The influence of working memory taxation during the recall of an aversive
memory on evaluative conditioned responses
S.J. Zelhorst Bsc, March 2017
3763919
word count: (- tables, figures, references, index & appendix) = 5000 words.
Thesis for the master program Clinical psychology & Health psychology at Utrecht University.
Supervisor: prof. dr. Iris Engelhard
1
Abstract
Introduction: Both post-traumatic stress disorder and anxiety disorders (together: anxiety
related disorders) can be explained with learning theory. A conditioned stimulus (CS) has become
associated with an unconditioned stimulus (US) leading to a conditioned response (CR) to the CS.
Although Exposure therapy (ET) has been widely used in dealing with anxiety related disorders
its working mechanism focusing on inhibitory learning seems ineffective in dealing with the
negative valence of conditioned stimuli. ET does not effectively decrease the disgust experienced
by the memory of the US nor does it effectively decrease the negative valence associated with
the CS caused by associative conditioning, yet this negative valence predicts return of fear.
Therefore, it is important to find an effective intervention that does reduce this. Eye movement
desensitisation and reprocessing (EMDR) works by a different mechanism namely imagination
deflation. The current research aims to test whether an EMDR intervention yields better results
in neutralizing the negative valence of a CS and whether it effectively reduces the vividness and
unpleasantness of the US memory compared to an exposure-based intervention. Additionally, we
test whether these effects will last at least until the following day and if they will result in
participants in the EM condition to be more inclined to interact with the actual food item
depicted as CS. Methods: Ninety-one participants were divided over three conditions and
completed a conditioning task. They were shown pictures of two food items (CSs), of which one
(CS+) was followed by a disgusting film fragment (US) and the other (CS-) was followed by a
neutral film fragment. One group then did an eye movement task (EM) while recalling the US,
one group did a recall only task (RO, akin to exposure), and the last group performed an
unassociated filler task (FT). CS valence was measured before and after conditioning, after
conditioning, after intervention and one day later. Us memory unpleasantness and vividness
were measured after conditioning, after intervention and one day later and on both days a
behavioral test was performed. Results: No significant reduction in CS valence was found.
Relative to the other conditions, eye movements resulted in a significant reduction of the
unpleasantness, but not the vividness, associated with the US memory. This effect remained until the
next day. All other measurements were insignificant. Discussion: The fact that no reduction in CS
valence was found in the EM condition might be attributed to the fact, in contrast to earlier
studies, we used disgust-relevant CS’s which might be less prone to extinction.
2
Preface
Although initially I was quite daunted by the large task of writing my master thesis I thoroughly
enjoyed the experience. While at times the process was frustrating it has been very instructive. I
would like to thank my supervisor prof. dr. Iris Engelhard for her guidance and expertise as well
as for giving me the opportunity to work on a novel project relevant for the science of clinical
psychology as a whole. I also would like to thank Richelle Waanders BSc and Evelien Peters BSc
with whom I have done the legwork of this research and who have encouraged me throughout
the process. I would like to thank Arne Leer PhD and Evi-Anne van Dis MSc for their help. Lastly, I
would like to give my special thanks to Angelos Krypotos PhD for his generous help.
3
Introduction
PTSD and anxiety disorders
In addition to the symptoms of Post-traumatic stress disorder (PTSD) specified in the DSM-5
(American Psychiatric Association, 2013), evidence suggests that many patients diagnosed with
PTSD show strong affective reactions, such as disgust, when confronted with reminders of a
trauma. (Dalgleish & Power, 2004; Engelhard, Olatunji, & De Jong, 2011). Feelings of disgust also
play a large role in the symptomology of certain anxiety disorders such as spider phobia, blood
injection injury phobia as well as contamination based obsessive compulsive disorder (Cisler,
Olatunji & Lohr, 2009).
In a systematic review, the worldwide lifetime prevalence rate of anxiety disorders
(including PTSD) was 10.6 to 16.6% (Somers, Goldner, Waraich & Hsu, 2006). Anxiety-related
disorders often interfere with patients’ functioning, professionally and socially. They place a
large burden on health services and welfare systems, making these disorders quite costly for
society (Kessler, 2000).
According to current learning theory, patients with anxiety-related disorders have
learned an association between certain conditioned stimuli (CS) and an unconditioned
(threatening) stimulus (US) (see: Engelhard et al., 2009). That is, the CS is thought to activate the
expectancy that the US will occur, which evokes a conditioned response (e.g. fear or disgust).
This conditioned response (CR) constitutes part of the symptomology experienced by patients
with anxiety-related disorders (Rothbaum & Davis, 2003).
Exposure therapy
Exposure therapy is a first-choice treatment for anxiety-related disorders based on several
meta-analyses (e.g. Bradley et al, 2005; Mendes et al, 2008; Parsons & Rizzo, 2008). Patients are
repeatedly exposed to the CSs they fear to experience that the US will not follow. It was
previously thought that by repeated exposure the association between the CS and US would be
forgotten and would be replaced with a “no danger” association (Foa & Kozak, 1986). It is now
known, however, that this new “no danger” relationship does not replace the old CS/US
relationship, but only inhibits it (Craske, 2015).
4
Exposure therapy has several limitations. Firstly, It seems unable to decrease the feelings
of disgust often associated with anxiety-related disorders (McKay, 2006; Pace-Scott, Verga,
Benett & Spencer, 2012; Olatunji et al, 2007). Secondly, refusal rates as high as 27% and 30.4%
(Garcia-Palacios, Botella, Hoffman & Fabregat, 2007; Issakides & Andrews, 2004) and a drop-out
rate of 10.4% (Issakides & Andrews, 2004) have been found. Thirdly, In their meta-analyses
using 66 studies Loerinc et al (2015) found a response rate of only roughly 50%. Lastly and
importantly, return of fear (ROF) occurs in 13 to 23% of patients (Fave et al, 2001a; Fave et al,
2001b).
How can ROF be explained? Apparently, there are several ways by which the old CS-US
association can become dominant again, causing ROF (Craske, 2015). Firstly, ROF can happen
spontaneously over time (Quirk, 2002). Secondly, a change of either the external environment
(Vansteenwegen et al, 2005; Mystkowski, Craske, Echiverri & Labus, 2006; Culver, Stoyanova &
Craske, 2011) or the internal state of patients (Mystkowski, Mineka, Vernon, & Zinbarg, 2003)
can cause ROF. Thirdly, unpaired representations of a new aversive event can cause ROF
(Hermans et al, 2005; Van Damme et al, 2006). Lastly and importantly, the individuals’ negative
evaluation of the CSs increases ROF (Zbozinek et al, 2015).
When a certain CS is associated with an aversive US, the CS itself will sometimes be seen
as more negative independently of the US. This is called evaluative conditioning (see also:
Engelhard, Leer, Lange, & Olatinji, 2014), and as mentioned above this negative evaluation
increases the likelihood of ROF. Studies have found that extinction learning, which is the model
for exposure therapy, does not reduce the negative valence of the CS (Mason & Richardson,
2010; Engelhard et al, 2014). A treatment option based on another working mechanism, able to
prevent ROF is urgently needed.
EMDR
Eye Movement Desensitization and Reprocessing (EMDR; Shapiro 1989) is a trauma therapy in
which patients make horizontal eye movements (EM) while recalling traumatic memories.
Meta-analyses found that EMDR is an effective treatment of PTSD (Bradley et al, 2005; Seidler &
Wagner, 2006; Bisson et al, 2007).
5
A recent meta-analysis by Lee and Cuijpers (2013) shows that EM in EMDR has an added
benefit on top of the other elements of the therapy. This can be explained with the working
memory (WM) theory (see: Van den Hout & Engelhard, 2012). This theory states that EMDR
works by taxing the WM with making EM while recalling traumatic memories. When traumatic
memories are recalled to the WM they can become temporarily labile, meaning that they can be
altered. Because there is not enough space in the WM for both the EM and memory recall, the
memory becomes less vivid and emotional and can be stored this way to the long-term memory
(Gunter & Bodner, 2008). This process is called imagination deflation (Van den Hout &
Engelhard, 2012).
The WM theory predicts that other demanding dual-tasks work as well, and this has
indeed been found, for instance, for vertical eye movements (Gunter & Bodner, 2008), playing
Tetris (Engelhard, van Uijen & Van den Hout, 2010), mental arithmetic (Engelhard, van den Hout
& Smeets, 2011), calculating out loud (Kemps & Tiggemann, 2007), mindful breathing (Van den
Hout et al, 2011), auditory shadowing (Gunter & Bodner, 2008) and copying a complex figure
(Gunter & Bodner, 2008).
Because EMDR seems to work by imagination deflation and not inhibitory learning it
could be more effective in reducing the negative valence of a CS than exposure therapy. One
preliminary lab study found evidence for this (Leer, Engelhard, Altink & Van den Hout, 2013).
Participants listened to a high and a low tone (CSs). One of those tones was followed by a
disgusting film fragment (US). Then, half of the participants did an eye movement (EM) task
while the other half did a recall only (RO) task. Participants making EM found the memory of the
film less unpleasant and less vivid. They also reported less fear and US expectancy towards the
tone that had been followed by the disgusting film in the conditioning task, and they evaluated
that tone less negatively than before the intervention and compared to participants in the RO
condition. This suggests that EM effectively reduced the unpleasantness and vividness of the
US-memory and also reduced the negative valence of the CS.
There were some limitations to this study. First, tones were used as CSs, and tones are
not usually related to disgust learning. This hampers the ecological validity. Second, the
research used a RO group as control group. Since RO contains exposure elements it is not an
6
ideal “no treatment” group. Third, because of the short interval between the intervention and
test-phase nothing could be said about the long-term effects of EM.
Current Study
The current study expands upon the study done by Leer et al (2013) by making some
adjustments. Firstly, to increase ecological validity, pictures of food items were used as CSs.
Secondly, to examine if the change in CS valence actually led to a change in behavior a
behavioral task was added, similar to a task used by Borg et al (2015). Thirdly, to provide a “no
treatment” control group, another group doing a filler task (FT) was added. Fourthly, to examine
the long-term effects of EM, a follow-up test on the next day was added. Lastly, In accordance
with recent research findings that a longer EM intervention is more effective, the intervention
phase was lengthened (Van Veen, Engelhard & Van den Hout, 2016). We hypothesize that (1)
after EM, relative to RO and FT, the memory of the US (disgusting film fragments) will be less
vivid and unpleasant then before EM. (2) After EM, relative to RO and FT, the CS+ will be
evaluated less negatively than before EM. (3) These changes will hold true in the follow-up test
one day later and (4) at follow-up participants in the EM condition would be being significantly
more willing to eat the CS+ than those that did RO or FT.
7
Methods
Participants
A power analysis based on a small to medium effect size (Cohen’s d=.17) yielded 27 participants
per condition. 13 more were added to control for potential drop-out. The final sample consisted
of 94 participants. Participants received course credit or a financial reward. The data of three
participants was excluded due to errors they made during the procedure, which invalidated
their data (e.g., eating the food items on day 1). The analyses were run on the remaining 91
participants (see: table 1). The study was approved by the board of ethics.
Table 1: gender and age per condition
Condition
Participants
Male (%)
Female
Age, M (SD)
Age, Range
Eye movement 30
12 (40%)
18
21.47 (3.14)
18-35
Response only
31
14 (45%)
17
21.23 (2.17)
18-27
Filler task
30
12 (40%)
18
21.10 (2.75)
18-28
Total sample
91
38 (42%)
53
21.26 (2.68)
18-35
Before inclusion participants completed an online screening questionnaire. They rated 44 food
items on a 7-point Likert scale (1: very tasteful … 7: very distasteful). If they rated the food items
used in the experiment as either very tasteful or very distasteful they were excluded. Other
exclusion criteria were lactose intolerance, a vegan diet, bad corrected vision and the use of
medication severely influencing concentration (See: figure 1). Participants with prior knowledge
of EMDR were included in accordance with the study by Littel et al (2016) who found no
influence of prior knowledge in EMDR research.
8
Potential participants filed out online
screening questionnaire (N=221).
Participants excluded based on online
screening (N=33).
Participants invited to the research
lab (N=188).
No appointment made, no-show or
excluded at first session screening (N=94).
Participants participating in study
(N=94)
Participants excluded because of errors in
testing. (N=3)
Participants used in study (N=91)
Participants in eye movement
(EM) condition (N=30)
Participants in recall only
(RO) condition (N=31)
Participants in filler task
(FT)(N=30)
Figure 1: inclusion and exclusion of participants
General procedure
For the order in which the different parts of the experiment were conducted see: figure 2. They
will be described in detail in separate paragraphs below. E-prime 2.0 (Psychology Software
Tools) was used to program the task.
Before the experiment participants were given written and oral information about the
research and were informed that they could stop their participation at any time.
9
Day 1. Information about the experiment is given (verbally & in writing).
Signing of the informed consent and exposure to the food items depicted as CS.
Test battery day 1 is completed. This includes: HS; DPSS-R; VOCI; STAI-R.
Habituation phase. Afterwards subjective fear, disgust and attraction towards the CSs are
measured.
Acquisition phase. Afterwards subjective fear, disgust and attraction towards the CSs are
measured as well as unpleasantness and vividness towards the US memory.
EM intervention
RO intervention
FT intervention
Test phase. Afterwards Subjective fear, disgust and attraction towards the CSs are measured,
as well as unpleasantness and vividness towards the US memory.
Behaviour and avoidance task. CS preference is measured.
Day 2. Test battery day 2 is completed. This includes: HS; PANAS; The half of the STAI-R
measuring state anxiety.
Follow-up. Subjective fear, disgust and attraction towards the CSs are measured as well as
unpleasantness and vividness towards the US memory.
Behaviour and avoidance task. CS preference is measured.
Figure 2: Procedure of the experiment, Day 1 & 2.
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Stimuli
In a pilot study to determine the CSs, we presented images of six pairs of food items (e.g.
crackers with salads; desserts) to eight participants. Participants rated how positive, attractive
and disgusting they found them, as well as how willing they were to eat them on a VAS scale
from 0 (not at all) to 100 (very). Crackers with celery and humus-curry salad were rated most
neutrally and similarly (see: table 2) and were used in the conditioning task.
Table 2: M and SD of the CSs in the pilot experiment on the different questions.
Question
CS
M (SD)
positivity
celery
42.25 (26.60)
Humus-curry
38.25 (21.83)
celery
35.75 (32.72)
Humus-curry
38.75 (35.89)
celery
42.00 (32.46)
Humus-curry
49.88 (32.04)
celery
30.63 (23.15)
Humus-curry
33.38 (25.01)
Willingness to eat
Disgust
attraction
Both photos (CSs) of- and actual food items were used in the experiment. The real and
photographed food were made to look as similar as possible. Both were of a roughly equal
weight (12-16 grams for the celery; 24-28 grams for the humus-curry) and were presented on a
white plate.
The US was a 12-s film clip of a woman vomiting (cf. Borg et al., 2015), which was cut
into three fragments of 4-s each to prevent habituation (cf. Leer et al., 2013).
11
Questionnaires in order of first administration
The Hungerscale consists of four questions and measures how much hunger participants
experience at that moment on a vas scale from 0 (not at all) to 100 (very). It was custom-made
for this research (see: appendix A).
The Disgust Propensity and Sensitivity Scale-Revised (DPSS-R) contains 16 questions
(never; almost never; sometimes; often; always) measuring the tendency to experience disgust
and sensitivity to disgust (Van Overveld, De Jong, Peters, Cavanagh & Davey, 2006). The DPSS-R
is both valid and reliable (Van Overveld et al, 2006; Olatunji et al, 2007).
The Vancouver Obsessive Compulsive Inventory (VOCI) measures fear of contamination
with 13 questions (barely; a little; neutral; somewhat; highly). The VOCI has both convergent
and divergent validity and is reliable (Thordarson et al, 2004).
The State-Trait Anxiety Inventory-revised (STAI-R) contains 20 questions measuring fear
as a current state and 20 questions measuring fear as a personality trait (Spielberger et al, 1982)
(almost never; sometimes; neutral; often; almost always). It is highly reliable and moderately
valid (Julian, 2011).
The Positive and Negative affect scale (PANAS) includes 20 words used to describe either
positive or negative affect. Participants indicate how well those words describe the way they
feel at that moment (barely; a little; neutral; somewhat; highly) (Watson, Clark & Tellegen,
1988). It is reliable and valid in a non-clinical population (Crawford & Henry, 2004).
Visual Analogue Scales (VAS)
During the experiment, many measurements were done making use of VAS scales scored on a
scaled line (10 cm) from 0 (not at all) to 100 (very much). Participants made a mark on paper.
12
Memory evaluation
At the end of acquisition, intervention and follow-up, participants evaluated their memories of
the disgusting film fragments. They brought to mind the disgusting film memory as vividly and
with as much detail as possible for ten seconds. Afterwards they filled out a questionnaire
asking them how vivid and how unpleasant their memory of the disgusting fragment currently
was on the VAS scale mentioned earlier.
Pre-habituation phase
Participants filled out the questionnaires for day one (see: questionnaires; general procedure).
After this, the two crackers were placed in front of the participant at an equal distance for 10
seconds, then the crackers were put out of sight.
Habituation phase
Both CSs were shown twice in random order for 6 seconds each time, with an inter-stimulus
interval (ISI) of 14 seconds. After this, participants completed two forms, one for each CS, which
asked them about the subjective fear, disgust and attraction experienced seeing the CSs.
Answers were given on the 0-100 VAS scale mentioned earlier.
Acquisition phase
Both CSs were shown three times in random order. For half of the participants, the humus-curry
cracker was the CS+ and was followed by disgusting film fragments while the celery cracker was
the CS- and was followed by neutral film fragments. For the other half of the participants, this
was the other way around. Images of the CSs were shown for 14 seconds and the film fragments
lasted 4 seconds. after each film fragment, there was an ISI of 4 seconds.
After this, participants completed two forms, one for each CS, which asked them about
the subjective fear, disgust and attraction they experienced seeing the CS. Answers were given
on the 0-100 VAS scale mentioned earlier. Afterward, they filled out two more questionnaires,
one for the disgusting, and one for the neutral film fragments. Participants had to score how
13
unpleasant and how disgusting they found the film fragments. Answers were given on the 0-100
VAS scale mentioned earlier.
Intervention phase
Participants evaluated their memory of the disgusting film (see: memory evaluation). After this,
participants performed different tasks depending on whether they were in the EM, RO or FT
group.
Eye movement task (EM)
A white dot with an 1 cm diameter moved horizontally over the screen for 24 seconds.
Participants followed the dot with their eyes while keeping the disgusting film memory in mind.
Afterward, they thought of something else for 10 seconds. This process was repeated 16 times
(resulting in a total exposure of 384 seconds). After the break following the eight and sixteenth
cycle participants were asked to evaluate their memory of the disgusting film (see: memory
evaluation).
Recall only task (RO)
The RO task was similar to the EM task. The only difference was that participants were not
asked to follow a dot with their eyes but instead were asked to keep their eyes focused on a
black computer screen.
Filler task (FT)
During FT participants watched a fixated cross on the computer screen for 2 seconds after which
they saw an image of a guitar for 6 seconds. 16 guitars were shown twice with a black screen
functioning as an ISI being displayed for 10 seconds in between. Participants pressed the ‘1’ key
on the keyboard if they saw the guitar for the first time and the ‘2’ key if they had already seen
the guitar. This is the same task as had been used in the research of Engelhard, Leer & Lange
(2014) but the length of the task has been adjusted to make the task the same length as the EM
and RO tasks. Afterwards, Participants were asked to evaluate their memory of the disgusting
film (see: memory evaluation).
14
Test phase
Both CSs were shown twice in random order. Participants were told that one of these pictures
might be followed by a disgusting film fragment, but no fragments were actually shown. CSs
were shown for 6 seconds with an ISI of 14 seconds. After this, participants completed two
forms, one for each CS, which asked them about the subjective fear, disgust, and attraction they
experienced seeing the CS and how probable they thought it was that CS would be followed by
a disgusting film fragment. Answers were again given on the 0-100 VAS scale mentioned earlier.
Participants in the RO and EM conditions filled out a questionnaire asking them how
much they had actually thought about the movie fragments on both a VAS scale and on a scale
that asked them on how many of the 16 periods they had actually thought about the film.
Behavioral avoidance task, day 1
The crackers covered by a glass bell were placed in front of participants at an equal distance.
The plate to the left contained the cracker with humus-curry and the one to the right contained
the cracker with celery. Participants decided which of the crackers to evaluate first. Their
chosen cracker was placed in front of them and they received a questionnaire asking them how
tasty they thought the cracker looked, and how likely they were they would eat the cracker on a
VAS scale. After this, the plate was put back and the procedure was repeated with the second
cracker. Afterward, participants completed two forms, one for each cracker, asking how similar
the food on the plates was to the CSs they saw before. This was done with a VAS scale.
Pre-avoidance, Day 2
Participants filled out the questionnaires for day 2 (see sections: questionnaires; general
procedure) after which, the test phase was repeated. This time, both CSs were shown once.
Avoidance task day 2
Participants did an avoidance task first used by Borg et al (2013) similar to the avoidance task at
day one. The difference being, that after filling out the questionnaires rating the crackers
participants could eat the cracker as soon as the examiner had lifted the glass bell. They had one
15
minute to eat as much as they liked. If they preferred not to eat, that was fine as well. After a
minute the plate was put back and participants were asked to drink some water. After this, the
procedure was repeated for the second cracker.
Participants choose which of the crackers they wanted to evaluate first which,
Unbeknownst the participants, was noted down. The researcher also noted down whether the
participant ate each cracker and how long it took the participant to take the first bite. After the
entire experiment was finished the crackers were weighed to examine how much had been
eaten.
Afterwards, participants completed two forms, one for each CS, which asked them how
similar the food on the plates was to the food depicted as CSs on a 0-100 VAS scale (0: not at all
similar; 100: very similar).
Participants were asked to evaluate their memory of the disgusting film (see: memory
evaluation). When this was done the experiment was over. A debriefing followed and
participants were given their money or course credit.
Data-analyses
First, we conducted several randomization checks. To examine whether the groups differed
significantly on age, highest level of completed education (1:primary education; 2:VMBO
3:HAVO 4:VWO/MBO; 5:Bachelor 6:Master; 7:Post-doc), questionnaire outcomes and the
evaluation of the CSs before intervention one-way ANOVA’s were used. Gender was compared
using a Chi-square analysis.
Then we did several manipulation checks. First, to examine whether participants found
the disgusting film more disgusting and unpleasant than the neutral film we used ANOVAs with
groups as between subjecs-factor. Second, to examine whether participants experienced
negative valence towards the CS+ after the conditioning, scores for subjective fear,
unpleasantness and attraction were compared pre- to post-conditioning making use of a
repeated measures ANOVA.
To test the first hypothesis (after EM, relative to RO and FT, the memory of the US will
be less vivid and unpleasant then before EM), we used repeated measure ANOVAs with group
16
as between subjects-factor.
To test the second hypothesis (After EM, relative to RO and FT, the CS+ will be evaluated
less negatively than before EM), repeated measure ANOVA’s were used with subjective fear,
unpleasantness and CS attraction as dependent variables and groups as between subjectsfactor. This was done for both the CS+ and CS-.
To test the third hypothesis (the predicted effects in hypotheses 1 and 2 remain in the
follow-up test), repeated measure ANOVA’s were used with time (post-conditioning, follow-up)
as within-subjects factor and groups as between subjects-factor.
To test the fourth hypothesis (after EM participants are more willing to eat the food
depicted as CS+ than after RO or FT).Chi-square tests were used to compare cracker preference
and willingness to eat. Group was the between subjects-factor. Only 42 (46%) participants ate
the cracker depicted as CS+ and only 45 (49%) ate the cracker depicted as CS-. Because of the
missing data we did not further analyze the time it took for participants to take a bite and how
much of each cracker the participants ate.
17
Results
Randomization checks
Firstly, no significant between-group difference was found for gender, X²(180)=182.0 p=.440,
age, and highest level of education completed, both Fs<1. Furthermore, the groups did not
differ significantly on the STAI trait, STAI state (day 1), PANAS, DPSSR disgust propensity, DPSSR
disgust sensitivity, VOCI, and experienced hunger on day 1 or 2 (largest effect: F(2,88)=2,260
p=.11 for experienced hunger on day 2; all other F-values≤1). There was no between-group
difference in disgust or attraction towards either cracker, all F values<1. In summary, the
randomization was successful.
Manipulation checks
Firstly, we tested whether the disgusting film was found to be more disgusting and unpleasant
than the neutral film with groups as between-subjects factor (descriptives: table 3). For disgust
we found a main effect for movie-type, F(1,88)=1291.69 p=<.001, no main effect for group, F<1,
and no movie type*group interaction effect, F(1,88)=1.49 p=.23. For unpleasantness we found a
main effect for movie type, (1,88)=742.95 p=<.001, no main effect for group, F<1, and no movie
type*group interaction effect, F(1,88)=1.16 p=.32. This means the film manipulation was
successful.
Table 3: Disgust and unpleasantness ratings of the neutral and disgusting film, per condition
intervention
Disgust of film
Unpleasantness
(M+SD)
of film (M+SD)
Neutral film
Disgusting film
Neutral film
Disgusting film
EM
1.17 (2.88)
77.41 (18.05)
3.83 (7.71)
76.86 (21.77)
RO
1.37 (2.79)
80.90 (18.84)
5.37 (12.18)
79.57 (20.13)
FT
2.57 (4.80)
73.33 (21.37)
6.30 (13.51)
71.60 (23.05)
Total
1.71 (3.63)
77.21 (19.52)
5.18 (11.36)
76.00 (21.70)
Scores are given on a VAS scale from 0-100
18
Secondly, we compared the subjective fear, disgust and attractiveness towards the CS+ pre- to
post-conditioning with groups as between-subject factor (descriptives: table 4-6). An increase in
score was found for subjective fear, F(1,88)=46.94 p<.001 ηp²=.35, and disgust, F(1,88)=35.75
p=<.001 ηp²=.29, while a decrease was found for attractiveness, F(1,88)=45.11 p=<.001 ηp²=.34.
No significant main effect for condition was found for subjective fear, F(1,88)=1.34 p=.27,
disgust, F<1, or attraction, F<1. There were no significant time*group interaction effects for
subjective fear, disgust, or attraction. All F values≤1. This means participants found the CS+
more unpleasant after conditioning independent of condition meaning the manipulation for
negative valence was a success.
For the CS- (descriptives: table 4-6), an increase in score was found for disgust,
F(1,87)=4.04 p=.048 ηp²=.048, and a decrease was found for attractiveness, F(1,87)=4.04 p=.048
ηp²=.044. No effect was found for subjective fear, F<1. No effects for condition were found for
subjective fear, F(1,87)=1.35 p=.27, disgust, F<1, and attraction, F<1. No time*group interaction
effects were found for subjective fear, F(2,87)=.2.65, p=.076, disgust, F<1, and attractiveness,
F(2,87)=1.70 p=.19. This means that some generalization, from the CS+ to the CS-, of disgust and
attractiveness but not of fear has occurred.
Table 4: scores on subjective fear towards the CSs pre- and post-acquisition, per condition
intervention
Fear post-
Fear post-
habituation
acquisition
(M+SD)
(M+SD)
CS+
CS-
CS+
CS-
EM
5.10 (11.67)
4.70 (12.12)
26.21 (28.29)
6.27 (10.00)
RO
9.55 (17.94)
10.26 (19.06)
24.18 (24.92)
6.19 (10.92)
FT
3.67 (6.45)
5.47 (8.58)
27.12 (23.56)
7.30 (10.38)
Total
6.14 (13.16)
6.85 (14.08)
26.21 (28.29)
6.58 (10.34)
Scores are given on a VAS scale from 0-100
19
Table 5: scores on disgust towards the CSs pre- and post-acquisition, per condition
intervention
Disgust post-
Disgust post-
habituation
acquisition
(M+SD)
(M+SD)
CS+
CS-
CS+
CS-
EM
10.37 (15.82)
7.93 (13.75)
23.10 (27.75)
13.72 (22.12)
RO
13.65 (18.90)
12.48 (16.27)
25.48 (23.73)
15.72 (19.80)
FT
11.23 (19.86)
14.27 (25.48)
23.90 (23.91)
16.60 (21.79)
Total
11.77 (18.13)
11.61 (19.16)
24.18 (24.92)
15.38 (21.03)
Scores are given on a VAS scale from 0-100
Table 6: scores on attractiveness towards the CSs pre- and post-acquisition, per condition
intervention
Attractiveness
Attractiveness
post-habituation
post-acquisition
(M+SD)
(M+SD)
CS+
CS-
CS+
CS-
EM
38.80 (29.06)
40.53 (27.95)
22.37 (23.93)
31.50 (28.29)
RO
42.29 (25.57)
39.23 (28.14)
29.81 (23.66)
40.26 (26.89)
FT
46.73 (26.56)
40.83 (24.70)
29.10 (23.15)
34.97 (25.92)
Total
42.60 (26.98)
40.18 (26.72)
27.12 (23.56)
27.00 (27.00)
Scores are given on a VAS scale from 0-100
Hypothesis 1: After EM, relative to RO and FT, the CS+ will be evaluated less negatively than
before EM
For memory vividness, comparing groups pre- to post-intervention, a main effect for time (i.e. a
reduction in score) F(1,88)=96.94 p≤.0001 d=.52, no main effect for condition, F=(1,88)=1.39
p=.25, and no significant time*group interaction effect, F(1,88)=2.59 p=.081 was found
20
(descriptives: table 7). This means that although US-memory vividness decreased for the
sample as a whole, no between-group difference was found. This is not in line with the research
hypothesis.
Table 7: US memory vividness scores pre- and post-intervention, per condition
Research
Vividness pre-
Vividness post-intervention
condition
intervention (M+SD)
(M+SD)
EM
73.33 (16.70)
48.60 (21.90)
RO
71.16 (19.35)
51.84 (23.78)
FT
74.47 (12.82)
60.70 (20.17)
Total
72.97 (16.43)
53.69 (22.37)
Scores are given on a scale from 0-100
Concerning unpleasantness, a main effect for time (i.e. a reduction in score) F(1,88)=19.08,
p≤.0001. d=.178, no main effect for condition, F(1,88)=0.306 p=.74, and a significant time*group
interaction effect, F(2,88)=3.10, p=0.05 d=.066, was found (descriptives: table 8).
To examine the direction of this time*group interaction effect a pairwise comparison
was run examining the conditions separately making use of one-way ANOVA’s (α=.016; Cohen’s
d/3). This revealed a significant reduction in the EM condition, F(1,29)=18.37 p=<.0001, d=.129,
but not in the RO, F(1,30)=3.27 p=.063, or FT condition, F(1,29)=1.40 p=.25, (Cohen’s d/3). This
means that in the EM condition, but not in the RO or FT condition, US unpleasantness decreased
significantly. This is in line with the research hypothesis.
21
Table 8: US memory unpleasantness scores pre- and post-intervention, per condition
Research
Unpleasantness pre-
Unpleasantness post-
condition
intervention (M+SD)
intervention (M+SD)
EM
64.50 (23.20)
43.03 (30.17)
RO
60.52 (23.22)
50.81 (28.35)
FT
53.67 (26.82)
48.63 (24.43)
Total
59.57 (24.61)
47.53 (27.65)
Scores are given on a scale from 0-100
Hypothesis 2: After EM, relative to RO and FT, the CS+ will be evaluated less negatively than
before EM
For subjective fear of the CS+, no main effect for time, F(1,88)=2.77, p=.10, condition
F(1,88)=.63 p=.54, and no time*group interaction effect, F(2,88)=.123 p=.88, was found
comparing groups pre- to post-intervention. For CS+ disgust no main effect for time,
F(1,88)=2.21, p=.14, condition, F(1,88)=.109 p=.90, and no time*group interaction effect,
F(2,88)=.039 p=.962, was found. For CS+ attractiveness no main effect for time, F(1,88)=2.48,
p=.12, condition, F(1,88)=1.71 p=.19, and no time*group interaction effect, F(2,88)=2.47,
p=.091, was found. This means that none of the conditions showed any change in CS-valence
after the intervention, this is not in line with the hypothesis.
For subjective fear of the CS- a main effect for time (i.e. an increase in score),
F(1,88)=15.95, p≤.0001, d=0.15, no main effect for condition F(1,88)=0.52 p=.59, and no
time*group interaction effect, F(1,88)=1.17 p=.31, was found. For CS- disgust, no main effect for
time, F(1,88)=2.06 p=.16, intervention, F(1,88)=0.07 p=.92, or time*group interaction effect,
F(1,88)=.15 p=.86, was found. For CS- attractiveness, no main effect for time, F(1,88)=0.08
p=.78, condition, F(1,88)=.56 p=.57, and no time*group interaction effect, F(1,88)=2.86 p=.063
was found. This means that none of the conditions showed any change in CS- valence after the
intervention, except for fear induction. Participants found the CS- to be more fear-inducing
post-intervention.
22
Hypothesis 3: the predicted effects in hypotheses 1 and 2 remain in follow-up
For US memory unpleasantness no significant main effect for time, F(1,88)=1.87 p=.35,
condition, F(1,88)=.55 p=.58, and no significant time*group interaction effect, F(2,88)=0.58
p=.56 was found, comparing groups post-intervention to follow-up (descriptives: table 9). This
means that the significant result of hypothesis 1 concerning US-unpleasantness remained until
follow-up. This is in line with our hypothesis.
Table 9: US memory unpleasantness scores post-intervention and at follow-up, per condition
Research
Unpleasantness post-
Unpleasantness follow-up
condition
intervention (M+SD)
(M+SD)
EM
43.03 (13.16)
46.44 (28.12)
RO
50.81 (28.34)
49.42 (21.75)
FT
48.63 (24.43)
52.97 (24.77)
Total
47.53 (27.64)
49.71 (25.83)
Scores are given on a scale from 0-100
Hypothesis 4: after EM participants are more willing to eat the food depicted as CS+ than after
RO or FT
There was no between-group difference when comparing how often participants took a bite of
the CS+, X²(2,91)=2.12, p=.34, or CS-, X²(2,91)=1.126, p=.53. There was no between-group
difference comparing how many participants rated the CS+ first on day 1, X²(2,91)=2.461, p=.29,
or day two, X²(2,91)=.45, p=.80. This means that after EM participants were not more willing to
interact with or eat either the CS+ or CS-. This is not in line with our hypothesis.
23
Discussion
The aim of this study was to examine whether EM decreases the negativity associated with the
CS and US used in a disgust-based conditioning task, whether these decreases would remain
until the next day and whether EM makes participants more likely to interact with the CS+. The
main findings were that EM during recall of an aversive memory, compared to RO or FT, did
reduce the unpleasantness, but not the vividness of the US memory. This reduction in US
memory unpleasantness remained until follow-up. None of the other measurements were
significant.
Given that we found a decrease in memory unpleasantness but not in vividness, the first
hypothesis, making EM during the recall of an aversive memory reduces the unpleasantness and
the vividness of the memory of the US, was only partially confirmed. The reduction in memory
unpleasantness did remain until follow-up and can be assumed to be relatively long-lasting. Our
second hypothesis, making EM during the recall of an aversive memory reduces the negative
valence of the CS, has been rejected. The negative valence in the EM condition did not decrease
more than in the RO or FT condition. On top of that, participants in the EM condition were not
more likely to eat the actual food items depicted as CS+ than participants in the RO or FT
conditions.
Leer et al (2013) did find a reduction in US-memory vividness and CS-associated negative
valence. It is, therefore, interesting to look at the differences between the two studies. One
difference is that Leer et al (2013) used high and low tones as CSs while our research used
pictures of food items. Research in fear conditioning found that although evaluative
conditioning can be achieved using both phobic-relevant and phobic-irrelevant stimuli as CSs,
participants conditioned to phobic-relevant CSs (e.g. snakes) showed a slower rate of extinction
than those conditioned with phobic-irrelevant CSs (e.g. mushrooms) ( Öhman, Erixon & Löfberg,
1975; Öhman, Eriksson & Olofsson, 1975; Öhman & Soares, 1993). Öhman and Mineka (2001)
propose an evolutionary theory stating that CSs that were dangerous to our ancestors are
relatively immune to extinction.
This theory might also apply to disgust learning. As argued by Bosman, Borg and De Jong
(2016), disgust played a key-role in the survival of our ancestors, making individuals sensitive to
24
associate certain stimuli (food, dirt, etc.) with illness. These stimuli would be disgust-relevant
and like the fear-relevant stimuli they may be relatively resistant to extinction. Stimuli like the
tones used by Leer et al (2013) might be disgust-irrelevant. This might explain why the negative
valence of the tones was more malleable by eye movements. This is an empirical hypothesis
that awaits testing.
Limitations
While our study used 384 seconds of eye movements, actual EMDR often takes multiple, much
longer, sessions. Even clinical studies reporting treatment effects after only one session used
interventions of at least 45 minutes (e.a. Marcus, Marquis & Sakai, 1997; Shubert, Lee &
Drummond, 2011), meaning that those interventions were more than 7 times longer than the
EM intervention we used. Other lab studies, however, used an EM intervention of only 96
seconds and did find significant results (Engelhard et al, 2010; Gunter & Bodner, 2008; Leer et
al, 2013). The study by Leer et al (2013) was quite similar to ours in design which makes it
unlikely that the insignificant results in our study were caused by the length of the EM
intervention.
25
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32
Appendix A: the Hungerscale
Probeer de onderstaande vragen zo nauwkeurig mogelijk te beantwoorden.
1. Hoe lang geleden heb je voor het laatst gegeten?
_______ uur ________ minuten
2. Hoeveel trek heb je op dit moment in eten? Omcirkel het antwoord dat het beste bij jou past.
Geen trek
1
2
3
4
5
6
7
Heel veel trek
3. Hoeveel van je favoriete voedsel zou je op dit moment kunnen eten?
Niets
1
2
3
4
5
6
7
Zoveel ik kan krijgen
4. Schat hoelang het duurt voor je je volgende maaltijd eet:
_______ uur ________ minuten
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