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Psychophysiology, Vol. 25, No.6, pp.683-688
Diff_decep88.doc
Differentiation of Deception as a Psychological
Process: A Psychophysiological Approach
JOHN J. FUREDY,
University of Toronto
CAROLINE DAVIS, AND MARIA GUREVICH
York University, Toronto
ABSTRACT
If psychophysiology is the study or differentiation of psychological processes by means of
physiological measures, then the experimental demonstration of deception as a psychophysiological
phenomenon requires a comparison of physiological responses to two conditions (experimental and
control) which differ only with respect to deception. To this end, the Differentiation-of-Deception
Paradigm controls for differential question significance and frequency of occurrence. Thirty-two
subjects were tested in this paradigm, with the skin conductance response as the dependent variable. We
examined, within subjects: a) the basic deception comparison which contrasted relatively neutral
autobiographical questions answered deceptively with those answered honestly, and b) the mode of
answering, which was either an immediate answer to the question (conventional method) or an
answer delayed by 10 seconds. The deception phenomenon (greater responding to deceptive relative to
honest trials) emerged significantly (and nondifferentially) to both the immediate and delayed
questions, but (perhaps because of response interference) not when responding was measured
immediately following the delayed answers. Future research should vary other conditions and
measure additional dependent variables with the aim of investigating possible psychological and
physiological mechanisms, as well as extending the deception phenomenon beyond its present
electrodermal form.
DESCRIPTORS: Deception differentiation, Skin conductance response, CQT polygraph},
Guilty knowledge technique, Control for significance and frequency, Response interference
The approach taken in this research is one that views
psychophysiology as the study or differentiation of
psychological processes by means of unobtrusively
measuring slight changes in physiological functions
(for details and criticisms of this perspective, see
Furedy, 1983,1984;Obrist, 1976, 1981; Stern, 1964,
1984). The initial step in such study is to demonstrate
the phenomenon under consideration, after which
issues
concerning
parametric
variations
and
mechanisms (both psychological and physiological)
can be raised. For example, if the
This research was supported by an operating grant and a PostDoctoral Fellowship, respectively, to JJF and CD from the National
Sciences and Engineering Council of Canada. We are indebted to M.
Dawson and an anonymous reviewer for comments on an earlier draft
of this paper.
Address requests for reprints to: John J. Furedy, Ph.D., Department
of Psychology, University of Toronto, Toronto, Ontario, Canada,
M5S IA1.
psychological process of interest is Pavlovian autonomic
(e.g., skin conductance response, SCR) conditioning, then
the demonstration of the conditioning phenomenon requires
that the experimental and control conditional stimuli be, in
principle, identical except for the process being studied:
the association between the (experimental) conditional
stimulus and the unconditional stimulus. Similarly, if
deception is the psychological process of interest, the
experimental and control stimuli should differ only with
respect to deception.
The investigator who wishes to differentiate and study
deception faces the same problem as presents itself in the
study of processes like Pavlovian conditioning. At the
initial phenomenon-demonstration stage there may be
differences between the experimental and control
conditions that do not involve deception, and yet may be
responsible for the observed experimental-control
differences in responsiveness. Although there are
innumerable potential confounds, two especially important
classes
684
Furedy, Davis, and Gurevich
of potential confounding variables to control in research on the phenomenon of deception are differential
significance and differential familiarity.
The confound of differential significance (or
emotionality, anxiety, or arousal level) between the two
sorts of questions appears to be particularly evident in
the polygraphic Control Question Technique (CQT).
For example, in a case involving child sex abuse (for
details, see Furedy & Liss, 1986, pp. 96-97), one
relevant (“experimental”) question was: “Did you lick
X’s vagina?” (where X was a four-year-old girl). The
so-called control question that was used as a
comparison was: “Did you ever do anything you were
ashamed of?” Even for an innocent examinee (and
perhaps all the more so), it is at least arguable that the
significance of the former question would exceed that of
the latter question. In the present differentiation-ofdeception paradigm, which was based on a procedure
originated by Hemsley (see Hemsley, Heslegrave, 8c
Furedy, 1980) and developed further by Heslegrave
(1982), the significance confound was controlled by
two methods. First, to eliminate gross differences in
significance between questions to which subjects were
instructed to be deceptive or honest, emotionally
neutral questions dealing with biographical issues were
employed. Second, to control for slight differences in
significance between different questions, the honest
and deceptive categories were equated across subjects
so that, on the average, each question (of the form, “I
was born in ...) received a deceptive and an honest
answer 50% of the time.
The differential familiarity or frequency of occurrence confound is the primary reason why the
Guilty Knowledge Technique (GKT) introduced by
Lykken (1959) does not necessarily assess deception,
although it is a more scientifically valid method of
assessing guilt than the CQT (for a more detailed
comparison of the CQT and GKT from a
psychophysiological perspective, see Furedy, 1986,
and Furedy & Heslegrave, 1988a, 1988b). According
to the GKT’s rationale, the guilty will produce bigger
responses to the relevant question (the one containing
the information that only the guilty know) than to the
control questions (which do not contain that
information). However, control questions occur more
frequently than do relevant questions, so that, for the
guilty (who, by assumption, are the only examinees
who can make the relevant:control distinction), the
rate of response habituation will be greater for the
control than for the relevant questions.
Accordingly, any difference between relevant and
control questions may be due not to deception but to
differential habituation rates. This, of course, does not
raise any concerns of confounding, if the aim
Vol. 25, No. 6
of the procedure is to detect guilt. Response habituation
has been proposed by some (e.g., Ben-Shakhar, 1977) as
an alternative mechanism to that of stimulus significance
in accounting for the demonstrated GKT phenomenon of
increased responding to relevant questions by the guilty.
However, if the purpose is to compare physiological
responses to the relevant and control questions in order to
differentiate the processes of deception and honesty, then
the frequency-of-occurrence difference between the two
conditions constitutes a serious confound particularly for
the skin conductance response, which clearly habituates
as a function of frequency of presentation (e.g., Furedy,
1968). In the present experiment, frequency was
controlled by having subjects answer 50% of the questions
deceptively (experimental) and 50% honestly (control), so
that, in all important respects, the only difference between
the Deceptive and Honest conditions would be the
presence of deception.
In this first full-length report of the differentiation-ofdeception paradigm (for previous abstract reports, see
Hemsley et al., 1980; Heslegrave, 1982), skin conductance
response (SCR) was measured as the dependent variable.
This choice was based on the SCR’s relatively high
sensitivity to psychological processes like attention
(orienting) and classical conditioning, and the fact that it is
one of the least esoteric (and hence most easily
replicable) of psychophysiological measures. In addition
to the basic Deceptive:Honest comparison we also varied,
within subjects, the verbal response latency—whether the
answer to the question was given immediately or after a
10-s delay. This factor was varied by Dawson (1980), who,
however, employed a laboratory version of the
polygraphic CQT. The purpose for introducing the
delayed-answer condition was that this condition could
possibly separate two hypothetical processes involved in
the deception phenomenon, namely the intention to
deceive (as indexed by SCRs to the question) and the act
of deception (as indexed by SCRs to the 10-s delayed
answer). It is possible that such a separation may produce
clearer Deceptive:Honest differentiation, as well as
provide clues to understanding the mechanisms of
deception.
Method
Subjects
Thirty-two volunteer subjects (16 males and 16 females)
aged 19-40 yrs were recruited through advertisements posted
at the University of Toronto. Each subject received $10 for
participation in the study.
Apparatus and Questionnaire Materials
Continuous skin conductance was recorded, through a
Coulbourn Instruments preamplifier (S71 -22; this unit
November, 1988
Electrodermal Differentiation of Deception
is based on specifications recommended by Lykken &
Venables, 1971) onto a Narco (E & M Instruments)
Physiograph (Model FOUR-A) running at a chart speed
of 1 cm/s. Two Grass Ag/AgCl electrodes (1 cm2 dia.)
in conjunction with a Beckman NaCl electrode paste
were attached by adhesive tape to the volar surfaces
of the subject’s distal phalanges of the first and second
fingers of the left hand (cleaned with soap and water).
The questionnaire materials comprised two lists of 10
questions (List 1 & List 2) such as “What is your
mother’s age,” and “How many brothers do you have?”.
Each pair of questions in the two lists was matched
for topic (e.g., the matched question for the first example would deal with the father’s age), so that the
biographical content of the two lists was roughly equal.
Procedure
Two experimenters (CD and MG) conducted the
study. On arrival at the laboratory, each subject was
given a brief written description of the study by CD.
after which MG attached the electrodes to the subject
but did not connect the leads to the polygraph.
In general, it can be argued that truthful answers
are easier to retrieve than deceptive answers. However,
it is possible to minimize the influence of this ease-ofretrieval factor by procedural modifications that: a)
render the retrieval component as easy as possible, and
b) present the task to the subject as a deception rather
than a memory test. Accordingly, the subject was then
taken by CD to a small room separate from the testing
area, and was helped to prepare honest and deceptive
answers, with CD indicating which 10 of the 20 questions should be answered deceptively. For deceptive
answers, the subject was asked to provide plausible
ones (e.g., if the question asked about father’s age, which
was 60, then a deceptive answer should not be, say.
35). The questions were grouped as in the two original
lists (List 1 and List 2), with half the subjects being
required to be honest to List 1 questions, and the remainder being asked to be honest to List 2 questions.
After agreeing on the answers, the subject and CD rehearsed the list of questions and answers until the subject felt confident with the prepared answers. No subject required more than one run through the list of
questions before indicating confidence with the answers, a fact that indicates the relative ease of the retrieval task. The subject was then told that, during the
interrogation (test) process. MG would ask the same
20 questions, but in a different order from that used
during the rehearsal process. The subject was also reminded that MG did not know which answers were
honest or deceptive, and that an attempt should be
made to appear honest at all times. Finally, it was
made clear that CD would not know what answers
were given to MG. As a result, the procedure was unlikely to be construed as a memory test by the subject.
The subject was then taken to the interrogation room
(immediately adjacent to the room containing the
physiograph and stimulus-control equipment), and the
electrode leads were attached to the physiograph via
685
cables extending through a hole in the wall adjoining the
two rooms. In the interrogation room, the subject and MG
were seated, facing each other, across a narrow (approx.
50 cm) table.
The questionnaire material was administered according to the following arrangement. The questions of
List 1 and List 2 were randomly allocated to a third, 20question list, List 3. The first and second 10 questions in
List 3 were presented under the Immediate and Delayed
conditions, respectively, for half the subjects, and the
reverse for the remaining subjects. In the Immediate
condition, the subject was instructed to answer as soon as
MG had completed the question (question duration was
approx. 2-3 s). In the Delayed condition, the subject was
asked to wait 10 s. A small light, mounted on a board
immediately in front of the subject, came on as soon as
MG had completed the question, and signalled the subject
to answer the question when it offset 10 s later.
Accordingly, with respect to the main within-subject
comparisons of interest (i.e., the Honest/Deceptive and
Immediate/Delayed
differences),
there
was
counterbalancing control for question content, frequency
of occurrence, and serial position in the list (List 3). The
between-subject factor was Sex, which was varied
orthogonally with the Truthfulness and Measurement
Method (MM). It will be noted that the MM factor can be
considered to comprise three levels: skin conductance
responses to the Immediate, Delayed-Question (Q), and
Delayed-Answer (A) conditions.
The timing of the questions was controlled by MG, who
had a small light (visible only to her) mounted on a
board in front of her. At the onset of each question, the
light was switched on, and remained on for either 15 s
(Immediate condition) or 25 s (Delayed condition). The
next question in the series was presented by MG following
light offset, so that the interval between the answer to the
last question and the next question was approximately 10
s throughout the experiment.
The interrogation did not begin until CD had completed
calibrating the physiograph. and was ready to begin
recording (indicated by closing the door between the
interrogation and recording rooms). Before beginning the
questions in List 3. CD asked the subject’s name, but the
response to this question was not scored.
The physiograph record was marked by MG to indicate
the onset of each question, and, in the Delayed condition,
the answer onset. Between the first and second set of 10
questions, there was a break of about 1 min. during which
time MG reminded the subject about the change in the
method of answering. At the completion of the questions
in List 3. the electrodes were removed, and the subject
was thanked and paid.
Results
The skin conductance response (SCR) for the Immediate
and Delayed(Q) conditions was defined as any response that
was initiated (showing an inflection point) within 1-5 s
following question onset. Magnitude (in mm, and then
convened to
686
Furedy, Davis, and Gurevich
microSiemens, S) was expressed as the difference
between response onset (inflection point) and the
highest point following response onset until the end of
the 1-5 s latency window. Non-occurrences of SCRs
were changes less than .5 mm change on the chart, and
were scored as zero responses. This chart-length
criterion varied among subjects (because of wide
individual differences in skin conductance level), but
was constant for all within-subject variables. The scoring
was the same for the Delayed(A) condition, except
that the latency window was 1-5 s following (delayed)
answer onset.
Initial ANOVAs including Sex, Truthfulness, and
MM as factors indicated that Sex was not significant
either as a main effect or in interaction with the other
factors. Accordingly, subsequent analyses collapsed the
data across Sex groups and tested only within-subject
effects.
A two-factor repeated-measures ANOVA with two
levels of Truthfulness (Honest and Deceptive) and
three levels of MM (Immediate and the two Delayed
conditions) was conducted, with an alpha level of .05
set for statistical significance. Univariate tests for
within-subject effects were adjusted for violation of
sphericity using the Greenhouse-Geisser epsilon
correction (epsilon=.9066). The only significant effect
was a Truthfulness X MM interaction, F(2/62)=4.16,
p=.0239, MS=0.215.
As suggested by inspection of Figure 1, this interaction was due to the Deceptive>Honest difference
being eliminated (but not reversed) under the
Delayed(A) condition. This account of the interaction
was confirmed by the following analyses: a) a 2 X 2,
Truthfulness X MM ANOVA using the Immediate and
Delayed(Q) conditions as the only (two) MM levels,
yielded a significant main effect only for
Truthfulness, F(1 /31) = 10.76, p=.0026, MS=0.370,
but no Truthfulness X MM interaction; and b) a t-test
of the Deceptive < Honest difference in the
Immediate(A) condition failed to reach significance,
t(30)=1.71, p<.l.
To test for response and deception-differentiation
habituation to the Immediate and Delayed(Q)
conditions, a 2 X 5 repeated-measures ANOVA was
conducted with Truthfulness and Trial Blocks as the
two factors. For each subject there were (interspersed)
10 trials with honest questions and 10 trials with
deceptive questions. The five levels of the trial block
factor were obtained by comparing skin conductance
responses (SCRs) across pairs of questions 1-2, 3-4, 56, 7-8, and 9-10. No evidence for habituation was
obtained, since the ANOVA yielded no significant
Trial Block effect, F<1, with mean SCR values of
0.63, 0.56, 0.53, 0.49, and 0.53 S for the first to fifth
Trial Block levels. Only the Truthfulness effect was
significant, F(1/31)=6.63,
Vol. 25, No. 6
Figure 1. Mean skin conductance responses to honest (H) and
deceptive (D) questions following the question in Immediate and
Delayed conditions, and following the answer in the Delayed
condition.
p=.0150, MS=0.071, with responding to the Deceptive
condition exceeding that to the Honest condition. The
Truthfulness X Trial Block interaction was also not
significant, F<1, so there was no evidence for
differentiation-of-deception (as represented by the
Deceptive >Honest effect) habituation.
Discussion
The major finding is that skin conductance responses
(SCRs) in the interval immediately following the question
in the differentiation-of-deception paradigm were clearly
and significantly greater when the question was answered
deceptively than when it was answered honestly. This
constitutes a relatively unequivocal demonstration of the
psycho-physiological deception phenomenon, because it
is at least plausible to suggest that the only relevant
difference between the experimental (deceptive) and control
(honest) conditions was the presence of deception.
It is also encouraging that although mean SCR
magnitude to the questions was relatively small (see Figure
1), and no greater than that typically obtained in orientingreaction (OR) studies with tones and lights as stimuli (e.g.,
Furedy, 1968), nevertheless, in contrast to those OR
studies, the SCR in this differentiation-of-deception
paradigm did not
November, 1988
Electrodermal Differentiation of Deception
habituate. Nor did the differentiation-of-deception
phenomenon itself diminish over trials.
The demonstration of a phenomenon is the initial
step in a process that requires the experimental
manipulation of a variety of additional factors in order
to uncover underlying mechanisms. It will be recalled
that we varied the measurement method (MM) of
deception differentiation, with the idea of separating
the intention to deceive from the act of deception, and
with the hope of producing clearer Deceptive:Honest
differentiation. This manipulation did not yield the
expected results. In the first instance, the Immediate
versus Delayed variable did not affect the extent of
SCR differentiation between deceptive and honest
questions. Secondly, and surprisingly, in the
Delayed(A) condition the Deceptive>Honest difference
was eliminated, with a nonsignificant tendency (p<.1) to
show a reversal, i.e., Deceptive<Honest (see Figure
1).
In terms of the hypothetical intention/act distinction, this pattern of outcomes suggests that it is only
the intention to deceive rather than the act of deception
that is responsible for the differentiation-of-deception
phenomenon. This account is consistent with the nodifference-in-differentiation finding between the
Immediate and Delayed(Q) conditions (i.e., the absence
of the act from the latter condition not affecting
differentiation), and the lack of differentiation in the
Delayed( A) condition (which has no intention
component).
An alternative account, however, is suggested by a
factor for which there is more direct psychophysiological evidence than for the hypothetical intention/act distinction. This is the factor of response
interference, which is known to be influential in skin
conductance measurement (see, e.g., Schell &
Grings, 1971, where skin conductance response
magnitude differentiated between subjective stimulus
intensities). Response-interference is a relativerefractory-period-like effect, whereby the response to a
stimulus is reduced as a function of a previously
occurring response. With a slow-onset-latency
response like the skin conductance response, the
effect is evident up to intervals of about 30 s, and
would be markedly influential with the present 10-s
interval between the question- and answer-elicited skin
conductance responses in the two
687
Delayed conditions. The effect is also a direct function of
the magnitude of the previously-occurring response,
which, because of the Deceptive:Honest differentiation in
the Delayed(Q) condition, would have been greater for the
Deceptive than the Honest conditions in the interval
immediately following the question. Accordingly, the
response-interference factor could have eliminated the
Deceptive:Honest differentiation to the answer in the
Delayed(A) condition, and could even have reversed it
(although this reversal did not reach significance in the
present study).
One way to distinguish between the psychological
intention/act and physiological response-interference
accounts would be to add a dependent physiological index
where, with a 10-s interval, the response-interference
problem is not as severe as with the skin conductance
response. The faster-acting event-related potential appears
to be an obvious and promising candidate for this purpose.
Another issue regarding causal mechanisms involved in the
deception phenomenon concerns the relative importance
of differential mental load (inasmuch as in the Deceptive
condition, the subject may have to think of both the true
and the false answer) and differential conflict (potentially
greater in the Deceptive condition, where there is a conflict
between the true and false answers). This psychological
issue can be investigated by adding to the Deceptive and
Honest conditions (Heslegrave, 1982). Finally, a
potentially informative physiological extension involves
adding cardiac performance variables, in order to more
clearly separate the roles of sympathetic and
parasympathetic influences in the deception phenomenon.
Specifically, with the joint measurement of heart rate and
one of the candidate sympathetic indices (e.g., pulse
transit time, T-wave amplitude, etc.), it is possible to
identify both sympathetic (change in the sympathetic index)
and parasympathetic (change in heart rate without change
in the sympathetic index) effects (Furedy, Heslegrave, &
Scher, 1984). In addition, the more general benefit of
providing these other dependent variables is that this
could serve to extend the differentiation of deception
beyond its present status as only an electrodermal
phenomenon.
REFERENCES
Ben-Shakhar, G. (1977). A further study of the dichotomization theory in detection of information. Psychophysiology, 14, 408-413.
Dawson, ME. (1980). Physiological detection of deception:
Measurement of responses to questions and answers
during countermeasure maneuvers. Psychophysiology, 17,
8-17.
Furedy, JJ. (1968). Human orienting reaction as a function of
electrodermal versus plethysmographic response modes and
single versus alternating stimulus series. Journal of
Experimental Psychology. 77, 70-78.
Furedy, J.J. (1983). Operational, analogical, and genuine
definitions of psychophysiology. International Journal of
Psychophysiology, 1. 13-19.
688
Furedy, Davis, and Gurevich
Furedy, J.J. (1984). Generalities and specifics in defining
psychophysiology: Reply to Stern (1964) and Stern
(1984). International Journal of Psychophysiology, 2, 24.
Furedy, JJ. (1986). Lie detection as psychophysiological
differentiation: Some fine lines. In M. Coles, E. Don-chin,
& E. Porges (Eds.). Psychophysiology: Systems,
processes, and applications—A handbook (pp. 683-700).
New York: Guilford Press.
Furedy, J.J., & Heslegrave, R.J. (1988a, in press). The
forensic use of the polygraph: A psychophysiological
analysis of current trends and future prospects. In J.
Jennings, M. Coles, & P. Ackles (Eds.), Advances in
psychophysiology (Vol. 4). Greenwich, CT: JAI Press.
Furedy, J.J., & Heslegrave, R.J. (1988b, in press). A reply to
commentators: Some elaborations on the specific-effects
orientation’s application to the North American CQT
polygraph. In J. Jennings, M. Coles, & P. Ackles (Eds.),
Advances in psychophysiology (Vol. 4). Greenwich, CT:
JAI Press.
Furedy, J.J., Heslegrave, R.J., & Scher, H. (1984). Psychophysiological and physiological aspects of T-wave
amplitude in the objective study of behavior. Pavlovian
Journal of Biological Science, 19, 182-94.
Furedy, J.J., & Liss, J. (1986). Countering confessions induced
by the polygraph: Of confessionals and psycho-
Vol. 25, No. 6
logical rubber hoses. The Criminal Law Quarterly, 29, 92114.
Hemsley, G.D., Heslegrave, R.J., & Furedy, J.J. (1980). Can
deception be detected when stimulus familiarity is
controlled? [Abstract]. Psychophysiology, 17, 286-287.
Heslegrave, R.J. (1982). An examination of the psychological
mechanisms
underlying
deception
[Abstract].
Psychophysiology, 19, 298.
Lykken, D.T. (1959). The GSR in the detection of guilt.
Journal of Applied Psychology, 43, 385-388.
Lykken, D.T & Venables, P.H. (1971). Direct measurement of
skin conductance: A proposal for standardization.
Psychophysiology, 8, 656-672.
Obrist, P.A. (1976). The cardiovascular-behavioral interaction—
As it appears today. Psychophysiology, 13,95-107.
Obrist, P.A. (1981). Cardiovascular psychophysiology: A
perspective. New York: Plenum Press.
Schell, A.M., & Grings, W.W. (1971). Judgments of UCS
intensity and diminution of the unconditioned GSR.
Psychophysiology, 8, 427-432.
Stern, J.A. (1964). Toward a definition of psychophysiology,
Psychophysiology, 7, 90-91.
Stern, J.A. (1984). On ‘Unobtrusive Psychophysiology’— Fact or
fiction? A rejoinder to Furedy (1983). International Journal
of Psychophysiology, 2, 1-2.
(Manuscript received October 21, 1987; accepted for publication April 23, 1988)