Psychology
2012. Vol.3, No.10, 883-891
Published Online October 2012 in SciRes (http://www.SciRP.org/journal/psych) http://dx.doi.org/10.4236/psych.2012.310133
Motivational Priming Predicts How Noxious
Unconditioned Stimuli Influence Affective
Reactions to Emotional Pictures
Amy E. Williams1, Jamie L. Rhudy2
1Department of Psychiatry and Behavioral Neurosciences & Department of Pediatrics,
Loyola University Medical Center, Maywood, USA
2Department of Psychology, The University of Tulsa, Tulsa, USA
Received July 18th, 2012, revised August 20th, 2012; accepted September 18th, 2012
Motivational priming theory (MPT) and preparedness theory generate competing hypotheses about the
impact of an aversive US on responses to an affective foreground. MPT predicts the aversive US will fa-
cilitate negative emotional reactions to unpleasant pictures and inhibit positive emotional reactions to
pleasant pictures. Preparedness theory predicts an aversive US will increase negative emotional reactions
to unpleasant pictures, but will not impact responses to pleasant pictures. The present study (N = 125)
compared these competing hypotheses by assessing how noxious shocks and non-noxious noises influ-
ence responses to emotional pictures. Following each picture, participants rated how the picture made
them feel using the Self Assessment Manikin. Results supported MPT—noxious USs, but not non-nox-
ious USs, facilitated negative emotional reactions to unpleasant pictures and inhibited positive emotional
reactions to pleasant pictures.
Keywords: Affect; Noxious Stimulation; Emotional Picture Ratings; Motivational Priming Theory;
Preparedness Theory
Introduction
Experience of an aversive stimulus can impact emotional re-
actions to an affective foreground, however, motivational pri-
ming theory (MPT) and preparedness theory generate com-
peting hypotheses about the direction of this relationship. Better
understanding of the nature of the influence of aversive stimuli
on emotional reactions to an affective foreground may have
important implications for research design and better under-
standing of emotional responses during clinical pain.
Motivati onal Priming Theory (MPT)
MPT conceptualizes emotion as emanating from two oppo-
nent motive systems that provide feedback about the environ-
ment (Bradley, Codispoti, Cuthbert, & Lang, 2001; Lang, 1995).
The defensive system is activated by stimuli and contexts that
represent a potential or actual threat (e.g., predation, attack,
noxious events), and activation of the defensive system pro-
motes protective behaviors (e.g., fight, flight, freezing) and the
subjective experience of negative affect. In contrast, the appeti-
tive system is activated by stimuli and contexts that advance
survival (e.g., sustenance, procreation), and activation of the
appetitive system promotes approach/appetitive behaviors (e.g.,
consummation, copulation) and the experience of positive affect.
MPT posits that defensive responses should be inhibited by
appetitive activation and concurrent positive affect, and facili-
tated by defensive activation and concurrent negative affect
(Lang, 1995). Supporting this, numerous studies have shown
that priming the defensive system using unpleasant environ-
mental stimuli results in larger startle reflexes (a defensive
response), whereas priming the appetitive system with pleasant
environmental stimuli generally results in smaller startle re-
flexes (e.g., Grillon, Ameli, Merikangas, Woods, & Davis,
1993; Jansen & Frijda, 1994; Lang, Bradley, & Cuthbert, 1990;
Vrana, Spence, & Lang, 1988). By contrast, MPT posits that
appetitive responses should be inhibited by defensive activation
and concurrent negative affect, and facilitated by appetitive
activation and concurrent positive affect (Lang, 1995). While
fewer studies have examined the modulation of appetitive re-
sponses, there is some existing evidence in humans that they
are modulated as predicted by MPT (e.g., Benning, Patrick, &
Lang, 2004).
Several studies have supported MPT; however, in the vast
majority the focus has been on the influence of an affectively-
charged perceptual foreground (pictures, sounds, odors, etc.) on
an unconditioned defensive reflex (e.g., startle reflex, with-
drawal response) to an aversive unconditioned stimulus (US;
e.g., noise burst, shock, airpuff) (Hawk & Cook, 1997; Rhudy,
Williams, McCabe, Russell, & Maynard, 2008; Vrana et al.,
1988). In addition, the anticipation of an aversive event (e.g.,
shock delivery) can also facilitate defensive reflexes to an aver-
sive US (Greenwald, Bradley, Cuthbert, & Lang, 1998; Grillon,
Ameli, Woods, & Merikangas, 1991), suggesting MPT may
provide a framework to explain a greater scope of emotional
reactions than what is most commonly studied.
More recently, this line of research has been expanded to as-
sess the influence of an affectively-charged foreground on the
subjective reaction to a noxious US, specifically the subjective
pain response (De Wied & Verbaten, 2001; Meagher, Arnau, &
Rhudy, 2001; Rhudy, Williams, McCabe, Nguyen, & Rambo,

A. E. WILLIAMS, J. L. RHUDY
2005). Consistent with MPT, pain is inhibited in the context of
a pleasant foreground and enhanced in the context of an un-
pleasant foreground. Again, in most of these studies, interest
has been on the influence of the affectively-charged foreground
on defensive responses to the US.
Less is known about the reverse; the effects of an aversive
US on subjective responses to the affective foreground (e.g.,
ratings of affectively-charged pictures). Some research has
indicated that presentation of a painful stimulus does alter par-
ticipant’s emotional state (Bresin, Gordon, Bender, Gordon, &
Joiner, 2010). Presumably if MPT is correct, then an aversive
US could influence emotional reactions to affectively-charged
pictures. In a study by Bradley and colleagues (Bradley, Codi-
spoti, Cuthbert, et al., 2001), participants viewed emotionally-
charged pictures and an aversive, but non-noxious, white noise
(50-ms, 96-dB) was delivered during half of the pictures. Im-
mediately following each picture, participants were asked to
rate their affective pleasure/valence and arousal response to the
picture. They found that noises slightly increased the arousal
ratings, but not the pleasure/valence ratings of pictures. While
the effects of the aversive US on responses to pictures were
minimal in that study, it is not clear whether a more potent (i.e.,
noxious) US would have a greater impact. Indeed, the degree of
motive system activation (as assessed from affective arousal/
intensity) is believed to influence the degree of motivational
priming effects (e.g., Bradley, Codispoti, Cuthbert et al., 2001;
Cuthbert, Bradley, & Lang, 1996; Rhudy et al., 2008). Spe-
cifically, unpleasant stimuli that elicit higher emotional arousal
elicit stronger facilitation of defensive responses, and pleasant
stimuli that elicit higher emotional arousal elicit stronger inhi-
bition of defensive responses. For example, our laboratory has
demonstrated that erotica (highly arousing pleasant stimuli)
inhibits pain and nociceptive reflexes to noxious shocks, but
that pictures of food or families (low arousal pleasant stimuli)
have little effect on pain and nociceptive reflexes (Rhudy et al.,
2010; Rhudy et al., 2008). Thus, MPT would predict that the
presentation of a noxious US during an affective foreground
would increase (facilitate) negative emotional responses to an
unpleasant foreground and decrease (inhibit) positive emotional
responses to a pleasant foreground.
Preparedness Theory
By contrast, the influence of the noxious US on emotional
reactions to affectively-charged pictures might be better pre-
dicted by preparedness theory (e.g., Peterson, Maier, & Selig-
man, 1993; Seligman, 1970, 1971). Research supporting pre-
paredness theory has primarily focused on the influence of an
aversive US on responses to an affective foreground. Specifi-
cally, preparedness theory posits that unpleasant, fear-relevant
stimuli are more readily associated with a noxious US than are
pleasant, non-fear-relevant stimuli (Peterson, et al., 1993; Selig-
man, 1970, 1971). Differences in cognitive mechanisms in-
volved in prepared vs un-prepared learning are thought to be
responsible for these differing outcomes (Ohman & Dimberg,
1978; Ohman & Soares, 1993). Prepared learning (associations
between fear-relevant stimuli and a noxious US) is a non-cog-
nitive learning process thought to be learned through evolution.
In contrast, un-prepared learning (associations between non-
fear-relevant stimuli and a noxious US) is dependent upon cog-
nitive associations and expectancies. As a result, when a US is
paired with an unpleasant stimulus (prepared learning), a condi-
tioned response will occur more quickly, will be a stronger
response, and will be more resistant to extinction (Ohman &
Dimberg, 1978; Ohman & Soares, 1993). For example, a recent
study found that pairing a noxious electric stimulus (US) with a
photograph of a fearful facial expression resulted in greater skin
conductance response, lower emotional valence ratings, and
higher emotional arousal ratings compared to when the photo-
graph was presented without the US (Williams & Rhudy, 2007).
However, there was not a significant change in physiological or
self-reported emotional response to a photograph of a happy
facial expression that had been paired with the same US. Thus,
preparedness theory predicts a different pattern of results than
MPT. Preparedness theory predicts that a noxious US would
increase negative emotional responses to an unpleasant picture,
but would not alter the emotional response to a pleasant picture
(Peterson et al., 1993; Seligman, 1970, 1971).
Present Study
The purpose of the present study was to examine the influ-
ence of a noxious US on emotional reactions to affectively-
charged pictures and determine which of these competing theo-
ries best explains the results. This could contribute to a better
understanding of how noxious stimuli impact emotional re-
sponses to affective foregrounds, which may have implications
for research designs and emotional responding in the presence
of clinical pain. Data were analyzed from a large study (N =
125) involving the presentation of a series of emotional pictures
during which noxious electric stimulations were delivered.
Following each picture, participants used the Self-Assessment
Manikin (SAM) to make ratings of hedonic valence/pleasure
and arousal. Consistent with prior research (Rhudy et al., 2005;
Rhudy, Williams, McCabe, Rambo, & Russell, 2006; Rhudy et
al., 2008), the results of the parent study found that arousing
unpleasant pictures (mutilation) enhanced pain and the nocicep-
tive flexion reflex (NFR, a spinally-mediated withdrawal re-
flex), whereas arousing pleasant pictures (erotica) inhibited
pain and the NFR (Rhudy et al., 2010). The present study
represents secondary analyses on this dataset to determine
whether the delivery of noxious shock USs influenced emo-
tional reactions to pictures by comparing affective ratings of
shocked and unshocked pictures. Because men and women
differ in their emotional reactivity to affective pictures (Bradley,
Codispoti, Sabatinelli, & Lang, 2001), we also included par-
ticipant sex as a factor in all analyses to control for these sex
effects. However, sex was not expected to moderate the influ-
ence of the US on emotional reactions to pictures.
Additionally, analyses were conducted to examine the impact
of aversive, but non-noxious, acoustic startle probes on emo-
tional reactions to pictures. Aversive acoustic startle probes
were expected to elicit less defensive activation than noxious
shocks, allowing for a comparison of two types of USs that
differ primarily in their threat value (degree of defensive sys-
tem activation). Exposure to noxious shocks can cause sensiti-
zation of responses to acoustic startle probes (Greenwald et al.,
1998); therefore, testing with acoustic probe USs always pre-
ceded testing with shock USs. We hypothesized that noxious
USs would lead to enhanced negative emotion when adminis-
tered during unpleasant images and inhibited positive emotion
when administered during pleasant images. In comparison,
non-noxious USs were hypothesized to have little to no impact
on emotional reactions to pictures.
884

A. E. WILLIAMS, J. L. RHUDY
Method
Participants
Participants were recruited from The University of Tulsa and
the Tulsa community through posted announcements on cam-
pus and on various community boards in the city of Tulsa. Par-
ticipants were 18 years of age or older and were excluded for a
self-reported history of any condition that may interfere with
emotion or pain processing: cardiovascular, neurological, and/
or circulatory problems; use of analgesic, antidepressant, or
anti-anxiety medication; recent psychological trauma; specific
phobia of snakes or spiders (due to picture-viewing); problems
healing; or Raynaud’s disease. All procedures were fully ap-
proved by The University of Tulsa ethics review board and
participants gave verbal and written informed consent after
details of the experiment were fully described to them. One
hundred fifty one participants completed the study, however,
one was excluded for incomplete data and 25 were excluded
because they did not experience the shock US as noxious (at
least 25 on the 0 - 100 numerical rating scale, see description
below). Participants (N = 125) were mostly female (62%),
White-non Hispanic (74%), single (56%), and employed (71%),
with an average age of 35 years (range 18 - 83; SD = 14.41).
Participants received $100 for their participation.
Apparatus
A computer running LabVIEW software (National Instruments,
Austin, TX) equipped with dual monitors and A/D board (Na-
tional Instruments, PCI-6036E) controlled all stimuli, ques-
tionnaire presentation, and data acquisition, and was used for
offline data reduction. One 17 flat panel monitor was used by
the experimenter to monitor physiological signals and experi-
mental timing. Pictures and questionnaires were projected onto
a screen about 3 m from the participant using an LCD projector.
Acoustic startle probes were delivered by a Coulbourn Instru-
ments (Allentown, PA) audio signal generator (Part number
A12-33) and amplified by a 40W amplifier (Radio Shack, Part
#32-2054). The noise probes were presented over TDH-49
Telephonics (Farmingdale, NY) headphones. Electrocutaneous
stimulations were delivered by a Grass Instruments stimulator
(Model S88 or S48, West Warwick, RI), stimulus isolation unit
(Model SIU8T), constant current unit (Model CCU1), and bi-
polar stimulating electrode (Nicolet, 019-401400, Madison,
WI). The stimulating electrode was attached to the left ankle
over the retromalleolar pathway of the sural nerve. The onset/
offset of the stimulator was controlled by computer, and a
computer-controlled voltage regulator varied the current to the
participant (max current = 40 mA). To apply stimulating elec-
trodes, first the skin was degreased with alcohol, slightly
abraded using NuPrep gel to achieve impedances below 5 K,
and then conductive gel (EC60, Grass Instruments) was applied.
Throughout testing, participants were seated in a recliner with a
small pillow positioned under their left ankle to facilitate re-
laxation. Sound attenuating headphones and a video camera
allowed the experimenter to communicate with and monitor the
participant from an adjacent room. Participant ratings were
made using a computer mouse positioned on a lap desk.
Picture-Viewing
Digital pictures from the International Affective Picture Sys-
tem (CSEA, 1999; Lang, Bradley, & Cuthbert, 1999) were
presented by computer and an LCD projector in a dimly lit
room. During testing with non-noxious acoustic probes, 54
pictures were presented consisting of 18 unpleasant (6 mutila-
tion, 6 attack, 6 death/loss), 18 pleasant (6 family, 6 adventure/
sports, 6 erotic) and 18 neutral pictures.1 The order of picture
presentation was randomized across participants with the limi-
tation that not more than two pictures of similar valence were
shown consecutively. During testing with noxious electrocute-
neous stimuli, pictures were presented in four blocks of 27
pictures with picture order randomized within each block.
There were 36 unpleasant (12 mutilation, 12 attack, 12 death/
loss), 36 pleasant (12 family, 12 adventure/sports, 12 erotic)
and 36 neutral pictures for a total of 108 pictures.2 Each block
contained three pictures from each emotional content and nine
neutral pictures. All pictures were presented for 6 s and startle
probes or electric shocks were delivered 3 - 5 s following pic-
ture onset. Inter-picture intervals varied randomly between 12
and 22 seconds.
Affective Valence and Arousal Ratings
Affective ratings of each picture were assessed using the
Self-Assessment Manikin (SAM; Bradley & Lang, 1994). The
SAM is a two item questionnaire that consists of two sets of
five pictographs depicting affective valence/pleasure (unpleas-
ant-pleasant) and arousal (calm-excited). A computerized ver-
sion of the SAM was used to rate affective valence and arousal.
Immediately following each picture the SAM was presented
and participants were asked to rate their emotional reaction to
the picture (Bradley, Codispoti, Cuthbert et al., 2001; Schupp,
Cuthbert, Bradley, & Birbaumer, 1997). To respond, partici-
pants dragged an indicator on or between any of the five picot-
graphs for each scale and submitted their answers by computer
mouse. This yielded ratings between 1 and 9 for each dimen-
sion, with higher scores indicating greater pleasure or arousal
for valence and arousal dimensions, respectively.
Unconditioned Stim ul i : No n- N ox io us Acoustic
Probes & Noxious Electric Stimulations
Acoustic probes were delivered randomly during 50% of the
pictures 3 - 5 s after picture onset, and were equally distributed
across picture contents and picture valences. Startle probes
were also delivered during 33.3% of inter-picture intervals, 11 -
21 s after interval onset. Each startle probe consisted of a 50 ms
1Image numbers during context of acoustic probe presentation were: Erotica
(4607, 4608, 4660, 4677, 4800, 4810), Adventure/Sports (5450, 8170, 8191
8210, 8251, 8380), Families (2160, 2222, 2331, 2345, 2442, 2550), Neutral
(2320, 5510, 7002. 7006, 7009, 7025, 7031, 7035, 7041, 7150, 7175, 7179,
7211, 7217, 7233, 7236, 7830, 7950), Death/Grieving (2455, 2700, 2900,
4598, 6020, 9001), Attack (1052, 1300, 1930, 3500, 6230, 6540), Mutila-
tion (3015, 3030, 3061, 3100, 3102, 3140).
2Image numbers during context of shock presentation were: Erotica (4647,
4651, 4652, 4658, 4659, 4664, 4670, 4672, 4681, 4683, 4687, 4689), Ad-
venture/Sports (2216, 5460, 5470, 5626, 8116, 8161, 8192, 8193, 8260,
8300, 8340, 8470), Families (2165, 2170, 2208, 2224, 2303, 2310, 2311,
2340, 2341, 2395, 2655, 2660), Neutral (2190, 2480. 2570, 2580, 2880,
5390, 5500, 5520, 2230, 5531, 5533, 5534, 6150, 7000, 7004, 7010, 7020,
7030, 7034, 7038, 7040, 7050, 7060, 7080, 7090, 7100, 7110, 7187, 7190,
7205, 7224, 7234, 7235, 7705, 7820, 7900), Death/Grieving (2141, 2205,
2276, 2800, 2810, 9000, 9220, 9421, 9430, 9440, 9480, 9490), Attack
(1050, 1120, 1321, 1525, 1931, 1932, 3530, 6250, 6260, 6350, 6510, 6550),
Mutilation (3051, 3062, 3063, 3064, 3068, 3110, 3150, 3168, 3250, 9252,
9253, 9405).

A. E. WILLIAMS, J. L. RHUDY
burst of white noise delivered over Telephonics headphones at
105 dB-A.
Noxious electric stimulations were delivered during 33.3% of
the pictures 3 - 5 s after picture onset. Noxious stimulations were
also delivered during 15% of inter-picture intervals, 11 - 21 s
after interval onset. Each electrocutaneous stimulus consisted of
a train of five 1-ms pulses at 250 Hz (3-ms ITI). The level of
electric stimulation was held constant during the picture view-
ing phase of the experiment and was set 20% above a physio-
logically-determined threshold, i.e., nociceptive flexion reflex
(NFR) threshold. The NFR is a spinally-mediated withdrawal
reflex elicited by activation of A-delta afferents (pain fibers)
(Sandrini et al., 1999). The muscle activity associated with the
NFR is quantified from biceps femoris (hamstring) muscle
electromyography (France, Rhudy, & McGlone, 2009; Rhudy
& France, 2007). The stimulus level that reliably elicits the
NFR (NFR threshold) correlates highly with subjective pain
threshold and requires the activation of pain fibers (Chan &
Dallaire, 1989; Guieu, Blin, Pouget, & Serratrice, 1992; San-
drini et al., 2005). Thus, setting the stimulus intensity above
NFR threshold maximizes the probability that the stimulations
will be noxious (i.e., activates pain fibers) and eliminates the
potential for report bias. NFR threshold was assessed immedi-
ately after testing with the acoustic probe and pictures, but prior
to testing with noxious electric stimulations and pictures. For a
detailed description of NFR threshold procedures see the parent
study (Rhudy et al., 2010).
Numerical rating scale. After each picture during which a
noxious stimulation was delivered, the computer presented a
vertical numerical rating scale ranging from 0 to 100 with la-
bels of 0 (no sensation), 1 (just noticeable), 25 (uncomfortable),
50 (painful), 75 (very painful), and 100 (maximum tolerable).
Participants dragged an indicator to the desired point to rate the
painfulness of the noxious stimulation. Participants were in-
cluded in analyses if their average NRS rating was ≥25.
Procedure
Upon arrival to the testing session, participants were pro-
vided with an overview of the study and informed consent was
obtained. A brief health questionnaire and interview were ad-
ministered to determine eligibility. Eligible participants were
then familiarized with the procedures and SAM ratings, and
then electrodes were applied. Participants were told that there
were several phases to the experiment. First, startle modulation
was examined by presenting acoustic startle probes (50 ms, 105
dB-A) during 50% of 54 pictures varying in emotional content
and 33.3% of inter-picture intervals.
After testing the acoustic probes, NFR threshold was deter-
mined. Finally, four blocks of 27 pictures (108 total) were pre-
sented during which electric stimulations set at 120% NFR
threshold (in mA) were randomly delivered during 33.3% of
pictures and 15% of inter-picture intervals. The SAM was ad-
ministered immediately after each picture in both phases to
assess emotional responses to the pictures (Bradley, Codispoti,
Cuthbert, et al., 2001; Schupp et al., 1997) and to ensure that
any effect of acoustic startle probes and noxious electrocutane-
ous stimulations on emotional reactions to pictures could be
assessed. Ratings from the 54 pictures during startle assessment
and the 108 pictures during noxious shock assessment are pre-
sented in this paper. When the experiment was completed, par-
ticipants were thanked and provided an honorarium.
Data Reduction and Analysis
Valence and arousal ratings were averaged by picture content
(mutilation, attack, death/loss, neutral, family, adventure/sports,
erotic) and US status (US presented vs US not presented). To
determine the influence of noxious shock US vs non-noxious
noise US administration on picture ratings, repeated measures
analysis of variance (ANOVA) were conducted separately for
valence and arousal ratings during noxious shock assessment
and noise probe assessments. Picture Content (mutilation, at-
tack, death/loss, neutral, family, adventure/sports, erotica) and
US Status (US vs no US) were entered as within-subjects vari-
ables and participant sex was entered as a between-subjects
variable (given that sex is known to influence affective ratings;
Bradley, Codispoti, Sabatinelli et al., 2001). If MPT is correct,
then a main effect of US Status for valence ratings should be
significant. However, if preparedness theory is correct, then a
US Status X Picture Content interaction for valence ratings will
be significant.
Bonferroni adjusted means were conducted for follow-up
contrasts to control for Type I error rate (reported p-values
reflect probabilities after Bonferroni correction). Greenhouse-
Geisser corrections were used to overcome sphericity violations
and epsilon (ε) values are reported following p-values. Partial
eta-squared (2
η
p
) was used as the effect size for F tests.
Results
Tables 1 and 2 report valence and arousal ratings and mean
normative ratings for each picture content during noxious shock
assessment and startle assessment, respectively.
The Influence of Noxious Electric Stimuli on
Emotional Reactions to Pictures
Valence/pleasure ratings. The main effect of picture con-
tent was significant for valence/pleasure ratings, F(6, 738) =
508.60, p < .001, ε = .41, 2 η
p
= .81. Valence/pleasure ratings of
pictures had the following relations; mutilation < (attack and
death) < neutral < (erotic and adventure/sports) < family (ps
< .01). There was a significant main effect of participant sex
[F(1, 123) = 3.90, p = .05, 2 η
p
= .03] with male participants (M
= 4.71, SD = 0.07) generally rating pictures with higher va-
lence/pleasure than female participants (M = 4.54, SD = 0.06)
regardless of picture content or US status. These effects were
qualified by a significant Picture Content X Sex interaction, F(6,
738) = 6.41, p = .001, ε = .78, 2 η
p
= .05. Male participants
provided higher valence ratings than female participants for
erotic pictures, and lower valence ratings for family pictures (ps
< .01).
The main effect of US status was significant for valence/
pleasure ratings, F(1, 123) = 10.75, p = .001, 2 η
p
= .08. Va-
lence/pleasure ratings were lower for shocked pictures (M =
4.58, SD =.05) compared to unshocked pictures (M = 4.67, SD
= 0.05). The Picture Content X US Status interaction, the US
Status X Sex interaction, and the 3-way interaction were not
significant (all ps > .20, all 2 η
p
s < .02). Notably, the effect size
for the main effect of US Status was 4 times the size of the
effect size for the US Status x Picture Content interaction.
Arousal ratings. The main effect of picture content was sig-
nificant for arousal ratings, F(6, 738) = 156.91, p < .001, ε
= .61, 2 η
p
= .56. Arousal ratings of pictures had the following
relations; neutral < family < deatenture/sports < (erotic, h < adv
886

A. E. WILLIAMS, J. L. RHUDY
Table 1.
Affective valence and arousal ratings during noxious shock assessment separated by shock status and participant sex.
Mutilation Attack Death/Grief Neutral Family Adv/Sports Erotica
M SD M SD M SD M SD M SD M SD M SD
Valence/Pleasure
Ratings (1 - 9)
Shocked 1.89 1.02 2.97 1.23 2.84 1.06 5.17 0.79 6.72 1.34 6.58 1.06 6.97 1.40
Men
Unshocked 2.12 0.99 3.29 1.29 3.01 0.97 5.21 0.786.89 1.16 6.59 1.01 7.03 1.39
Shocked 1.74 0.97 2.58 1.33 2.58 1.15 5.14 0.88 7.35 1.14 6.47 1.14 5.96 1.73
Women
Unshocked 1.77 0.87 2.82 1.22 2.65 0.93 5.24 0.797.42 1.09 6.40 1.09 5.98 1.80
Shocked 1.81 0.99 2.74 1.30 2.69 1.02 5.15 0.84 7.09 1.26 6.52 1.10 6.37 1.67
Totals
Unshocked 1.91 0.94 3.01 1.27 2.80 0.96 5.23 0.787.20 1.14 6.48 1.06 6.41 1.72
Normative Valence Ratings 1.93 1.32 3.02 1.78 3.05 1.72 5.06 1.23 7.33 1.60 6.92 1.60 6.66 1.88
Arousal Ratings (1 - 9)
Shocked 6.09 1.87 5.93 1.92 4.58 1.66 3.11 1.65 3.81 1.71 5.27 1.74 6.20 2.02
Men
Unshocked 5.81 1.87 5.79 1.89 4.21 1.54 2.94 1.593.76 1.87 5.47 1.83 6.16 2.13
Shocked 6.04 2.05 5.87 2.13 4.49 1.61 2.89 1.52 3.46 1.70 4.92 2.01 5.57 2.36
Women
Unshocked 5.93 2.03 5.73 2.06 4.32 1.63 2.72 1.483.47 1.86 4.98 1.91 5.51 2.17
Shocked 6.06 1.97 5.89 2.04 4.53 1.63 2.98 1.57 3.60 1.71 5.06 1.91 5.82 2.24
Totals
Unshocked 5.88 1.96 5.75 1.99 4.28 1.59 2.81 1.533.59 1.73 5.18 1.91 5.78 2.17
Normative Arousal Ratings 6.23 2.37 6.82 2.04 4.85 2.12 2.82 1.92 4.62 2.27 5.99 2.23 6.54 2.02
Note: Normative ratings were taken from the IAPS manual (Lang, Bradley, & Cuthbert, 2005). Adv/Sports = Adventure/Sport.
Table 2.
Affective valence and arousal ratings during acoustic probe assessment separated by probe status and participant sex.
Mutilation Attack Death/Grief Neutral Family Adv/Sports Erotica
M SD M SD M SD M SD M SD M SD M SD
Valence/Pleasure
Ratings (1 - 9)
Probed 1.94 1.20 3.00 1.25 3.69 1.05 5.18 0.47 6.53 1.00 6.85 0.90 6.78 1.28
Men
Unprobed 1.93 1.06 3.08 1.26 3.69 0.95 5.16 0.35 6.63 1.05 6.67 1.03 6.97 1.11
Probed 1.80 1.03 2.61 1.22 3.34 1.31 5.31 0.75 7.25 1.21 6.52 1.08 5.98 1.44
Women
Unprobed 1.83 1.06 2.62 1.25 3.44 1.22 5.30 0.68 7.16 1.19 6.71 1.27 6.09 1.54
Probed 1.85 1.09 2.76 1.24 3.47 1.22 5.26 0.65 6.97 1.18 6.65 1.02 6.29 1.43
Totals
Unprobed 1.87 1.06 2.80 1.27 3.54 1.12 5.24 0.58 6.95 1.16 6.69 1.18 6.43 1.45
Normative Valence Ratings 1.76 1.25 2.94 1.67 3.57 1.92 5.02 1.19 7.21 1.58 6.99 1.54 6.85 1.80
Arousal Ratings (1 - 9)
Probed 5.65 1.82 5.92 2.04 4.18 1.69 2.64 1.23 2.76 1.27 5.47 1.97 5.99 2.06
Men
Unprobed 5.64 1.81 5.78 2.06 3.88 1.61 2.43 1.36 3.04 1.47 5.33 1.98 6.13 1.95
Probed 5.89 1.88 6.04 1.97 4.11 1.56 2.58 1.36 2.97 1.61 4.85 1.87 5.50 1.88
Women
Unprobed 5.82 1.85 6.05 1.96 4.04 1.54 2.36 1.23 2.96 1.58 5.17 2.09 5.45 1.99
Probed 5.80 1.85 5.99 1.99 4.14 1.61 2.60 1.31 2.89 1.49 5.09 1.93 5.69 1.96
Totals
Unprobed 5.75 1.83 5.95 2.00 3.98 1.56 2.39 1.27 2.99 1.54 5.23 2.04 5.71 1.99
Normative Arousal Ratings 6.23 2.40 6.82 2.08 4.85 2.16 2.83 1.90 4.61 2.25 5.98 2.23 6.55 2.00
N
ote: Normative ratings were taken from the IAPS manual (Lang et al., 2005). Adv/Sports = Adventure/Sport.

A. E. WILLIAMS, J. L. RHUDY
attack, and mutilation) (ps < .001). There were no differences in
arousal for erotic, mutilation, and attack pictures (ps = 1.00).
The main effect of US status was significant for arousal ratings
[F(1, 123) = 12.75, p = .001, 2 η
p
= .09] with higher arousal
ratings for shocked (M = 5.01, SD = 0.13) compared to un-
shocked pictures (M = 4.88, SD = 0.14). All other effects were
non-significant (all ps > .05, all 2 η
p
s < .02).
The Influence of Non-Noxious Acoustic Probes on
Emotional Reactions to Pictures
Valence/pleasure ratings. The main effect of picture con-
tent was significant for valence/pleasure ratings, F(6, 738) =
511.48, p < .001, ε = .45, 2
η
p
= .81. Valence/pleasure ratings of
pictures had the following relations; mutilation < attack < death
< neutral < (family and adventure/sports) (ps < .02). Valence
ratings of family pictures were significantly lower compared to
erotic pictures (p < .001) which did not differ from adventure/
sports picture ratings (p = .44). This effect was qualified by a
significant Picture Content X Sex interaction, F(6, 738) = 6.42,
p = .001, ε = .76, 2 η
p
= .05. Male participants provided higher
valence ratings than female participants for attack and erotic
pictures, and lower valence ratings for family pictures (ps
< .05). The main effect of US status and the interaction effects
were not significant (all ps > .28, all 2 η
p
s < .01).
Arousal ratings. The main effect of picture content was sig-
nificant for arousal ratings, F(6, 738) = 237.83, p < .001, ε
= .61, 2 η
p
= .66. Arousal ratings of pictures had the following
relations; neutral < family < death < adventure/sports < (erotic,
attack, and mutilation) (ps < .01). There were no differences in
arousal for erotic, attack, and mutilation (ps > .57). This effect
was qualified by a significant Picture Content X Sex interaction,
F(6, 738) = 2.63, p = .04, ε = .87, 2 η
p
= .02. However, follow-
up comparisons revealed no significant differences between
male and female ratings of pictures after Bonferroni corrections
(ps > .09). The main effect of US status and the US status in-
teractions were not significant (all ps > .14, all 2 η
p
s < .02).
Discussion
The present study sought to determine whether motivational
priming theory (MPT) or preparedness theory best explained
the influence of a noxious shock on emotional reactions to af-
fectively-charged pictures. MPT predicts an increase (facilita-
tion) in negative emotional responses to an unpleasant fore-
ground and decrease (inhibition) in positive emotional re-
sponses to a pleasant foreground (Bradley, Codispoti, Cuthbert,
et al., 2001). In contrast, preparedness theory predicts an in-
crease in negative emotional responses to an unpleasant picture,
but no change in the emotional response to a pleasant picture
(Peterson et al., 1993; Seligman, 1970, 1971). Data were ana-
lyzed from a study involving the presentation of a series of
emotional pictures (mutilation, attack, death/loss, neutral, fam-
ily, adventure/sports, and erotic) during which noxious shocks
were delivered during 33% of the pictures. Following each
picture, participants used the Self Assessment Manikin (SAM)
to rate how the picture made them feel.
In general, subjective ratings of emotional valence and
arousal were consistent with picture content (i.e. negative pic-
tures having lower valence than positive pictures; positive and
negative pictures more arousing than neutral). Results indicated
that valence/pleasure ratings were lower (more displeasure) and
arousal ratings were higher for pictures (regardless of picture
content) during which participants received a shock US com-
pared to pictures without a shock US. This suggests that pres-
entation of the noxious US led to enhanced negative emotional
responses to unpleasant pictures and inhibited positive emo-
tional responses to pleasant pictures, which is consistent with
MPT.
A similar experimental protocol was used to assess the im-
pact of a non-noxious US (acoustic startle probe) on emotional
reactions to affectively-charged pictures. During this procedure,
pictures also elicited the expected emotional responses from
participants (i.e. negative pictures having lower valence than
positive pictures; positive and negative pictures more arousing
than neutral). In contrast to results from noxious shock USs, the
presence of an aversive, but non-noxious, acoustic probe did
not influence reactions to the pictures.
The results of this study contribute to the generalization of,
and research support for, our theoretical understanding of how
noxious events/stimuli can impact emotional responses. Emo-
tion has been proposed to emanate from two opponent motive
systems, defensive and appetitive (Bradley, Codispoti, Cuthbert
et al., 2001). According to MPT, activation of the defensive
system should facilitate defensive responses and inhibit appeti-
tive responses; whereas activation of the appetitive system
should facilitate appetitive responses and inhibit defensive re-
sponses. Research supports these hypotheses, but has generally
focused on the influence of an affective foreground (e.g., pic-
ture presentation, odors) on defensive responses to an aversive
unconditioned stimulus (US; shock, loud noise).
In contrast, the present study sought to assess the effects of
an aversive and noxious US on responses to an affective fore-
ground. MPT would predict that priming the defensive system
by the aversive US would lead to enhanced defensive responses
and inhibited appetitive responses, including subjective experi-
ence. In comparison, preparedness theory would predict that the
aversive US would increase negative affect in response to un-
pleasant pictures but would have no effect on emotional re-
sponse to pleasant pictures. Results supported MPT; noxious
shock USs enhanced displeasure to unpleasant pictures and
reduced pleasure to pleasant pictures, relative to unshocked
pictures. In addition, subjective arousal ratings were enhanced
during shocked pictures compared to unshocked pictures. This
indicates an individual may have a different emotional response
to an affective foreground when a noxious US is presented.
As predicted by MPT, these data suggest the presence of a
noxious US will impact reactions to unpleasant and pleasant
affective foregrounds. Nonetheless, it should be noted that the
means in Table 1 suggest a possible trend towards a US Status
× Picture Content interaction with noxious USs having a
slightly larger impact on ratings of unpleasant compared to
pleasant pictures. This begs the question of whether a signifi-
cant interaction would have been found with a larger sample,
thus providing support for preparedness theory. However, the
difference in magnitude of the main effect of US Status and the
US Status x Picture Content interaction suggests the main effect,
and thus MPT, represents a stronger and more relevant influ-
ence on emotional ratings. Indeed, the US Status × Picture
Content interaction (which tests preparedness theory) was a
small effect that accounted for only 2% of the variance in va-
lence ratings. By contrast, the effect size for the main effect of
US Status (which tests the MPT hypothesis) was four times
larger and explained 8% of the variance in valence ratings. As a
888

A. E. WILLIAMS, J. L. RHUDY
result, this helps bolster confidence in the conclusion that MPT
predicts the effect of a noxious US on valence reactions to pic-
tures.
In contrast to the effect of noxious stimuli on ratings of un-
pleasant and pleasant affective foregrounds, when the experi-
ment involved an aversive but non-noxious US (white noise)
the presence of the US during a picture did not influence emo-
tional reactions to the affective foreground. This suggests that
the defensive activation in response to non-noxious acoustic
probes was not strong enough to impact reactions to the fore-
ground. This is also consistent with MPT which predicts that
greater levels of defensive activation are elicited by more
threatening or emotionally arousing stimuli, such as a noxious
shock, compared to less threatening stimuli such as white noise.
Increased defensive activation would then lead to greater fa-
cilitation of defensive responses and greater reduction of appe-
titive responses as seen in the present study.
The lack of impact of white noise on ratings of the affective
foreground in the present study is similar to the results of
Bradley, Codispoti, Cuthbert, & Lang (2001) who also found
no influence of white noise on valence/pleasure ratings of an
affective foreground. In contrast to the present results, they did
find a small increase in arousal ratings of pictures during which
white noise was presented. Inspection of the current data also
indicates a very small increase in arousal ratings for pictures
with acoustic USs (M = 4.61) versus those without USs (M =
4.58), but this effect was not statistically significant (p = .41,
2
η
p
= .01). Thus, both studies suggest that non-noxious acoustic
probes have minimal effect on affective reactions to the fore-
ground.
Although not a main goal of the study, our results confirm
prior reports of sex differences in emotional reactions to pic-
tures. Specifically, men typically have greater appetitive active-
tion to erotica and women typically have greater defensive
activation to most unpleasant pictures (Bradley, Codispoti,
Sabatinelli et al., 2001). In the present study, men had higher
valence/pleasure to erotic pictures and women had higher va-
lence/pleasure ratings for family pictures. Additionally in the
series of pictures during which startle probes were presented,
women had lower valence ratings of attack pictures. Thus, the
present study shows a similar pattern of sex differences in va-
lence ratings of affective pictures as seen in previous studies.
However, there were no sex differences associated with the
influence of the noxious US on emotional responses to pictures,
indicating that the presence of a noxious US had the same ef-
fect on ratings of emotional pictures for males and females.
Implications
Results of this study have implications for research design.
As evidenced by these data, presentation of a noxious US alters
participant reactions to the affective foreground. While this
effect resulted in only minor changes in affective ratings, this
could nonetheless alter the efficacy of experimental factors
meant to manipulate participant affect. Thus, it is important that
studies including a noxious US employ adequate manipulation
checks to ensure participant’s responses to affective fore-
grounds are not significantly altered by US presentation. Fur-
ther, this effect on the affective foreground could present a
confound in studies attempting to make comparisons to norma-
tive data or to groups that do not receive the same noxious US.
Monitoring the effect of non-noxious USs is warranted as well,
but may be less likely to alter reactions to affective fore-
grounds.
The present study makes several contributions to the current
research literature. First, the study examined the influence of
presentation of a noxious stimulus on ratings of an affective
foreground, which although similar, is the reverse of most
studies which look at the influence of an affective foreground
on response to a noxious stimulus. Studies that have looked at
similar outcomes have found mixed results. Bresin and col-
leagues (2010) found that ratings of both positive and negative
affect decreased following an experimental pain stimulus,
however, these ratings did not refer to a specific foreground.
Hollin and Derbyshire (2009) found that cold pressor pain de-
creased ratings of fear during concurrent presentation of a spi-
der. The present study extended these studies to assess the in-
fluence of noxious and non-noxious stimuli on emotional rat-
ings of affective foregrounds (with multiple valence and arousal
levels), and results have implications for research (discussed
above). Moreover, there may also be clinical implications. The
present study suggests that persons experiencing pain may ex-
perience less positive emotion in response to a pleasant event,
and greater negative emotion in response to an unpleasant event,
compared to a person not experiencing pain. This could partly
explain the relationship between chronic pain and depression
(Kroenke et al., 2011), because pain may promote anhedonia
(low positive affect) and enhanced negative affect.
Limitations
One factor of note in the present study is that pictures dif-
fered not only due to the presence, or lack thereof, of a noxious
electric stimulation; but shocked pictures also were followed by
a numerical rating scale (NRS) to rate the intensity of the
stimulation. It is possible that the presence of the NRS altered
the context in such a way as to bias participant ratings of pic-
ture-evoked emotional responses on the Self-Assessment Man-
ikin (SAM). However, the motivational relevance of a noxious
electric stimulation should be much greater than that of the
NRS, and thus the contextual salience of the electric stimu-
lation should overshadow that of the NRS. Moreover, the NRS
and SAM were presented simultaneously following pictures
with concurrent electrical stimulation. Participants were free to
choose which scale to complete first and informal observations
made by experimenters indicated there was significant variabil-
ity in the order in which participants completed the NRS and
SAM. Therefore, a subset of participants rated emotional re-
sponses to pictures prior to rating the electrical stimulation.
This may have reduced any potential confound of the NRS on
SAM ratings. Nonetheless, future studies should seek to repli-
cate these data with experimental designs that explicitly control
for potential contextual confounds, although presenting the
NRS in the absence of an electric stimulus might confuse par-
ticipants and create additional problems.
Another limitation of this study was that it only assessed the
impact of aversive USs. MPT would predict that appetitive USs
would also effect reactions to affective foregrounds (facilitating
appetitive reactions and inhibiting defensive reactions). Thus,
future research is needed to confirm this hypothesis.
Summary
The present study compared competing hypotheses based

A. E. WILLIAMS, J. L. RHUDY
upon MPT and preparedness theory to determine which would
better predict the impact of a noxious US on emotional reac-
tions to affectively-charged pictures. These data supported
MPT indicating that the presentation of a noxious US (but not a
non-noxious US) can influence reactions to the affective fore-
ground by facilitating negative emotional reactions to unpleas-
ant pictures and inhibiting positive emotional reactions to
pleasant pictures. Prior research supporting MPT has found that
the presentation of an affective foreground influences physio-
logical and emotional reactions to a noxious US. However, the
present study is the first to our knowledge to find the reverse.
This study highlights importance of understanding the potential
impact of aversive stimuli on emotional reactivity in research
and clinical settings in which an aversive stimulus is adminis-
tered.
REFERENCES
Benning, S. D., Patrick, C. J., & Lang, A. R. (2004). Emotional modu-
lation of the post-auricular reflex. Psychophysiology, 41, 426-432.
doi:10.1111/j.1469-8986.00160.x
Bradley, M. M., Codispoti, M., Cuthbert, B. N., & Lang, P. J. (2001).
Emotion and motivation I: Defensive and appetitive reactions in pic-
ture processing. Emotion, 1, 276-298.
doi:10.1037/1528-3542.1.3.276
Bradley, M. M., Codispoti, M., Sabatinelli, D., & Lang, P. J. (2001).
Emotion and motivation II: Sex differences in picture processing.
Emotion, 1, 300-319. doi:10.1037/1528-3542.1.3.300
Bradley, M. M., & Lang, P. J. (1994). Measuring emotion: The
Self-Assessment Manikin and the semantic differential. Journal of
Behavior Therapy and Expe r i me n ta l Psychiatry, 25, 49-59.
doi:10.1016/0005-7916(94)90063-9
Bresin, K., Gordon, K. H., Bender, T. W., Gordon, L. J., & Joiner, T. E.
(2010). NO pain, no change: Reductions in prior negative affect fol-
lowing physical pain. Motivation & Emotion, 34, 280-287.
doi:10.1007/s11031-010-9168-7
Chan, C. W., & Dallaire, M. (1989). Subjective pain sensation is line-
arly correlated with the flexion reflex in man. Brain Research, 479,
145-150. doi:10.1016/0006-8993(89)91344-9
CSEA (1999). The international affective picture system: Digitized
photographs. Gainesville, FL: University of Florida, The Center for
Research in Psychophysiology.
Cuthbert, B. N., Bradley, M. M., & Lang, P. J. (1996). Probing picture
perception: Activation and emotion. Psychophysio l ogy, 33, 103-111.
doi:10.1111/j.1469-8986.1996.tb02114.x
De Wied, M., & Verbaten, M. N. (2001). Affective pictures processing,
attention, and pain tolerance. Pain, 90, 163-172.
doi:10.1016/S0304-3959(00)00400-0
France, C. R., Rhudy, J. L., & McGlone, S. (2009). Using normalized
EMG to define the Nociceptive Flexion Reflex (NFR) threshold:
Further evaluation of standardized scoring criteria. Pain, 145, 211-
218. doi:10.1016/j.pain.2009.06.022
Greenwald, M. K., Bradley, M. M., Cuthbert, B. N., & Lang, P. J.
(1998). Startle potentiation: Shock sensitization, aversive learning,
and affective picture modulation. Behavioral Neuroscience, 112,
1069-1079. doi:10.1037/0735-7044.112.5.1069
Grillon, C., Ameli, R., Merikangas, K., Woods, S. W., & Davis, M.
(1993). Measuring the time course of anticipatory anxiety using the
fear-potentiated startle reflex. P s ychophysiology, 30, 340-346.
doi:10.1111/j.1469-8986.1993.tb02055.x
Grillon, C., Ameli, R., Woods, S. W., & Merikangas, K. (1991).
Fear-potentiated startle in humans: Effects of anticipatory anxiety on
the acoustic blink reflex. Psychophysiology, 28, 588.
doi:10.1111/j.1469-8986.1991.tb01999.x
Guieu, R., Blin, P., Pouget, J., & Serratrice, G. (1992). High level
sportsmen and nociceptive flexion reflex of the lower limb. Cana-
dian Journal of Neuroscience, 19, 69-71.
Hawk, L. W., & Cook III, E. W. (1997). Affective modulation of tactile
startle. Psychophysiology, 34, 23.
doi:10.1111/j.1469-8986.1997.tb02412.x
Hollin, G. J. S., & Derbyshire, S. W. G. (2009). Cold pressor pain re-
duces phobic fear but fear does not reduce pain. The Journal of Pain,
10, 1058-1064. doi:10.1016/j.jpain.2009.03.015
Jansen, D. M., & Frijda, N. H. (1994). Modulation of the acoustic star-
tle response by film-induced fear and sexual arousal. Psychophysi-
ology, 31, 565-571. doi:10.1111/j.1469-8986.1994.tb02349.x
Kroenke, K., Wu, J., Bair, M. J., Krebs, E. E., Damush, T. M., & Tu, W.
(2011). Reciprocal relationship between pain and depression: A
12-month longitudinal analysis in primary care. Journal of Pain, 12,
964-973. doi:10.1016/j.jpain.2011.03.003
Lang, P. J. (1995). The emotion probe: Studies of motivation and atten-
tion. American Psychologist, 50, 372-385.
doi:10.1037/0003-066X.50.5.372
Lang, P. J., Bradley, M. M., & Cuthbert, B. (2005). The International
Affective Picture System (IAPS): Affective ratings of pictures and
instruction manual. Technical Report A-6. Gainesville, FL: Univer-
sity of Florida.
Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1990). Emotion, atten-
tion, and the startle reflex. Psychological Review, 97, 377-395.
doi:10.1037/0033-295X.97.3.377
Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1999). International
affective picture system (IAPS): Instruction manual and affective
ratings. Technical Report A-4. Gainesville, FL: The Center for Re-
search in Psychophysiology, University of Florida.
Meagher, M. W., Arnau, R. C., & Rhudy, J. L. (2001). Pain and emo-
tion: Effects of affective picture modulation. Psychosomatic Medi-
cine, 63, 79-90.
Ohman, A., & Dimberg, U. (1978). Facial expressions as conditioned
stimuli for electrodermal responses: A case of “preparedness”?
Journal of Personality & Social Psychology, 3 6, 1251-1258.
doi:10.1037/0022-3514.36.11.1251
Ohman, A., & Soares, J. J. F. (1993). On the automatic nature of phobic
fear: Conditioned electrodermal responses to masked fear-relevant
stimuli. Journal of Abnormal Psychology, 102, 121-132.
doi:10.1037/0021-843X.102.1.121
Peterson, C., Maier, S. F., & Seligman, M. E. P. (1993). Learned Help-
lessness: A theory for age of personal control. New York, NY: Ox-
ford University Press.
Rhudy, J. L., Bartley, E. J., Williams, A. E., McCabe, K. M., Chandler,
M. C., Russell, J. L. et al. (2010). Are there sex differences in affec-
tive modulation of spinal nociception and pain? The Journal of Pain,
11, 1429-1441. doi:10.1016/j.jpain.2010.04.003
Rhudy, J. L., & France, C. R. (2007). Defining the nociceptive flexion
reflex (NFR) threshold in human participants: A comparison of dif-
ferent scoring criteria. Pain, 128, 244-253.
doi:10.1016/j.pain.2006.09.024
Rhudy, J. L., Williams, A. E., McCabe, K. M., Nguyen, M. A., &
Rambo, P. L. (2005). Affective modulation of nociception at spinal
and supraspinal levels. Psychophysiology, 42, 579-587.
Rhudy, J. L., Williams, A. E., McCabe, K. M., Rambo, P. L., & Russell,
J. L. (2006). Emotional modulation of spinal nociception and pain:
The impact of predictable noxious stimulation. Pain, 126, 221-233.
doi:10.1016/j.pain.2006.06.027
Rhudy, J. L., Williams, A. E., McCabe, K. M., Russell, J. L., & May-
nard, L. J. (2008). Emotional control of nociceptive reactions
(ECON): Do affective valence and arousal play a role? Pain, 136,
250-261. doi:10.1016/j.pain.2007.06.031
Sandrini, G., Milanov, I., Willer, J. C., Alfonsi, E., Moglia, A., &
Nappi, G. (1999). Different effect of high doses of naloxone on spi-
nal reflexes in normal subjects and chronic paraplegic patients. Neu-
roscience Letters, 261, 5-8. doi:10.1016/S0304-3940(98)01000-3
Sandrini, G., Serrao, M., Rossi, P., Romaniello, A., Cruccu, G., &
Willer, J. C. (2005). The lower limb flexion reflex in humans. Pro-
gress in Neurobiology, 77, 353-395.
doi:10.1016/j.pneurobio.2005.11.003
Schupp, H. T., Cuthbert, B. N., Bradley, M. M., & Birbaumer, N.
(1997). Probe P3 and blinks: Two measures of affective startle
modulation. P sychophysiology, 34, 1-6.
doi:10.1111/j.1469-8986.1997.tb02409.x
890

A. E. WILLIAMS, J. L. RHUDY
Seligman, M. E. (1970). On the generality of the laws of learning. Psy-
chological Review, 77, 406-418. doi:10.1037/h0029790
Seligman, M. E. (1971). Phobias and preparedness. Behavior Therapy,
2, 307-320. doi:10.1016/S0005-7894(71)80064-3
Vrana, S. R., Spence, E. L., & Lang, P. J. (1988). The startle probe
response: A new measure of emotion? Journal of Abnormal Psy-
chology, 97, 487-491. doi:10.1037/0021-843X.97.4.487
Williams, A. E., & Rhudy, J. L. (2007). The influence of conditioned
fear on human pain thresholds: Does preparedness play a role. The
Journal of Pain, 8, 598-606. doi:10.1016/j.jpain.2007.03.004