC: Police Executive Research Forum.

Scrivner, E. M. (1994). Controlling police use of excessive

force: The role of the police psychologist.Washington,

DC: U.S. Department of Justice.

Twersky-Glasner, A. (2005). Police personality: What is it

and why are they like that? Journal of Police and

Criminal Psychology, 20(1), 56–67.

U.S. Department of Justice. (1999). Use of force by police:

Overview of national and local data.Washington, DC:

Author.

Worden, R. E. (1995). Police officers’ belief systems:

A framework for analysis. American Journal of

Police, 14(1), 49–81.

POLYGRAPH AND

POLYGRAPHTECHNIQUES

Polygraph is a general term that refers to the use of

autonomic physiological measures to make assess-

ments about a person’s credibility. Polygraph tech-

niques find wide application in the criminal justice

and national security systems of many countries, and

their use is growing worldwide. There are two major

families of polygraph techniques. Knowledge approaches

look for responses that indicate knowledge possessed

by a person attempting deception. Deception approaches

assess credibility by examining a person’s response to

accusatory questions that directly address the issues

under investigation. Both approaches have strengths

and weaknesses, and both are the subject of contro-

versy in the scientific literature. This entry describes

the approaches, their strengths and weaknesses, their

application in practice, and the controversy concern-

ing them.

History

The desire to use physiological responses as indices of

truth or deception is a very old one. The lore of many

cultures contains stories of trials by ordeal that have

some basis in autonomic physiology. For example,

many Asian cultures have legends of placing dry rice

in the mouth of the accused. If the accused was able to

spit out the rice it was assumed that he or she was not

nervous and that he or she was truthful. If, however,

the mouth was dry and the rice stuck, it was assumed

that he or she was deceptive. Scientific research on the

topic also has a long history, with reports of attempts

to detect deception with physiological measures going

back to the first psychologists and the end of the 19th

century. However, this approach has one basic diffi-

culty: To date, no specific physiological response, or

pattern of physiological responses, has been identified

that is uniquely identified with truth or deception.

Therefore, efforts to use physiological measures have

to rely on techniques of stimulus control and inference

to assess credibility. During much of the 20th century,

there was little interest in credibility assessment by

scientific psychology, and the application of the poly-

graph for that purpose grew as a profession in law

enforcement and national security agencies, primarily

in the United States. A modern era of research began

in the early 1970s in the laboratory of David Raskin at

the University of Utah. In the past decade, applica-

tions of the polygraph and research on physiological

deception detection have grown rapidly worldwide.

Standard Physiological Measures

in Modern Polygraphs

Several companies around the world manufacture

polygraph instruments for use in the field as credibil-

ity assessment devices. A typical field polygraph

instrument takes measures of respiration, blood pres-

sure, and the electrodermal response. Respiration is

measured from stretch sensors placed over the upper

chest and abdomen. A continuous measure of relative

blood pressure is monitored from an inflated cuff on

the upper arm. Electrodermal activity (galvanic skin

response) is recorded from the palmar surface of the

hand. Some polygraph instruments in current field

use also measure the peripheral vasomotor response

(blood flow near the surface of the skin), usually from

the thumb. Most of the instruments in current field use

are digital computer-based systems. Currently, there is

little controversy concerning the ability of field poly-

graph instruments to adequately measure the physio-

logical values they claim to measure.

During the past decade, the U.S. government has

invested in a number of research projects in an

effort to find new dependent physiological measures

for credibility assessment. Electroencephalograms,

neural imaging, thermal imaging, eye movement, and

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