Responses to Monaural Startle Probes During Emotional Imagery:

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Responses to Monaural Startle Probes During
Emotional Imagery Preliminary Analyses Adam K.
Wilke, Jeffrey M. Engelmann, and Bruce N.
Cuthbert, Ph.D. Department of Psychology,
University of Minnesota
Abstract The human startle reflex elicited by
an acoustic startle probe and measured from
electromyographic (EMG) recording of the
obicularis oculi (blink) muscle has been used
as an indicator of emotional processing and
attention. Previous studies in which subjects
imagined themselves participating in an emotional
situation indicate that startle responses are
potentiatied during personally engaging pleasant
and unpleasant situations, and this covaries with
reported arousal (Miller et al., 2002 Witvliet
et al., 1995). Furthermore, studies using startle
probes presented monaurally to either the left or
right ear suggest that emotional processing is
lateralized in the central nervous system
(Bradley et al., 1996 Grillon et al., 1995). To
extend prior research, we used verbally narrated
imagery scripts and presented monaural startle
probes during the imagination period. We
hypothesize that the startle response during
imagery of highly arousing pleasant and
unpleasant situations will be potentiatied in
relation to low arousal or neutral situations.
Heart rate, skin conductance, and facial muscle
activity were also collected in order to ensure
that that the imagery scenes elicited the
expected patterns of emotional responses, thus
providing a basis to interpret the subsequent
analyses of the startle data. Results for two of
these measures are presented here, and confirm
that the anticipated results were achieved.
Methods Subjects were undergraduate psychology
students aged 18-25 who participated for course
credits. Eligibility was determined by a brief
questionnaire. Those eligible were administered
the Fear Survey Schedule (FSS), Emotionality,
Activity, Sociability, Impulsivity (EASI) Scale,
and State Trait Anxiety Inventory (STAI).
Participants listened to 24 emotionally relevant
scripts (8 pleasant, 8 neutral/low arousal, 8
unpleasant, presented in a random order with
respect to category), with each script presented
twice for a total of 48 imagery trials.  The
pre-recorded scripts were presented for nine
seconds to both ears through headphones, and the
participants were instructed to imagine
themselves participating in the situation for a
total of 12 seconds after the script finished
playing (the beginning and end of this period was
indicated by quiet tones played through the
headphones).  During the imagery period, startle
probes (95 dB white noise bursts, 50 ms duration,
instantaneous rise time) were delivered to the
right or the left ear (42 probes per ear,
delivered in a random order with respect to ear).
 The startle blink reflex in response to the
noise bursts was measured via EMG recordings of
orbicularis oculi muscle activity for both eyes.
 Throughout the procedure, skin conductance
responses (SCR), heart rate (HR), and corrugator
("frown") muscle EMG were also recorded.  For EMG
recording, skin-electrode impedances were
maintained at less than 5KO.  Data for these
measures were analyzed using analysis of variance
with valence (pleasant, neutral, or unpleasant)
and time point during the imagery period as
within-subjects factors.  Significance was tested
using multivariate tests (Wilks' lambda
approximate F).
Figure Caption Corrugator (upper panel) and skin
conductance (lower panel) responses during
emotional imagery trial.  Data are presented as
the mean change in corrugator EMG or skin
conductance level from each trial's 6-s pre
imagery baseline for pleasant, neutral, or
unpleasant scripts, in 3-second time bins.  The
imagery script was playing during bins 1, 2, and
3.  Bins 4-7 represent the 12-s imagination
period.  Error bars represent mean - SEM. On the
y-axis, 0.0 indicates no change from baseline.
Corrugator data from 10 subjects were excluded
due to high skin-electrode impedance.
Discussion As expected, corrugator EMG activity
increased across the unpleasant trials in
relation to pleasant and neutral, confirming the
pattern for affective valence that has been
observed in prior imagery studies (Miller et al.,
2002). Skin conductance activity was greater for
pleasant imagery scripts, and to some extent for
unpleasant scripts as well, compared to neutral
this result was also anticipated, as skin
conductance is typically larger for
higher-arousal stimuli, irrespective of valence
(i.e., pleasant vs. unpleasant content).  The
larger response for pleasant scenes was somewhat
unexpected, and will be explored further by
examining subjects' ratings of subjective valence
and arousal for each script. These preliminary
analyses confirm that emotionally relevant
situations produce a reliable physiological
response in this sample, and thus provide a basis
for analyses of the laterality effects in startle
blink responses. 
Results Corrugator EMG activity showed a
significant main effect of valence (F2,20
4.8290, p lt .02) and time points (F6,16
5.1029, p lt .005), though there was not a
significant valence x time point interaction
effect (F12,10 1.37972, p gt .30). Skin
conductance activity showed a main effect of
valence (F2,30 10.4353, p lt .004), time
points (F6,26 2.25378, p lt .07) and a valence
x time point interaction effect (F12,20
4.6521, p lt .02).
References Bradley, M. M., Cuthbert, B. N.,
Lang, P. J. (1996). Lateralized startle probes in
the study of emotion. Psychophysiology, 33,
156-161. Grillon, C. Davis, M. (1995).
Acoustic startle and anticipatory anxiety in
humans Effects of monaural right and left
stimulation. Psychophysiology, 32,
155-161. Miller, M.W., Patrick, C.J.,
Levenston, G.K. (2002). Affective imagery and the
startle response Probing mechanisms of
modulation during pleasant scenes, personal
experiences, and discrete negative emotions.
Psychophsyiology, 39, 519-529. Witvliet, C.V.,
Vrana, S.R. (1995). Psychophysiological responses
as indices of affective dimensions.
Psychophysiology, 32, 436-443.
Acknowledgement The research was funded by a
grant from the Undergraduate Research Opportunity
Program (UROP) in the College of Liberal Arts at
the University of Minnesota. Special thanks to
Meggan Boerner-Ott, and Julia Langer for their
generous help and support.