2013. Vol.4, No.4, 389-395
Published Online April 2013 in SciRes (
Copyright © 2013 SciRes. 389
Modulation of the Startle Reflex during Brief and Sustained
Exposure to Emotional Pictures
Aimee Mavratzakis1,2, Elaine Molloy1, Peter Walla1,2*
1Faculty of Science and Information Technology, School of Psychology, University of Newcastle,
Callaghan, Australia
2Centre for Translational Neuroscience and Mental Health Research, University of Newcastle,
Callaghan, Australia
Email: *
Received December 6th, 2012; revised January 7th, 2013; accepted February 5th, 2013
Copyright © 2013 Aimee Mavratzakis et al. This is an open access article distributed under the Creative Com-
mons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, pro-
vided the original work is properly cited.
Previous investigations using pictures to elicit an emotional response have shown that the startle reflex
habituates over time due to decreased excitation in the obligatory startle processing pathway, an effect
that is independent of emotion modulation aspects of the startle response. However, in some instances,
startle magnitude has been selectively potentiated during sustained exposure to passively viewed un-
pleasant pictures. This study assessed startle modulation during brief, alternating and sustained exposure
to emotional pictures. Self-reported ratings of emotion were collected online with picture viewing to de-
termine if any change in startle magnitude was observable in explicit emotional responses. Self-reported
ratings of pleasantness and arousal were no different across the brief and sustained picture presentations.
However, a significant main effect (independent from emotion category) of presentation condition was
found for startle magnitudes, showing that, contrary to previous research involving passive picture view-
ing, mean startle magnitudes during sustained exposure were reduced relative to brief exposure. These
findings are likely the result of a general habituation of the startle reflex in the obligatory pathway. The
findings are also discussed in terms of the effect of the concurrent emotion rating task, which may have
differently affected the cumulative effects of emotion exposure compared to passive picture viewing.
Keywords: Emotion; Explicit; Implicit; Brief Exposure; Sustained Exposure
The startle reflex is an indicator of the brains aversive moti-
vational system via its structural connection to motivation sys-
tems at the synaptic level (Yeomans & Frankland, 1995). It is a
sudden involuntary movement involving the whole body (mus-
cle contractions), and is thought to serve as a mechanism for
quickly withdrawing the whole organism from harm. The reflex
is activated in response to an intense unexpected stimulus with
a rapid rising time and can be elicited via any of the senses (e.g.
loud noise, flash of light, air puff). Reflexes are by definition
automatic, however it is also known that activation patterns of
reflexes vary as a function of psychological factors (Filion,
Dawson, & Schell, 1998).
Previous investigations of the neural circuitry influencing
acoustic startle magnitude suggest input from two distinct cir-
cuits. The primary obligatory circuit projects from the cochlear
nucleus to the spinal cord and the secondary modulatory circuit,
which includes the amygdala connects with the primary obliga-
tory circuit causing its modulation (Yeomans & Frankland,
1995). The obligatory circuit is thought to be responsible for
the early excitatory startle reactivity seen in initial startles,
which rapidly habituates after about six trials (Blumenthal et al.,
2005). Bradley and colleagues demonstrated habituation of the
obligatory pathway in a study investigating startle responses to
repeated presentations of the same unpleasant, pleasant and
neutral pictures over time (Bradley, Lang, & Cuthbert, 1993).
They showed that while the overall strength of the reflex gra-
dually reduced, blink magnitude continued to discriminate be-
tween negative and positive stimuli, which shows that habitua-
tion of the startle reflex is more sensitive to factors related to
the obligatory pathway than to psychological factors.
In terms of understanding the temporal effects of a sustained
emotion context on the startle response, a variety of stimulus ex-
posure conditions have been used to manipulate emotional states.
Some of these approaches involved increasing exposure time to
a single picture (Codispoti, Bradley, & Lang, 2001; Sutton,
Davidson, Donzella, Irwin, & Dottl, 1997), repetitive presenta-
tions of identical pictures (Ferrari, Bradley, Codispoti, & Lang,
2010), rapid presentations of a series of pictures shown at vary-
ing rates (Smith, Löw, Bradley, & Lang, 2006) as well as exa-
mining persistence of emotion effects into the interstimulus in-
terval (Bradley, Cuthbert, & Lang, 1996). While many of these
studies implicate factors such as novelty and attention, limiting
generalisability of the results to the specific effects of emotio-
nal valence, a prominent finding nonetheless has been that con-
sistently activating a negative emotional state heightens or main-
tains defensive responses across time.
Using a passive picture viewing paradigm, Smith, Bradley
*Corresponding author.
and Lang (2005) attempted to separate potential effects of emo-
tion (the psychological pathway) from general habituation ef-
fects (the obligatory pathway) by analysing startle magnitudes
occurring early and late within three successive blocks of pic-
tures, and then comparing startles during the first block to star-
tles during the last block. Within blocks, they found potentia-
tion of startles occurring later compared to startles occurring ear-
lier for unpleasant pictures, but not for pleasant or neutral pic-
tures, indicating selective potentiation of aversive motivatio-
nal processes during sustained emotion exposure. When startle
responses were compared across rather than within the three
blocks however, there was no change in magnitude for unplea-
sant or neutral pictures, but there was a decrease in startle mag-
nitude for pleasant pictures, indicating selective attenuation of
appetitive motivational processes after a longer induction of emo-
tional states. They further suggest that this was not due to habi-
tuation of the obligatory pathway since the rate of reduction of
the startle magnitude was not consistent across valence conditions.
In the current experiment, rather than assessing the cumula-
tive effects of sustained emotion exposure on the startle re-
sponse early and late in a block of emotional pictures, the aim
was to investigate how startle responses differ during brief, al-
ternating exposure to emotional pictures compared to during sus-
tained exposure. In addition, this study aimed to compare startle
responses with online emotional response rating for each pic-
ture to see whether any effect of sustained exposure to emotio-
nal pictures could be observed in changes in explicit selfreports
of emotional responses. This is of special interest, because pre-
vious studies demonstrated that some aspects of affective infor-
mation processing modify startle reflex amplitudes while leav-
ing explicit rating unchanged (Walla et al., 2010; Geiser et al.,
2011; Grahl et al., 2012; Walla et al., 2013). This phenomenon
gives reason to believe that self reported emotion reflects only a
fraction of ongoing raw affective processing (see Walla & Pank-
sepp, 2013), an idea that deserves more attention than it has pre-
viously got.
In this experiment, two modified picture viewing paradigms
were used—one in which consistently-valanced stimuli were
presented over an extended amount of time and one in which
the valence of the presented stimuli was randomised and there-
fore continually alternating. The design, therefore, involved six
response conditions and was analysed using a 2 (Presentation
order: Block, Mix) by 3 (Picture valence: Unpleasant, Neutral,
Pleasant) within-subjects design. To do this, 90 novel pictures
from the IAPS were used, 45 in each paradigm and 15 per va-
lence condition (unpleasant, pleasant and neutral). Pictures from
each valence category were chosen so that all categories were
matched on intensity of valence and arousal based on pre-eva-
luations of the IAPS picture collection. Pictures high in arousal
were chosen to accentuate valence effects in the startle response
(Cuthbert, Bradley, & Lang, 1996). Self-reported arousal rat-
ings were collected to verify these conditions as well as autono-
mic physiological arousal indices by recording skin conduc-
tance changes. Self-reported pleasantness and arousal ratings
were assessed using the Self-Assessment Manikin (SAM), a pic-
torial rating system accompanying the IAPS collection, which
has demonstrated reliability for predicting emotional responses
to these picture stimuli, and is widely used in startle research. In
addition, mood (The Affect Grid) was assessed prior to the ex-
periment in order to reference ratings to a baseline affective state.
Consistent with previous findings, we expected that picture
presentations in the mixed and blocked viewing paradigms
would result in emotion-dependent modulation of the startle re-
sponse magnitude, specifically that startle responses would be
largest when viewing unpleasant pictures compared to neutral
and smallest when viewing pleasant pictures compared to neu-
tral. Consistent with findings reported by Smith, Bradley and
Lang (2005), we expected startle responses to be largest during
blocked unpleasant pictures, reflecting a potentiation effect dur-
ing sustained exposure to unpleasant stimuli. Since current the-
ory holds that the emotion-modulated startle response is an on-
line indicator of an internal emotional state, it was hypothesis-
ed that self-reported pleasantness ratings would also reflect the
direction of startle magnitude, specifically that pleasantness ra-
tings would be lowest for blocked unpleasant pictures compar-
ed to be mixed.
Ethics Statement
The ethics committee of the University of Newcastle appro-
ved this study (H-2010-1061).
The present study is based on 17 consenting participants.
They were all undergraduate students of the University of New-
castle (16 females). Mean age was 21.53 years (SD = 3.48, range
18 - 29 years). Participants were right-handed in accordance
with Oldfield’s criteria (Oldfield, 1971), non-smokers with nor-
mal hearing and normal or corrected vision and had no history
of neuropathology.
Assessments and Measures
Current Mood
Ongoing mood can influence decision making behaviour and
alter startle baseline reactivity (Grüsser, Wölfling, Mörsen, Ka-
thmann, & Flor, 2007). Therefore, immediately following the
consenting procedure participant’s mood was assessed using
the Affect Grid (Russell, Weiss, & Mendelsohn, 1989). The Af-
fect Grid is a single item two dimensional bipolar assessment of
pleasure-displeasure and arousal-calm. Users are instructed to
place a cross within the two dimensional grid, which is then
converted to two individual scores ranging from one to nine for
each axis.
Self-Reported Valence and Arousal Ratings
A computerised version of the Self-Assessment Manikin
(SAM); (Bradley & Lang, 1994) was used to assess affect along
valence and arousal dimensions using two nine-point likert scales
(1 = negative valence or low arousal, respectively; 9 = positive
valence or high arousal, respectively). Each SAM scale includes
a non-verbal pictorial assessment of a human-like stimulus with
visible emotional expressions. Using five figures for each scale,
SAM permits the assessment of core valence and arousal di-
mensions of emotional experience. This is a standard assess-
ment technique for evaluating affective responses for the IAPS
collection and is widely used in startle research.
Physiological Measures
NeXus-10 (produced by Mind Media BV) wireless recording
and Bio-trace + software was used to measure and process both
Copyright © 2013 SciRes.
skin conductance and eye blink responses. Skin conductance
was recorded at a rate of 32 samples/s with a Nexus-10-SC/
GSR sensor (two finger sensor) connected to the Nexus-10 re-
cording system with a 24 bit resolution which is able to reg-
ister changes of less than .0001 microsiemens. We attached one
sensor to the middle finger and the other sensor to the ring fin-
ger of the left hand.
Eye blinks were elicited by a repeatedly presented startle
stimulus (see below for details). With bipolar electromyography
(EMG) carried out with the Nexus-10 muscle potential changes
of the musculus orbicularis oculi (which elicit eye blinks) of the
left eye of every study participant were measured and stored on
the hard drive of a lap top computer. We used a dual channel
electrode cable with carbon coating and active shielding tech-
nology for low noise and an additional ground electrode cable.
EMG sampling rate was 2048 per s. A band pass filter from 20
Hz to 500 Hz was applied during online recording. Raw EMG
data were then recalculated by using the root mean square
(RMS) method to transform EMG signals into amplitudes. The
resulting amplitudes were then subject to statistical analysis.
Visual Stimuli
The emotion eliciting stimuli were 90 pictures (30 neutral, 30
unpleasant and 30 pleasant) from the International Affective
Picture System collection (IAPS); (Lang, Bradley, & Cuthbert,
2005). Pictures were selected based on pre-evaluated ratings of
picture pleasantness and arousal. Pictures rated high for valence
(unpleasant and pleasant) and arousal (unpleasant, neutral and
pleasant) dimensions were selected. An Analysis of Variance
(ANOVA) and t-tests were used to confirm respective criteria
matched across picture categories. The means and standard de-
viations of the pictures for this experiment are displayed in Ta-
ble 1. The pictures were presented in colour against a black
background on a computer monitor screen.
Acoustic Startle Stimuli
Our startle stimulus was a 50 ms burst of acoustic white
noise at 105 dB sound pressure level delivered through profes-
sional headphones fully covering both ears. Sound pressure le-
vel was measured with a mobile measuring device (produced
by Voltcraft). To achieve the respective loudness a commercial
headphone pre-amplifier was used (Behringer; MicroAMP
Pictures were randomly allocated to the mixed or blocked
Table 1.
Mean values of visual picture stimuli based on pre-evaluations using
the Self Assessment Manikin (SAM) rating system.
Pleasantness Arousal
Unpleasant 2.65 .45 6.58 .36
Neutral 4.52 .23 5.41 .62
Pleasant 7.28 .46 6.60 .38
presentation session using a random number generator. Pictures
in the mixed presentation session were further quasi-randomly
arranged to ensure constant variation in picture valence. To
minimise the potential for order effects, five uniquely random-
ised lists of pictures were used interchangeably throughout the
recruiting period. Hence, each new list contained a different
combination of pictures in each viewing session, and all six ex-
perimental conditions were fully counterbalanced. Four of the
15 pictures in each valence category were simultaneously asso-
ciated with a startle-eliciting stimulus at the fifth second of view-
ing. Pictures associated with the startle-eliciting stimulus were
also varied. The interval between two startle-eliciting stimuli
was randomised to occur at approximately 35, 57 or 79 seconds
to prevent learning effects. For both sessions, each picture trial
lasted approximately 22 seconds and included a one second
cross fixation screen, a six second presentation of the lead pic-
ture stimulus, a user-paced SAM pleasantness rating screen and
a user-paced SAM arousal rating screen. A black screen of one
second duration was used to transition between rating and pic-
ture screens.
Experimental testing was conducted within a two month re-
cruiting period at the University of Newcastle Callaghan Cam-
pus Functional Neuro-imaging laboratory in individual two
hour sessions at regulated temperature (20.5˚C). Consenting parti-
cipants completed assessments for demographics and pre-ex-
perimental affect respectively before being seated in front of a
computer monitor and connected to the physiological recording
equipment by the experimenter. Participants were instructed to
pay close attention to their feelings throughout the session and
to quickly rate their immediate reaction to each picture for all
trials by using a computer mouse to click on the SAM rating.
Participants were also told to ignore any loud bursts of noise
through the headphones. Prior to commencing the sessions par-
ticipants practised using the rating system for three trials in-
cluding one item of extreme valence from each category (un-
pleasant and pleasant extremes and one neutral) which served
as an anchor for subsequent picture rating. The mixed and blo-
cked sessions were separated by a two minute break interval.
Three pilot trials were conducted prior to official data collec-
Data Reduction
Subjective reports of emotion on trials associated with the
acoustic startle may be biased by the inherently startling nature
of the probe. Therefore SAM ratings for each valence category
were taken from four startle-unassociated trials. Similarly, other
physiological measures can be augmented by the startle probe.
To avoid this unwanted source of variation data for skin con-
ductance were taken exclusively from the six second picture
presentation interval on startle-associated trials for each valence
category. Extracted values were then averaged to form mean
physiological values for each of the six valence-viewing condi-
A trigger sound detector was used to identify onset of the
acoustic probe in the data read out. This served as a reference
for detecting the true onset of startle reactivity. The startle blink
value was defined as the peak rise in EMG waveform on startle
associated trials. Trials for which peak rise in EMG waveform
was less than 5 μV were scored as missing. To decrease the
Copyright © 2013 SciRes. 391
probability of artifact being mistaken for a true response a trial
was scored as rejected if excessive noise occurred. For each
participant trial scores were averaged to create a mean value for
each valence category.
Statistical Analysis
Normality checks of the EMG data distribution revealed a
unimodal significant positive skew of startle data (z = 8.47, p
< .01). To partial out floor effects, the EMG distribution was
log transformed prior to inferential statistical analyses. Cova-
riation of the dependent variables Self-reported Pleasantness
and Startle Modulation with the variable Current Mood (va-
lence dimension) was assessed by performing respective biva-
riate correlations. No significant relationship was found therefore
current mood was not included as a covariate.
To assess the independent effects of self-reported and startle
reflex responses, a repeated measures Analyses of Variance
(ANOVA) was carried out for each dependent variable under a
2 (Presentation order: Block, Mix) by 3 (Picture valence: Un-
pleasant, Neutral, Pleasant) within subjects design. Simple con-
trasts were used to determine the direction of significant main
effects (p < .05). Greenhouse-Gessier corrections for sphericity
(if є < .75) and Bonferroni corrections were applied where re-
Emotional Valence Measures
Self-Reported Pleasantness
The descriptive statistics for emotional valence measures in-
cluding pleasantness ratings and startle blink magnitudes are
displayed in Table 2. For the main effect of picture valence on
self-reported pleasantness Mauchly’s test indicated a violation
of sphericity, χ2 = 11.12, p = .004, є = .65. However, as theory
would predict, picture valence had a strongly significant effect
on pleasantness ratings in the expected directions (F (1.29,
Table 2.
Mean emotional responses to unpleasant, neutral and pleasant pictures
as a function of presentation order.
Mix Block
Variable M (SE) 95% CI M (SE) 95% CI
Unpleasant 2.33 (.24) [1.82, 2.84] 2.30 (.24) [1.78, 2.81]
Neutral 3.92 (.22) [3.46, 4.39] 3.94 (.28) [3.35, 4.50]
Pleasant 6.05 (.29) [5.44, 6.67] 5.86 (.27) [5.30, 6.40]
Total 4.10 (.15) [3.79, 4.41] 4.03 (.20) [3.61, 4.46]
Startle blink reflexa
Unpleasant 3.35 (.12) [3.11, 3.60] 3.13 (.14) [2.85, 3.42]
Neutral 3.15 (.16) [2.81, 3.49] 3.15 (.16) [2.81, 3.48]
Pleasant 3.11 (.11) [2.88, 3.34] 2.96 (.14) [2.66, 3.25]
Total 3.21 (.12) [2.95, 3.46] 3.08 (.14) [2.79, 3.37]
Note: M = Mean; SE = Standard Error; CI = Confidence Interval. Values repre-
sent adjusted mean and parameter estimates. aStartle blink reflex amplitudes (μV)
represent the natural logarithm of the sample distribution.
19.38) = 80.33, p < .001, η2 = .84, after Greenhouse Geisser
corrections for sphericity violation). As shown in Figure 1,
unpleasant pictures were rated as significantly more unpleasant
than neutral pictures (F (1, 15) = 99.2, p < .001, η2 = .87) and
pleasant pictures (F (1, 15) = 100.6, p < .001, η2 = .87), while
pleasant pictures were rated as significantly more pleasant than
neutral pictures (F (1, 15) = 45.31, p < .001, η2 = .75).
Neither the main effect of presentation order, nor its interac-
tion with picture valence resulted in significant augmentation of
ratings (F (1, 15) = .18, p = .67, η2 = .01; F (2, 30) = .25, p
= .78, η2 = .02, respectively). Non-significant tests were how-
ever, associated with low observed power (7% and 9%, respec-
Startle Blink Reflex
Figure 2 shows the mean startle reflex magnitudes for each
picture viewing condition. For the main effect of picture valence
on startle blink magnitude Mauchly’s test indicated a violation
of sphericity (χ2 = 6.55, p = .038, є = .74), however there was a
moderately significant main effect (F (1.48, 23.64) = 4.77, p
= .027, η2 = .23, after Greenhouse Geisser corrections for
Figure 1.
Bar graph representing mean self-reported pleasantness ratings and stan-
dard error bars as a function of picture viewing conditions.
Figure 2.
Bar graph representing mean self-reported arousal ratings and stan-
dard error bars as a function of picture viewing conditions.
Copyright © 2013 SciRes.
sphericity violation). Despite sphericity violations, the main
ANOVA was used to interpret significant effects due to the
small sample size and low power associated with multivariate
analyses. Contrasts revealed that mean startle responses to un-
pleasant pictures were significantly potentiated compared to
those for pleasant pictures (F (1, 16) = 13.94, p = .002, η2 = .47),
with high observed power for detecting a small effect (94%),
but not compared to those for neutral pictures (F (1, 16) = 1.24,
p = .283, η2 = .07). However, observed power was low (18%).
Mean startle responses to pleasant pictures were reduced com-
pared to neutral pictures, and the difference was approaching
significance (F (1, 16) = 3.91, p = .065, η2 = .20), with moder-
ate power for detecting an effect (46%).
The main effect of presentation order was marginally signi-
ficant (F (1, 16) = 4.68, p = .046, η2 = .23) with moderate ob-
served power (53%), and corresponds to an overall reduction in
mean startle responses to blocked picture presentations. The
mean effect size of blocked order ( .13 ln μV) corresponded to
a large effect (F = .54). Together, power and effect size esti-
mates suggest low probability of type two errors.
The interaction of presentation order and picture valence was
not significant F (2, 32) = 2.31, p = .115, however two paired
sample t-tests were run to further evaluate the relationship be-
tween variables of interest (corrected p = .025). Although ap-
proaching significance, the mean magnitude of startle responses
during blocked unpleasant pictures were not significantly re-
duced compared to those during mixed unpleasant pictures
(t(16) = 2.3, p = .035). The mean magnitude of startle responses
during blocked pleasant pictures were also not significantly re-
duced compared to those during mixed pleasant pictures, t(16) =
1.73, p = .103.
Emotional Arousal Measures
Self-Reported Arousal
Descriptive statistics for arousal measures including arousal
ratings and skin conductance are included in Table 3. There
was a main effect of picture valence on self-reported arousal
ratings (F (2, 30) = 13.45, p < .001, η2 = .47; Figure 3). Con-
trasts revealed that unpleasant pictures were significantly more
arousing than both pleasant (F (1, 15) = 15.62, p < .001, η2
= .51) and neutral pictures (F (1, 15) = 18.8, p = .001, η2 = .56),
and corresponds to high observed power (96% and 98%, re-
spectively). Pleasant pictures were no more arousing than neu-
tral pictures (F (1, 15) = .98, p = .338, η2 = .06). There was
however low observed test power for detecting a significant
effect of picture valence on arousal (15%).
There was no main effect of presentation order on self-re-
ported arousal (F (1, 15) = .26, p = .62, η2 = .02), nor was there
an interaction between presentation order and picture valence
(F (2, 30) = .63, p = .54, η2 = .04). These effects also corre-
spond to low observed test power (8% and 15%, respectively).
Skin Conductance
There was no main effect of picture valence on skin conduc-
tance (F (2, 30) = .08, p = .92, η2 = .01), however there was a
significant main effect of presentation order, F (1, 15) = 8.3, p
= .011, η2 = .36 (Figure 4). Blocked picture presentations elic-
ited marginally lower skin conductance responses (M = 3.14,
SE = .27, CI = 2.57, 3.72) than did mixed presentations (M =
3.24, SE = .27, CI = 2.67, 3.81). The mean effect of blocked order
( .01 μS) was large (F = .75) and corresponds to acceptable
Table 3.
Mean arousal responses to unpleasant, neutral and pleasant pictures as a
function of presentation order.
Variable Mix Block
M (SE)95% CI M (SE) 95% CI
Self-reported arousal
Unpleasant 6.34 (.31)[5.68, 7.01] 6.45 (.37) [5.66, 7.25]
Neutral 5.29 (.34)[4.57, 6.01] 4.98 (.36) [4.21, 5.75]
Pleasant 5.40 (.38)[4.62, 6.20] 5.28 (.29) [4.66, 5.91]
Total 5.68 (.30)[5.04, 6.33] 5.57 (.28) [4.98, 6.16]
Skin conductance
Unpleasant 3.23 (.27)[2.66, 3.8] 3.16 (.27) [2.58, 3.74]
Neutral 3.24 (.27)[2.67, 3.8] 3.13 (.27) [2.55, 3.72]
Pleasant 3.25 (.27)[2.69, 3.82] 3.14 (.27) [2.57, 3.71]
Total 3.24 (.27)[2.67, 3.81] 3.14 (.27) [2.57, 3.72]
Figure 3.
Bar graph representing mean self-reported arousal ratings and stan-
dard error bars as a function of picture viewing conditions.
Figure 4.
Bar graph representing mean skin conductance levels and standard error
bars as a function of picture viewing conditions.
Copyright © 2013 SciRes. 393
observed power (77%). There was no interaction between pre-
sentation order and picture valence (F (2, 30) = .67, p = .52, η2
= .04).
Three paired sample t tests (corrected p = .017) were carried
out on variables of interest. The t-tests revealed that mean skin
conductance levels were significantly reduced during blocked
compared to mixed neutral pictures (t(15) = 2.83, p = .013), but
not during blocked compared to mixed pleasant (t(15) = 2.45, p
= .027) or unpleasant (t(15) = 1.88, p = .08) pictures.
The question addressed in the current study was whether emo-
tional responses are differently affected by sustained exposure
to emotional stimuli compared to brief exposure, as measured
by self-reported emotional responses and the affective startle-
blink reflex. Previous research using a passive picture viewing
paradigm has demonstrated that cumulative exposure can po-
tentiate startles during negative conditions (Smith et al., 2005).
Therefore, it was hypothesised that sustained exposure to un-
pleasant emotional pictures would potentiate startle responses.
It was further hypothesised that self-reported emotional responses
would reflect these changes in startle responses. The results do
not support either hypothesis, and instead, suggest that sustain-
ed exposure to emotional pictures caused a general attenuation
of startle magnitudes across all valence conditions. In addition,
this effect was not observed in selfreported emotional responses,
which instead showed no difference in ratings across brief and
sustained emotion exposure conditions.
This study assessed the effects of sustained exposure to emo-
tional stimuli while also recording immediate self-reported emo-
tional reactions to the presented stimuli. This procedure differs
to the procedure used by Smith, Bradley and Lang (2005) where
participants were required to passively view emotional pictures
without any additional rating task. Recently, Wangelin, Low,
McTeague, Bradley, and Lang (2011) investigated the effects of
a cognitive distractor task on startle responses during sustained
aversive exposure. They found that embedded distractor tasks
did eliminate potentiation of startles during sustained exposure
to unpleasant pictures compared to when pictures were viewed
passively. This suggests that sustained effects of emotion on the
startle reflex are quite sensitive to cognitive and perceptual dis-
tractions. This is also strengthened by additional data from an
earlier experiment (Bradley et al., 1996) which showed that star-
tle responses were maintained over time when a passive picture
viewing task was combined with a concurrent auditory-based
emotion word recognition task (which was used to ensure par-
ticipants paid attention to the acoustic startle stimuli). Therefore
a possible explanation for why startles were not potentiated as
expected during unpleasant picture viewing was that the rating
task itself inadvertently acted as a distraction, momentarily di-
verting attention from the sustained emotion, eliminating or
downgrading cumulative effects. However, to draw any conclu-
sions in this area would require a deliberate comparison of star-
tle responses to “actively” and “passively” viewed pictures in a
single experiment.
Alternatively, research examining perceptual differences re-
lated to different emotional tasks has found differences in neu-
ral activity extending to limbic regions as a function of task ins-
tructions such rating an emotional reaction compared to recog-
nising a specific emotion (e.g. Liberzon et al., 2000). Therefore,
use of a rating task in the current study may have differently
affected perceptual processing and subsequent motivational
system activation compared to other studies of sustained emo-
tion that used a recognition task or a simple passive viewing
task. Said differently, it is possible that actively paying atten-
tion to ones own emotions rather than simply observing emo-
tional events can have a regulatory influence, impeding the for-
mation of a stronger negative emotional state. Walla et al. (2013a)
found that self referenced negative emotion images were rated
more negative that un-referenced negative images and self-re-
ferenced positive images were rated more positive than un-re-
ferenced positive images. In their study, startle responses were
enhanced as a result of self reference regardless of emotion va-
lence. This finding was interpreted as being reflective of moti-
vation as indicated by startle reflex modulation data. Thus, the
notion arises that in the current study too motivation is reflected
in the startle reflex modulation data and motivation is reduced
over time if emotion valence is kept constant over longer peri-
ods of time.
A second important finding was that contrary to what would
be predicted by past empirical investigations, startle responses
elicited across all unpleasant pictures were not significantly po-
tentiated relative to neutral, nor were startle responses during
pleasant pictures significantly reduced relative to neutral. This
raises concern as to whether the lead stimuli used in this ex-
periment were effective for inducing the desired emotional
states. One possible explanation is that the trend towards atte-
nuated startle responses may have washed out the potentiation
effects for unpleasant pictures. However, this does not explain
the null effect produced by pleasant pictures, which may alter-
natively be the result of lower than expected arousal levels
associated with pleasant pictures, which is apparent in the low
self-reports of arousal for pleasant pictures. It should be noted
that most of our participants were female and most of the
pleasant pictures from the IAPS involve erotica, which are gen-
erally rated as more pleasant by males than females. Thus, these
unexpected findings were most likely caused by a gender bias
in the sample. However, it should also be noted that the IAPS
collection has to be treated with caution, because some of the
images that are pre-evaluated as neutral may elicit affective
valence, perhaps depending on cultural background. After all,
startle reflex modulation has been repeatedly shown to be sen-
sitive to raw affective processing in a variety of experiments us-
ing many different lead stimuli. Urban neighbourhoods (Geiser
et al., 2011), food intake (Walla et al., 2010), bottle shape
(Grahl et al., 2012) and brand attitude (Walla et al., 2011) were
shown to significantly modulate startle responses.
A third and incidental finding was differences between self-
reported arousal ratings and skin conductance levels. While there
was no effect of mixed and blocked order on self-reported arou-
sal ratings, skin conductance was reduced during blocked pre-
sentations, with post hoc tests revealing that the effect was only
significant for neutral pictures. Habituation of skin conductance
levels over time has previously been documented by Bradley,
Lang, & Cuthbert (1993), who also documented the relationship
between arousal and the startle response (Cuthbert et al., 1996),
showing that changes in arousal moderate the affective startle
response such that a high level of arousal is necessary for va-
lence-modulated differences to take effect. Therefore, it is like-
ly that despite efforts to control for arousal across valence and
order conditions, reduced startle response magnitudes seen in the
current study were simply the result of habituated arousal levels.
It should still be noted that several functional MRI studies
have documented habituation of amygdala responses during re-
Copyright © 2013 SciRes.
Copyright © 2013 SciRes. 395
peated exposure to negative emotional stimuli such as pictures
of fearful faces (Wright et al., 2001) and other unpleasant pic-
tures (Liberzon et al., 2000). Zald (2003) reviewed studies of
amygdala activation patterns during emotional evaluations of
visual stimuli and concluded that habituation “may reflect a pro-
cess through which stimuli are rapidly re-evaluated based on
the lack of consequences arising from their previous exposure.”
(Zald, 2003: p. 104). Given that the amygdala is a region im-
plicated in the startle neural circuitry (Yeomans & Frankland,
1995), it is possible that reduced startle responses may be re-
flecting activation related to amygdala circuitry.
Several important implications for emotion research have
arisen from the current experiment. Firstly, neural pathways in-
volved in the affective modulation of the startle response may
be more sensitive to emotion exposure than can be observed via
self-reported emotional responses. Hence, although the startle
reflex is able to predict general directional differences in emo-
tional states, a closer investigation suggests it is, at least in part,
measuring emotion processing activity that is somewhat differ-
ent to and inaccessible by self-reports. Second, this study pro-
vides conflicting results compared to other studies investigating
the effect of sustained exposure to emotional pictures, and sug-
gests that certain conditions of picture viewing, specifically, ac-
tive emotional rating compared to passive viewing, may diffe-
rently affect the way emotional stimuli are processed. This find-
ing may be relevant for research directed at understanding or
developing cognitive strategies for optimised and adaptive emo-
tional perception and comprehension, and may also be an im-
portant factor to consider when deciding how to best design
emotion experiments. Finally, the findings of this study may
have useful implications for clinical populations (see Arthur-
Kelly et al., 2013) as well as for advancing consumer neurosci-
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