ARTICLE IN PRESS
Behaviour Research and Therapy 43 (2005) 323–336
www.elsevier.com/locate/brt
Return of fear in a human differential conditioning paradigm
caused by a return to the original acquistion context
Debora Vansteenwegen1,, Dirk Hermans, Bram Vervliet, Geert Francken,
Tom Beckers1, Frank Baeyens, Paul Eelen
Department of Psychology, Centre for the Psychology of Learning and Behaviour Therapy, University of Leuven,
Tiensestraat 102, Leuven B-3000, Belgium
Received 17 September 2003; received in revised form 10 November 2003; accepted 21 January 2004
Abstract
In a differential human fear conditioning paradigm evidence for ABA-renewal was obtained
manipulating the lighting in the experimental room. During acquisition in either a dark or illuminated
room, one neutral slide was sometimes paired with a loud aversive noise whereas another slide was not.
Subsequently, extinction took place in the opposite lighting context. When afterwards the participants were
tested again in the original acquisition context, measurements revealed a recovery of the conditioned
electrodermal response and an increase in the retrospective verbal US-expectancy ratings. No response
recovery was obtained in an AAA-group that received acquisition, extinction and test trials in one and the
same context. Several theoretical explanations for this type of return of fear as well as implications for
clinical practice are discussed.
r 2004 Elsevier Ltd. All rights reserved.
Keywords: Human fear conditioning; Context-specificity; Exposure; Return of fear; Skin conductance
Corresponding author. Tel: +32-16-32-61-34; fax: +32-16-32-59-24.
E-mail address: deb.vansteenwegen@psy.kuleuven.ac.be (D. Vansteenwegen).
Debora Vansteenwegen and Tom Beckers are postdoctoral researchers of the Fund for Scientific Research
FWO-Vlaanderen.
1
0005-7967/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.brat.2004.01.001
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1. Introduction
Powerful therapeutic tools exist for the treatment of specific phobias. Most often the
behavioural treatment involves repeated and systematic exposure to the fear-provoking stimulus
(e.g. Öst, 1997). Although such exposure-based treatment is highly effective, there is substantial
evidence in the clinical literature that fear may return with the passage of time. Rachman and
colleagues (e.g. Rachman, 1989) have studied the phenomenon of return of fear extensively and
explored (post)treatment and individual difference variables that predispose individuals to the
return of fear. Although findings across various studies are rather mixed and it is too early to
make any firm predictions, several suggestions have been made in literature. Research indicates
that individual difference variables such as mood during exposure (Salkovskis & Mills, 1994) and
initial level of heart rate (Wood & McGlynn, 2000; Grey, Rachman, & Sartory, 1980) may
correlate with levels of return of fear. There are also indications that for example the strength of
covariation bias immediately after treatment (De Jong, Vandenhout, & Merckelbach, 1995), the
incompleteness of fear reduction at the end of exposure (Rachman, Robinson, & Lopatka, 1987)
and the speed of fear reduction can be predictive for a return of fear. Furthermore, research
indicates that distraction during exposure can have a facilitative effect on return of fear
(Kamphuis & Telch, 2000). Treatment variables that might reduce the return of fear are the use of
varied stimuli instead of the same stimulus during exposure (Rowe & Craske, 1998a) and the use
of an expanding-spaced instead of massed exposure schedule (Rowe & Craske (1998b) though see
Lang & Craske (2000), for a lack of replication).
The post-treatment variable of interest for the research presented in this manuscript is contextchange after exposure. There is good evidence from clinical studies that return of fear may be
facilitated by entering a new context. Mineka, Mystkowski, Hladek, and Rodriguez (1999)
showed a return of self-reported fear one week after a one-session exposure-based treatment when
treated spider-phobics were tested in a different room. Rodriguez, Craske, Mineka, and Hladek
(1999) showed a return in the level of heart rate responding for one specific stimulus two weeks
after exposure treatment when the incidental (room) and meaningful (therapist) context were
changed. Finally, Mystkowski, Craske, and Echiverri (2002) manipulated the contexts in a more
naturalistic way and used an inside and an outside context. They showed a clear return of fear in
self-report data one week after a one-session exposure-based therapy when participants were
tested in the other context.
The results of these clinical studies show a striking resemblance to the substantial experimental
evidence from the animal conditioning literature that conditioned responses return after a context
change. These studies demonstrate a context-dependency of extinction, analogous to the contextdependency of exposure treatment. It is assumed that exposure therapy involves processes
analogous to extinction: repeatedly presenting the conditioned stimulus (CS) without the
unconditioned stimulus (US) after acquisition most often leads to a decrease in conditioned
responding. The most frequently observation reported is ABA-renewal. Bouton and colleagues
(e.g. Bouton & King, 1983; Rosas & Bouton, 1997; Bouton & Swartzentruber, 1986)
demonstrated that conditioned responding is renewed when after extinction in a context different
from the acquisition context, animals are again tested in the original acquisition context. The
effect was not only demonstrated in traditional animal fear conditioning paradigms such as
conditioned suppression (Bouton & King, 1983), but also in appetitive conditioning (Bouton &
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Peck, 1989) and in a taste aversion paradigm (Rosas & Bouton, 1996). Similar effects are obtained
when after extinction in a different context, transfer of extinction is tested in a third context
(ABC-renewal, Bouton & Brooks, 1993; Bouton & Swartzentruber, 1986). The clinical studies
described above can best be compared with the latter type of renewal: exposure therapy most
often takes place in a context different from the original acquisition context, and return of fear is
then observed in a new, third context. Finally, AAB-renewal was also demonstrated in animals
(Bouton & Ricker, 1994). In such a procedure acquisition and extinction take place in an identical
context but testing is executed in a new context.
Classical conditioning theory and the findings from animal conditioning studies might be very
helpful in clarifying the context-specificity effect of exposure. They may provide insight in the
learning mechanisms that are responsible for return of fear. Recent conditioning theories about
extinction (for a review see Rescorla, 2001) suggest that extinction should not be equated with
unlearning. Instead extinction would involve learning about additional context-specific
information (Bouton, 1988, 1994, 2000). As a result the extinction context acquires a modulatory
role and helps to disambiguate between the old (acquisition) and the new (extinction) information.
Translating this idea to a clinical context, this would suggest that during exposure the original
association of the fearful object with fear is not subjected to change. Rather, one learns that
sometimes the fearful object is not to be feared. This additional information will only come to
expression when the therapy context is present. According to this approach, expectations with
regard to the generality and permanence of the effect of exposure are rather pessimistic.
In the animal conditioning literature, this contextual theory of extinction has received a lot of
attention. Nonetheless, there are two other mechanisms that were traditionally used to explain the
context-specificity of extinction. The first mechanism is the formation of a direct inhibitory
association between the extinction context and the US. In the clinical literature this inhibitory
context is called a safety signal. It predicts the non-occurrence of the US and as such protects the
CS from extinction (Lovibond, Davis, & O’Flaherty, 2000). When leaving the therapy context, the
inhibitory power of the context/therapist is no longer present and fear will return. The second
mechanism received less attention in the literature. It is possible that the fearful object is perceived
differently in the exposure context than in the acquisition context. In this respect, exposure might
have involved a (partially) wrong stimulus and fear will return when the original acquisition
stimulus is presented. In the animal conditioning literature, this mechanism is called
generalisation decrement. From an a priori point of view, these mechanisms can be at work in
ABA- and ABC-renewal demonstrations in animals as well as in the clinical studies. However,
Bouton and his colleagues showed that in their animal conditioning preparations the context did
not become inhibitory during extinction and excluded this explanation for their renewal effects
(e.g. Bouton & King, 1983, Bouton & Swartzentruber, 1986). Moreover, they also showed no
generalisation decrement between acquisition and extinction, excluding the second alternative
mechanism. Hence they made a very strong case in favour of the modulatory mechanism in their
conditioning preparations.
Because contexts and stimuli in different conditioning preparations might serve different
functions due to differences in salience, meaning, distance, etc., these animal conditioning findings
cannot immediately be generalised to human fear conditioning studies. All three mechanisms can
in principle play a role in human ABA-renewal demonstrations. A replication of the renewaleffect in a human conditioning study with experimentally induced fear might be a first step
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towards unravelling these mechanisms. Additionally, it might complement the existing evidence
from clinical studies. Despite the loss of some ecological validity, the strength of such a human
study with experimentally induced fear is that it brings the theoretical assumptions to their essence
and allows studying the phenomenon under strictly controlled circumstances. First of all, in a
clinical context one does not have control over the acquisition of fear. Therefore, studying the
equivalent of an ABA-renewal effect for instance, is rather difficult. Often the original acquisition
context is not known and even if it was known, recreating this context is often practically/ethically
impossible. Moreover, in clinical studies it is very difficult to know what the differences are
between the acquisition and the extinction context, information that might be useful when one
wants to differentiate between different mechanisms. Secondly, not only acquisition but also, and
importantly, extinction is strictly under control of the experimenter. This might be important if
one wants to make an analysis of the underlying mechanisms. When studying return of fear after
exposure-based treatment, this treatment involves often more than what is included in a simple
extinction-procedure, such as modelling, counterconditioning, social reinforcement, etc.
In sum, it might be worthwhile to fill the gap between clinical experiments and animal
conditioning studies. This was the main intention of our research. As a first step in disentangling
the possible underlying mechanisms, we wanted to demonstrate the ABA-renewal effect in a
human differential fear-conditioning paradigm with visual stimuli as CSs and a loud aversive
noise as US (Vansteenwegen, Crombez, Baeyens, & Eelen, 1998). Contexts were manipulated by
switching the central lighting in the experimental room on or off. One group (ABA) either
received acquisition and test in the dark context and extinction in the illuminated context or vice
versa. For the other group (AAA) acquisition, extinction and test were conducted in the same
context (all dark or all illuminated). In the first place, we aimed to demonstrate the ABA-renewal
effect using a psychophysiological index namely electrodermal responding. The evidence for
renewal in clinical studies is mainly based on verbal self-reports. If one wants to study
the phenomenon of the return of a real emotional response such as fear, it can be important
not to rely solely on verbal indices of fear, as bodily responses are an integrative part of
emotional responding. Moreover, correlations between verbal, physiological and behavioural
indices are often low (Ohman, 1987). In this respect, demonstrating ABA renewal with skin
conductance is not without relevance. The psychophysiological index was complemented with
US-expectancy ratings in order to see whether we could replicate the already existing
clinical evidence for a return in verbal indices under the more strictly controlled conditions of
this human fear conditioning study. However, we took the option to formulate these ratings
in a retrospective in order not to interfere with the natural development of the electrodermal
responses.
2. Method
2.1. Participants
Forty first-year psychology students participated in order to fulfil course requirements.
Twenty participants were assigned to the ABA-group and twenty to the AAA-group.
They all gave informed consent and were informed that they could decline to participate
at any time.
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2.2. Apparatus
Two clearly distinct line drawings of pictorial faces served as conditioned stimuli. For half of
the participants, one picture was sometimes followed by the US (CS+) and the other stimulus was
not (CS), for the other half of the participants this assignment was reversed. The slides were
projected with a Kodak Carousel slide projector and shutter, controlled by Labtech Notebook
programme and an IBM computer, which also controlled the stimulus sequence, the presentation
duration and the intertrial intervals. Slides were projected at eye level at 40 cm 60 cm.
A 95 dB (A) (Bruël and Kjaer, type 2107) burst of white noise with instantaneous rise time
presented binaurally for 500 ms through headphones (Sony dynamic stereo, MDR-CD270),
served as US.
Electrodermal activity was recorded with Fukuda standard Ag/AgCl electrodes (1 cm diameter)
filled with a Unibase electrolyte and attached to the hypothenar palm of the left hand which was
cleaned with tap water. The inter-electrode distance was 2.5 cm. The Coulbourn skin conductance
coupler (S71-22) provided a constant 0.5 V across electrodes. The analog signal was passed
through a 12 bit AD-converter and digitised at 10 Hz from 4 s prior to conditional stimulus onset
until 4 s after conditional stimulus offset.
Participants were seated in an armchair (screen distance 1.5 m) in a sound attenuated
experimental room, adjacent to the experimenter’s room. Verbal communication was possible
through an intercom system. The experimenter could manipulate the central lighting of the
experimental room from the outside. When the central lighting in the room was turned off, a very
low intensity dimming light was still present.
2.3. Procedure
At the beginning of the experiment the participants were instructed that from time to time a
loud aversive noise would be presented and that they had to watch the slides attentively. They
were instructed to focus on the moments when the loud aversive noise occurred. No further
instructions were given with regard to the contingencies between CSs and the US. During
acquisition, extinction and test, slides were presented for 8 s. Intertrial intervals varied between 16
and 24 s (average 20 s) and electrodermal activity was recorded from 4 s before CS onset to 4 s
after CS offset. During acquisition CS+ and CS were presented 10 times in a semi-randomised
order. No more than two consecutive trials of CS+ or CS were presented. Eight out of 10 CS+
presentations were immediately followed by the loud noise. Within each block of five trials one
CS+ was not followed by the US. The US never followed the ten presentations of the CS.
During extinction, CS+ and CS were again presented 10 times each, but now both without
noise, in a semi-randomised order. Finally during test, CS+ and CS were presented three times
each, in a semi-randomised order. For half of participants of the ABA-group, acquisition and test
occurred with the central lighting in the experimental room switched off, whereas during
extinction the lighting was switched on. For the other half of the participants of the ABA-group,
acquisition and test took place in a dark room whereas for extinction the central lighting was
switched off. Half of the participants of the AAA-group were trained and tested in dark, the other
half with the central lighting on.
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After the test phase, the recording electrodes were removed and the participants were taken to
the adjacent experimenter’s room. The participants were asked to complete a graph representing
the evolution of their US-expectancies during the just finished experiment. The experimenter
explained the meaning of the two axes. The Y-axis of the graph depicted an 11-point USexpectancy scale starting at 0 (never) and ending at 10 (always). On the X-axis four different
moments were indicated. For the ABA-participants, the first moment was described as just before
it became dark (/light), the second as just after it became dark (/light), the third as at the end of the
dark (/light) phase and the fourth as when it became light again. For the AAA-participants similar
ratings had to be given for four different moments. Because of the fact that no context-change
took place in this group and hence no references to this context-change could be included in the
instructions, the instructions were adjusted. The first three moments were described as the
evolution (increases or decreases in expectation) across the experiment, except for the last six
presentations. The rating of the fourth moment was described as the mean expectancy across these
last six presentations. After the instructions, the participants of both groups saw a picture of the
CS+ and were asked to give the four ratings for the CS+ first. Then they were asked to do the
same for the CS. Afterwards participants had to rate the pleasantness of the US on an 11-point
graphic scale (anchored: 10, unpleasant and +10, pleasant) and US-intensity on a 5-point
categorical scale (weak, moderate, intense, enormous and unbearable).
3. Results
3.1. US-ratings
The mean pleasantness rating for the US was 6.44 (SD=2.66), and the mean intensity score
lay near the third label, namely intense (M ¼ 3:00, SD=0.59). Previous research by the authors
(Vansteenwegen et al., 1998) that used this US independently of a conditioning procedure2
revealed similar ratings for the loud noise. The mean pleasantness rating was 5.833 and the
mean intensity rating was 3.056.
3.2. Skin conductance
Skin conductance responses were visually inspected and corrected for artefacts before they were
analysed statistically. Skin conductance response amplitudes were defined as the maximal increase
starting within 1–4 s after conditional stimulus onset (Prokasy & Kumpfer, 1973). Zero responses
were included in all analyses in order to include the information about response frequencies as
well (Dawson, Schell, & Filion, 2000). Magnitudes were range corrected using the largest
(unconditioned) response (peak between 9 and 13 s during the acquisition phase) elicited by the
loud aversive noise (Lykken & Venables, 1971) as the maximum range for each individual. The
range-corrected response magnitudes were subjected to a square root transformation in order to
normalise the distribution prior to statistical analysis.
2
In fact, the loud noise was used as a startle-eliciting probe in order to be able to measure startle eye-blink reflex
modulation during picture-viewing.
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In Fig. 1 mean amplitudes for CS+ and CS are presented separately for the ABA-group and
the AAA-group for the 10 acquisition trials, 10 extinction trials and three test trials. In this figure
one can notice that both groups show acquisition and extinction, although extinction developed
somewhat slower in the AAA-group than in the ABA-group. Changing the context between
acquisition and extinction in the latter group did not seem to have a large impact on the learned
differentiation, indicating only small, if any, generalisation decrement. In the ABA-group, after a
return to the original acquisition context, the CS+/CS differential conditioned responding was
clearly renewed. This renewal was not observed in the AAA-group. Statistical analyses confirm
this data pattern.
Mean amplitudes for CS+ and CS for five crucial moments: the first (acq1) and the last
acquisition trial (acq10), the first (ext1) and the last extinction trail (ext10) and the first testtrial
Fig. 1. Mean range-corrected first interval skin conductance response amplitudes during viewing CS+ and CS for ten acquisition
trials (acq1–acq10), for ten extinction trials (ext1–ext10) and three test trials (test1–test3) are presented separately for the ABA-group
and the AAA-group. The means are presented square rooted because this was necessary to obtain normally distributed data for
statistical analyses.
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(test1), for the AAA-group and the ABA-group were first analysed for each group separately.
Then between-group comparisons were made within a Group (ABA/AAA) X Moment (acq1,
acq10, ext1, ext10, test1) X CS-type (CS+/CS) ANOVA with repeated measurements on the
last two variables.3 Only 34 participants were included in this analysis. Three participants from
each group were excluded because one of the necessary data-points was not available due to
technical shortcomings.
Acquisition and extinction: In the ABA-group at the end of acquisition (acq 10), there was a
significant CS+/CS differentiation, F ð1; 16Þ ¼ 13:63, p ¼ 0:002, MSE=0.086 that was not
present at the beginning of acquisition Fð1; 16Þ41. The CS+/CS differentiation was
significantly larger at acq10 than at the start of acquisition (acq1), Fð1; 16Þ ¼ 4:58, p ¼ 0:048,
MSE=0.082. Furthermore, there was no significant CS+/CS differentiation left at the end of
extinction, F ð1; 16Þo1 and hence a significant (CS+/CS) (acq10, ext10) was observed,
F ð1; 16Þ ¼ 7:33, p ¼ 0:016, MSE=0.09, indicating a strong decrease in responding during
extinction. Hence the ABA-group clearly showed acquisition and extinction.
In the AAA-group, the CS+/CS differentiation at the end of acquisition was almost
significant, F ð1; 16Þ ¼ 3:12, p ¼ 0:09, MSE=1.4 whereas no differentiation was obtained at the
beginning of acquisition, F ð1; 16Þo1. The (acq1, acq10) CS-type interaction was not significant,
F ð1; 16Þ ¼ 2:37, p ¼ 0:14, whereas the (acq1, ext1) CS-type interaction clearly was,
F ð1; 16Þ ¼ 7:03, p ¼ 0:018, MSE=0.067. This is evidence for an acquisition-effect although the
effect developed rather slow. Furthermore, at the end of extinction the CS+/CS-differentiation
has disappeared (ext10), F ð1; 16Þo1. The decrease from beginning to end of extinction was not
significant however, F ð1; 16Þ ¼ 2:097, p ¼ 0:35, indicating that extinction in this group was less
strong.
However, the between-group interactions concerning acquisition and extinction were all nonsignificant. The most important interaction Group CS-type (acq10, ext10) for example,
revealed the following statistics, F ð1; 32Þ ¼ 1:25, p ¼ 0:27.
Generalisation decrement: In light of the alternative accounts of renewal spelled out in the
introduction, it is important to check the impact of the context-change between acquisition and
extinction in the ABA-group. This context-change did not seem to have a strong impact on
conditioned responding. The CS+/CS differentiation was still present at the first extinction
trial, F ð1; 16Þ ¼ 4:73, p ¼ 0:044, MSE=0.08. Although the means show a smaller differentiation
between CS+ and CS at the first extinction trial than at the end of acquisition, this
differentiation was not significant, F ð1; 16Þ ¼ 1:86, p ¼ 0:18. As expected, in the control group—
where no context-change occurred—no differences between the last acquisition and first
extinction trial were obtained either, F ð1; 16Þo1. The means even show a larger instead of a
smaller differentiation. When comparing both between-group effects directly; no significant
differences were obtained. The Group CS-type interaction was neither significant at the last
acquisition trial nor at the first extinction trial, both F ð1; 32Þo1, nor was the three-way
interaction Group CS-type (acq10 and ext1) significant, Fð1; 32Þ ¼ 1:19, p ¼ 0:58.
Renewal of conditioned responding: In the ABA-group, the difference between CS+ and CS
was significant at test, Fð1; 16Þ ¼ 13:82, p ¼ 0:002, MSE=0.12. The increase in responding to the
3
When analyses were executed that included the dark/light manipulation as an additional between-group variable,
there was no significant main effect of this variable nor were there significant interaction effects.
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CS+ from the last extinction trial towards test was significant, F ð1; 16Þ ¼ 19:59, po0:001,
MSE=0.122. Furthermore, also the CS-type (ext10, test1) interaction was significant
F ð1; 16Þ ¼ 11:17, p ¼ 0:004, MSE=0.079. Hence a return of conditioned responding was
observed in the ABA-group.
In the AAA-group, the difference between CS+ and CS during test was not significant,
F ð1; 16Þ ¼ 2:92, p ¼ 0:107. The increase for CS+ from extinction to test and the CStype (Ext10, test1) interaction were not significant either, both F ð1; 16Þo1, so there was no
evidence for a return in this group.
When comparing the two between-group effects directly, responses to the CS+ at the first test
trial were larger in the ABA-group than in the AAA-group, F ð1; 32Þ ¼ 9:10, p ¼ 0:006,
MSE=0.17, as was the increase from the end of extinction to test for CS+, F ð1; 32Þ ¼ 8:9,
p ¼ 0:006, MSE=0.10. When taking into account the changes for the CS, the between-group
interactions were not significant: the CS+/CS differentiation at test did not differ significantly,
F ð1; 32Þ ¼ 2:55, p ¼ 0:12 and also the Group CS-type (ext10, test1) interaction did not reach
significance, F ð1; 32Þ ¼ 2:15, p ¼ 0:15.
3.3. Retrospective US-expectancy ratings
In Fig. 2 mean US-expectancy ratings for CS+ and CS for the 4 retrospective test moments
are presented, for the ABA-group and the AAA-group separately. In this figure one can notice
that both groups show clear acquisition. In the AAA-group the CS+/CS differentiation
becomes smaller towards the end of the experiment, indicating extinction. However the
Fig. 2. Mean retrospective US-expectancy ratings are presented for CS+ and CS during four moments separately for the ABAgroup and the AAA-group: first block of acquisition (M1), second block of acquisition (M2), extinction (M3), and test (M4).
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differentiation did not completely disappear. In the ABA-group, when comparing the second and
the third moment, extinction is observed as well, however in this group a clear return of USexpectancy for the CS+ is observed at the last moment. Statistical analyses confirm this data
pattern.
Mean US-expectancy for CS+ and CS for the four moments were first analysed for each
group separately. Then the between-group comparisons were calculated within a Group (ABA/
AAA) Moment (acq10, ext1, ext10, test1) CS-type (CS+/CS) ANOVA with repeated
measurements on the two last variables.
Acquisition and extinction: Planned comparisons confirm that both groups show acquisition.
Note that the instructions with regard to these first three moments were different in the two
groups. Hence between group comparisons will not be executed. For the acquisition rating
(Moment 1), there was a significant CS+/CS differentiation in the ABA-group,
F ð1; 19Þ ¼ 22:92, po0:001, MSE=6.98. In the AAA-group, this differentiation was manifest at
moment 2, F ð1; 19Þ ¼ 161:21, po0:001, MSE=3.04, whereas the differentiation at moment 1 was
only marginally significant, F ð1; 19Þ ¼ 3:29, p ¼ 0:085, MSE=3.50. In the ABA-group at the end
of extinction (Moment 3) no differentiation between CS+ and CS was observed anymore
F ð1; 19Þo1. In the AAA-group, the CS+ still elicited a higher US-expectancy than the CS at
moment 3, Fð1; 19Þ ¼ 41:11, po0:001, MSE=6.11. However in both groups there was evidence
for extinction when looking at the decrease in differentiation between the beginning of extinction
(moment 2) and the end of extinction (moment 3), both F ð1; 19Þ44:78.
Generalisation decrement: The US-expectancy ratings do not allow us to draw strong
conclusions with regard to the generalisation decrement caused by the context-change based on
between-group comparisons. It was impossible to create a reference point for the AAA-control
group that was comparable with the obvious context-change present in the ABA-group. For the
ABA-group however, no significant decrease in CS+/CS differentiation was observed after the
context-change, F ð1; 19Þo1, and the CS+/CS differentiation at the beginning of extinction
(moment 2) was highly significant, F ð1; 19Þ ¼ 33:89, po0:001, MSE=5.20.
Renewal of conditioned responding: In the ABA-group the difference between CS+ and CS
was significant at test, F ð1; 19Þ ¼ 34:63, po0:001, MSE=4.79. The increase for the CS+ from the
last extinction trial towards the test was significant, F ð1; 19Þ ¼ 10:54, p ¼ 0:004, MSE=7.20.
Furthermore, also the CS-type (ext10, test) interaction was significant, F ð1; 19Þ ¼ 10:65,
p ¼ 0:004, MSE=5.24, all indicating renewed conditioned responding after the context change.
In the AAA-group, the difference between CS+ and CS during test was also significant,
F ð1; 19Þ ¼ 7:01, p ¼ 0:015, MSE=2.69, indicating that also in the control group some
conditioned responding was still present. However this can not be taken as evidence for a return
because the US-expectancy for the CS+ diminished from extinction to test, F ð1; 19Þ ¼ 26:63,
po0:001, MSE=3.96. Also when taking into account the changes for CS, a significant CStype (Ext10, test) interaction was obtained, F ð1; 19Þ ¼ 18:88, po0:001, MSE=3.43 indicating a
continuing decrease.
When comparing the two between-groups directly, responses to CS+ at test were larger in the
ABA-group than in the AAA-group, F ð1; 39Þ ¼ 12:55, po0:001, MSE=7.28 and also the increase
from the end of extinction to the test for CS+ was significantly larger for the ABA-group,
F ð1; 39Þ ¼ 32:12, po0:001, MSE=5.60.When taking into account the changes for the CS as
well, significant between-group interactions were obtained: The CS+/CS differentiation at test
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was stronger in the ABA-group than in the AAA-group, F ð1; 39Þ ¼ 9:18, p ¼ 0:001, MSE=3.77,
and also the Group CS-type (ext10, test) interaction was significant, F ð1; 39Þ ¼ 27:66,
po0:001, MSE=4.36, indicating a return of responding in the ABA-group that was not observed
in the AAA-group.
4. Discussion
It was the intention of this study to demonstrate a return of conditioned electrodermal
responding after extinction when returning to the original acquisition context. The experimental
as well as the control group showed clear acquisition. Acquisition developed somewhat slower in
the AAA-group as on the last acquisition trial no significant CS+/CS differentiation was
observed yet. However, the data from the first extinction trial clearly show that these participants
have learned the differentiation. This trial can be considered as a valid assessment of acquisition
because the measurement of the skin conductance took place before the US-omission and no
context-change took place between acquisition and extinction in this group. Extinction took place
in both groups: At the end of extinction no differentiation between CS+ and CS was left
anymore. In contrast to the ABA-group, in the AAA-group we did not obtain a significant
decrease in differentiation from the beginning to the end of extinction. This suggests that
extinction effects in this group were not really strong. However, it was clear from the data that in
this group at the end of extinction and during test no significant CS+/CS differentiations were
observed anymore.
Given the evidence for acquisition and extinction of differential electrodermal responding, we
can start interpreting the data with respect to our main hypothesis regarding a return of
electrodermal responding after a context-change. The data demonstrate a clear return of
conditioned responding in the ABA-group, whereas in the AAA-group no such return was
obtained. There was in the former group a significant difference between CS+ and CS at test
that was not observed in the AAA-group; also the difference in responses to the CS+ between the
end of extinction and the test was significantly larger for the ABA-group than for the AAA-group.
We consider this as good evidence for ABA-renewal. It demonstrates that extinction-effects are
context-specific and that electrodermal conditioned responding may recover after a return to the
original acquisition context. One might have noticed that no significant between-group
interactions were obtained when the CS+/CS differentiation was taken into account, however
they were significant when only CS+ was taken into account. Significant effects based on a CS+/
CS differentiation are known to be more difficult to obtain for two reasons. First, these
comparisons only take into account influences that are specific to associative conditioning and
exclude all alternative influences such as familiarity of the context that might influence CS+ as
well as CS. In this respect, they are stricter than some other conditioning procedures. Second, it
is known that in these human conditioning paradigms the unreinforced presentation of the CS+
during test can have immediate impact on the responses to the subsequent presentation of CS
and vice versa (e.g. Lovibond, 2003).
The retrospective US-expectancy ratings corroborate the skin conductance data pattern. Both
groups showed acquisition as well as extinction. As expected, the control group showed a steady
decline in differentiation towards the end of the experiment, whereas the ABA-group showed an
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increase in differentiation from the third to the fourth moment, indicating that the return to the
original acquisition context caused a recovery effect. Note that these ratings were taken
retrospectively and should be interpreted with caution. However, a recovery-effect was obtained
despite the fact that the subjects in fact experienced no loud noises in the test phase. This makes
clear that the participants were able to interpret the graph and the US-expectancy scale in a
proper way, also it makes it less probable that the ratings exclusively reflected demand-effects.
Nevertheless, these data can only be suggestive for effects that one would have obtained with online verbal ratings.
With regard to the mechanisms that may underlie the return of fear in humans we can only
draw some preliminary conclusions. The fact that we have no evidence for a generalisation
decrement between acquisition and extinction in the skin conductance data, at least makes one of
the three mechanisms less plausible. It seems not to be the case that the CS was perceived
differently in the extinction context than in the acquisition context. The two other mechanisms
can still play a role. First, participants may have learned that the extinction context is safe. A
direct inhibitory association may have developed between the context and the US, protecting the
CS from extinction. Second, the context might have come to play a modulatory role, arbitrating
between situations in which the CS is followed by the US and situations in which the CS is not
followed by the US. It is reasonable to assume that also in a clinical context both mechanisms can
play a role. On the one hand, the therapy room and the presence of the therapist can become
safety signals, paradoxically protecting the fear-object from extinction. On the other hand, one
might learn an exception to the rule such as that the fear-object is no longer dangerous in the
therapy context or in the presence of the therapist, but remains dangerous once outside.
One of the aims for further research will be to try to disentangle these two mechanisms and see
whether both or only one of these mechanisms is responsible for the effects obtained.
Disentangling the mechanisms is only interesting for the clinical practice when these mechanisms
suggest different methods for preventing the return of fear. In general terms, one could state that
in the case of a modulatory role of the context, the advice would be to equate as much as possible
the exposure context with the context wherein the patient has to function in the future. Equating
the exposure context with the relevant contexts for the future would also be beneficial in case the
context became directly inhibitory and the context-dependency effect is based on the second
mechanism. On the other hand, focusing on an equation of the exposure context with the original
acquisition context is only beneficial when one wants to prevent that the context and the therapist
become safety-signals.
In the animal conditioning literature, two additional methods are described in order to reduce
return of fear after a context change. It seems that these methods are effective in reducing return
of fear that is based on either of the two mechanisms described above. A first method is to vary
the contexts or stimuli used during exposure therapy. There is evidence from two animal
conditioning experiments that conducting extinction in different contexts might be effective in
reducing the response recovery when entering a new context (Chelonis, Calton, Hart, &
Schachtman, 1999; Gunther, Denniston, & Miller, 1998). Also in the clinical study of Rowe and
Craske (1998a, b) there is evidence that using varied stimuli is effective in reducing the return of
fear when confronted with a new stimulus. Indeed, using multiple contexts as well as using
different stimuli might prevent that the context protects the CS from extinction. Moreover, it also
enhances the likelihood that the additional association formed during extinction becomes active in
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several new contexts. A second method is to make use of retrieval cues that help to reactivate the
extinction information. Brooks and Bouton (1994) (see also Brooks, Palmatier, Garcia, &
Johnson, 1999, for the effect on spontaneous recovery) demonstrated in an animal conditioning
experiment that presenting a cue during extinction as well as during test overcomes part of the
recovery of the conditioned responses due to context-change. As long as retrieval cues contribute
to the retrieval of the extinction information, they may be helpful in preventing return of fear.
Either when the direct context–US association is responsible or when the CS–noUS association is
under control of the context, making the extinction information more prominent might be
beneficial.
Regardless of the underlying mechanism that might be responsible for the effects, the present
data are quite convincing evidence for the context-specificity of extinction in a human fear
conditioning paradigm using electrodermal responding and retrospective US-expectancy ratings
as indices of learning. This study fills the gap between the demonstrations in the animal
conditioning literature on the one hand and the clinical demonstrations of a return of fear due to a
context change after successful treatment.
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