Psychiatry Research: Neuroimaging 224 (2014) 133–138
Contents lists available at ScienceDirect
Psychiatry Research: Neuroimaging
journal homepage: www.elsevier.com/locate/psychresns
Enhanced action tendencies in high versus low obsessive-compulsive
symptoms: An event-related potential study
Adi Dayan n, Andrea Berger, Gideon Emanuel Anholt
Department of Psychology, Ben-Gurion University of the Negev, Beer Sheva 8410501, Israel
art ic l e i nf o
a b s t r a c t
Article history:
Received 30 July 2013
Received in revised form
20 May 2014
Accepted 16 July 2014
Available online 28 July 2014
Obsessive-compulsive disorder (OCD) is an anxiety disorder characterized by repeated thoughts and
behaviors. Inhibitory deficits are presumably related to the onset and maintenance of this disorder. The
present study investigated whether obsessive-compulsive (OC) symptoms are related to enhanced
response tendencies in reaction to external stimuli. Our goal was to search for direct evidence of an early
response preparation process by examining the event-related potential (ERP) component of the
readiness potential (RP). An enhanced response tendency might underlie inhibitory deficits in OCD.
Response to novel stimuli was studied using a dishabituation paradigm in which a small number of
schematic faces (angry or neutral) were presented. An analog sample of healthy subjects was divided
into groups of high and low OC levels and high and low trait anxiety levels. The high OC group presented
with a greater RP slope gradient that was enhanced under negative valence, compared to the low OC
group. No such effect was found in the high versus low trait anxiety groups or in behavioral reaction
times (ms). Results support the hypothesis that a stronger readiness for action might characterize
subjects with OC symptoms, especially in the presence of threatening stimuli. This finding, specific to OC
symptoms and not to anxiety symptoms, may underlie habitual and embodiment tendencies in OCD.
This study suggests that early stages of motor preparation might be important to the etiology and
maintenance of OC symptoms.
& 2014 Elsevier Ireland Ltd. All rights reserved.
Keywords:
Anxiety
Readiness potential
Event-related potential (ERP)
1. Introduction
Obsessive-compulsive disorder (OCD) is an anxiety disorder
characterized by persistent, intrusive, and distressing obsessions
and/or compulsions, and associated with marked impairments in
quality of life (Eisen et al., 2006; American Psychiatric Association,
2013). Neuropsychological studies of OCD patients indicate that
they show deficits in executive functions (Abramovitch et al., 2011).
Response inhibition is one of the most extensively investigated
functions that has been found to be impaired in OCD patients.
Response inhibition refers to the ability to voluntarily select a taskappropriate, goal-directed response while suppressing a more
compelling – but task-inappropriate – response (e.g., Verbruggen
and Logan, 2008; Luna et al., 2010).
The literature regarding the executive function of response
inhibition in relation to OCD is quite diverse. On the one hand,
some research shows evidence of inhibitory deficits in OCD
patients and their first degree relatives in measures such as stop
response latencies in the stop signal task and higher interference
in the Stroop task (Bannon et al., 2002; Chamberlain et al., 2006;
n
Corresponding author. Tel.: þ 972 8 6477204; fax: þ972 8 6472072.
E-mail address: [email protected] (A. Dayan).
http://dx.doi.org/10.1016/j.pscychresns.2014.07.007
0925-4927/& 2014 Elsevier Ireland Ltd. All rights reserved.
Menzies et al., 2007; Penades et al., 2007; for review, see
Abramovitch et al. (2013)). On the other hand, other research
has found no deficits in behavioral response inhibition in OCD
patients (Maltby et al., 2005; Roth et al., 2007; Krishna et al., 2011).
Findings in both directions (both supporting and disputing inhibitory deficits in OCD) are focused on stages pertaining to the
inhibition of the executed response. However, earlier stages of
stimulus processing and their relation to response initiation
(before inhibition of the response) have been far less studied
(Greenberg et al., 2000; Okasha et al., 2000; Hajcak and Simons,
2002; Gilbert et al., 2004). Possibly, it is not solely the inability to
stop a response that impairs inhibition. Perhaps, the early and
more intense initiation of a response to a stimulus impairs
inhibitory processes as well.
Indeed, preliminary evidence found in the electrophysiological
and functional imaging literature suggests that a more intense
connectivity between stimulus perception and motor response
initiation may be an additional characteristic of OCD symptomology. For instance, Yucel et al. (2007) have shown that OCD patients
have a greater relative activation of the supplementary motor area
compared with control participants. Another study using transcranial magnetic stimulation (TMS) has shown that subjects with
OCD have a lower threshold of motor-evoked potential and an
increased intra-cortical disinhibition in comparison to healthy
134
A. Dayan et al. / Psychiatry Research: Neuroimaging 224 (2014) 133–138
control subjects (Greenberg et al., 2000). The hypothesis of an
enhanced motor response initiation has yet to be investigated in
relation to specific motor responses to external stimuli. However,
event-related potential (ERP) studies have shown subjects with
OCD to have higher amplitudes in different components (Okasha
et al., 2000; Hajcak and Simons, 2002), generally considered to
indicate a stronger reactivity of stimulus processing.
Stronger action tendencies in reaction to external stimuli
would most likely be manifested in enhanced motor preparatory
processes. A well-known electrophysiological correlate of such a
preparatory process is the readiness potential (RP), which seems to
be the most suitable indicator for assessing brain reaction related
to motor activity in response to external stimuli (for a review, see
Colebatch (2007)). Therefore, the aim of the present study was to
investigate whether OC symptoms are related to enhanced
response tendencies in reaction to environmental stimuli. In the
current study, the RP component was specifically tested within a
simple cognitive dishabituation task in which participants were
required to respond to novel stimuli.
We expected subjects with higher OC symptoms to exhibit
faster reaction times and greater RP than subjects with lower OC
symptoms. This hypothesis relied on research that has shown
greater activation of motoric areas, lowered threshold of motorevoked potentials, and higher ERP amplitudes in various components related to stimulus processing in OCD relative to control
subjects. (Greenberg et al., 2000; Okasha et al., 2000; Hajcak and
Simons, 2002; Yucel et al., 2007). Furthermore, since OC symptoms
demonstrate comorbidity with anxiety disorders (Nestadt et al.,
2001; Klein Hofmeijer-Sevink et al., 2013), it was important to
establish the specificity of our findings to OCD and to preclude the
alternative explanation that trait anxiety explained our results. We
expected our effects to be specific to OC symptoms relative to trait
anxiety symptoms. Relying on research that indicates higher selfsensitivity and increased vigilance to affective stimuli – specifically
danger cues – in OCD (e.g., Doron and Kyrios, 2005), we also
expected this effect to be exacerbated in a negative emotional
context.
2. Methods
2.1. Subjects
2.2. Experimental task
A numerical quantity change task was designed that was similar to the one
used by Cantlon et al. (2006). In each experimental trial, subjects were presented
with a sequence of stimuli of the same numerical quantity (the habituation stage)
followed by a sequence-breaking stimulus of a different numerical quantity (the
dishabituation stage) to which subjects were asked to respond with a key press (see
Fig. 1). The numerical quantities used were within the subitizing range (1–4) and
the stimuli were schematic faces (either angry or neutral, in separate blocks). The
length of the habituation sequence was either six or nine slides. In the dishabituation stage, the subjects were presented with a new numerical quantity and
were asked to respond with a key press according to the new numerical quantity
(e.g., “Press key one when the new numerical quantity is one”). The new numerical
quantity would then become the new habituated numerical quantity for the
following trial. Each subject was presented with 480 experimental trials. Once
subjects pressed any of the four keys indicating the detection of a numerical
quantity change, the trial was terminated and the responded-to numerical quantity
then became the numerical quantity presented throughout the following set. Each
slide was presented for a duration of 600–800 ms followed by a break of 200–
400 ms in which the subjects were presented with a black screen.
The stimuli were schematic faces – angry and neutral – created for the purpose
of this experiment. Schematic faces were chosen on the assumption that similar
neurological mechanisms stand at the base of real-face and schematic-face
perception. Further, schematic faces are perceived by an early visual perception
mechanism resembling that of threat detection (Sagiv and Bentin, 2001). Each
experimental trial consisted of one emotional valence (i.e., angry or neutral)
Table 1
Age, gender, OCI-R score and group (high or low), anxiety score and group (high or
low) and values of the readiness potential (RP) slope gradient for each of the 14
participants.
Participant Age Gender OCI-R
score
OCI-R
group
STAI
score
STAI
group
RP slope
gradient
1
2
3
4
5
6
7
8
9
10
11
12
13
14
High
High
High
High
High
High
High
Low
Low
Low
Low
Low
Low
Low
53
37
33
37
29
27
42
46
39
48
34
37
37
25
High
Low
Low
High
Low
Low
High
High
High
High
Low
High
Low
Low
0.02856
0.01620
0.02576
0.02602
0.01892
0.05248
0.04546
0.02673
0.02569
0.02913
0.01205
0.02425
0.02311
0.02771
22
25
22
21
23
23
23
23
24
24
24
25
22
22
Female
Female
Female
Female
Male
Female
Female
Female
Female
Female
Female
Female
Female
Female
25
24
15
44
12
26
17
1
8
8
2
6
12
3
OCI-R, Obsessive-Compulsive Inventory-Revised. STAI, State-Trait Anxiety Inventory.
This study involved 14 undergraduate students who received course credit for
participation in this experiment (mean age¼ 23; S.D.¼ 1.2; 13 females, one male).
Exclusion criteria included a history of neurological disorders, current use of
medication, head injury, learning disabilities, and left-hand dominance. The study
was approved by the Helsinki Ethics Board of Soroka University Medical Center and
the Ethics Committee of the Ben-Gurion University of the Negev Psychology
Department. All participants provided written and signed informed consent, and
were informed that they might be asked for feedback on their questionnaire scores
and performance at the end of the experiment.
OCD symptoms were evaluated using the Obsessive-Compulsive InventoryRevised (OCI-R; Foa et al., 2002). Subjects were divided into two groups according
to the OCI-R: high versus low, according to the median OCI-R score (median OCI-R
score¼ 12). In addition, subjects were redivided based on their scores on the StateTrait Anxiety Inventory (STAI; Spielberger, 1983) according to the median STAI
score (median STAI score¼37). The high OCI-R group included seven participants
(six females, one male, mean OCI-R score¼23.29, S.D. ¼ 10.61, mean STAI
score¼ 36.86, S.D.¼ 8.8) and the low OCI-R group included seven participants (all
females, mean OCI-R score¼ 5.71, S.D. ¼ 3.95, mean STAI score ¼ 38, S.D.¼ 7.66). The
groups did not differ in age (t[12]¼ 1.12, p ¼ 0.142, one-tailed, mean age¼ 23.01,
S.D. ¼1.21). It is important to note that these OCI-R scores were well within the
normal range for college students (Sulkowski et al., 2011). Please see Supplementary Table for demographic data.
The high anxiety group included seven participants (all females, mean STAItrait score¼43.14, S.D. ¼ 6.09, mean OCI-R score¼15.57, S.D.¼ 14.82) and the low
anxiety group included seven participants (six females and one male, mean STAItrait score¼31.71, S.D.¼ 4.79, mean OCI-R score¼13.43, S.D.¼ 9.27). The groups did
not differ significantly in age (t[12] ¼0.65, p¼ 0.27, mean age¼23.07, one-tailed,
and S.D. ¼1.21) (Table 1).
Fig. 1. Example of an experimental trial: habituation to the quantity of four
followed by a dishabituation step in which the quantity of one appears and later
becomes the new habituated quantity.
A. Dayan et al. / Psychiatry Research: Neuroimaging 224 (2014) 133–138
randomly ordered between subjects. The order of valence was manipulated only
between blocks, so that half of the subjects performed three angry blocks followed
by three neutral blocks, whereas the other half performed the task in the opposite
order. Participants were told that they would be presented with different numerical
quantities of schematic faces that would remain the same for a certain sequence of
slides and occasionally change, beginning a different numerical quantity set.
Participants were instructed to look carefully at the presented numerical quantities
and to press one of four keys according to the appearance of a new numerical
quantity.
To ensure that subjects were habituated to the numerical quantity of stimuli
and not to other characteristics of the stimuli, the location of stimuli on the screen
and the size of the stimuli presented were randomly varied within each experimental trial throughout each numerical quantity set. For each numerical quantity
(1–4), the size of the stimulus presented on the screen was randomly sampled from
a pool of six possible sizes, ranging from 25 to 95 pixels. A pilot phase showed that
25 pixels was the minimum possible size that allowed a clear view of the stimuli on
the screen. The random location of the stimuli on the screen was accomplished by
randomly sampling the stimulus from a 200-pixel screen frame that was divided
into a grid. Participants were tested in one session consisting of 480 trials
presented in random order. The experiment was divided into six blocks, allowing
for five short intermissions and one short practice block.
2.3. Experimental set-up and data acquisition
The experiment was programmed using E-prime 2 software (Schneider et al.,
2002), adapted to EGI Netstation version 4.5. Displays were generated by a Dell
computer attached to a 17-inch CRT monitor, using a 1024 768 resolution graphic
mode. Responses were collected using a button-press response box. Participants
were seated at a viewing distance of 80 cm from the monitor, and the experiment
was conducted in a relatively dark room. The duration of the experiment was
approximately 1 h.
Electrophysiological data were recorded while participants performed the
dishabituation task. Continuous EEG was recorded using a Geodesic Sensor Net
(V2.1; Electrical Geodesic, Inc., Eugene, OR) consisting of 128 electrodes evenly
distributed across the scalp. During collection, EEG data were referenced to the
vertex and then re-referenced offline to a PARE-corrected average reference. The
EEG signal was recorded with a 0.1- to 100-Hz band-pass filter and digitized at a
250-Hz sampling rate with a 24-bit A/D converter. Continuous EEG data were
processed offline using Netstation 4.5 (Electrical Geodesics Inc., Eugene, OR) and
segmented into stimuli synchronized epochs, which were extracted at 200 ms
before (baseline) until 800 ms after stimulus onset. EEG signals containing artifacts
(EEG Max–Min 4100 μV) were automatically removed from further analysis. Eye
blinks and eye movements were removed based on a criterion of Max–
Min4 100 μV and a criterion of Max–Min 485 μV, respectively. Before derivation
of the ERPs, the EEG signal was subjected to low-pass digital filtering of 40 Hz to
ensure that electrical main noise did not affect our data while losing as little signal
as possible.
2.4. Data analysis
Based on previous research (Boulenger et al., 2008; Fontana et al., 2012) and a
review of the grand mean ERPs of the different experimental conditions of interest,
a time window and brain region for the RP component were preselected for
analysis. EEG epochs, in which participants detected numerical quantity change,
were averaged into the dishabituation ERP waveform. The ERP segments were
135
stimulus-locked, meaning they were measured with respect to the moment the
eliciting stimulus appeared. The RP component was extracted for each participant
for each condition. The RP amplitude was scored as the mean amplitude (in mV) in
the time interval from 200 ms to 750 ms following stimulus onset and was
examined over centro-parietal sites collapsing across eight electrodes situated
between Cz and Pz of the 10–20 system. These electrodes were chosen for analysis
on the basis of previous research showing that RP is most dominant over centroparietal scalp regions (Kilner et al., 2004; Boulenger et al., 2008; Fontana et al.,
2012).
2.5. Statistical analysis
Independent sample t-tests were used to assess between-group differences in
reaction times (measured in milliseconds) and readiness potentials. An alpha level
of 0.05 was used for all t-tests. We used one-tailed t-tests because our hypothesis
was unidirectional in theory. We chose to conduct t-tests despite the small sample
size because our sample met the necessary criteria for doing so, as suggested by De
Winter (2013). First, t-tests on small samples require that the two populations be of
equal variance. We assessed this condition using the Levene test, which indicated
that equal variances can be assumed (F [1,12] ¼ 3.64, p ¼ 0.081). The second
condition that had to be met was a large effect size. The effect size for this analysis
(d ¼ 1.097) was found to exceed Cohen’s (1992) convention for a large effect
(d ¼ 0.80).
Following Kilner et al. (2004) and Boulenger et al. (2008), the OCI-R related
modulations in the ERP gradient of slope were examined using independent t-tests
for the RP component between groups (high and low STAI, high and low OCI-R).
The slope gradient measure used here was previously shown to provide a clear and
reliable differentiation between clinical groups (Korostenskaja et al., 2003). Further
analysis included t-tests to separately compare the RP gradient of slope between
groups under angry valence and neutral valence conditions.
We further conducted an analysis of covariance (ANCOVA) of RPs in high versus
low OC participants with trait anxiety as a covariate.
3. Results
3.1. ERP results/readiness potential
ERP data revealed a strong RP over the central region (see Fig. 2b),
indicating preparation to perform an action (see Supplementary
Table). As expected, participants with higher OCI-R scores showed
a significantly higher slope gradient for the RP component (mean¼
0.0307 0.013) than did participants with low OCI-R scores (mean¼
0.00870.025; t[12]¼2.052, p¼0.031, one-tailed; see Fig. 2a and b).
No latency effect was found for the OCI-R or anxiety groups (t[12]¼
0.74, p¼0. 237, one-tailed). Negative valence stimuli (compared with
neutral valence stimuli) were more strongly differentiated between
the OCI-R groups. This phenomenon was indicated by a significant
effect for the angry stimuli (t[12]¼2.151, p¼0.026, one-tailed; see
Fig. 3), whereas under the neutral condition, no significant effect was
found (t[12]¼1.444, p¼0.087, one-tailed; see Fig. 3).
Fig. 2. a. Mean gradient of the slope of the RP (in mV) (presented in absolute values) as a function of OCI-R group (high in red and low in blue), nP o0.05, one-tailed. b. Grand
average ERP waveforms time-locked to the stimulus electrodes situated between Cz and Pz (in the 10–20 system) over the centro-parietal scalp sites for the high OCI-R group
(red line) and the low OCI-R group (blue line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
136
A. Dayan et al. / Psychiatry Research: Neuroimaging 224 (2014) 133–138
4. Discussion
Fig. 3. Mean gradient of the slope of the RP as a function of OCI-R group (high in
red and low in pink), under the different valence conditions (angry and neutral),
and mean gradient of the slope of the RP as a function of STAI group (high in red
and low in pink). *Po 0.05 and #Po 0.1, one-tailed. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
No group differences in RP slope gradient were found between
the high STAI group (mean¼0.13770.029) and low STAI group
(mean¼ 0.025 70.013; t[12]¼0.949, p¼0.181, one-tailed). No significant differences were found when the two groups were compared under each valence condition (angry valence: t[12]¼ 0.904,
p¼0.192, one-tailed; neutral valence: t[12]¼0.824, p¼ 0.213, onetailed). Further, the ANCOVA of readiness potential in high versus
low OC participants with trait anxiety as a covariate revealed that
differences between OCI-R groups in RP remained significant even
when accounting for anxiety levels (t[12]¼1.981, p¼0.037, onetailed).
3.2. Behavioral results
There was no significant difference in reaction times (ms) on the
dishabituation task for the high OCI-R group (mean¼ 709.95792.68)
versus the low OCI-R group (mean¼666.57788.54; t[12]¼0.895,
p¼0.194, one-tailed). Likewise, no significant difference in reaction times (ms) for the high anxiety group (mean¼679.35 782.33)
versus the low anxiety group (mean¼ 697.177102.77; t[12]¼0.358,
p¼0.364, one-tailed) was found.
No significant differences in reaction times (ms) were found when
OCI-R groups were further compared within the angry valence
condition (mean high OCI-R group¼702.29795.34, mean low OCIR group¼672.97775.78; t[12]¼0.637, p¼0.268, one-tailed), and the
neutral valence condition (mean high OCI-R group¼717.60794.58,
mean low OCI-R group¼ 660.177107.41; t[12]¼1.062, p¼0.155, onetailed).
Finally, no significant differences in reaction times (ms) were
found when STAI groups were further compared within the angry
valence condition (mean high STAI group¼671.23 791.05, mean
low STAI group¼ 704.03 780.11; t[12]¼ 0.716, p¼ 0.244, onetailed), and the neutral valence condition (mean high STAI
group¼687.47 776.77, mean low STAI group¼690.30 7128.49; t
[12] ¼0.05, p ¼0.481, one-tailed).
The present study used the ERP component of the readiness
potential (RP) to assess the influence of OCD symptoms on
reaction patterns to external stimuli. Results suggest that participants who scored higher on the OCI-R have a significantly higher
slope gradient for RP over centro-parietal brain regions for the
appearance of a dishabituation stimulus in a numerical quantity
task in the subitizing range. These group differences were found to
be enhanced in a negatively valenced stimulus and were not found
when the groups were divided according to levels of general
anxiety.
The group differences found in RP could be attributed to a
greater cortical hyperarousal before a motor response, which is
found in patients diagnosed with OCD (Greenberg et al., 2000;
Gilbert et al., 2004). However, the two OCI-R groups did not differ
throughout the entire ERP segment except, specifically, in the
component of RP. Therefore, an arousal of a specific and unique
nature seems to characterize stimulus response in subjects with
more OC symptoms. Moreover, the effects of the RP component
were seen not only in the amplitude of the wave but in the gradient
of the slope, which takes into account the amplitude of the
wave as well as its duration; this is indicative of a more intense
response process rather than simply a stronger one. In OCD
symptomology there seems to be a form of increased readiness
for action. The differences seen in the gradient of slope for the RP
may reflect better translation of stimulus perception to motor
action plans. Conversely, it may reflect differential response initiation without a preferential perception process for OCD symptomology. Future research may examine the specific nature of this
RP effect.
Researchers have suggested that goal-directed action may be
compromised in OCD patients and that compulsions may be
driven by maladaptive habits (Boulougouris et al., 2009). Neural
support for this theory is found in research showing dysfunction
in orbito-frontal cingulate cortices and the caudate nucleus in
OCD. These same brain regions have also been implicated in goaldirected control, supporting the claim for over-reliance on habitual
control and enactment tendencies in patients with OCD (Gillan
et al., 2011). It seems that in an ever-changing environment,
patients with OCD rely on procedural learning to compensate for
their deficits in the ability to suppress actions that are no longer
effective by using goal-directed behavior (Verbruggen and Logan,
2008).
The specific pattern of brain reactivity seen in our results may
serve as a basic process underlying dual-system theories. According to such theories, an overactivation of the habitual system is a
result of an environmental stimulus triggering the habitual
response and circumventing intentional goal-directed behavior
(Dickinson and Balleine, 1993). It is plausible that enhanced action
tendencies, alongside impairments in inhibition of thought and
action, are causal to the excessive use of habitual behavior that
characterizes OCD symptomology. Therefore, it is plausible
that patients with OCD present with increased performance of
habitual actions in response to contextual stimuli (e.g., a light
switch) due to enhanced embodiment tendencies and diminished
control over goal-directed behavior. This assumption can potentially expand the common view that OCD deficits of response
inhibition are due to difficulty in suppressing a response, perhaps
to show alterations in the initiation and strength of the response
itself.
According to Anholt et al. (2012), the thought-action cycle in
OCD may be ignited by automatically triggered behaviors (or urges
to behave) that are interpreted to be important. These experiences
may lead to increased anxiety and compulsive behaviors such as
repeated checking. According to Kalanthroff et al. (2013), the
A. Dayan et al. / Psychiatry Research: Neuroimaging 224 (2014) 133–138
performance of irrelevant behavior elicited by intrusive thoughts
inflates the perceived importance of these thoughts, in turn leading
to further compulsive behavior. In accordance with such a model,
enhanced response tendencies in OCD (as seen in the current study)
may play a role in such a cycle by eliciting stronger action
tendencies in patients. Furthermore, intrusive thoughts may serve
as a trigger for behavior (an internal stimulus triggering enhanced
action tendencies), leading to a greater sense of importance
regarding that behavior and a higher likelihood that it will reoccur
(e.g., losing control and hurting loved ones). Modifying these action
tendencies may provide novel ways for breaking this cycle.
In terms of emotional valence, it appears that high valence
stimuli (angry faces) evoke a greater difference between high and
low OCI-R groups, underlying the main effect for the group. These
results are compatible with research relating higher self-sensitivity
and increased vigilance to affective stimuli in OCD (Doron et al.,
2008).
It is important to note that group differences in RP are unique
to OC symptoms and cannot be generalized to trait anxiety.
Dividing the groups according to their median STAI score showed
no effect in reaction times (ms) or in the gradient of slope. Further,
an ANCOVA of readiness potential in high versus low OC participants with trait anxiety as a covariate remained significant. This
result further supports the specific effect of OC symptoms on the
RP. Possibly, the tendency to act upon the presentation of a
stimulus is specific to OCD as a compulsory disorder involving
repeated habitual behavior.
The physical properties of objects automatically and rapidly
activate a motor response, which is sometimes visible only in
subtle neurological measures such as TMS (Gibson, 1979; Makris et
al., 2011). Indeed, in the current study, a response tendency to a
numerical quantity change did not manifest itself in reaction time,
but instead was significantly found in the more subtle measures of
the ERP. Perhaps, a more salient change in stimulus or a more
symptom-relevant one would produce behavioral group differences. Conversely, such differences are limited to early cognitive
processes evened out between groups before reaching the point of
behavioral response execution.
A limitation of the current study is the relatively small size of
the nonclinical sample used. Future studies with a larger sample
size of subjects and perhaps a clinical population could contribute
to the ability to generalize the current findings. It is, however,
important to note that research has shown that analog studies are
highly relevant and applicable to the understanding of OC-related
phenomena in individuals diagnosed with OCD (for a review, see
Abramowitz et al. (2014)). Further, although we assessed participants for OCD symptoms and trait anxiety symptoms, other
psychopathologies were not assessed, further restricting the
ability to generalize this research. Finally, the fact that most
subjects were female may also limit the generalizability of the
current study in terms of gender differences.
5. Conclusions
In conclusion, the novel approach of the current study differs
from most studies on OCD inhibitory deficits in that it examines
the early cognitive process – the initiation of a response rather
than the difficulty in inhibiting one – using the ERP component of
RP. Results suggest that early stages of motor preparation might be
important to the etiology and maintenance of OC symptoms and
offer specificity in relation to general anxiety. Furthermore, this
process seems particularly robust under emotionally valenced
stimuli. Future studies may examine the RP in clinical populations,
using various experimental paradigms. Such research may allow
for clinical applications of these ideas in the treatment of OCD.
137
Appendix A. Supporting information
Supplementary data associated with this article can be found in
the online version at http://dx.doi.org/10.1016/j.pscychresns.2014.
07.007.
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