Encyclopedia of Psychology and Law

overall accuracy rate of about 54%. The different decep-

tion detection measures are highly inter-correlated.

A deception detection accuracy (sometimes referred

to as lie/truth discrimination) of 54% is the typical

result over a variety of receiver samples, sender sam-

ples, deception media, types of lies, and contexts.

Conceivably, there might be certain conditions under

which judges will show different accuracy rates. To

evaluate these possibilities, an inspection of various

subsets of the research literature on deception judg-

ments is needed. In the following section, a number of

factors that may moderate deception detection accu-

racy are discussed.

Deception Medium

Lies and truths can be evaluated over different media. It

is of interest to compare detection rates for lies that can

be seen, heard, or read. For example, the video medium

might encourage the use of a liar stereotype. Having

access to verbal content only may give the receiver the

chance to analyze the messages more thoroughly.

Results have shown that lie/truth discrimination

accuracy is lower if judgments are made in the video-

only medium (rather than audiovisual and audio-only,

as well as written transcripts). Further results show

that messages are perceived as most truthful if judged

from audiovisual or audio presentations, followed by

written transcripts and video presentations.

The medium in which deception is attempted thus

affects its likelihood of detection—lies being more

evident when they can be heard. Given that the stereo-

type of a liar is largely visual (eye contact, fidgeting,

gestures), this stereotype is most strongly brought to

mind by the video medium. Those senders who appear

nervous, tormented, or distressed are then judged to

be lying; but these expressions may be the result of

factors other than deceit.

Preparation

Sometimes people have anticipated that they have to

lie and are therefore prepared in their attempted

deceit. On other occasions, the lie is told in response

to an unanticipated need, and people are then unpre-

pared for the task of lying. Being prepared or not

should, in principle, affect the sender’s believability.

The available research suggests that receivers achieve

higher deception detection accuracy when judging

unprepared than prepared messages. It has been found

that it is easier to discriminate between unprepared

lies and truths than between prepared lies and truths.

Furthermore, prepared messages appear more truthful

than messages that were unprepared.

However, differences in experimental design have

been shown to lead to differences in accuracy rates.

Studies in which the senders produced both prepared

and unprepared messages yielded the result just

described. Studies in which the preparation factor was

examined by having messages from unprepared partic-

ipants compared with those from prepared participants

did not show any reliable difference in receivers’ abil-

ity to detect deception and truth. Here, the unprepared

messages were more often judged as truthful. Further

research on this issue is certainly needed.

Baseline Familiarity

Common sense would predict that a receiver should

more correctly pinpoint the lies of a sender he or she

has some familiarity with (“baseline exposure”). If

one has more knowledge of someone’s behavior than

one gets from just watching a few minutes on a

videotape, one should be able to detect deviations

from that behavior if telling a lie causes deviations in

behavior.

Results indicate that baseline exposure does indeed

improve lie/truth discrimination: Receivers achieve

a higher accuracy when given a baseline exposure.

However, one should be aware that senders who are

familiar to the receiver are more likely to be judged as

truthful. People seem unwilling to infer that someone

familiar to them is lying.

Motivation

Sometimes deception studies are criticized because

the research participants do not have any incentive to

be believed, and this lack of motivation in the task

could influence participants’ believability. Deception

research has, however, addressed this issue and inves-

tigated the effects of different levels of sender motiva-

tion. Furthermore, the influential deception scholar

Bella DePaulo has hypothesized that senders are

undermined by their efforts to get away with lying.

According to her motivational impairment hypothesis,

the truths and lies of highly motivated senders will

be more easily discriminated than those of unmoti-

vated senders. Experimental studies show that lies are

easier to discriminate from truths if they are told by

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