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The application of subliminal priming in lie detection:
Scenario for identification of members of a terrorist ring
MING LUIa,b and J. PETER ROSENFELDa
aDepartment of Psychology, Northwestern University, Evanston, Illinois, USAbDepartment of Psychology, National University of Singapore, Singapore
Abstract
We studied a lie detection protocol immune to countermeasures. The 4 stimulus conditions were (1 and 2) supra-
liminal acquaintance name primed by subliminal acquaintance name (A-A) versus subliminal nonacquaintance name
(N-A) and (3 and 4) supraliminal nonacquaintance name primed by subliminal acquaintance name (A-N) versus
subliminal nonacquaintance name (N-N). In Experiment 1 and replication, principal components analysis-derived
event-related potential components revealed significant differences between dishonestly answered supraliminal
acquaintance conditions with differing primes (A-A vs. N-A). In Experiment 2 subjects were required to lie in A-N
and N-N conditions, in contrast to Experiment 1, in which subjects lied in A-A and N-A conditions. No significant
effects were found. In Experiment 3, the lying task was removed and no significant differences were found. We
conclude that subliminal primes modulate ERPs in conditions with supraliminal acquaintance name when the task
involves lying.
Descriptors: Cognition, Learning/memory, Unconscious processes, EEG/ERP
There is a recent growth of cognitive neuroscience studies in
deception using different experimental paradigms, including
mock crime scenarios (Kozel et al., 2005; Mohamed et al., 2006;
Lui & Rosenfeld, 2008), autobiographical information (Ganis,
Kosslyn, Stose, Thompson, & Yurgelun-Todd, 2003; Nunez,
Casey, Egner, Hare, & Hirsch, 2005; Spence et al., 2001), guilty
knowledge tests (Langleben et al., 2002, 2005), and malingering
tests (Lee et al., 2005). Past studies approached deception by
investigating the related cognitive processes, including attention,
memory, and response generation processes. For instance, a
piece of information that a person intends to lie about (guilty
information) is usually more attention catching. And one may
involuntarily and automatically retrieve the related contextual
memory when perceiving the guilty information. Lying is also
supposed to pose more demand on executive control than truth
telling (Johnson, Barnhardt, & Zhu, 2005). Before lying, one
must hold and manipulate competing pieces of truthful and
false information in working memory. To give a lying response,
one needs to suppress the prepotent truthful response. The in-
hibition (Falkenstein, Hoormann, Christ, & Hohnsbein, 2000;
Gehring, Goss, Coles,Meyer, &Donchin, 1993) andmonitoring
of response conflicts involves executive control (Botvinick,
Nystrom, Fissell, Carer, & Cohen, 1999; Carter et al., 1998).
Neuroimaging data supported the involvement of executive con-
trol brain regions in deception. In a recent study by Ganis and
colleagues, there were stronger activations in anterior prefrontal
cortices (bilaterally), parahippocampal gyrus (bilaterally), the
right precuneus, and the left cerebellum in the lying compared to
truth-telling conditions. Enhanced activations in the anterior
cingulate cortex (ACC) and the superior frontal gyrus were also
found in another fMRI deception study (Langleben et al., 2002).
It is believed that that there is no specific brain region or
electrophysiological marker responsible for lying alone; rather,
there is a combination of emotional and cognitive processes re-
lated to lying. The present study aimed at developing a paradigm
to detect lies by capturing the lie-related memory processes at the
individual level.
Past ERP Studies on Deception
Many previous event-related potential (ERP) studies of decep-
tion focused on the P300 component. The P300 is a positive-
going component that occurs between 300 and 800 ms after
stimulus onset. It is an endogenous ERP component related to
meaningfulness and rareness of stimuli (Donchin &Coles, 1988).
In previous studies of deception, diagnoses depended upon the
comparison of the P300 amplitude in response to meaningful ver-
sus to other (irrelevant) stimuli on the assumption that the former
have more salience than the latter (Allen, Iacono, & Danielson,
1992; Farwell & Donchin, 1991; Rosenfeld, Angell, Johnson, &
Qian, 1991; Rosenfeld et al., 1988). These P300-based tests are
This research was supported by the Department of Defense Poly-
graph Institute Grants DODP198-P-0001 and DoDPI04-P-0002
awarded to J. Peter Rosenfeld. We thank Andreas Keil and an anon-
ymous reviewer for excellent suggestions regarding an earlier draft of this
report.Address reprint requests to: Dr. Ming Lui, Department of Psy-
chology, National University of Singapore, SG117570, Singapore.E-mail: m-lui@u.northwestern.edu
Psychophysiology, 46 (2009), 889–903. Wiley Periodicals, Inc. Printed in the USA.Copyright r 2009 Society for Psychophysiological ResearchDOI: 10.1111/j.1469-8986.2009.00810.x
889
based on the fact that a rarely presented item of concealed,
meaningful information, a probe, which is recognized by the
subject (even if behaviorally denied), will elicit the familiar P300
response, whereas other, frequently presented and nonmeaning-
ful items of information (irrelevants) will not elicit an increased
P300 (Donchin&Coles, 1988). Only guilty subjects are supposed
to show a significant difference between the guilty (probe) and
nonguilty (irrelevant) conditions.
Countermeasure to Lie Detection and the Use of
Subliminal Stimuli
Nevertheless, recent studies (Mertens & Allen, 2008; Rosenfeld,
Soskins, Bosh, & Ryan, 2004) found successful countermeasures
to this lie detection paradigm. A countermeasure is anything a
subject attempts to do during the test that tends to prevent the
detection of concealed information (Honts, Devitt, Winbush, &
Kircher, 1996). The countermeasure studies have involved train-
ing subjects to make concealed responses (e.g., wiggling the toe)
to the nonmeaningful items, which significantly increased the
P300 response to these irrelevant stimuli, and, therefore, no
difference was found between guilty and irrelevant stimulus con-
ditions. This makes it virtually impossible to distinguish probe
and irrelevant P300s, whose differences would otherwise be usu-
ally diagnostic for deception.
An obviously important requirement of physiologically based
methods for identifying deception is that such methods be resis-
tant to subjects’ attempts to defeat them, that is, with counter-
measures. In view of this, subliminal stimuli are here proposed to
be used in lie detection because they should be immune to coun-
termeasure use: If a key stimulus is presented subliminally, be-
cause it cannot be consciously perceived, subjects would not be
able to apply specific countermeasures to it. The current study
uses the paradigm of subliminal priming. Priming is a phenom-
enon of faster and more accurate response to stimuli that have
had prior exposure (e.g., Tulving & Schacter, 1990). Priming of
semantically related and unrelated words was found tomodulate
the amplitude and duration of ERP components (e.g., Besson,
Kutas, & van Petten, 1992). In the present study, a priming test
stimulus is presented subliminally prior to a supraliminally pre-
sented stimulus that evokes an ERP. It is expected that the sub-
liminal presentation of key test stimuli subliminally processed
uniquely by guilty subjects will affect ERP responses to the su-
praliminally presented stimuli in such a way as to allow discrim-
ination of guilty versus innocent subjects. (However, another
novel approach to P300-based deception detection which is re-
sistant to countermeasures was recently reported by Rosenfeld
et al. (2008).)
Outline of the Present Study
We attempt here to model a lie detection test for someone sus-
pected of being a terrorist, the aim being to identify members of a
terrorist ring. If stimuli were names of other terrorists in the
secret ring, only fellow terrorists (guilty subjects) should show a
difference of brain response between terrorists’ names and non-
terrorists’ names. In our study, college students were recruited
as subjects, and stimuli were supraliminal acquaintance names
preceded by a different subliminal acquaintance name versus a
nonacquaintance name. Other stimuli were supraliminal nonac-
quaintance names preceded by a subliminal acquaintance name
versus a different subliminal nonacquaintance name. It was
hypothesized that the subliminal priming of acquaintance and
nonacquaintance names would modulate ERP amplitude. Given
that task demand was found tomodulate subliminal priming in a
previous study (Nakamura et al., 2006), the current study ex-
amined the effect of the task demand associated with lying on
subliminal priming. It is hypothesized that lying would orient
subjects’ sensitivities toward the familiarity of the names, which
would increase the ERP difference between conditions primed
with acquaintance versus nonacquaintance names.
In this study, there were five groups of participants. Two of
these (Experiment 1 and the replication study) are near replica-
tions of each other and attempt to demonstrate a specific sub-
liminal priming effect during deception. Two other groups
(Experiments 2 and 3) were intended to control for two differing
respective effects that do not involve subliminal priming or
deception, but which could mediate putative priming effects in
Experiment 1 and its replication. The fifth groupwas an innocent
(nondeceptive) control group that allowed us to estimate the false
positive rate. We note that the groups were actually run in the
following order: Experiment 1, Experiment 2, Replication of 1,
Experiment 3, and, finally, the innocent group.
EXPERIMENT 1
Method
Participants
Fourteen (average age: 19.3 years, 9 men) Northwestern Uni-
versity undergraduate students participated in the present study
for the fulfillment of an introductory Psychology course require-
ment. They were all right-handed and had normal or corrected
vision. All signed an Institutional Review Board (IRB)-approved
consent form.
Procedures
Subjects were first asked to provide the last names of five people
they knew very well. They were also asked to select 4 names from
a list of 20 last names that did not have any personal meaning to
them. These 5145 9 names were the stimuli they would view
subliminally and supraliminally on the ERP test (see Table 1a).
They sat about 1 m from a computer screen. On the screen, brief
(subliminal) and long (supraliminal) presentations of last names
and symbols were shown. As shown in Figure 1 (trial structure),
in each trial, a name appeared on screen for 17 ms (subliminal),
preceded by a 100-ms forward mask and followed by a 17-ms
890 M. Lui and J.P. Rosenfeld
Table 1a. Experiments 1 and 3 Stimulus Arrangement and Response Requirement
Condition Symbol Subliminal prime Supraliminal target Expt. 1 task Expt. 3 task (half of the subjects)
1 A-A Acquaintance Acquaintance No Right2 N-A Nonacquaintance Acquaintance No Right3 A-N Acquaintance Nonacquaintance No Right4 N-N Nonacquaintance Nonacquaintance No Right5 Asterisks Acquaintance Yes Left
backward mask composed of symbols ‘‘$$##$$##$$##$$.’’
These were followed by another name, which appeared for
150 ms (supraliminal). Subjects were asked to respond to the
supraliminally presented names with a ‘‘yes’’ or ‘‘no’’ button
press. They were told that ‘‘yes’’ means ‘‘I DO know a person by
this name,’’ and ‘‘no’’ means ‘‘I DONOT know a person by this
name.’’ In the ERP collection session, subjects were instructed to
choose only one of the supraliminally presented acquaintance
names to respond truthfully to by pressing the ‘‘yes’’ button. For
the other four acquaintance names, they denied knowing themby
pressing the ‘‘no’’ button. For the 4 nonacquaintance names they
selected from the list, they responded truthfully by pressing the
‘‘no’’ button. They were asked to respond as soon as they could
following the supraliminal stimulus.
There were five stimulus-response conditions with different
response requirements and stimulus arrangements (see Table 1a)
in this first experiment and the replication: (1) supraliminal
acquaintance name preceded/primed by subliminal acquaintance
name (A-A), (2) supraliminal acquaintance name preceded/
primed by subliminal nonacquaintance name (N-A), (3) supra-
liminal nonacquaintance name preceded/primed by subliminal
acquaintance name (A-N), (4) supraliminal nonacquaintance
name preceded/primed by subliminal nonacquaintance name
(N-N), and (5) supraliminal acquaintance name preceded by as-
terisks, with no priming (this was simply an attention forcing
condition). Again, subjects responded ‘‘no’’ to the first four
conditions, but ‘‘yes’’ to the fifth. The stimuli were ordered in a
way such that no exact repetition occurred in a single trial. That
is, in conditions (A-A) and (N-N), the subliminal prime and
supraliminal target were always different even though they were
both acquaintance or nonacquaintance names (i.e., the priming
was ‘‘conceptual’’). Condition 5 served as a condition to main-
tain subjects’ attention by varying the response requirement
(‘‘yes’’ instead of ‘‘no,’’ which was the response in the other four
conditions); the data from this conditionwere not included in any
analysis. There were 20 practice trials and 360 actual trials, with
80 trials in each of the Conditions 1–4 and only 40 trials for
Condition 5.
After all the experimental trials, subjects were given an
awareness test (see below) to check the visibility of the subliminal
stimuli in individual subjects. Stimuli were similar to those in the
experimental trials except the subliminal stimuli were either non-
sense character strings (e.g., dfgiaesfr) or acquaintance names.
Subjects were required to do a lexical decision task by deciding
whether the subliminal stimuli were words or nonwords. Before
the awareness test each subject was also asked whether he/she
saw any of the subliminal stimuli, and their subjective reports
were recorded. In the awareness test, subjects were given
10 practice trials and 120 actual trials.
In subsequent material, because the data from the five groups
are meant to be compared, some methods used for all five
experiments are described together.
Statistical Analysis Procedures: PCA and BootstrappingMethods
(Used in All Five Experiments)
Spatial principal component analysis (PCA) on various sites on
the scalp is amethod utilized to identify clusters of electrodes that
are highly intercorrelated. It linearly combines the highly corre-
lated electrodes to form a virtual component or factor. The
component or factor yields the ‘‘virtual site’’ data to be used in
later analyses. This has the advantage of capturing most of the
relevant variance and therefore preserving the information from
the many actual electrodes, and at the same time reducing the
redundancy among them (Spencer, Dien, & Donchin, 2001).
Additionally, the linear combination method of PCA can pro-
duce orthogonal factors. Follow up, temporal PCA uses the same
principles except that the virtual temporal components are
formed by grouping of highly intercorrelated time point data
within each spatial component.
Subliminal priming in lie detection 891
Table 1b. Experiment 2 Stimulus Arrangement and Response
Requirement
Condition SymbolSubliminal
primeSupraliminal
targetExpt. 2task
1 A-A Acquaintance Acquaintance Yes2 N-A Nonacquaintance Acquaintance Yes3 A-N Acquaintance Nonacquaintance Yes4 N-N Nonacquaintance Nonacquaintance Yes5 Asterisks Nonacquaintance No
$$##$$##$
$$##$$##$
Baseline Recording
104 ms
100 ms
17 ms
EEG Epoch2048 ms
Yes or NoResponse
1660 ms
Mask
Mask
17 ms
150 ms
SubliminalName
SupraliminalName
Figure 1. Timing of mask and stimulus presentations in a single ERP epoch.
The present PCA data sets were obtained from an average
of ERPs at each time point within a given window of all trials of
the same stimulus type. First, spatial factors were extracted by
Varimax rotation, which produces factors with high loadings on a
small number of variables and low loadings on other variables
(Kaiser, 1960). Also, factors remain uncorrelated after Varimax
rotation, which prevents the problem of multicollinearity among
factors. Standardized factor loadings were the correlations be-
tween a variable (original site) and its corresponding factor (vir-
tual electrode). A site variable was selected only if its factor
loading exceeded 0.6 and if such a high loading for this site vari-
able was restricted to one factor. The factor scores were formed
by summing the site values multiplied by respective factor score
coefficients (Spencer et al., 2001). The spatial ERP components
were then subjected to a subsequent temporal PCA. For each
individual subject, spatial temporal components were formed
from the factor loadings obtained from the group spatial tem-
poral PCA. The spatial temporal components were first analyzed
by multivariate analysis of variance (ANOVA) on group data
with appropriate follow-up analysis to localize effects. The spa-
tial-temporal PCA andANOVAswere donewith SPSS software.
Individual diagnoses using bootstrapping procedures and
t tests on spatial-temporal components followed. A bootstrap-
ping procedure was applied to the spatial temporal components
in each individual. For example, assume there were x and y trials
in Conditions 1 and 2, respectively, in one subject. X and y trials
were drawn randomly (with replacement) from the actual pool of
spatial temporal component data in each of the Conditions,
1 and 2 separately and respectively, and an ERP average was
calculated for each randomly selected trial set within each con-
dition. The random selection process is repeated 100 times to get
100 sets of bootstrapped averages in each trial set. The boot-
strapping and averaging procedure was done with a MATLAB
script written by the first author. T tests were then applied to test
possible amplitude differences between mean amplitudes of
bootstrapped distributions for various pairs of conditions.
We note that in these experiments, PCAs were performed on
databases developed in two ways: (1) Within-study PCA: Each
group in each experiment yielded one data set for all conditions
within that specific experiment. (2) Combined PCA: Data from
all five groups were combined into one database, and a single set
of spatial-temporal components was determined for all studies.
The first method allows analyses optimized for each group, and
the variance source is principally the condition differences within
the group. The secondmethod allows differences between groups
as well to be a source of variance. It was found that the com-
bined-PCAmethod did not perform better than the within-study
PCA method in group analyses and in individual diagnoses. We
therefore report the statistical results of the within-study PCA
only hereafter.
Electroencephalogram Recordings (All Five Groups)
The electroencephalogram (EEG) data were referentially re-
corded from 30 tin electrodes in an Electrocap (Electrocap
International, Inc). The reference electrode was put on the nose
tip, with the forehead connected to the chassis of the isolated side
of the amplifier system (ground). A 0.3-Hz high-pass and a
30-Hz low-pass filter were used (Contact Precision Instruments
EEG 8 system). The sampling rate was at 125 Hz, and the EEG
signal was amplified by a factor of 50,000. Electrooculogram
(EOG) was recorded differentially from two electrodes diago-
nally placed above and below the left eye, so as to monitor both
vertical and horizontal eye movement. Trials containing 80 mVor
more deflections in the EOG electrodes were automatically re-
jected (without subject’s knowledge). Also, off-line visual in-
spection was done on individual trials to remove trials with
especially subtle eyemovement artifacts. All electrode resistances
weremaintained at or below 5 kO. As shown in Figure 1, all trials
began with a 104-ms baseline recording window, followed by a
forward mask (100 ms), a subliminal name (17 ms), a backward
mask (17 ms), a supraliminal name (150 ms), and a response
window (1660 ms). The length of an epoch was 2048 ms. The
latencies of ERPs in analyses were timed from the onset of the
subliminal stimulus, as we presumed that the ERP elicited by
supraliminal stimulus would be affected by the preceding sub-
liminal stimulus.
For all group analyses and displays, single sweeps and aver-
ages were digitally filtered off-line to remove higher frequencies;
3 db point5 4.23 Hz. Separate sets of group analyses were done
on 10-Hz low-pass data. No significant effects were found.1 We
therefore report only the analysis results of the 4.23-Hz low-pass
data in the result session.
Results
Behavioral
All subjects responded correctly (i.e., pressing ‘‘yes’’ to Condi-
tion 5 stimuli and pressing ‘‘no’’ to all others) in more than 97%
of trials. There was no significant difference in mean reaction
times between all conditions (p4.05).
Awareness Test
The d0 indices ranged from � .32 to 1.38. Chi-squared test
showed that only 1 out of the 15 subjects had a significant
difference in response to word and nonword conditions
(w2 5 5.17, p5 .023). This awareness test result was also consis-
tent with the subject’s subjective report. The subject’s data were
excluded from further analysis.
ERP Data and PCA
Figure 2 shows a graphical illustration of the ERP (pre-PCA)
grand averages of 4 (Fz, Cz, Pz, and Oz) out of 30 electrode sites
for Experiment 1. For the within-study PCA in Experiment 1, a
covariance-based PCA was applied on the 30-sites data from 0
ms to 1396 ms after stimulus onset for extraction of spatial
components. The data matrix consisted of 30 (number of elec-
trodes) � 4 (number of conditions) � 176 (number of time
points per trial) � 14 (number of subjects) cases. The spatial
PCA extracted four spatial components (accounting for 88.3%
of the variance): frontal-central-parietal (34.6%), occipital-
parietal (31.4%), frontal (14.7%), and prefrontal (7.8%). The
actual sites included in each component were (1) frontal-central-
parietal component (FCP: Pz, C3, P3, Fz, Fc1, Fc5, Cp1, Cp5,
C4, Cz, Fc2, Cp2), (2) occipital-parietal component (OP: O1, P7,
Oz, P4, O2, P8, Cp6), (3) frontal component (F3, F7, Af3, F4, F8,
Fc6) and (4) prefrontal component (Fp2, Fp1, Af4). It is noted
892 M. Lui and J.P. Rosenfeld
1In previous P300 studies, low-pass filterwas usually set lower than 10Hz. For instance, Fabiani, Gratton, Karis, and Donchin (1987) filtered(low-passed) P300 averages at 6.29 Hz and single sweeps at 3.13 Hz. Webelieved that the main ERP component that revealed the difference be-tween conditions in the current study was the P300, which has a meanfrequency under 2 Hz (Duncan-Johnson & Donchin, 1979). The inclu-sion of high frequency noise in 10 Hz low-pass datamay have diminishedthe P300 effect.
that components have names in common (e.g., frontal, central)
but these components have different actual electrodes contrib-
uting to the component. A temporal PCAwas then performed on
the four spatial component data. The temporal PCA resulted in
five temporal components (accounting for 91.39% of the vari-
ance): 36–324 ms (12.4%), 332–516 ms (20.2%), 524–668 ms
(13.4%), 676–908 ms (16.1%), and 916–1396 ms (29.4%).
Group ERP Analysis and Individual Diagnosis
Table 2a–d shows the analytic results for the components ex-
tracted with the within-study PCA. In each of the five temporal
components, a separate multivariate analysis of variance
(MANOVA) was done. In each MANOVA, the four spatial
components were four dependent variables. Condition (i.e., the
stimulus–response condition) was the independent variable. The
omnibus MANOVAs showed that the effect of condition was
significant in the following temporal components: (1) 332–516
ms: Wilks’ l5 .48, F(12,96)5 2.59, p5 .005; (2) 524–668 ms:
Wilks’ l5 .38, F(12,96)5 3.55, po.001; (3) 916–1396 ms:
Wilks’ l5 .47, F(12,96)5 2.61, p5 .005 (see Table 2a).
For the component 332–516 ms, the effect of condition was
significant in all spatial components (po.05). However, Bon-
feronni pairwise comparisons showed no other significant differ-
ences between any meaningful pairwise comparisons excepting a
marginal p value for the OP component (see Table 2c).
For the component 524–668 ms, the effect of condition was
significant in the frontal-central-parietal, F(3,39)5 10.12,
po.001, and occipital-parietal, F(3,39)5 14.43, po.001, spatial
components. Bonferroni pairwise comparison showed that
Condition 2 (N-A) was significantly more positive than Condi-
tion 1 (A-A) for the frontal-central-parietal component
(p5 .035) and the occipital-parietal component (po.001).
Because the conservative Bonferonni tests revealed some signifi-
cant pairwise group differences at 524–668 ms, we did individual
Subliminal priming in lie detection 893
–200 0 200 400 600 800 1000 1200 1400
–5
0
5
10
ms
mic
ro-v
olts
FZ–5
0
5
10
CZ
–5
0
5
10
mic
ro-v
olts
PZ–5
0
5
10
OZ
–200 0 200 400 600 800 1000 1200 1400
–200 0 200 400 600 800 1000 1200 1400–200 0 200 400 600 800 1000 1200 1400
mic
ro-v
olts
mic
ro-v
olts
ms
msms
Figure 2. Experiment 1 raw (pre-PCA) grand averages from 4 of the 30 actual sites.
Table 2a. Experiment 1 Omnibus MANOVAs: Main Effect of
Condition
Temporal component (ms)
36–324 332–516 524–668 676–908 916–1396
Wilk’s l .615 .475 .377 .683 .473Fstatistic 1.607 2.587 3.545 1.236 2.607p .103 .005nn .000nn .270 .005nn
Note: Results based on within-study PCA-extracted components.nnpo.01.
Table 2b. Experiment 1 Univariate ANOVAs p Values
Temporal component (ms)
36–324 332–516 524–668 676–908 916–1396
FCP .319 .022n .000nn .493 .017n
OP .011n .028n .000nn .079 .014n
F .589 .047n .049n .914 .629Pre-F .534 .009nn .043n .764 .813
Note: Results based on within-study PCA-extracted components. FCP:frontal-central-parietal component; OP: occipital-parietal component; F:frontal component; Pre-F: prefrontal component.npo.05, nnpo.01.
diagnoses in these cases (and also in some other near significant
cases in Table 2c): Bootstrapping of amplitude difference was
done between Condition 1 (A-A) and Condition 2 (N-A). Table
2d shows that 11 of 14 (78.6%) subjects have significantly more
positive frontal-central-parietal amplitude for Condition 2
(N-A) than for Condition 1 (A-A), whereas 12 out of 14 (85.7%)
subjects had significantly more positive occipital-parietal ampli-
tude for Condition 2 (N-A) than for Condition 1 (A-A). It is
noted that for A-N versus N-N, no Bonferonni tests were sig-
nificant, so no follow-up individual diagnostics were performed.
For the component 916–1396 ms, the effect of condition was
significant only in the frontal-central-parietal, F(3,39)5 3.83,
p5 .017, and the occipital-parietal,F(3,39)5 3.99, p5 .014) com-
ponents. Bonferroni pairwise comparison showed that Condition
2 (N-A) was significantly more positive than Condition 1 (A-A)
for the occipital-parietal (p5 .026) but not for the frontal-
central-parietal component. Bootstrapping of amplitude differences
was done on the occipital-parietal component. Table 2d shows that
11 out of 14 subjects (78.6%) had significantly more positive
amplitude in Condition 2 (N-A) than in Condition 1 (A-A).
Discussion and Introduction to the Replication Study
The results of the first experiment revealed dramatic subliminal
priming effects reaching diagnostic utility levels. Experiments
2 and 3 below were directed at controlling and investigating
possible confounding factors, but it seemed important to us to
be able to replicate the results in the original study. Therefore,
Experiment 1 was replicated as fully as possible in a new group of
subjects. In the replication, the procedures were similar to those
in Experiment 1, except that the new subjects were asked to pick
4 names from a pool of 100 names rather than only 20 names as
in Experiment 1. Another difference was that subjects were asked
to pick nonacquaintance names that had equal numbers of syl-
lables as the acquaintance names they had written down. The
stimulus arrangements, procedures, and task requirements were
otherwise identical to those in Experiment 1.
REPLICATION STUDY
Results
PCA Results
The spatial, within-study PCA in this replication extracted three
spatial components (accounting for 90.7% of the variance):
frontal-central-parietal (38.3%), occipital-parietal (31.5%), and
frontal (20.9%). The actual sites included in each components
were frontal-central-parietal (Cp1, C3, Cz, Fc1, Cp2, Pz, Fc2,
C4, Cp5, P3, Fc5), occipital-parietal (O2, Oz, O1, P7, P4, Cp6),
and frontal (Fp2, Af4, F8, Fp1, Af3, F4, Fz, F3, Fc6). This
result was very similar to that of Experiment 1 (see above). A
temporal PCA was then performed on the three spatial compo-
nent data. The temporal PCA resulted in four temporal compo-
nents (accounting for 87.9% of the variance): 12–316 ms
(20.6%), 324–508 ms (27.5%), 588–796 ms (15.4%), and 804–
1396 ms (24.4%). This was also similar, though not identical, to
the results of the original study, Experiment 1 (see Figure 3).
Behavioral RT Data
The mean reaction time in the replication was 438.45 ms, almost
identical to the value from Experiment 1 at 435.77 ms. There
were no differences among conditions.
Awareness Test
The d0 indices ranged from � .40 to 1.30, and no significant
results were found in the chi-squared tests (all p4.05), showing
that subjects could not discriminate subliminal words from sub-
liminal nonwords.
ERP Data
The grand average ERPs for the two spatial components and two
condition contrasts are shown in Figures 4 and 5 along with data
from other experimental groups. Table 3a–d shows the detailed
analysis results for the replication, just as for Table 2a–d for
Experiment 1. Only the 588–796-ms temporal component at
FCP shows a significant Bonferonni result: Again, Condition 2
(N-A) was found to be significantly more positive than Condi-
tion 1 (A-A) whereas no difference was found between Condi-
tions 3 (A-N) and 4 (N-N). This time the significant difference
was restricted to the 588–796-ms temporal component of the
frontal-central-parietal spatial component (p5 .032). This com-
pares reasonably, given slight procedural differences (see above)
and a new subject sample, to the result found in the same spatial
component in the original study, which had a slightly earlier
temporal component at 524–668 ms. In individual diagnosis, 12
out of 14 (85.7%) of the subjects had significantly more positive
N-A than A-A conditions. (It is also the case that, in the Ex-
periment 1, the occipital-parietal component additionally
showed significant pairwise effects that were not observed in
the replication.)
EXPERIMENT 2
As we reported above, in Experiment 1, no priming effect was
found in conditions with supraliminal nonacquaintance names
(Condition 3 and Condition 4 in Table 1a). Because in Exper-
iment 1, subjects were lying in Conditions 1 (A-A) and 2 (N-A),
894 M. Lui and J.P. Rosenfeld
Table 2c.Experiment 1 Bonferroni Tests: Condition 1 (A-A) versus
Condition 2 (N-A)
Temporal component (ms)
36–324 332–516 524–668 676–908 916–1396
FCP 1.000 .673 .035n 1.000 .506OP .065 .056 .000nn .051 .026n
F 1.000 1.000 1.000 1.000 1.000Pre-F 1.000 1.000 1.000 1.000 1.000
Note: Results based on within-study PCA-extracted components. FCP:frontal-central-parietal component; OP: occipital-parietal component;F: frontal component; Pre-F: prefrontal component.npo.05, nnpo.01.
Table 2d. Experiment 1 Individual Diagnosis Based on A-A
versus N-A
Temporalcomponent (ms) Spatial component Detection rate
524–668 frontal-central-parietal 11/14 (78.6%)524–668 occipital-parietal 12/14 (85.7%)916–1396 occipital-parietal 11/14 (78.6%)332–516 occipital-parietal 11/14 (78.6%)676–908 occipital-parietal 10/14 (71.4%)
conditions with supraliminal acquaintance names, but telling the
truth in Conditions 3 (A-N) and 4 (N-N), conditions with su-
praliminal nonacquaintance names, two possible, non-mutually-
exclusive explanations for the findings are viable: It could be that
lying is necessary to get the effect, which occurs when the subjects
say ‘‘no’’ to supraliminal acquaintance names but not to non-
acquaintance names. However, it may also be the case that less
familiar supraliminal nonacquaintance names are not primed. To
investigate these possibilities, in Experiment 2, the response re-
quirement was reversed: subjects lied in conditions with supra-
liminal nonacquaintance names rather than in conditions with
supraliminal acquaintance names. The attention demanding
condition (Condition 5) was also a supraliminal nonacquain-
tance name (see Table 1b). It was predicted that no priming effect
would be found in conditions with supraliminal nonacquaintance
names (A-N and N-N) due to the lack of familiarity and long-
term memory representation for nonacquaintance names.
Methods
Participants
Thirteen (average age: 19.2 years, 7 men) Northwestern Uni-
versity undergraduate students who were not in Experiment 1
participated in Experiment 2 for the fulfillment of an introduc-
tory Psychology course requirement. They were all right-handed
and had normal or corrected vision. All signed an IRB-approved
consent form.
Stimuli and Procedures
The timing and construction of stimuli were similar to that in
Experiment 1 except that the attention catching condition was a
nonacquaintance name instead of an acquaintance name (see
Table 1b). Subjects were required to press ‘‘yes’’ to all conditions
and ‘‘no’’ to one of the nonacquaintance names they chose. In
that way subjects were lying to the conditions with supraliminal
nonacquaintance names (Conditions 3 and 4), and they were
telling the truth to conditions with supraliminal acquaintance
names (Conditions 1 and 2).
Results
Behavioral Data
All subjects responded correctly to over 95% of trials. There was
no significant difference in reaction times among all conditions.
Awareness Test
The d0 indices ranged from � .34 to 1.31, and no significant
results were found in the chi-squared tests (all p4.05), showing
that subjects could not discriminate subliminal words from sub-
liminal nonwords.
PCA
A covariance-based, within-study PCA was applied on the 30-
sites data from 0ms to 1396ms after stimulus onset for extraction
of spatial components. The data matrix consisted of 30 (number
of electrodes) � 4 (number of conditions) � 176 (number of
time points per trial) � 13 (number of subjects) cases. The spa-
tial PCA extracted three spatial components (accounting for
88.7% of the total variance): frontal-central-parietal (36.8%),
occipital-parietal (31.2%), and frontal (20.7%). The actual sites
included in each components are frontal-central-parietal (Pz, C3,
P3, Fc1, Fc5, Cp1, Cp5, C4, Cz, Fc2, Cp2), occipital-parietal
(O1, P7, Oz, P4, O2, T8, P8, Cp6), and frontal (F3, F7, Fz, Af3,
Fp2, F4, F8, Fp1, Af4, Fc6). A temporal PCA was then per-
formed on the three spatial component data. The temporal PCA
resulted in six temporal components (accounting for 93.7% of
the variance): 0–236 ms (16.5%), 244–340 ms (5.4%), 348–556
ms (25.7%), 564–732 ms (17.2%), 740–1060 ms (16.2%), and
1068–1396 ms (12.8%). The spatial components found in Ex-
periment 2 are similar to those found in Experiment 1 except that
the prefrontal sites (which were grouped to a separate prefrontal
component in Experiment 1) were included in the frontal com-
ponent in Experiment 2. For the temporal PCA, Experiments 1
and 2 obtained similar first two components (see Figure 3), but
the later temporal component structure appears different.
Group Analysis and Individual Diagnosis
Figures 4 and 5 show that, for both the FCP and OP spatial
components, differences between waveforms are restricted to
later portions on the epoch, after 700 ms. In each of the six
Subliminal priming in lie detection 895
Figure 3.Diagram indicating statistical significance in different temporal regions. Time 0 is the subliminal stimulus onset. The areas
shaded in black are temporal regions with significant effects among experimental conditions. Significant effects were only found in
Experiment 1 and the replication study.
temporal components, separate MANOVAs were done as de-
scribed previously for Experiment 1 and its near replication. In
each MANOVA, the three spatial components were three de-
pendent variables, condition was the independent variable. The
omnibusMANOVAs showed that the effect of conditionwas not
significant in any analyses. No significant effects were found in
univariate ANOVAs. Therefore no further analysis was done.
Discussion
Results indicated that the effect of subliminal priming was
absent even when subjects lied in conditions with supraliminal
nonacquaintance names (i.e., A-N and N-N). The lack of long-
term memory representation for nonacquaintance names possi-
bly prevented priming from taking effect (discussed further
below). Moreover, when subjects were instructed to tell the truth
in conditions with supraliminal acquaintance names (i.e., A-A
andN-A), the effect of subliminal priming found inExperiment 1
disappeared. Lying is therefore not sufficient to produce the
subliminal priming effects seen in Experiment 1 and its replica-
tion. But lying may be necessary to produce the effect. Exper-
iment 3 was intended to test this hypothesis, by replicating the
conditions of Experiment 1 except with the lying behavior
removed.
896 M. Lui and J.P. Rosenfeld
AA vs NA AN vs NN
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Figure 4. ERPs of the frontal-central-parietal component in Experiments 1–3 and the replication study.
EXPERIMENT 3
Lying was removed in this experiment; hence the possible mod-
ulation of task requirement (i.e., deception) on stimulus-driven
subliminal priming effects could be observed by comparing the
results of Experiments 1 and 3.With the elimination of the lying
task and the associated meaning of lies, in Experiment 3 we
expected that the processing of acquaintance and nonacquain-
tance names would be different and the subliminal priming
effect would be attenuated. No difference was expected between
Conditions 1 (A-A) and 2 (N-A), and no difference was ex-
pected for the comparison between Conditions 3 (A-N) and
4 (N-N).
Methods
Participants
Twelve (average age: 19.3 years, 6 men)NorthwesternUniversity
undergraduate students who were not in Experiment 1 or 2 par-
ticipated in Experiment 3 for the fulfillment of an introductory
Psychology course requirement. They were all right-handed and
had normal or corrected vision. All signed an IRB-approved
consent form.
Stimuli and Procedures
The timing and construction of stimuli were identical to that in
Experiment 1 except that subjects were required to press a right
Subliminal priming in lie detection 897
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button to all conditions and to press a left button to one of the
acquaintance names which they chose (see Table 1a). (The left/
right key assignment was counterbalanced across subjects.) That
is, there were no ‘‘yes’’ and ‘‘no’’ buttons, just ‘‘right’’ and ‘‘left’’
buttons. This procedure excluded the admitting and denying of
acquaintance name recognition as in Experiment 1. Also, sub-
jects in Experiment 3 were asked to select four names from a list
of 100 common names rather than only 20 names as in Exper-
iment 1, and they were asked to pick the nonacquaintance names
that have equal numbers of syllables to the acquaintance names
they wrote down.
Results
Behavioral Data
All subjects responded correctly (i.e., pressing one button to
Condition 5 stimuli and pressing another button to all others) to
over 95% of trials. There was no significant difference in RT
among all conditions (p4.05).
Awareness Test
The d0 indices ranged from � .34 to 1.42, and chi-squared tests
showed none of the subjects responded significantly differently in
response to word and nonword conditions.
PCA
Figure 6 shows a graphical illustration of the ERP (pre-PCA)
grand averages of 4 (Fz, Cz, Pz, and Oz) out of 30 eletrode sites
for Experiment 3. A covariance-based within-study PCA was
applied on 30 sites data from 0ms to 1396ms after stimulus onset
for extraction of spatial components. The data matrix consisted
of 30 (number of electrodes) � 4 (number of conditions) �176 (number of time points per trial) � 12 (number of subjects)
cases. The spatial PCA extracted three components which ac-
counted for 85.6% of total variance: frontal-central-parietal
(36.1%), frontal (28.0%), and occipital-parietal (21.4%). The
actual sites included in each component are frontal-central-
parietal (C3, Cp1, Cz, Fc5, Fc1, Fc2, Cp2, Cp5, C4, Pz, P3, F3,
Fz, T7, Fc6, P4), frontal (Fp2, Af3, F7, F4, T8, Fp1, F8, Af4),
and occipital-parietal (O2, P8, O1, Oz, P7, Cp6). A temporal
PCA was then performed on the three spatial components. The
temporal PCA resulted in four temporal components (92.1% of
the variance explained): 0–348ms (20.4%), 356–596ms (17.7%),
604–1012 ms (34.0%), and 1020–1396 ms (20.0%).
Spatial components obtained in Experiment 3 are very similar
to those in Experiment 2. However, the temporal components
obtained in Experiment 3 are different from those in Experiment
1 and its replication and Experiment 2 starting from 500–600 ms.
In Experiments 1 and 2, three components were obtained after
around 500–600 ms (e.g., 524–668 ms, 676–908 ms, and 916–
1396 ms) whereas in Experiment 3 only two components were
obtained (604–1012 ms and 1020–1396 ms; see Figure 3).
Group Analysis and Individual Diagnosis
Figures 4 and 5 show grand average ERPs from virtual compo-
nent sites. It appears from visual inspection that the ERPs are not
different among all conditions at both virtual sites.
In each of the four temporal components, a separate
MANOVA was done as before. In each MANOVA, the three
spatial components were three dependent variables. Condition
was the independent variable. The omnibusMANOVAs resulted
in no significant effects in all analyses (p4.05). Therefore no
individual diagnosis was carried out.
Discussion
Removal of the deception requirement in Experiment 3 led to an
absence of subliminal priming effects, and therefore, an inability
to find any significant pairwise comparisons of interest, which
would suggest that deception is a necessary element in the pro-
tocol of Experiment 1 ( Table 1a) that produces ERP differences
between differentially primed, dishonest denials of acquaintance
recognition.
898 M. Lui and J.P. Rosenfeld
Table 3a. Replication Study Omnibus MANOVAs: Main Effect
of Condition
Temporal component (ms)
12–316 324–580 588–796 804–1396
Wilk’s l .703 .852 .739 .557Fstatistic 1.560 0.683 1.326 2.726p .140 .723 .235 .007nn
Note: Results based on within-study PCA-extracted components.nnpo.01.
Table 3b. Replication Study Univariate ANOVAs p Values
Temporal component (ms)
12–316 324–580 588–796 804–1396
FCP .078 .328 .047n .001nn
F .260 .206 .053 .091OP .234 .711 .145 .100
Note: Results based on within-study PCA-extracted components. FCP:frontal-central-parietal component; OP: occipital-parietal component; F:frontal component.npo.05, nnpo.01.
Table 3c. Replication Study Bonferroni Tests: Condition 1 (A-A)
versus Condition 2 (N-A)
Temporal component (ms)
12–316 324–580 588–796 804–1396
FCP .548 .651 .032n .187F 1.000 1.000 .145 .903OP 1.000 1.000 .168 .944
Note: Results based on within-study PCA-extracted components. FCP:frontal-central-parietal component; F: frontal component; OP: occipital-parietal component.npo.05.
Table 3d. Replication Study Individual Diagnosis Based on A-A
versus N-A
Temporal component (ms) Spatial component Detection rate
588–796 frontal-central-parietal 12/14 (85.7%)
Note: Results based on within-study PCA-extracted components.
INNOCENT GROUP
Methods
Participants
Eleven (average age: 18.5 years, 4 men) Northwestern University
undergraduate students who were not in Experiments 1 or 2 or 3
participated in the innocent group experiment for the fulfillment
of an introductory Psychology course requirement. They were all
right-handed and had normal or corrected vision. All signed an
IRB-approved consent form.
Stimuli and Procedures
The procedures were similar to that in the replication study ex-
cept that subjects were asked to provide only one acquaintance
name (to be used as ‘‘attention catching’’ or target stimuli) and
choose 8 nonacquaintance names from the list of 100 common
names. They were asked to choose two 1-syllable names, four
2-syllable names, and two 3-syllable names. Half of the names
selected were denoted as ‘‘pseudo acquaintance names’’ and half
of them as nonacquaintance names in the data analyses. The
pseudo acquaintance names and nonacquaintance names
have the same number of syllables (one 1-syllable name, two
2-syllable names, and one 3-syllable name).
The timing and construction of stimuli were similar to that in
the replication study. Subjects were required to press a ‘‘no’’ to all
stimuli except the target, which was an acquaintance name sub-
jects provided. The button positions were counterbalanced (half
of the subjects pressed the left button for ‘‘yes’’ response and the
right button for ‘‘no’’ response and half of the subjects responded
in the other way).
Results
Behavioral Data
All subjects responded correctly (i.e., pressing ‘‘yes’’ to Condi-
tion 5 stimuli (target stimuli; see Table 1) and pressing ‘‘no’’ to all
others) to over 92% of trials. There was no significant difference
among all conditions (p4.05) in RT.
Awareness Test
The d0 indices ranged from � .31 to 1.20, and chi-squared tests
showed none of the subjects responded significantly differently in
response to word and nonword conditions (p4.05).
ERP Data
For the innocent control study, the spatial temporal components
identified in the replication group were utilized to analyze the
data in the control group. We could have used the components
from Experiment 1, but the treatment of the replication group
was more similar in all other ways but guilt and innocence to that
of the control group than was the treatment of the Experiment 1
group. (The components extracted from Experiment 1 and the
replication were relatively similar anyway, as shown in Figure 3
and its discussion below.) The analytic results showed no sig-
nificant main effects in MANOVA or in univariate ANOVA
tests. Consistent with these results, Figure 7 shows virtual site
grand average ERPs for the innocent control group, FCP com-
ponent (top), and OP component (bottom). At FCP, there is not
Subliminal priming in lie detection 899
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Figure 6. Experiment 3 raw (pre-PCA) grand averages from 4 of the 30 actual sites.
much difference between A-A and N-A waveforms and, where
there is a difference, A-A appears mostly more positive, unlike the
priming effects seen in Experiment 1 and the replication. The OP
component shows the same null results. For the A-N versus N-N
comparison, both FCP and OP show some apparently more neg-
ative segments for A-N, but as noted above, none of these effects
in the control group reached or approached significance.
We did individual diagnostics in this innocent control group
on components comparable to those utilized in Experiment 1 and
the replication, however, because we wanted to see what the false
positive rates would be. These rates varied from 2/11 to 5/11. In
the replication study most comparable to the innocent group, we
correctly detected 12/14 (86.7%) subjects using the within-rep-
lication study PCA-extracted FCP component, 588–796 ms. The
same spatial and temporal component in the innocent group led
to 4/11 (36.3%) false positives. This yields a Grier (1971) A0
index of test efficiency of .84. (Table 4a,b shows A0 values forvarious pairings of hit rates fromExperiment 1 and its replication
with false positive rates from the innocent control groups.)
Summary of Differences among the Five Groups
In Experiments 1 and 2, subjects were asked to choose nonac-
quaintance names from a list of 20 names, and the number(s) of
syllables of the acquaintance and nonacquaintance names were
not matched. In the replication, Experiment 3, and the innocent
groups, subjects were asked to choose nonacquaintance names
from 100 common surnames in the United States. The names
were selected from a web site (Most Common Names and Sur-
names in the U.S., n.d.) listing all surnames with over .001%
frequency in the U.S. population during the 1990 census. They
were also instructed to choose names thatmatched the number of
syllables of the acquaintance names they provided.
RT Data for All Studies, Averaged across Conditions
These results (in milliseonds) were as follows: Experiment 1:
435.77, Experiment 2: 447.13, Experiment 3: 404.08, Replica-
tion: 438.45, Innocent: 369.4. It is also noted that there were no
significant differences in overall reaction time among the three
experiments plus the replication of Experiment 1. However, a
1 � 5 ANOVA including the innocent group yielded F(4,63)5
5.039, p5 .001. This suggested that the mean RTof the innocent
group was different than the mean of the experimental groups,
and, indeed, F(1,62)5 14.54, po.001, for this test. Clearly, the
lack of lying and related manipulations in the innocent group
affected RTuniquely in the innocent group in comparison to the
other groups.
900 M. Lui and J.P. Rosenfeld
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Table 4a. Experiment 1 and Innocent Group Individual Diagnosis,
A-A versus N-A, within-study PCA
Temporalcomponent(ms)
Spatialcomponent Detection rate
False positive(innocentgroup) A0
524–668 frontal-central-parietal
11/14 (78.6%) 4/11 (36.4%) .80
524–668 occipital-parietal 12/14 (85.7%) 5/11 (45.5%) .81916–1396 occipital-parietal 11/14 (78.6%) 2/11 (18.2%) .88
Table 4b. Replication and Innocent Group Individual Diagnosis,
A-A versus N-A, within-study PCA
Temporalcomponent(ms)
Spatialcomponent Detection rate
False positive(innocentgroup) A0
588–796 frontal-central-parietal
12/14 (85.7%) 4/11 (36.4%) .84
Qualitative ERP Data in All Studies
Figures 4 and 5 show the grand averages for each experimental
group in the two spatial components, frontal-central-parietal
(FCP, Figure 4) and occipital-parietal (OP, Figure 5), extracted
from the within-study PCAs, respectively, each component ac-
counting for more than 20% of the variance in the data. The two
columns in each figure show superimposed wave forms for the
A-A versus N-A comparison at the left, and A-N versus N-N at
the right. Recall that in Experiment 1 and the replication, priming
was expected for the A-A versus N-A comparison, but not the
A-N versus N-N comparison. For the FCP comparison in Fig-
ure 4, in Experiment 1 and in the replication, the priming effect
appears to be a negative shift throughout, but seenmostly between
500 and 800 ms, which is present only in A-A versus N-A, as
expected. In theOP component (Figure 5), the same differences are
seen; the contrasts between A-A versus N-A and A-N versus N-N
seem very clear. For Experiments 2 and 3, there are no apparent
priming effects for FCP or OP in any contrast, as expected.
General Discussion
Experiment 1 and its replication demonstrated a protocol in
which ERPs to dishonestly answered primed by subliminal non-
acquaintance names, supraliminally presented acquaintance
probes could be discriminated from primed by subliminal non-
acquaintance names, supraliminally presented acquaintance
probes. (We are noting only results obtaining in both the orig-
inal and replication studies.) The discrimination was good
enough so that about 80%–86% of the subjects (depending on
selection of specific spatial and temporal components analyzed)
could be identified in their dishonest denials of acquaintance
recognition (e.g., saying ‘‘no’’ to supraliminally presented ac-
quaintance names). In addition to the difference in dishonest
behavior between conditions A-A and N-A, on the one hand,
versus A-N and N-N, on the other, is the difference in the nature
of supraliminal stimuli in the pairs of conditions (A in A-A and
N-A vs. N in A-N and N-N). Experiment 2 was directed at
identifying possible key necessary factors for producing the
effects seen in Experiment 1 and its replication. Conditions 1 and
2 in Experiment 2 were exactly like those in Experiment 1 except
that subjects told the truth and did not lie in Conditions 1 and
2 of Experiment 2 (Table 1, cf. a and b). Subliminal A did not
prime supraliminal A in Experiment 2 as it did in Experiment 1,
in the absence of deception. (We assume the priming of one
stimulus by another requires identical types of stimuli. It also
appears that familiar stimuliFacquaintancesFbut not unfa-
miliar stimuli are more effective in priming; see below.) We con-
clude that the specific nature of the subliminal prime is not
sufficient to generate the priming effect. Neither is deception per
se sufficient, as Conditions 3 and 4 produced no priming in
Experiment 2. Experiment 3 reproduced the stimulus conditions
of Experiment 1, but with the deception requirement removed
and, again, no priming occurred.
Taken together, all these results suggest deception is necessary
but not sufficient to produce priming effects. The other necessary
factors likely include whether or not the stimuli are familiar (see
below) as well as the relationship or interaction of subliminal and
supraliminal stimuli. To answer this question, one must perform
further parametric studies. Nevertheless, the present results sug-
gest that a countermeasure-resistant protocol for detecting con-
cealed information may be developed around the protocol of
Experiment 1.
P300 Effects
In Experiments 1–3, we have tried to systematically look at the
effect of the lying task requirement and stimulus type on sub-
liminal priming. In all three experiments, stimuli consisted of
subliminal primes of acquaintance or nonacquaintance names
preceding a supraliminal target of different acquaintance or
nonacquaintance names. Results of Experiment 1 indicated that
the ERP response differed when different subliminal primes pre-
ceded supraliminal acquaintance names (A-A and N-A). The
condition with a congruent prime–target pair (acquaintance
preceding acquaintance names) produced a smaller positive am-
plitude than the condition with an incongruent pair (nonac-
quaintance preceding acquaintance names) in the 524–668-ms
temporal segment, which is in the typical P300 region. It was
hypothesized that P300 is related to decision making (Kutas,
McCathy, & Donchin, 1977) and the end of a decision process
(Donchin & Coles, 1988). The ‘‘context-update hypothesis’’
suggested that P300 signifies the updating of working memory
when processing unexpected events (Donchin, 1981). In Exper-
iment 1 and the replication, the supraliminal stimulus in Con-
dition 2 (N-A) was supposed to be less expected than in
Condition 1 (A-A) due to the incongruency of the prime–target
pair andmay therefore elicit a larger P300 during the updating of
working memory.
In fact, a modulation of P300 by subliminal primes was re-
ported by Dehaene, Kerszberg, and Changeux (1998), though
the modulation was in terms of latency but not amplitude. The
stimuli were numerals 1–9 in Arabic or word form. A suprali-
minal target numeral was preceded by a subliminal prime nu-
meral. Subjects performed a simple semantic categorization task
on the target numeral. Primes and targets were either congruent
or incongruent in the response requirement. The ERP compo-
nent that showed a prime–target congruity effect was the central
positivity at around 600 ms, which was delayed by around 24 ms
in incongruent trials compared with congruent trials.
Top-Down Effects of Long Term Memory
The results in Experiments 1 and 2 revealed that, under the same
task requirement and stimulus conditions, subliminal neural
priming occurs only in conditions with supraliminal acquain-
tances but not with supraliminal nonacquaintances. The present
results of the presence and absence of priming effect in acquain-
tance and nonacquaintance conditions, respectively, may pro-
vide hints about the interaction between perceptual processing of
stimuli and preexisting long-term memory representation (Hen-
son, 2003). Some studies have found priming for both familiar
and unfamiliar words and faces (Bowers, 1994; Goshen-Gott-
stein & Ganel, 2000; Stark & McClelland, 2000). However, be-
havioral priming effects are generally larger for familiar than for
unfamiliar stimuli. Also, there were previous studies that found
priming only for familiar but not for unfamiliar stimuli (e.g.,
Ellis, Young, & Flude, 1990). The findings in conscious priming
generally indicated that priming of stimuli with preexisting rep-
resentation in long-term memory undergoes different mecha-
nisms compared to priming of novel stimuli lacking
representation in long-term memory. The present study differed
from the aforementioned studies in that subliminal stimuli were
used. This may explain why different results of priming were
found in supraliminal acquaintance name conditions (A-A and
N-A) and supraliminal nonacquaintance name conditions (A-N
andN-N). It maybe the case that the signals of subliminal primes
were too weak to activate and facilitate the formation of a new
Subliminal priming in lie detection 901
cortical network representing the nonacquaintance names, and
therefore no subliminal priming effects were found in A-N and
N-N. For supraliminal acquaintance name conditions A-A
and N-A, with preexisting representation, subliminal primes
were able to impose an effect on the supraliminal target and
therefore significantly modulated the ERP amplitude.
Top-Down Effects of Task Requirement
Experiment 1 and Experiment 3 had identical stimuli, and even
the behavioral response requirements were the same: pressing
one button in response to one of the acquaintance names and
pressing another button in response to all the other names. The
only difference between the two experiments was the meaning of
the button pressing. The responses in Experiment 1 involve ad-
mitting and denying the recognition of acquaintance and non-
acquaintance names, whereas responses in Experiment 3 do not.
As mentioned in previous sections, the task requirement may
modulate how the cognitive system processes input stimuli. The
meaning of denying and admitting recognizing the names did
affect how subjects processed subliminally primed acquaintance
names (A-A and N-A), as the neural priming effect was found
only when the task carries the denying/admitting meaning but
not when the task carries no such meaning. It may be the case
that the meaning tuned subjects’ attention to processing the fa-
miliarity of the names, which increased the processing differences
between the subliminal acquaintance and nonacquaintance
names, and therefore a ERP difference was found between
A-A and N-A in Experiment 1 but not in Experiment 3. The
same priming phenomenon was not observed in supraliminal
nonacquaintance conditions (A-N and N-N) in both Experi-
ments 1 and 3. The reason may again be attributed to the lack of
preexisting representation for priming to occur (as mentioned in
the previous paragraph).
To conclude, the paradigm of priming, which is well studied
and has a long history in cognitive psychology, may potentially
be used in individual diagnosis of lying. The present study dem-
onstrated that the priming paradigm may reveal the presence or
absence of memory representation in subjects’ brains during
suspected deception. Acquaintance names, which have long-term
memory representation, were successfully primed by a different
subliminal acquaintance name, as demonstrated by a smaller
positive ERP amplitude. This was not the case in nonacquain-
tance name conditions. The results indicated that information
with and without long-term memory representation can be dis-
tinguished by the presence and absence of the priming effect,
respectively. Moreover, because the primes were subliminal,
subjects are not expected to be able to develop differential covert
responses to conditions with different subliminal primes so as to
implement countermeasures. Further studies may be done so as
to verify the effectiveness of the present paradigm in obviating
countermeasures.
The spatial-temporal PCA and bootstrapping techniques
were used in the present study to improve signal-to-noise ratio
(Kobayashi & Kuriki, 1999), which is particularly important in
individual diagnosis where the amount of data is relatively lim-
ited (Lui & Rosenfeld, 2008). Further development of data pro-
cessing techniques on EEG data is needed to improve the
detection rate and lower the false positives in lie detection. The
multivariate nonlinear high-dimensionality pattern classification
technique (Lao et al., 2004) may potentially be applied to EEG
data in classifying lying and truth telling, as it was used in a fMRI
deception study (Davatzikos et al., 2005).
Compared to most other cognitive neuroscience techniques,
EEG is relatively portable, low cost, and without the need of
extensive medical expertise, which makes it a good candidate in
real-life applications such as police interrogation or employee
screening. Nevertheless, amidst the fast growing interest and re-
search development in lie detection, the authors acknowledge
that the ethical issues of humanmind reading should be carefully
discussed and investigated before further development of the
techniques.
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(Received March 18, 2008; Accepted September 5, 2008)
Subliminal priming in lie detection 903