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We tested the hypothesis derived from eye blink literature that when liars experience cognitive demand, their lies would be associated with a decrease in eye blinks, directly followed by an increase in eye blinks when the demand has ceased after the lie is told. A total of 13 liars and 13 truth tellers lied or told the truth in a target period; liars and truth tellers both told the truth in two baseline periods. Their eye blinks during the target and baseline periods and directly after the target period (target offset period) were recorded. The predicted pattern (compared to the baseline periods, a decrease in eye blinks during the target period and an increase in eye blinks during the target offset period) was found in liars and was strikingly different from the pattern obtained in truth tellers. They showed an increase in eye blinks during the target period compared to the baseline periods, whereas their pattern of eye blinks in the target offset period did not differ from baseline periods. The implications for lie detection are discussed.
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ORIGINAL PAPER
Blinking During and After Lying
Sharon Leal Æ Aldert Vrij
Ó Springer Science+Business Media, LLC 2008
Abstract We tested the hypothesis derived from eye blink literature that when liars
experience cognitive demand, their lies would be associated with a decrease in eye blinks,
directly followed by an increase in eye blinks when the demand has ceased after the lie is
told. A total of 13 liars and 13 truth tellers lied or told the truth in a target period; liars and
truth tellers both told the truth in two baseline periods. Their eye blinks during the target
and baseline periods and directly after the target period (target offset period) were
recorded. The predicted pattern (compared to the baseline periods, a decrease in eye blinks
during the target period and an increase in eye blinks during the target offset period) was
found in liars and was strikingly different from the pattern obtained in truth tellers. They
showed an increase in eye blinks during the target period compared to the baseline periods,
whereas their pattern of eye blinks in the target offset period did not differ from baseline
periods. The implications for lie detection are discussed.
Keywords Eye blinks Deception
Introduction
Research has shown that eye blinks decrease when cognitive demand increases (Bageley
and Manelis 1979; Bauer et al. 1987; Drew 1951; Goldstein et al. 1992; Holland and
Tarlow 1972, 1975; Wallbott and Scherer 1991). For example, Holland and Tarlow (1972)
found that participants blinked less when they had to memorize an 8 digit number com-
pared to a 4 digit number over a period of 70 s. Research further suggests that during gaps
of cognitive demand a flurry of blinks occurs (Holland and Tarlow 1972; Leal 2005;
Malmstrom et al. 1977; Stern et al. 1984). For example, Holland and Tarlow (1972)
S. Leal (&) A. Vrij
Department of Psychology, University of Portsmouth (UK), King Henry I St.,
Portsmouth, England PO1 2DY
e-mail: sharon.leal@port.ac.uk
A. Vrij
e-mail: Aldert.vrij@port.ac.uk
123
J Nonverbal Behav
DOI 10.1007/s10919-008-0051-0
instructed participants to add up numbers presented to them during trials containing 10 s
intervals. For nine trials the number to add up on intervals 2, 4, and 6 was zero (which
makes the summation task easy on these intervals). For the other nine trials, none of the
numbers were zero. The trials that contained zeros resulted in more eye blinks than the
trials that did not contain zeros, due to an increase in eye blinks during the intervals when
the zeros were presented.
We thought that these findings could be relevant to predict eye blinks displayed during
and directly after lying, and examined this in the present experiment. Lying is sometimes
more cognitively demanding than truth telling (see below), and in such situations lying
would result in a decrease in eye blinks. Once the lie is told, a break in cognitive demand
occurs, which would result in an increase in blinking.
Cognitive Demand
Lying can be more cognitively demanding than truth telling (DePaulo et al. 2003; Zuck-
erman et al. 1981), and several aspects of lying contribute to this increased mental load
(Vrij 2004, 2008; Vrij et al. 2006b, in press, 2008). First, formulating the lie itself may be
cognitively taxing (Vrij 2008). Liars must need to make up their stories and must monitor
their fabrication so that they are plausible and adhere to everything the observer knows or
might find out. In addition, liars must remember their earlier statements, so that they appear
consistent when re-telling their story, and know what they told to whom. Liars should also
avoid making slips of the tongue, and should refrain from providing new leads. Second,
liars are typically less likely than truth tellers to take their credibility for granted (DePaulo
et al. 2003; Gilovich et al. 1998; Kassin 2005; Kassin and Gudjonsson 2004; Kassin and
Norwick 2004; Vrij et al. 2006c). As such, liars will be more inclined than truth tellers to
monitor and control their demeanor so that they will appear honest to the lie detector
(DePaulo and Kirkendol 1989), which should be cognitively demanding. Third, because
liars do not take credibility for granted, they may monitor the interviewer’s reactions more
carefully in order to assess whether they are getting away with their lie (Buller and
Burgoon 1996; Schweitzer et al. 2002). Carefully monitoring the interviewer also imposes
cognitive load. Fourth, liars may be preoccupied by the task of reminding themselves to act
and role-play (DePaulo et al. 2003), which requires extra cognitive effort. Fifth, liars have
to suppress the truth while they are lying and this is also cognitively demanding (Spence
et al. 2001). Finally, whereas activating the truth often happens automatically, activating a
lie is more intentional and deliberate, and thus requires mental effort (Gilbert 1991;
Walczyk et al. 2003, 2005).
Obviously, lying is not always more cognitively demanding than truth telling
(McCornack 1997). Perhaps the earlier stated reasons given as to why lying is more
cognitively demanding could give us insight into when it is more cognitively demanding.
That is, lying is more cognitively demanding to the degree that these six principles are in
effect. For example, lying is likely to be more demanding than truth telling only when
interviewees are motivated to be believed. Only under those circumstances can it be assumed
that liars take their credibility less for granted than truth tellers and hence will be more
inclined than truth tellers to monitor their own behavior and/or the interviewer’s reactions.
Second, for lying to be more cognitively demanding than truth telling, liars must be able to
retrieve their truthful activity easily and have a clear memory of it. Only when liars’
knowledge of the truth is easily and clearly accessed will it be difficult for them to suppress
the truth. On the other side of the equation, truth tellers also need to have easy access to the
truth for the task to be relatively undemanding. If truth tellers have to think hard to remember
J Nonverbal Behav
123
the target event (e.g., because it was not distinctive or it occurred long ago), their cognitive
demands may exceed the cognitive demands that liars require for fabricating a story.
In experimental studies researchers ensure that interviewees are motivated (typically by
giving a reward for making a credible impression) and that the target event is easily
retrieved (typically by interviewing the suspects shortly after informing them about the
target event), and the present experiment is no exception to this. When using this exper-
imental setting, lying has been found to be more demanding than truth telling in various
settings. Participants who have directly assessed their own cognitive load report that lying
is more cognitively demanding than truth telling. This occurred not only when lengthy,
elaborative responses, were required (Granhag and Stro
¨
mwall 2002; Hartwig et al. 2006;
Stro
¨
mwall et al. 2006; Vrij et al. 2001, 2006c; Vrij and Mann 2006; White and Burgoon
2001), but also when short responses were sufficient (Caso et al. 2005; Vrij et al. 1996,
2006c). In fMRI deception research, lying and truth telling is differentiated only by the act
of pressing either a ‘lie’ or ‘truth’ button. Nevertheless, participants’ brain activity
reveals that lying is more cognitively demanding than truth telling (Spence et al. 2004).
In forensic settings, we can reasonably assume that interviewees will be motivated to be
believed, but we cannot assume that interviewees will always be able to retrieve the target
event easily, as this will vary from one case to another. Analyses of police interviews with
real-life suspects, however, suggests that lying is often more cognitively demanding than
truth telling in the forensic setting. First, in those police interviews, lies were accompanied
by decreased blinking, increased pauses, and decreased hand and finger movements, all of
which are signs of cognitive load (Mann et al. 2002; Vrij and Mann 2003). Second, police
officers who saw videotapes of these suspect interviews reported that the suspects appeared
to be thinking harder when they lied than when they told the truth (Mann and Vrij 2006).
Hypotheses
We expected the following patterns for eye blinks in liars and truth tellers. Liars, who make
up an alibi about the target period, should experience more cognitive demand when
recalling the target period deceptively than when recalling the baseline periods truthfully
(see the Method section for details). We therefore predicted that liars would show less
blinking when recalling the target period than when recalling the baseline periods. We
further predicted that when this high cognitive demand ceases, i.e., directly after the lie is
told, a flurry of blinks would occur (which we label the compensatory effect).
Truth tellers tell the truth during all periods, and should therefore experience equal
cognitive demand during the target period and baseline periods. This would result in the
same amount of blinking during the target and baseline periods. Since the target period is
not associated with heightened cognitive demand in truth tellers, there is no theoretical
reason why the compensatory effect would occur in truth tellers directly after the target
period.
Method
Participants
In the experiment 26 participants (18 female, 8 male) ranging in age from 18 to 41
(M = 22.38, SD = 6.89) took part.
J Nonverbal Behav
123
Procedure
Participants were approached with the question whether they were willing to participate in
an experiment examining if deception could be detected by looking at changes in physi-
ology. The experimental protocol involved two control (baseline) free recall periods and
one experimental (target) free recall period. In the first baseline period, participants spent
time with the experimenter in the psychophysiology lab and received information about the
experiment. During this time, participants selected an envelope that they were to open
when alone at the end of the session. They were informed that the envelope contained
information as to whether they would be assigned to a ‘liar’ or ‘truth-teller’ condition and
also instructions regarding what to do during this ‘target’ period of time. In the target
period, 13 truth tellers were told to go about their normal business for 10 min but not to do
anything that they may later have to lie about. The thirteen liars were asked to steal an
exam paper from a professor’s office. They were instructed to deny having stolen the paper
later and to pretend to have done something else instead. All participants completed the
study as requested. After the 10 target minutes, liars and truth tellers returned to the
psychophysiology lab. They then received information about the physical measures that
would be taken (second baseline period). The experimenter, unaware of the veracity
condition to which the participants were allocated, asked each participant to freely recall
exactly what they were doing, including as much detail as possible during the 1st, 2nd, or
3rd 10 min time period. After the interviewee finished their recall about one period, the
experimenter waited ten seconds before asking the question about the next period. The
order in which the two baseline periods and target period were recalled was counterbal-
anced. The response length of baseline period 1 (M = 59.2, SD = 21.9), baseline period 2
(M = 68.60, SD = 21.6), and target period (M = 67.61, SD = 26.5) did not differ
significantly for truth tellers and liars (all F(1,24)s \ 0,55, all p’s [ 0.46).
To motivate participants they were informed that if they gave a detailed and convincing
account of what they were doing during each period then they would be entered into a draw
to win a £100 bookstore voucher. (In reality all participants were entered into the draw.)
The participants were also told that they would take part in a polygraph test to examine the
veracity of their statements. (We submitted them to a guilty knowledge polygraph test, not
discussed in this article.) Previous research revealed that polygraph tests appeal to par-
ticipants and motivate them to perform well (Vrij et al. 1997). The experiment was
conducted in accordance with BPS guidelines. After the experiment had finished, all
participants received a full debriefing and were assured that the ‘stolen’ exam paper was
not in fact a real copy but rather one devised by the experimenter who had no knowledge as
to which questions would subsequently be asked in their real exam.
Blink rates were recorded using a Neuroscan 4 amplification and software package. Two
electrodes above and below the left eye monitored blinks, while electrodes placed at the
side of both eyes monitored horizontal eye movements. Impedances were kept below 5 KX
and signals were filtered with a bandpass of 0.15–50 Hz. The gain was set at 250 for each
of the electrodes. Blink data were digitized at a sampling frequency of 250 Hz and stored
on disc for later analysis. Recordings of blinks began 10 s pre-stimulus, and continued
throughout the experimental session. The scores of the two baseline periods were com-
bined for the data analyses. Changes in blinking during the target period and baseline
periods were calculated for each participant by subtracting their baseline values from the
target period responses. To measure the compensatory effect, we calculated for each
participant the eye blinks displayed during the 6 s immediately after the target period, and
subtracted the baseline values from this offset value.
J Nonverbal Behav
123
Results
No differences in blink rate emerged between truth tellers and liars in the baseline
period, F(1, 24) = 1.26, ns, g
2
= .05 or target period, F(1, 24) = .86, ns, g
2
= .04,
whereas in the target offset period truth tellers (M = .65, SD = .44) displayed fewer
eyeblinks than liars (M = 1.53, SD = 1.1), F(1, 24) = 7.07, p \ .05, g
2
= .23. How-
ever, it is common practice in psychophysiological research to use ‘change’ or
‘percentage’ scores in preference to raw values (M =+.02, SD = .17). These methods
are used to avoid individual differences in participants’ initial physiological values
distorting the means.
Changes in eye blinks from baseline that occurred during and immediately following
the target period are illustrated in Fig. 1. A mixed 2 (Veracity: truth vs. lie) 9 2 (Phase:
during target and target offset) ANOVA was conducted. No main effect for Veracity was
found, F(1, 24) = 2.30, ns, g
2
= .09, but there was a main effect for Phase, F(1,
24) = 7.05, p \ .01, g
2
= .23, whereby overall there were fewer blinks per second
during the target period (M =+.02, SD = .17) than in the target offset period
(M =+.48, SD = .93). There was also a Veracity 9 Phase interaction effect, F(1,
24) = 6.76, p \ .05, g
2
= .22. Follow up t-tests on liars and truth tellers separately
revealed that, as reported in Fig. 1, liars displayed a reduction in blink rate during the
target period compared to baseline (M =-.07, SD = .11), (t(12) = 2.29, p \ .05,
d = .64), and that, conforming with the compensatory effect hypothesis, this was fol-
lowed by an increase in blink rate in the target offset period compared to baseline
(M =+.84, SD = 1.16), (t(12) = 2.56, p \ .05, d = .72). In contrast, truth tellers’ blink
rate increased during the target period compared to baseline (M =+.12, SD = .16),
(t(12) = 2.58, p \ .05, d = .75), whereas no significant difference occurred in blinks in
the target offset period comparison to baseline (M = 13, SD = .42), t(12) = 1.09, ns.
When we compared the blinks during the target period with the target offset period, we
found a significant difference for liars (they displayed an increase in blinks during the
target offset period compared to the target period), F(1, 12) = 8.06, p \ .05, g
2
= .40,
but not for truth tellers, F(1, 12) = .001, ns, g
2
= .00. In total, 10 out of 13 liars (77%)
demonstrated the pattern associated with deception (e.g., inhibition of blinking during the
target period and the increase in blinking during the offset period) whereas only two out
of truth tellers (15%) showed this pattern.
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Liar
Truth teller
Target
Target offset
Fig. 1 Changes in blink rate per
second during the target period
and directly after the target
period (target offset)
J Nonverbal Behav
123
Discussion
This experiment demonstrated that in situations when lying requires cognitive demand,
lying is associated with a decrease in eye blinks followed by a compensatory effect: An
increase in eye blinks directly after the lie is told and cognitive demand has ceased. It is
striking what different patterns in eye blinks emerged for liars and truth tellers (see Fig. 1);
such striking differences in behavior between liars and truth tellers are rarely seen in
deception research (DePaulo et al. 2003; Vrij 2008). Liars displayed a decrease in blinks
during deception (i.e., the target period) compared to baseline and this was followed by an
increase in blinks in the offset period when the lie was told (compared to both target period
and baseline). Truth tellers showed an increase in eye blinks during the target period
compared to baseline which was not followed by a change in blinks directly after the target
period (compared to both target period and baseline). The increase in eye blinks in truth
tellers was not predicted but could perhaps be explained in terms of anxiety. Perhaps truth
tellers experienced more anxiety during the target period than during baseline, as they may
have realized that the target period is the key component of the test where their credibility
would be assessed. Anxiety is associated with an increase in eye blinks (Chiba 1985;
Harrigan and O’Connell 1996; Tecce 1992). Since the target period is not associated with
heightened cognitive demand in truth tellers, there is no theoretical reason why the
compensatory effect would occur in truth tellers, and, indeed, it did not occur.
Whether lie detectors unknown to our findings will interpret the eye blinks displayed by
liars and truth tellers correctly remains to be seen. Research has demonstrated that lie
detectors typically associate an increase in eye blinks with deception (Stro
¨
mwall et al.
2004; Taylor and Hick 2007; Vrij et al. 2006a). Our findings suggest that they would (i)
incorrectly classify truth tellers as liars and (ii) incorrectly classify liars as truth tellers
when they rely upon eye blinks to detecting deception in circumstances where lying
requires cognitive load.
Skeptics may argue that we used a low-stakes situation and that our findings that liars
reduced their blinking when they experience cognitive load may not hold true when the
stakes are high. Perhaps in high-stakes situations, where the outcomes really matter to liars,
the anxiety that liars experience gets the overhand and that they will show increased eye
blinks when lying. Mann et al.’s (2002) research, in which the eye blinks displayed by
suspects in police interviews when they told the truth and lied during these interviews were
examined, suggest that the skeptics may be wrong. Mann et al.’s study was clearly a high-
stakes study as the suspects were suspected of serious crimes such as murder, rape, and
arson. Yet the suspects showed a decrease in eye blinks when lying. Whether this was
followed by a compensatory effect immediately after the lie was told is unknown, as this
has not been analyzed. It cannot be analyzed either because of the ground truth. Although
Mann et al. have established the ground truth during the truths and lies, the ground truth of
the statements directly after the truths and lies is unknown in their dataset.
As a practical implication of our findings, we believe that patterns of blink rate could be
monitored to help professional lie-catchers identify parts of suspects’ statements that are
indicative of deception and thus warrant further scrutiny. A benefit of monitoring blink rate
rather than other physiological measures is that it can be done non-intrusively via a remote
camera that could pick up eye blinks by monitoring occlusion of the retina (Stern 2006,
personal communication to Sharon Leal) which makes it applicable in many situations.
Our observations for liars may not just be related to eye blinks. For example, when
Clinton testified before the Grand Jury in the Monica Lewinsky case, he sat very still when
he answered potentially incriminating questions about whether or not he ordered his
J Nonverbal Behav
123
personal secretary to go to Lewinsky’s home to collect the presents she had received from
him (Vrij 2002). However, he made several subtle shifting movements after answering
these questions. We hope that our article will stimulate further research into the behaviors
displayed by liars during and directly after the lie in situations where they experience
cognitive load.
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... Karson et al. (1981) rejected an effect of mouth movements. In certain speaking conditions, locution does not imply any SBR increase (Descroix et al., 2018;Fukuda, 2001;Leal & Vrij, 2008. ...
... Within the context of conversation, the observed SBRs, which get higher overall, tend to be erroneously attributed to a communication function only (e.g., Oertel et al., 2011). Correlatively, a protagonist who blinks little within a conversation can be suspected of being little involved indeed: as a listener, s/he may not process the received messages; as an emitter, s/ he may be open to more important external attention, and refrain from blinking, as when lying (Fukuda, 2001;Leal & Vrij, 2008). ...
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Why do eye-blinks activate during conversation? We manipulated informational content and communicative intent exchanged within dyads. By comparison to a silent situation, both emitters and receivers increased their blink rate when the former delivered a treasure hunt route to the latter. When the previously known route was repeated, or when the alphabet was reeled off within the same dyads, the receiver did not increase the rate, although the emitter did. The emitter’s rate increased as well when formulating the route not vocally but silently in an inner voice; none reacted when the emitter was really silent. Therefore, the high rates of spontaneous blinking commonly observed during a conversation can be explained outside of a bilateral communication function. It seems primarily related to individual cognitive processing of afferent or efferent information. The speaker blinks when handling the speech; the listener blinks only when taking heed of a useful content.
... The blink rate has been linked to attention in several circumstances and varies according to mental activities. Blinks are perceived as communicative signals in human face-to-face interaction, directly influence speakers' communicative behavior in this context [12] and can be used to distinguish liars from truth-tellers [13]. An increase of the eye-blink rate has been correlated with a decrease of attention, and vice versa [14][15][16]. ...
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Thesis
Le Clignement Spontané des yeux (CS) se distingue du clignement volontaire et du clignement reflexe. Les variations du taux de CS (TCS) ne sont pas expliquées par la seule nécessité de lubrifier la cornée. Des baisses de TCS ont été corrélées avec l’attention, la concentration et la perception visuelle, des hausses de TCS avec la mémorisation et la parole. L’augmentation du TCS observée durant la conversation, a été attribuée à un mécanisme méta-langagier destiné à organiser les échanges et ponctuer le discours entre partenaires. La présente thèse relativise le rôle du CS dans la communication humaine. En effet nos deux premières études (Article 1 et 2) montrent que les variations du CS entre partenaires (des mères avec leur nourrisson) ne sont pas mimétiques ni même l’effet d’un entrainement entre partenaires. Au contraire nous montrons (Article 3, Expérience 1) que le CS dépendrait d’abord d’un mécanisme individuel de traitement de l’information. La fonction interpersonnelle de communication du CS serait donc subsidiaire (Article 3, Expérience2) ; le CS serait essentiellement relié à des processus cognitifs individuels (unilatéraux), utiles à la communication mais dédiés à une fonction plus générale de gestion d’information. Pour confirmer cette hypothèse, nous avons testé (de manière inédite) la variation des CS lors du traitement d’informations haptiques, avec ou sans la vision (Article 4, Expérience1). Nous montrons (Article 4, Expérience 2) que le CS émerge prioritairement de l’activation co-occurrente de processus top down (représentation mentale et intention) et bottom up (sensorialité). A l’issue de ces résultats, nous soutenons que le CS est un phénomène qui accompagne le traitement attentionnel des informations. Le CS serait le marqueur du traitement conscient des informations internes (réflexives) ou externe (sensorielles) que nous tentons d’expliquer par le modèle énactif.
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