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Social Research, Vol. 63, No. 3, 801-817 (Fall 1996)
Paul Ekman’s research is supported by a Research Scientist Award from
the National Institute of Mental Health (MH06092).
Why Don’t We Catch Liars?
Paul Ekman
Our research (Ekman and O’Sullivan, 1990; Frank and Ekman, forthcoming; Ekman, Frank,
and O’Sullivan, forthcoming) suggests that most people cannot tell from demeanor whether
someone is lying or telling the truth. Such poor performance is not because lies are told
flawlessly. Most liars make mistakes which could be detected but usually are missed. Both
perpetrating a lie and detecting a lie, in most people, seem to be poorly developed skills. In this
article, I consider six explanations for why most of us do not catch liars from demeanor. I will
first explain how I distinguish lying from other forms of deceit, and then discuss the evidence
which suggests that people are such poor lie catchers.
The intent of the liar is one of the two criteria I (Ekman, [1985] 1992) use to distingui sh lies
from other kinds of deception. The liar deliberately
actually tell the truth, but that is not their intent. And truthful people may provide false
information—bad advice from a stock broker—but that is not their intent. The~ liar has a choice;
the liar could chose not to lie. We are all tempted to lie, but we do not always do so. Lying is not
irresistible; it is, by my definition, a conscious, considered choice. I do recognize that lying can
become a habit and then performed with little consideration, but, at least initially, all such habits
began as considered choices about whether or not to do so. Presumably, a pathological liar is
compelled to lie and by my definition, therefore, is not a liar.
The second criterion for distinguishing lies from other deceptions is that the target is not
notified about the liar’s intention to mislead. A magician is not a liar by this criterion, but Uri
Geller is a liar, since Geller clai
impostor is. Let the buyer beware is one example of an explicit warning that products or services
may not be what they are presented to be. (Of course, that warning does not appear in
advertisements, nearly all of which are designed to convey the opposite message.) Poker is still
another situation in which the rules of the game sanction and notify the players that deception
will occur, and, therefore, one cannot consider bluffing to be a lie.
Sometimes notification of an intention to mislead is implicit in the framing, to use Goffman’s
(1974) term, of the situation. In real estate transactions, the potential buyer is implicitly notified
that the seller’s asking price is not the actual price the seller would accept. Various forms of
politeness are other instances in which the nature of the situation notifies the target that the truth
may not be spoken. The host would not properly’ scrutinize the dinner guest to determine if the
guest’s claim to have enjoyed the evening is true anymore than the aunt should worry whether
the nephew is lying when he says th at he appreciated being given a tie for Christmas. Deception
is expected; even if the target might suspect that the truth is not being told, it is improper to
question it. Only certain types of deception may be allowable: the poker player cannot use
marked cards; the home seller cannot conceal a known defect.
In courtship, it is ambiguous whether the parties should expect truthfulness. The saying “all’s
fair in love and war” would seem to warn lovers not to believe all they are told. Recent public
opinion polls suggest that lies that downplay the number of previous sexual partners are common
among college-aged adults. Yet I expect that lovers want to believe in the truthfulness of their
lover. Many popular songs testify to the betrayal felt when lies are discovered (although some do
warn that lies may be expected). Romantic love requires collusive efforts to develop and
maintain myths about each other and the nature of the relationship.
I differ from Bok (1982), who only considers false state ments to be lies. I (Ekman, [1985]
1992) argued that one can falsify without words, and one need not falsify, verbally or
nonverbally, to lie. Concealment is just as much a lie as falsification, if there is an expectation
that information will be revealed. When filling out a job application that asks for a listing of all
previous employment, omitting the one from which one was fired would be a concealment lie,
for there is an obligation to reveal. In personal relationships it is not always so clear cut, and the
liar, once discovered, and the target of the lie may disagree about whether or not an obligation to
reveal the concealed information was in force.
Concealment and falsification are different techniques for accomplishing the same objective.
The issue is the motive, not the technique employed to accomplish it. If the motive is to mislead,
then the choice between falsifying or concealing is simply a matter of which technique will work
better in a given instance. Elsewhere (Ekman, [198531992) I have explained why most liars
would prefer to conceal rather than falsify if the situation will allow it and also described some
other techniques for implementing a lie.
Now let us consider what we know about how well people can detect lies from demeanor. The
evidence that most people do poorly in catching lies comes from the following type of
experiment. Students are recruited to lie or tell the truth about something which usually does not
matter much to them. It has no relevance to their past or their expected future life. Sometimes in
a weak (in my judgment) attempt to motivate them, they are told it is important to be able to lie,
or that smart or successful people succeed in this task. Videotapes of their behavior are shown to
other students who are asked to identify who is lying and who is telling the truth. Typically, most
of those trying to catch the liars perform at chance or just slightly better than chance. Our
(Ekman and Friesen, 1974; Ekman, Frank, and O’Sullivan, forthcoming) resear ch has differed in
a number of ways.
We have tried to make the lies relevant to their lives and to set the stakes for success or failure
as high as we could. We attempted this for two reasons. It is only in high stake lies that emotions
about lying (fear, guilt, excitement, or what I have called duping delight) are likely to be aroused
and betray the lie. It is not just the leakage of these strong emotions which provide behavioral
clues to deceit, but these strong emotions also max’ disruPt the liar’s cognitive processing and
result in evasive, implausible, and stumbling accounts. A second reason for studying high stake
lies is that these are the lies with which society is most concerned.
In one of our experimental scenarios, we examined how well nurses could conceal the
negative emotions they felt when witnessing films showing amputations and burns. They were
highly motivated to succeed in this lie, because they thought our experiment offered them the
opportunity to develop a skill they would need to use when confronting just such upsetting
scenes in their future work. In another of our scenarios, the subjects had a chance to take and
keep $50 if they could convince the interrogator they’ had not taken the money. Those subjects
who did not take the money could earn $10 if the interrogator believed them when they’ said
they had not taken the $50. In our last scenario, we first identified the social issues the subjects
felt most strongly about, and then asked them to describe that opinion honestly (and earn $10 if
believed) or claim to have the opposite of their true opinion (and earn $50 if believed).
In our most recent work we gave some of our subjects the choice as to whether to lie or tell
the truth, as people have in real life. There are many reasons why some people choose not to lie,
one of which is their own knowledge, based on past experience, that they are almost always
caught. Including in the sample of liars such terrible liars, people who would not choose to lie
unless fo rced to do so by the experimenter, could inflate the detection rate. In virtually all
previous research, on either interpersonal deception or polygraph lie detection, subjects were not
given the choice as to whether to lie or be truthful. One exception is the study of the polygraph
by Ginton, Daie, Elaad, and Ben-Shakhar (1982), in which they were able to know which
policemen had cheated on a test for eligibility for promotion; Stiff, Corman, Knizek, and Snider
(1994) in a similar fashion knew which students cheated on a quiz. Bradley (1988) also allowed
subjects to choose whether to lie or tell the truth in a polygraph study.
Another unique feature of our recent experiments is that we told the subjects that they would
be punished, and it was a considerable punishment, if the interrogator judged them to be lying.
Both the truthful person mistakenly judged to be lying and the liar who was detected would
receive the same punishment. Thus, for the first time in research on lying, both the truthful
per son and the liar might be afraid—of being disbelieved if telling the truth, of being caught if
lying. If it is only the liar who might be afraid of being accused of lying, it is too easy’ for the lie
catcher and not relevant to most of real life. And if neither liar nor the truthful person fear
punishment, it should have little relevance to the lies that occur in the criminal justice world or in
national security, let alone in marital disputes, parent-child conflicts, and so on.
Although our recent experiments can claim to have more ecological validity than our older
studies, or than most of the literature on either interpersonal deceit or polygraph lie detection, the
findings about detectability were not much different. Most of those who saw the videotapes and
made their judgments operated at a chance level or only slightly better than chance. Before
proceeding to consider why people do so poorly as lie-catchers, let us consider some limitations
of our research which could have led us to undere stimate the ability to detect lies from
For the most part, the observers who judged who was lying and who was telling the truth
had no vital interest at stake in achieving accuracy. They were not offered higher pay if they
were more accurate. And catching liars was not intrinsically rewarding, for most of these people
did not make a living catching liars. This limitation was addressed in our (Ekman and
O’Sullivan, 1991) study and work by other research groups (Kraut and Poe, 1980; DePaulo and
Pfeifer, 1986) which did study professionals concerned with catching liars. We found that
customs officials, policemen, trial court judges, F.B.I., C.I.A., B.A.T.F., D.E.A., forensic
psychiatrists, and trial lawyers were not much better than chance.
Perhaps accuracy would be higher if those making the judgments had been able to ask the
questions, rather than being passive observers. I cannot rule this out, although I doubt it would be
so. The requirement to formulate questions might well detract f rom the ability to process the
information provided by the person being judged. It is for this reason that in many interrogations
one person asks the questions while another sits passively considering the suspects responses. It
would be interesting to have professional interrogators ask the questions in our experiments and
then determine if those who see the videotapes generated were more accurate than has been so
far found.
Our observers were not familiar with those whom they judged, and it might be argued that
such familiarity would benefit accuracy. There are, of course, many situations in which
judgments about lying are made without any prior familiarity with the person being evaluated,
and our experiments at least are relevant to those instances. But I doubt that familiarity always
benefits lie detection. While it should provide the basis for discounting idiosyncratic behaviors, it
may do so at a cost. We tend to become invested in our friendships and work relationships, and
the wish to prese rve them may lead us to develop blindness to behaviors which could disrupt
them. Trust makes one vulnerable to being misled, as usual levels of wariness are reduced and
the benefit of the doubt is routinely given.
Involvement in a relationship can lead also to confidence in one’s ability to detect deception
(Sillars and Scott, 1983), and such confidence may itself make one more vulnerable (Levine and
McCornack, 1992). Familiarity should be an unmitigated benefit only when it is with a person
one has had reason to distrust, and about whom one has acquired knowledge of how and when
they betray the relationship.
In our experiments, the observers were only shown a few minutes of each interview before
being required to make their judgment. But longer samples may not necessarily benefit lie detec-
tion. We did do one study in which the samples shown were twice as long, and accuracy did not
improve. Furthermore, we know from the behavioral measurements we have done that there are
clues to deceit in thes e shorter samples. Nevertheless, we cannot rule out this limitation. If
people were given much longer samples to judge, of an hour or two, accuracy might improve.
A critic might also have wondered if accuracy was so poor because there were few
behavioral clues to deceit, but, as I have just mentioned, that is not the case in our experiments.
Measurements we and our collaborators have done of the facial movements, voice, and speech
show that high levels of accuracy are possible—over 80 percent correct classifications of who is
lying and who is telling the truth. While those measurements required slowed motion replays, we
also know that accurate judgments are possible just by viewing the videotapes at real time. A
small percent of those we have studied have reached 80 percent or better accuracy, and they have
done so in judging more than one scenario, so it is unlikely their accuracy was a fluke. And we
have found a few occupational groups which as a group were highly accurate. The United States
Se cret Service were highly accurate on the emotion lie; none of them scored at or below chance,
and a third were above 80 percent accurate. Interrogators specially selected for their known skills
and given a week of training showed similar accuracy on the opinion lie.
Although the stakes in the lies we studied were much higher than in other research on lying,
certainly they were not as high as they are in many criminal or national security cases. Perhaps if
the stakes were much higher, the videotapes would have contained many obvious signs of deceit,
resulting in much higher accuracy. I cannot argue against that possibility but, as I just described,
there were some occupational groups who were accurate when judging our videotapes. The
question remains why were all these other groups not accurate.
The information is there, and it can be detected by some but not by most. Before considering
why the overwhelming majority of people do poorly, consider one more feature of our
experiments which probably ben efited accuracy and may have led us to over- rather than under-
estimate accuracy. In all of our recent studies we have told our observers that between 40 and 60
percent of the people they will see are lying. Initially we did not give this instruction, and found
that a group of policemen judged everyone they saw on the videotape as lying, later explaining
that everyone lies, especially to the police. Knowing the base rate of lies is an advantage people
do not always have, and should enhance lie detection. I have more to say about this later.
Granting that our evidence is not conclusive, nevertheless, our videotapes do contain
behavioral clues to deceit, which some people can recognize accurately but most do not. For the
purpose of this discussion, let us consider this evidence as suggesting that in actual life most
people, the overwhelming majority of people, do not detect high stake lies from demeanor. The
question I pose is why not, why can we not all do better at this? It is not that we do not car e.
Public opinion polls time and again show that honesty is among the top five characteristics
people want in a leader, friend, or lover. And the world of entertainment is full of stories, films,
and songs which describe the tragic consequences of betrayal.
My first explanation of why we may be such poor lie catchers is that we are not prepared by
our evolutionary history to be either very good lie catchers or lie perpetrators.
1 I suspect that
our ancestral environment was not one in which there were many opportunities to lie and get
away with it, and the costs for being caught in a lie might have been severe. If this speculation is
correct, there would not have been any selection for those people who were unusually adept in
catching or perpetrating lies. The fossil record does not tell us much about social life, so one
must speculate about what life as hunter-gatherers might have been like. I add to that my
experience thirty years ago working in what was then a stone-age preliterate culture in wh at is
now called Papua New Guinea.
There were no rooms with doors, little privacy in this group living, small village, in which
everyone knew and saw everyone else every day. Lies would most often be betrayed by the
target or someone else observing actions which contradicted the lie or by other physical
evidence. Adultery was an activity which lying often attempted to conceal in the village where I
lived. Such lies were uncovered not by reading the betrayer’s demeanor when proclaiming
fidelity, but by stumbling over him or her in the bush.
Perhaps lies about beliefs, emotions, and plans could have better avoided detection in such
an environment.
2 But some of those lies would eventually lead to one or another action, and then
my argument about how hard it is to conceal or falsify actions in a setting in which there is no
privacy would apply.
In a society in which an individual’s survival depended on cooperative efforts with other
members of their village, the reputational loss for being caugh t in a high stake lie might well be
deadly. No one might cooperate with someone known to have engaged in serious lies. One could
not change spouses, jobs, or villages with any ease.
Cheney and Seyfarth (1990), in their chapter on animal deception, make very similar points.
An important constraint against lying
. . . arises from a species social structure. Animals that live in stable social groups face special
problems in any attempt at deceptive communication. . . . Among socially living animals deceptive
signals will probably have to be more subtle and occur at lower frequencies if they are to go
undetected. Equally important, if animals live in social groups in which some degree of cooperation
is essential for survival, the need for cooperation can reduce the rate at which unreliable signals are
given (1990, p. 189).
To have had some special skill in detecting (or perpetrating for that matter) lies would not
have had much adaptive value in such circumstances. Serious, high stake lies probably di d not
occur that often because of limited opportunity and high costs. When lies were suspected or
uncovered, it was probably not by judgments of demeanor. (Note I have focused just on intra-
group lies; certainly lies might between groups, and their costs and detection could be quite
While there are altruistic lies, my discussion has dealt with less friendly lies, lies that occur
when one person gains an advantage, often at the cost of the target of the lie. When the
advantage is gained by violating a rule or expectation, we call that cheating. Lies sometimes may
be required to accomplish the cheating activity, and lies are always required to conceal having
cheated. Those cheated do not typically appreciate being cheated and are motivated to uncover
any lies involved. But cheating is not likely to have occurred often enough in our ancestral
environment to confer some advantage on those who might have been unusually adept at spotting
when it did occur. And as I argued earlier, there was probably so little privacy that cheats would
be caught by means other than discerning their misdeeds from their demeanor. The biologist
Alan Grafen wrote:
The incidence of cheating must be low enough that signaling remains on average honest. As
signalers maximize their fitness, this implies that the occasions on which cheating is
advantageous must be limited. Perhaps the signalers for whom cheating is advantageous are in a
minority, or that only on a minority of occasions does it pay a signaler to cheat. . . . Cheating is
expected in evolutionarily stable signal systems, but the system can be stable only if there is some
reason why on most occasions cheating does not pay. Cheats impose a kind of tax on the meaning
of the signal. The central fact about stable signaling systems is honesty, and the debasement of
the meaning of the signal by cheats must be limited if stability is to be maintained (1990, p. 533).
By this reasoning, signals that cheat, which I would call lies, should have a low incidenc e.
Cosmides and Tooby’s (1992) findings suggest that we have evolved a sensitivity to rule
infractions and do not reward cheaters, and this may explain why cheating does not occur often.
However, our findings suggest that we are not likely to catch cheaters based on our ability to spot
their lies from their demeanor but by other means.
To summarize my argument, our ancestral environment did not prepare us to be astute lie
catchers. Those who might have been most adept in identifying a liar from demeanor would have
had minimal advantage in the circumstances in which our ancestors probably lived. Serious lies
probably did not occur often, because a lack of privacy would have made the chances of being
caught high. Such a lack of privacy would also mean that lies would typically be discovered by
direct observation or other physical evidence, rather than having to rely upon judgments of
demeanor. Finally, in a cooperative, closed, small society, when lies are uncovered the
reputational costs to the i ndividual would be high and inescapable.
In modern industrial societies, the situation is nearly the reverse. The opportunities for lying
are plentiful; privacy is easy to achieve, there are many closed doors. When caught, the social
consequences need not be disastrous, for one can change jobs, change spouses, change villages.
A damaged reputation need not follow you. By this reasoning we live now in circumstances
which encourage rather than discourage lying, when evidence and activity are more easily
concealed and the need to rely upon demeanor to make our judgments would be greater. And we
have not been prepared by our evolutionary history to be very sensitive to the behavioral clues
relevant to lying.
If we grant that our evolutionary history did not prepare us to detect lies from demeanor,
why do we not learn how to do so in the course of growing up? One possibility is that our parents
teach us not to identify their lies. Their privacy may often require that they mislead their children
about j ust what they are doing, when they are doing it, and why they are doing it. While sexual
activity is one obvious focus of such lies, there might well be other activities which parents want
to conceal from their children.
A third explanation is that we generally prefer not to catch liars, because a trusting rather
than a suspicious stance enriches life, despite the possible costs. To always doubt, to make false
accusations, is not only unpleasant for the doubter, but undermines much chance of establishing
intimacy in mating, friendships, or on-going work relationships. We cannot afford to disbelieve a
friend, our child, or our spouse when they are actually telling the truth, and so we err on the side
of believing the liar. Trusting others is not only required, but it makes life easier to live. What
matter if the cost is not detecting some who take advantage of that trust, for one might never
know about it. It is only the paranoid who foregoes such peace of mind, and those whose lives
are actually a t some risk if they are not constantly alert to betrayal. Consistent with this
formulation we (Ekman, Bugental, and Frank, unpublished data) obtained preliminary evidence
that abused children living in an institutional setting were more accurate than other children in
detecting lies from demeanor.
My fourth explanation is that we often want to be misled, we collude in the lie unwittingly
because we have a stake in not knowing the truth.
5 Consider two examples from spousal
relationships. It may not be in the interest of a mother with a number of very young children to
catch her mate’s lie which conceals his infidelity, particularly if he is having a fling in which he
is not diverting resources which would otherwise go to her and her children. The philanderer
does not want to be caught, so they both have an interest in the lie not being uncovered. A
similar logic is at work in this next, more altruistic lie and collusive belief. A wife asks her
husband, “Was there any other woman at the party wh om you thought was more attractive than
me?” He lies by claiming she was the most attractive when she was not. He does not want to
make her jealous, and he does not want to deal with her having such feelings, and she may want
to believe she was the most attractive.
In some collusions the target who wants to believe the liar may not benefit from the lie or
benefit only in the short run. Consider what was perhaps the most infamous example in this
century of a target believing a liar who meant him harm. I refer to the meeting between the
British Prime Minister, Nevelle Chamberlain, and Adolph Hitler, the Chancellor of Germany, on
September 15, 1938.
The world watches, aware that this may be the last hope of avoiding another world war. (Just six
months earlier Hitler’s troops had marched into Austria, annexing it to Germany. England and
France had protested but done nothing further.) On September 12, three days before he is to meet
Chamberlain, Hitler demands to have part of Czechoslovakia annexed to Germans’ and incites
rioting in that country. Hitler has already secretly mobilized the German Army to attack
Czechoslovakia, but his army won’t be ready until the end of September. If he can keep the
Czechs from mobilizing their army for a few more weeks, Hitler will have the advantage of a
surprise attack. Stalling for time, Hitler conceals his war plans from Chamberlain, giving his
word that peace can be preserved if the Czechs will meet his demands. Chamberlain is fooled; he
tries to persuade the Czechs not to mobilize their army while there is still a chance to negotiate
with Hitler. After his meeting with Hitler, Chamberlain writes to his sister, ‘. . . in spite of the
hardness and ruthlessness I thought 1 saw in his face, I got the impression that here was a man
who could be relied upon when he had given his word . . . Defending his policies against those
who doubt Hitler’s word, Chamberlain five days later in a speech to Parliament explains that his
personal contact with Hitler allows him to say that Hitler ‘means what he says’ (Ekman, [1985]
1992, pp. 15, 16).
Hitler reportedly wrote, “The victor will not be asked afterward whether he told the truth. In
starting and waging war it is not justice that matters but victory.” Why did Chamberlain believe
Hitler? Not everyone did, there were many in the opposition party in Britain and elsewhere who
recognized that Hitler was not a man of his word. Chamberlain unwittingly, I believe, colluded in
Hitler’s lie because he had to believe Hitler. If Chamberlain were to have recognized Hitler’s lie,
he would have to confront the fact that his policy of appeasement had put his country at grave
risk. Since he had to face that fact just a few weeks later, one might ask why did he not recognize
it during this meeting with Hitler? That would be rational but not psychological. Most of us
operate on the unwritten principle of postponing having to confront anything which is very
unpleasant. and we may do so by collusively overlook ing a liar’s mistakes.
Chamberlain was not unique. The targets of lies, often unwittingly, collusively want to
believe the liar. The same motive—not wanting to recognize impending disaster—explains why
the businessman who mistakenly hired an embezzler continues to miss the signs of the
embezzlement. Rationally speaking, the sooner he discovers the embezzlement the better, but
psychologically that discovery will mean he must face not only his company’s losses, but his
own mistake in having hired such a rascal. In a similar fashion, everyone but the cuckolded
spouse may know what is happening. Or the pre-adolescent using hard drugs may be convinced
that her parents surely must know what she is doing, while they unwittingly strive to avoid
spotting the lies which would force them to deal with the possibility that they have failed as
parents and now have a terrible struggle on their hands. One is nearly always better off in the
short run to cooperate with the lie, even if that means that the co nsequences tomorrow will be
even worse.
A fifth explanation is based on Erving Goffman’s writings (1974). We are brought up to be
polite in our interactions, not to steal information which is not given to us. A rather remarkable
example of this is how we unwittingly avert our gaze when someone we are talking to cleans
their ears or picks their nose. Goffman would also argue that the false message sometimes may
be the more socially important message than the truth. It is the acknowledged information, the
information for which the person who states it is willing to take responsibility. When the
secretary who is miserable about a fight with her husband the previous night answers, “Just
fine,” when her boss asks, “How are you this morning?” that false message may be the one
relevant to the boss’ interactions with her. It tells him that she is going to do her job. The true
message—that she is miserable—he may not care to know about at all as long as she does not
intend to let it impair her job performance.
None of the explanations I have offered so far can explain why most members of the
criminal justice and intelligence communities do so poorly in identifying liars from demeanor.
Police and counter-intelligence interrogators are not taking a trusting stance with their suspects,
they are not colluding in being misled, and they are willing to steal information not given to
them. Why do they’ not do better in identifying liars from demeanor? I believe they are
handicapped by a high base-rate and inadequate feedback. Most of the people they deal with
probably are lying to them. Those with whom I have spoken estimate the base rate of lying as
more than three-fourths. Such a high base rate is not optimal for learning to be alert to the subtle
behavioral clues to deceit. Their orientation all too often is not how to spot the liar, but how to
get the evidence to nail the liar. And when they make a mistake and learn that someone was
wrongfully punished, that feedback comes too late, to o far removed from the mistaken judgment
to be corrective.
This suggests that if you expose people to a lower base-rate of lying, around 50 percent, and
give them corrective feedback after each judgment they make, they might well learn how to
accurately identify lies from demeanor. This is an experiment we are now planning. I do not
expect that accuracy will reach one hundred percent, and for that reason I do not believe that
judgments about who is lying should be allowable evidence in court. Such judgments, however,
may provide a sounder basis for deciding, at least initially, whom to investigate further, and
when to ask more questions to clarify why something unusual has been noticed.
1I am grateful to Helena Cronin, London School of Economics, for asking me why evolution
had not prepared us to be better lie catchers, also to Mark Frank. Rutgers University, and Richard
Schuster, University of Haifa, for their many helpful comments on this manuscript.
2 Helena Cronin raised this possibilit y.
3 I am grateful to Leda Cosmides and John Tooby, University of California, Berkeley, and to
Richard Schuster, University of Haifa, for pointing this out.
4 I am grateful to Alison Gopnik, University of California, Berkeley, for suggesting this
5 For evidence consistent with my reasoning see Tooby and Cosmides, 1989.
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