Emotional modulation of the postauricular reflex
Emotional modulation of the postauricular reflex
Emotional modulation of the postauricular reflex
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Psychophysiology, 41 (2004), 426–432. Blackwell Publishing Inc. Printed in <strong>the</strong> USA.<br />
Copyright r 2004 Society for Psychophysiological Research<br />
DOI: 10.1111/j.1469-8986.00160.x<br />
BRIEF REPORT<br />
<strong>Emotional</strong> <strong>modulation</strong> <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong><br />
STEPHEN D. BENNING, a CHRISTOPHER J. PATRICK, a and ALAN R. LANG b<br />
a Department <strong>of</strong> Psychology, University <strong>of</strong> Minnesota–Twin Cities, Minneapolis, Minnesota, USA<br />
b Department <strong>of</strong> Psychology, Florida State University, Tallahassee, Florida 32306, USA<br />
Abstract<br />
A large literature now exists on emotional <strong>modulation</strong> <strong>of</strong> <strong>the</strong> startle blink <strong>reflex</strong>. The current study examined affective<br />
<strong>modulation</strong> <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong>, which can be measured in relation to <strong>the</strong> same noise probe used to evoke <strong>the</strong><br />
startle <strong>reflex</strong>. We recorded <strong>the</strong> post-auricular <strong>reflex</strong> during viewing <strong>of</strong> pictures that varied systematically in emotional<br />
valence, content, and intensity. A significant linear valence <strong>modulation</strong> effect was found, with pleasant pictures<br />
potentiating and aversive pictures inhibiting <strong>the</strong> post-auricular <strong>reflex</strong> in comparison with neutral pictures. This<br />
modulatory effect did not vary as a function <strong>of</strong> picture content, but it was most robust for highly intense emotional<br />
pictures. Implications for <strong>the</strong> assessment <strong>of</strong> basic emotional action tendencies are discussed.<br />
Descriptors: Post-auricular, Emotion, Appetitive, Startle, Reflex, Post-auricular <strong>reflex</strong><br />
It is well known that <strong>the</strong> startle blink <strong>reflex</strong> to an abrupt acoustic<br />
probe is modulated by <strong>the</strong> emotional valence <strong>of</strong> foreground<br />
stimulation. Startle magnitude is enhanced (potentiated) during<br />
viewing <strong>of</strong> unpleasant pictures compared with neutral pictures,<br />
and inhibited during viewing <strong>of</strong> pleasant pictures (cf. Lang,<br />
Bradley, & Cuthbert, 1990; Vrana, Spence, & Lang, 1988). A<br />
different <strong>reflex</strong> evoked by <strong>the</strong> same noise probe used to elicit<br />
startle is <strong>the</strong> post-auricular <strong>reflex</strong>. Although several studies have<br />
investigated attentional <strong>modulation</strong> <strong>of</strong> this <strong>reflex</strong> (e.g., Hackley,<br />
Woldorff, & Hillyard, 1987; Patuzzi & O’Beirne, 1999; Sollers &<br />
Hackley, 1997), <strong>the</strong> emotional <strong>modulation</strong> <strong>of</strong> <strong>the</strong> post-auricular<br />
<strong>reflex</strong> has not been similarly investigated. The current study<br />
examined post-auricular <strong>reflex</strong> <strong>modulation</strong> as a function <strong>of</strong> <strong>the</strong><br />
valence, <strong>the</strong>matic content, and affective intensity <strong>of</strong> picture<br />
stimuli to determine whe<strong>the</strong>r this <strong>reflex</strong> might provide unique<br />
information about on-line affective processing.<br />
Emotion and Reflex Modulation<br />
Reflexes are valuable to measure in studies <strong>of</strong> emotion because<br />
<strong>the</strong>y have <strong>the</strong> potential to tap <strong>the</strong> basic action dispositionsFappetitive-approach<br />
and defensive-withdrawalFthat underlie posi-<br />
This study was supported by grants MH17069, MH52384, and<br />
MH65137 from <strong>the</strong> National Institute <strong>of</strong> Mental Health, Grant<br />
AA12164 from NIAAA, and by funds from <strong>the</strong> Hathaway endowment<br />
at <strong>the</strong> University <strong>of</strong> Minnesota. We are grateful to Daniel Blonigen and<br />
Brian Hicks for <strong>the</strong>ir assistance with stimulus selection, counterbalancing,<br />
and collection <strong>of</strong> data, and to Edward Bernat for his scholarly<br />
comments on drafts <strong>of</strong> this manuscript.<br />
Address reprint requests to: Christopher J. Patrick, Department <strong>of</strong><br />
Psychology, University <strong>of</strong> Minnesota, Elliott Hall, 75 East River Road,<br />
Minneapolis, MN 55455, USA. E-mail: cpatrick@tc.umn.edu.<br />
426<br />
tive and negative emotional states. In this regard, Lang et al.<br />
(1990) proposed a response-matching explanation for <strong>the</strong> linear<br />
valence <strong>modulation</strong> effect observed for <strong>the</strong> startle <strong>reflex</strong>: A<br />
defensive <strong>reflex</strong>, such as startle, is enhanced during aversive picture<br />
viewing because <strong>the</strong> motivational state induced by <strong>the</strong> picture is<br />
defensive, leading to a synergistic facilitation. Conversely, startle is<br />
inhibited during pleasant pictures because here <strong>the</strong> ongoing<br />
approach disposition opposes <strong>the</strong> defensive startle reaction. From<br />
this perspective, a reverse pattern <strong>of</strong> <strong>modulation</strong> would be<br />
expected for an appetitive <strong>reflex</strong>Fthat is, potentiation during<br />
pleasant pictures and inhibition during aversive pictures.<br />
If this response-matching explanation <strong>of</strong> startle <strong>modulation</strong> in<br />
humans is accurate, <strong>the</strong>n intense emotional pictures that evoke<br />
strong appetitive or defensive motivational states should produce<br />
maximal modulatory effects on startle. Consistent with this,<br />
Cuthbert, Bradley, and Lang (1996) reported that blink potentiation<br />
was greater for high- versus low-arousal aversive pictures, and<br />
that blink inhibition was greater for high- versus low-arousal<br />
pleasant pictures. There is also evidence that modulatory effects<br />
are stronger for picture contents that are tied to primary motives:<br />
Blink inhibition is maximal for pleasant pictures that are sexual in<br />
content, and potentiation is maximal for directly threatening<br />
aversive pictures (Bradley, Codispoti, Cuthbert, & Lang, 2001;<br />
Levenston, Patrick, Bradley, & Lang, 2000). The idea that startle<br />
potentiation during aversive picture viewing reflects defensive<br />
mobilization also fits with neuroscience research indicating that<br />
fear-potentiated startle in rats is mediated by input from <strong>the</strong><br />
subcortical amygdala to <strong>the</strong> midbrain component <strong>of</strong> <strong>the</strong> startle<br />
circuit, <strong>the</strong> nucleus reticularis pontis caudalis (Davis, Gendelman,<br />
Tischler, & Gendelman, 1982; Hitchcock & Davis, 1986).<br />
From this response-matching perspective, o<strong>the</strong>r defensive<br />
<strong>reflex</strong>es should show modulatory patterns akin to startle.
Emotion and <strong>the</strong> post-auricular <strong>reflex</strong> 427<br />
Moulder, Bradley, Requin, and Lang (1995) reported a parallel<br />
linear valence <strong>modulation</strong> pattern (i.e., aversive4pleasant) for <strong>the</strong><br />
H<strong>of</strong>fman <strong>reflex</strong>, a spinal flexion <strong>reflex</strong> elicited by aversive electric<br />
shock. In this study, <strong>modulation</strong> effects were stronger for<br />
emotional pictures <strong>of</strong> high intensity, and more pronounced for<br />
participants who rated <strong>the</strong> shock as aversive. In contrast to this,<br />
<strong>the</strong> magnitude <strong>of</strong> <strong>the</strong> spinal T <strong>reflex</strong>, elicited by nonaversive<br />
tapping or vibratory stimulation <strong>of</strong> <strong>the</strong> Achilles tendon, is<br />
comparably enhanced during both pleasant and unpleasant<br />
pictures in relation to neutral (Bonnet, Bradley, Lang, & Requin,<br />
1995)Fimplying facilitation by arousal (i.e., nonspecific activation;<br />
cf. Lang et al., 1990). An opposing quadratic pattern,<br />
involving inhibited probe response during both pleasant and<br />
aversive pictures compared with neutral, has been reported for<br />
o<strong>the</strong>r measures (e.g., noise-evoked P300 brain potential; Schupp,<br />
Cuthbert, Bradley, Birbaumer, & Lang, 1997). This pattern<br />
indicates a cross-modal attentional effect (cf. Anthony & Graham,<br />
1985) arising from <strong>the</strong> fact that visual affective stimuli draw more<br />
attention away from <strong>the</strong> acoustic modality (Lang et al., 1990).<br />
The Post-Auricular Reflex<br />
The post-auricular <strong>reflex</strong> is a vestigial muscle response in humans<br />
that acts to pull <strong>the</strong> ear backward (Gray, 1901/1995). It is<br />
recorded by positioning electrodes over <strong>the</strong> post-auricular muscle<br />
behind <strong>the</strong> ear (O’Beirne & Patuzzi, 1999). Because this <strong>reflex</strong> is<br />
evoked by an acoustic probe stimulus, it can be assessed<br />
concurrently with <strong>the</strong> startle blink (cf. Hackley, 1993). The<br />
post-auricular <strong>reflex</strong> has a much faster latency than <strong>the</strong> blink<br />
<strong>reflex</strong> (i.e., 9–11 ms vs. 45–50 ms; Hackley et al., 1987), implying<br />
a simpler brain stem circuitry. Following Cassella and Davis<br />
(1986), Hackley (1993) <strong>the</strong>orized that <strong>the</strong> circuit for <strong>the</strong> <strong>postauricular</strong><br />
<strong>reflex</strong> parallels <strong>the</strong> startle circuit in terms <strong>of</strong> input (i.e.,<br />
cochlear nucleus) and output (facial motor nucleus) components,<br />
but that it does not include <strong>the</strong> nucleus reticularis pontis<br />
caudalisF<strong>the</strong> juncture <strong>of</strong> <strong>the</strong> startle circuit at which input is<br />
received from <strong>the</strong> amygdala, accounting for <strong>the</strong> fear-potentiated<br />
startle effect (Davis et al., 1982). If this model <strong>of</strong> <strong>the</strong> <strong>postauricular</strong><br />
circuit is correct, one might expect a different pattern <strong>of</strong><br />
<strong>modulation</strong> for <strong>the</strong> post-auricular <strong>reflex</strong> compared with <strong>the</strong><br />
startle <strong>reflex</strong>.<br />
The post-auricular <strong>reflex</strong> has been assessed in a small number<br />
<strong>of</strong> attention studies in humans. The magnitude <strong>of</strong> this <strong>reflex</strong>, like<br />
that <strong>of</strong> startle, is attenuated if <strong>the</strong> <strong>reflex</strong>-eliciting noise is preceded<br />
by <strong>the</strong> occurrence <strong>of</strong> a transient acoustic stimulus (prepulse)Fan<br />
effect known as ‘‘prepulse inhibition’’ (Hackley, 1993; Hackley et<br />
al., 1987). Prepulse inhibition is thought to reflect a low-level<br />
sensory gating mechanism that affords ‘‘protection’’ at early<br />
stages <strong>of</strong> perceptual processing (Braff, Geyer, & Swerdlow, 2001;<br />
Graham, 1975). On <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> post-auricular <strong>reflex</strong><br />
appears less subject to controlled attentional influences than<br />
startle. Hackley et al. (1987) reported that prepulse inhibition<br />
was enhanced for <strong>the</strong> startle <strong>reflex</strong>, but not <strong>the</strong> post-auricular<br />
<strong>reflex</strong>, when participants were instructed to attend to <strong>the</strong> prepulse<br />
stimulus. This dissociation in effects was interpreted in terms <strong>of</strong><br />
<strong>the</strong> faster, simpler circuitry <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> (see also<br />
Hackley, 1993).<br />
However, when instructed to attend to one ear or <strong>the</strong> o<strong>the</strong>r in<br />
an auditory task, participants showed generally enhanced <strong>postauricular</strong><br />
<strong>reflex</strong> magnitudes, and enhanced prepulse inhibition <strong>of</strong><br />
this <strong>reflex</strong>, on <strong>the</strong> side to which attention was directed (Hackley,<br />
1993; Hackley et al., 1987). Hackley et al. (1987) attributed this<br />
effect to motor priming (i.e., a tensing <strong>of</strong> muscles on <strong>the</strong><br />
instructed side) ra<strong>the</strong>r than attention per se. Consistent with this,<br />
Patuzzi and O’Beirne (1999) reported a unilateral increase in<br />
baseline activity <strong>of</strong> <strong>the</strong> post-auricular muscle, and an affiliated<br />
increase in <strong>the</strong> magnitude <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> to noise<br />
probes, when participants were instructed to rotate <strong>the</strong>ir eyes<br />
toward one side <strong>of</strong> <strong>the</strong> head or <strong>the</strong> o<strong>the</strong>r. On <strong>the</strong> o<strong>the</strong>r hand,<br />
it has been shown that activity in <strong>the</strong> post-auricular muscle region<br />
decreases during processing <strong>of</strong> near-threshold auditory<br />
stimulation compared with more intense auditory stimulationFconsistent<br />
with <strong>the</strong> idea that somatic activation decreases<br />
to enhance perceptual sensitivity during orienting (Stekelenburg<br />
& van Boxtel, 2001, 2002). However, <strong>the</strong> post-auricular <strong>reflex</strong><br />
was not assessed in <strong>the</strong>se latter studies, so it is unclear what<br />
impact <strong>the</strong>se changes in baseline EMG activity would have on its<br />
magnitude.<br />
Current Study<br />
The current study was conducted to examine modulatory effects<br />
<strong>of</strong> emotion on <strong>the</strong> post-auricular <strong>reflex</strong>. To do this, we delivered<br />
unwarned noise probes to participants during viewing <strong>of</strong><br />
pleasant, neutral, and unpleasant pictures and recorded<br />
responses <strong>of</strong> <strong>the</strong> post-auricular muscle behind each ear. To gain<br />
additional information about modulatory effects, we manipulated<br />
both <strong>the</strong> intensity and <strong>the</strong>matic content <strong>of</strong> pleasant and<br />
unpleasant pictures.<br />
The status <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> as a defensive or<br />
appetitive <strong>reflex</strong> is unclear. However, <strong>the</strong> response-matching<br />
hypo<strong>the</strong>sis (Lang et al., 1990) makes clear predictions in ei<strong>the</strong>r<br />
case. If <strong>the</strong> post-auricular <strong>reflex</strong> is defensive in nature, it should<br />
be potentiated during aversive pictures and inhibited during<br />
pleasant pictures. If it is appetitive, it should be inhibited during<br />
unpleasant pictures and potentiated during pleasant pictures.<br />
Based on findings with <strong>the</strong> startle <strong>reflex</strong>, it was fur<strong>the</strong>r predicted<br />
that modulatory effects in ei<strong>the</strong>r case would be maximal for<br />
pleasant and aversive pictures <strong>of</strong> high intensity.<br />
The literature on affective <strong>modulation</strong> <strong>of</strong> startle and o<strong>the</strong>r<br />
<strong>reflex</strong>es provided a basis for alternative hypo<strong>the</strong>ses as well. One is<br />
that <strong>the</strong> post-auricular <strong>reflex</strong> might be facilitated by nonspecific<br />
arousal ra<strong>the</strong>r than valence, with magnitude greater during both<br />
pleasant and aversive pictures compared to neutral (cf. spinal T<br />
<strong>reflex</strong>; Bonnet et al., 1995). Ano<strong>the</strong>r is that <strong>the</strong> post-auricular<br />
<strong>reflex</strong> would be inhibited as a function <strong>of</strong> cross-modal attention,<br />
with <strong>reflex</strong> magnitude diminished during both pleasant and<br />
unpleasant pictures relative to neutral (cf. probe-elicited P300;<br />
Schupp et al., 1997).<br />
Method<br />
Participants<br />
Participants were 24 male undergraduates (M age 5 19.2 years,<br />
SD 5 1.25) recruited from psychology classes at <strong>the</strong> University <strong>of</strong><br />
Minnesota. The sample included only men because <strong>the</strong> current<br />
data were collected as part <strong>of</strong> a pilot for a project involving male<br />
prisoners. Individuals with visual or hearing impairments, as<br />
assessed via a screening questionnaire, were excluded from <strong>the</strong><br />
study. Students received course credit for <strong>the</strong>ir participation.<br />
Experimental Stimuli and Design<br />
Participants viewed digitized color photographs (22 pleasant, 22<br />
neutral, and 22 unpleasant) selected from <strong>the</strong> International<br />
Affective Picture System (IAPS; Center for <strong>the</strong> Study <strong>of</strong> Emotion
428 S.D. Benning, C.J. Patrick, and A.R. Lang<br />
and Attention, 1999). Fifty-four <strong>of</strong> <strong>the</strong> pictures were selected to<br />
represent specific <strong>the</strong>matic contents, as follows: 1<br />
Pleasant contents: erotic scenes (n 5 9; e.g., nude females,<br />
intimate couples); adventure scenes (n 5 9; e.g., cliff diving,<br />
motorcycle racing).<br />
Neutral contents: inactive people or neutral human faces<br />
(n 5 9); household objects or kitchen utensils (n 5 9).<br />
Unpleasant contents: scenes <strong>of</strong> victimization <strong>of</strong> o<strong>the</strong>r people<br />
(n 5 9; e.g., aggression, physical brutality, and combat);<br />
threatening figures or weapons directed at <strong>the</strong> viewer (n 5 9;<br />
e.g., pointed guns, menacing attackers).<br />
Subsets <strong>of</strong> low and high intensity pictures, as defined by IAPS<br />
normative ratings, were included in each emotional content<br />
category (erotic, adventure, victim, threat). High-intensity pleasant<br />
pictures were higher in rated valence and arousal, Ms(SDs) 5 7.33<br />
(0.31) and 6.49 (0.53), respectively, than low-intensity pleasant<br />
pictures, Ms (SDs) 5 5.92 (0.47) and 4.66 (0.63). High-intensity<br />
unpleasant pictures were lower in normative valence and higher in<br />
arousal, Ms(SDs) 5 2.79 (0.25) and 6.49 (0.52), respectively, than<br />
low-intensity unpleasant pictures, Ms(SDs) 5 3.91 (0.36) and 4.64<br />
(0.63). Low-intensity pleasant and unpleasant pictures were<br />
equidistant from neutral in terms <strong>of</strong> rated valence and arousal,<br />
as were high-intensity pleasant and unpleasant pictures.<br />
Between 3 s and 5 s after <strong>the</strong> onset <strong>of</strong> each <strong>of</strong> <strong>the</strong>se 54 pictures,<br />
a brief binaural white noise probe (50 ms, 105 dB,o10 ms rise<br />
time) was presented that elicited <strong>the</strong> post-auricular <strong>reflex</strong>. To<br />
diminish <strong>the</strong> predictability <strong>of</strong> <strong>the</strong> noises, nine no-probe picture<br />
trials were interspersed with <strong>the</strong> probe trials. Additionally, three<br />
probed picture trials (IAPS numbers 4650, 7080, and 9252) were<br />
included at <strong>the</strong> start <strong>of</strong> <strong>the</strong> series to familiarize participants with<br />
<strong>the</strong> stimuli and to habituate large initial startle reactions.<br />
Habituation trials and no-probe picture trials were excluded<br />
from <strong>the</strong> analyses.<br />
Noise probes were generated using a Coulbourn S81-02 white<br />
noise module and S82-24 audio amplifier. The probe was<br />
presented binaurally through Telephonics headphones (first half<br />
<strong>of</strong> participant sample) or Etymotic insert earphones (second<br />
half). Statistical tests revealed no significant effects <strong>of</strong> method <strong>of</strong><br />
noise delivery, so <strong>the</strong> data were collapsed across this factor in all<br />
analyses reported. The noise probes occurred 3, 4, or 5 s after<br />
picture onset. A total <strong>of</strong> nine probes were also delivered at<br />
varying points during intertrial intervals (ITIs) to reduce <strong>the</strong><br />
predictability <strong>of</strong> <strong>the</strong> noise stimulus.<br />
Six stimulus orders were used to balance <strong>the</strong> presentation <strong>of</strong><br />
pictures and startle probes across participants. As noted, each<br />
order included 3 habituation trials followed by 54 probed picture<br />
trials, interspersed with 9 no-probe picture trials. The 54 probed<br />
picture trials were organized into three blocks, each consisting <strong>of</strong><br />
three pleasant, three neutral, and three unpleasant pictures.<br />
Within and between orders, <strong>the</strong> positioning <strong>of</strong> pictures and<br />
1 The 54 probed pictures, listed by <strong>the</strong>ir IAPS identification numbers,<br />
were as follows: eroticF2381, 4000, 4233 (4617), 4274, 4230, 4653<br />
(4750), 4690, 4687, 4290 (4651); adventureF4533 (8032), 8041, 8033,<br />
5622 (8250), 5626, 5623, 8370 (8180), 8080, 8042; neutralF2190, 2210,<br />
2214, 2372, 2480, 2495, 2850, 2890, 9700, 7002, 7030, 7034, 7040, 7050,<br />
7150, 7205, 7705, 7710; victimF6010, 2520, 9594 (4621), 6571, 9400,<br />
6530 (3550), 9250, 3400, 6350 (3500); threatF2100 (6241), 2682, 2130,<br />
6242 (6244), 6370, 6243, 6510 (6250), 6260, 6230. The pictures in<br />
paren<strong>the</strong>ses are alternate exemplars from <strong>the</strong> same content category that<br />
were substituted within some stimulus orders to achieve counterbalancing<br />
<strong>of</strong> conditions (valence, content, intensity) across run orders.<br />
startle probes was counterbalanced such that all valence, content,<br />
and intensity conditions were represented equally across orders<br />
at each serial position. Not more than two pictures <strong>of</strong> <strong>the</strong> same<br />
valence occurred consecutively within any stimulus order, and<br />
pictures <strong>of</strong> <strong>the</strong> same content never appeared consecutively.<br />
During <strong>the</strong> experiment, participants sat in a padded recliner at<br />
a distance <strong>of</strong> 120 cm from a 21-in. computer monitor positioned<br />
directly in front <strong>of</strong> <strong>the</strong>m. Physiological responses were recorded<br />
using a PC computer running VPM data acquisition s<strong>of</strong>tware<br />
(version 11.2; Cook, Atkinson, & Lang, 1987). A second<br />
computer controlled picture presentation. The post-auricular<br />
<strong>reflex</strong> data for <strong>the</strong> current sample were collected as part <strong>of</strong> a<br />
larger sample investigation <strong>of</strong> emotion and picture viewing in<br />
which a variety <strong>of</strong> o<strong>the</strong>r response measures (i.e., heart rate, skin<br />
conductance, facial muscle activity, startle blink, EEG, and<br />
affective ratings) were recorded. 2 The current report is limited to<br />
<strong>the</strong> post-auricular data because this response measure was<br />
available for only a subset <strong>of</strong> participants and we wished to<br />
highlight findings for this novel measure here.<br />
Physiological Measures<br />
The post-auricular <strong>reflex</strong> was measured as described by Sollers<br />
and Hackley (1997). The pinna (outer ear) was pulled forward,<br />
and behind each ear, a pair <strong>of</strong> Med Associates 0.25 cm Ag-AgCl<br />
electrodes was positioned around <strong>the</strong> tendon <strong>of</strong> insertion for <strong>the</strong><br />
post-auricular muscleFreadily identifiable in most cases as a<br />
fibrous strip connecting <strong>the</strong> pinna and <strong>the</strong> scalp midway up <strong>the</strong><br />
pinna. One electrode was placed directly adjacent to <strong>the</strong> tendon<br />
on <strong>the</strong> surface <strong>of</strong> <strong>the</strong> pinna, and <strong>the</strong> o<strong>the</strong>r electrode was placed on<br />
<strong>the</strong> scalp over <strong>the</strong> post-auricular muscle. Prior to placement, sites<br />
were scrubbed with conductive gel to reduce impedances below 5<br />
kO. Raw electromyographic (EMG) signals for each ear were<br />
recorded for 50 ms before noise probe onset until 250 ms after<br />
probe onset using a Coulbourn S75-01 high gain bioamplifier.<br />
The sampling rate was 1,000 Hz.<br />
The data were filtered on-line with a bandpass <strong>of</strong> 8–1,000 Hz,<br />
and rectified <strong>of</strong>f-line using Matlab s<strong>of</strong>tware (MathWorks, 2000).<br />
Post-auricular <strong>reflex</strong>es were scored after averaging <strong>the</strong> rectified<br />
waveformsacrosstrialswithinconditions(Hackleyetal.,1987;<br />
Sollers & Hackley, 1997). The magnitude <strong>of</strong> <strong>the</strong> post-auricular<br />
<strong>reflex</strong> was scored from <strong>the</strong> aggregate waveform as a baseline-topeak<br />
measure. The peak was calculated as <strong>the</strong> maximum EMG<br />
activity within a window <strong>of</strong> 8–30 ms after noise probe onset, 3<br />
whereas <strong>the</strong> baseline was calculated as <strong>the</strong> average rectified <strong>postauricular</strong><br />
EMG activity during <strong>the</strong> 50 ms before <strong>the</strong> onset <strong>of</strong> <strong>the</strong><br />
noise probe (Sollers & Hackley, 1997). Although all participants<br />
showed substantial increases in post-auricular EMG activity<br />
during <strong>the</strong> 8–30 ms post-probe-onset window, several participants<br />
had <strong>reflex</strong> magnitudes that were difficult to differentiate from<br />
background EMG activity. Therefore, <strong>the</strong> peak <strong>of</strong> each aggregate<br />
waveform was manually scored to ensure that <strong>the</strong> algorithm<br />
detected responses appropriately (cf. Sollers & Hackley, 1997); in<br />
all but three aggregate waveforms, <strong>the</strong> manually assigned peak<br />
was identical to <strong>the</strong> algorithmically picked peak.<br />
2 Startle blink data for this subset <strong>of</strong> participants followed <strong>the</strong> usual<br />
valence <strong>modulation</strong> pattern, with blink magnitudes during pleasant<br />
pictures inhibited and those during unpleasant pictures potentiated<br />
compared to those during neutral pictures (cf. Benning, Patrick, Hicks,<br />
Blonigen, & Lang, 2001).<br />
3 Analyses conducted with <strong>the</strong> peak calculated as <strong>the</strong> mean <strong>postauricular</strong><br />
activity within <strong>the</strong> 8–30 ms post-probe window and <strong>the</strong> baseline<br />
calculated as above yielded identical patterns <strong>of</strong> results.
Emotion and <strong>the</strong> post-auricular <strong>reflex</strong> 429<br />
Procedure<br />
Participants provided informed written consent and <strong>the</strong>n<br />
completed a biographical form that screened for physical<br />
ailments, medication use, and visual and auditory impairments.<br />
Following electrode attachment, participants were advised <strong>the</strong>y<br />
would be viewing a series <strong>of</strong> pictures and rating <strong>the</strong>ir reactions to<br />
each. They were instructed to watch each picture <strong>the</strong> entire time it<br />
was on <strong>the</strong> screen and disregard occasional noises occurring<br />
through <strong>the</strong> headphones or earphones. Before <strong>the</strong> main picture<br />
series began, participants were given a demonstration <strong>of</strong> <strong>the</strong> Self-<br />
Assessment Manikin (SAM; Lang, 1980) rating procedure, in<br />
which <strong>the</strong>y characterized <strong>the</strong>ir reactions to pictures on dimensions<br />
<strong>of</strong> valence, arousal, and dominance (cf. Lang, 1980), as well<br />
as interest (cf. Levenston et al., 2000). Each <strong>of</strong> <strong>the</strong> 66 pictures was<br />
preceded by a blank screen for 3 s and was <strong>the</strong>n presented for 6 s.<br />
Seven seconds after picture <strong>of</strong>fset, <strong>the</strong> ratings display appeared<br />
and <strong>the</strong> participant completed <strong>the</strong> four ratings. The interval<br />
between completion <strong>of</strong> <strong>the</strong> ratings and <strong>the</strong> onset <strong>of</strong> <strong>the</strong> next<br />
picture ranged between 8 s and 14 s, averaging 11 s.<br />
Data Processing and Analysis<br />
Because <strong>the</strong> post-auricular <strong>reflex</strong> is a ‘‘micro<strong>reflex</strong>’’ with a low<br />
signal-to-noise ratio (cf. Hackley et al., 1987), averaging <strong>of</strong> trials<br />
within condition was required to score <strong>the</strong> <strong>reflex</strong>. For one set <strong>of</strong><br />
analyses, we aggregated <strong>the</strong> rectified post-auricular waveforms<br />
by <strong>the</strong>matic content within picture valence category. Because<br />
<strong>the</strong>re were equivalent numbers <strong>of</strong> human and object pictures<br />
within <strong>the</strong> neutral category, we aggregated across trials within<br />
each <strong>of</strong> <strong>the</strong>se neutral contents, and we also aggregated across<br />
trials for erotic and adventure contents within <strong>the</strong> pleasant<br />
category, and victim and threat contents within <strong>the</strong> unpleasant<br />
category. Each aggregate waveform thus incorporated data for<br />
nine picture trials. A nine-trial aggregate waveform incorporating<br />
data for all ITI probes was also formed. Post-auricular <strong>reflex</strong><br />
peak magnitude was scored from <strong>the</strong>se aggregate waveforms,<br />
along with mean post-auricular muscle activity during <strong>the</strong> preprobe<br />
baseline. Effects <strong>of</strong> picture valence were examined by<br />
collapsing magnitude scores across contents within valence<br />
category. A subsidiary set <strong>of</strong> analyses was performed to examine<br />
effects <strong>of</strong> affective stimulus intensity on post-auricular <strong>reflex</strong><br />
magnitude. For <strong>the</strong>se analyses, we aggregated post-auricular<br />
waveforms by picture intensity level (low, high) within pleasant<br />
and unpleasant valence categories, again yielding aggregate<br />
waveforms consisting <strong>of</strong> nine trials per condition, and extracted<br />
peak magnitude scores from <strong>the</strong>se aggregates.<br />
Using <strong>the</strong> resultant scores, <strong>the</strong> following analyses were<br />
performed:<br />
1. To examine <strong>the</strong> effect <strong>of</strong> visual foreground engagement on<br />
post-auricular <strong>reflex</strong> magnitude, we conducted a one-way<br />
repeated measures ANOVA in which <strong>the</strong> neutral picture<br />
condition was compared against <strong>the</strong> ITI (no-picture) condition.<br />
A parallel one-way ANOVA was conducted to examine<br />
<strong>the</strong> effect <strong>of</strong> foreground engagement on post-auricular<br />
baseline activity.<br />
2. To examine effects <strong>of</strong> picture valence (pleasant, neutral,<br />
unpleasant) and ear recording site (left, right) on <strong>postauricular</strong><br />
magnitude, a 3 2 multivariate ANOVA was<br />
performed with <strong>the</strong>se variables included as within-subjects<br />
factors. Significant main effects were subsequently examined<br />
in terms <strong>of</strong> orthogonal linear (e.g., pleasant vs. unpleasant)<br />
and quadratic (e.g., pleasant/unpleasant vs. neutral) contrasts<br />
(cf. Bradley, Cuthbert, & Lang, 1993; Bonnet et al., 1995;<br />
Moulder et al., 1995). A supplemental one-way MANOVA<br />
was performed to examine effects <strong>of</strong> picture valence on<br />
baseline post-auricular activity.<br />
3. With regard to picture content and intensity, we were<br />
interested in whe<strong>the</strong>r affect-<strong>modulation</strong> effects for <strong>the</strong> <strong>postauricular</strong><br />
<strong>reflex</strong> would be tied to specific contents or to<br />
pictures <strong>of</strong> high intensity. We addressed <strong>the</strong>se questions by<br />
performing two sets <strong>of</strong> planned contrasts using one-way<br />
ANOVAs. One involved comparisons <strong>of</strong> affective contents<br />
within each valence against each o<strong>the</strong>r, and <strong>the</strong> o<strong>the</strong>r entailed<br />
contrasts <strong>of</strong> pleasant and unpleasant pictures <strong>of</strong> each intensity<br />
(low, high) against each o<strong>the</strong>r.<br />
An a level <strong>of</strong> .05 was used as <strong>the</strong> criterion for significance in all<br />
statistical tests.<br />
Results<br />
Picture Foreground versus ITI<br />
Post-auricular <strong>reflex</strong> magnitudes were smaller during neutral<br />
pictures compared with ITIs, Ms(SDs) 5 6.64 (6.18) mVand 7.98<br />
(5.71) mV, respectively, F(1,23) 5 4.65, p 5 .04, Z 2 5 .17. There was<br />
also a trend for baseline post-auricular EMG activity during neutral<br />
pictures to be smaller than during ITIs, Ms(SDs) 5 0.74 (0.32) mV<br />
and 0.84 (0.36) mV, respectively, F(1,23) 5 2.92, p 5 .10, Z 2 5 .11.<br />
Picture Valence<br />
Figure 1 displays grand average waveforms for <strong>the</strong> post-auricular<br />
<strong>reflex</strong> by picture valence, with average <strong>reflex</strong> magnitudes depicted<br />
in <strong>the</strong> inset bar graph. A significant main effect <strong>of</strong> picture valence<br />
was found for post-auricular <strong>reflex</strong> magnitude, F(2,22) 5 4.16,<br />
p 5 .03, Z 2 5 .27. 4 As shown in Figure 1, <strong>the</strong> post-auricular <strong>reflex</strong><br />
was larger during pleasant pictures than unpleasant pictures,<br />
linear Valence F(1,23) 5 8.50, p 5 .01, Z 2 5 .27. Follow-up<br />
paired t tests showed that post-auricular magnitudes tended to<br />
be greater during pleasant than neutral pictures, t(23) 5 1.94,<br />
p 5 .07, whereas post-auricular magnitudes during neutral and<br />
unpleasant pictures did not differ, t(23) 5 1.11, p 5 .28. No main<br />
effect <strong>of</strong> ear recording site (right vs. left) was found,<br />
F(1,23) 5 1.00, p 5 .33, Z 2 5 .04, and <strong>the</strong> Ear Valence interaction<br />
was not significant, F(2,22) 5 0.31, p 5 .74, Z 2 5 .01.<br />
As fur<strong>the</strong>r evidence <strong>of</strong> <strong>the</strong> consistency <strong>of</strong> <strong>the</strong> post-auricular<br />
valence <strong>modulation</strong> effect, 75% (18/24; 95% confidence interval<br />
5 55%–88%) <strong>of</strong> participants showed numerically greater<br />
post-auricular <strong>reflex</strong> magnitudes during pleasant compared with<br />
unpleasant pictures, and 71% (17/24; 95% confidence interval<br />
5 51%–85%) showed numerically greater post-auricular<br />
<strong>reflex</strong> magnitudes during pleasant versus neutral pictures. Both<br />
proportions significantly exceeded chance, according to formulae<br />
provided by Newcombe (1998).<br />
The MANOVA with picture valence as <strong>the</strong> within-subjects<br />
factor and mean pre-probe baseline post-auricular EMG activity<br />
4 A supplementary analysis was performed in which picture trials were<br />
subdivided into three sequential blocks, and post-auricular waveforms<br />
were aggregated by valence (pleasant, neutral, unpleasant) within each<br />
block. As in <strong>the</strong> primary MANOVA, this analysis yielded a significant<br />
valence main effect, and also a significant main effect for block,<br />
F(2,22) 5 6.77, p 5 .011, Z 2 5 .338, but no Block Valence interaction,<br />
F(4,20) 5 0.95, p 5 .441, Z 2 5 .040. Thus, while <strong>the</strong> magnitude <strong>of</strong> <strong>the</strong><br />
post-auricular <strong>reflex</strong> declined over <strong>the</strong> session, <strong>the</strong> emotional <strong>modulation</strong><br />
<strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> remained constantFconsistent with <strong>the</strong><br />
findings <strong>of</strong> Bradley et al. (1993) for <strong>the</strong> startle blink <strong>reflex</strong>.
430 S.D. Benning, C.J. Patrick, and A.R. Lang<br />
PA EMG Activity (µV)<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
0<br />
-25 0 25 50 75 100 125<br />
as <strong>the</strong> dependent variable revealed no effect <strong>of</strong> picture valence,<br />
F(2,22) 5 0.30, p 5 .74, Z 2 5 .03. Post-auricular baseline Ms<br />
(SDs) for pleasant, neutral, and unpleasant pictures were as<br />
follows: 0.74 (0.29) mV, 0.75 (0.32) mV, and 0.72 (0.34) mV,<br />
respectively.<br />
Affective Content and Intensity<br />
Within pleasant contents, <strong>the</strong> magnitude <strong>of</strong> post-auricular <strong>reflex</strong>es<br />
during erotic pictures did not differ from those during adventure<br />
pictures, Ms 5 7.23 and 7.21 mV (SDs 5 5.86 and 6.12), respectively,<br />
F(1,23) 5 0.00, p 5 .96, Z 2 5 .00. Likewise, within unpleasant<br />
contents, post-auricular <strong>reflex</strong> magnitudes did not differ<br />
between victim and threat pictures, Ms 5 6.24 and 6.38 mV(SDs 5<br />
5.20 and 5.58), respectively, F(1,23) 5 0.11, p 5 .75, Z 2 5 .01.<br />
Post-auricular <strong>reflex</strong> magnitudes were significantly greater during<br />
high-intensity pleasant pictures than during high-intensity<br />
unpleasant pictures, Ms 5 8.11 and 6.81 mV (SDs 5 6.87 and<br />
5.59), respectively, F(1,23) 5 7.78, p 5 .01, Z 2 5 .25, but <strong>postauricular</strong><br />
<strong>reflex</strong> magnitudes during low-intensity pleasant and<br />
unpleasant pictures did not differ significantly from each o<strong>the</strong>r,<br />
Ms 5 7.77 and 7.18 mV (SDs 5 6.48 and 6.18), respectively,<br />
F(1,23) 5 2.31, p 5 .14, Z 2 5 .09.<br />
Discussion<br />
Pleasant<br />
Neutral<br />
Unpleasant<br />
PA Peak Magnitude (µV)<br />
8<br />
7<br />
6<br />
5<br />
Time Relative to Probe Onset (ms)<br />
Pleasant Neutral Unpleasant<br />
Picture Valence<br />
Figure 1. Grand average post-auricular (PA) <strong>reflex</strong> waveforms (main<br />
panel) and magnitudes SE (inset) by picture valence.<br />
Our findings indicate that <strong>the</strong> magnitude <strong>of</strong> <strong>the</strong> post-auricular<br />
<strong>reflex</strong> is reliably modulated by emotional valence. Specifically, we<br />
found that <strong>the</strong> post-auricular <strong>reflex</strong> tended to be potentiated<br />
during viewing <strong>of</strong> pleasant pictures compared with neutral, and<br />
inhibited during viewing <strong>of</strong> aversive pictures, particularly during<br />
high-intensity pictures. 5 This linear <strong>modulation</strong> pattern is<br />
5 In a previous investigation <strong>of</strong> affect and attention during picture<br />
viewing that employed a wider range <strong>of</strong> probe times (Bradley, Drobes, &<br />
Lang, 1996), measurement <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> was included along<br />
with assessment <strong>of</strong> blink startle and tone probe responses (M. M.<br />
Bradley, pers. comm., May 7, 2003). Although post-auricular <strong>reflex</strong><br />
magnitude in this study was somewhat higher during pleasant versus<br />
unpleasant pictures, <strong>the</strong> difference was not significant. On <strong>the</strong> o<strong>the</strong>r hand,<br />
more recently, a significant linear valence effect on post-auricular <strong>reflex</strong><br />
magnitude, mirroring <strong>the</strong> finding reported here, was obtained by investigators<br />
at Indiana University (Ames, Merritt, Stout, & Hetrick, 2003).<br />
opposite to that observed for <strong>the</strong> defensive startle blink <strong>reflex</strong><br />
(Lang et al., 1990). Analyses <strong>of</strong> post-auricular muscle activity<br />
during <strong>the</strong> pre-probe baseline period indicated that this modulatory<br />
effect was not attributable to differences in baseline EMG<br />
(as would be expected if <strong>the</strong>se results were due to head motion or<br />
eye gaze; Patuzzi & O’Beirne, 1999; Stekelenburg & van Boxtel,<br />
2001, 2002), because baseline post-auricular activity did not differ<br />
across picture valence categories. On <strong>the</strong> o<strong>the</strong>r hand, baseline<br />
post-auricular activity was reduced in connection with attenuated<br />
post-auricular <strong>reflex</strong> response during viewing <strong>of</strong> neutral foregrounds<br />
in relation to ITIs. This finding is consistent with <strong>the</strong> idea<br />
that tonic activity in various somatic systems, including <strong>the</strong> <strong>postauricular</strong><br />
musculature, decreases to enhance perceptual sensitivity<br />
during orienting (Stekelenburg & van Boxtel, 2001, 2002).<br />
Lang et al. (1990) proposed a motivational priming hypo<strong>the</strong>sis<br />
to account for modulatory effects <strong>of</strong> emotional valence on<br />
<strong>the</strong> startle <strong>reflex</strong>. Citing Konorski (1967), <strong>the</strong>y postulated that<br />
defensive <strong>reflex</strong>es like <strong>the</strong> startle blink are primed during negative<br />
emotional states and inhibited during positive emotional states.<br />
The potentiation effects observed for <strong>the</strong> neck (Cassella, Harty,<br />
& Davis, 1986), blink (Lang et al., 1990), and whole-body (Davis<br />
et al., 1982) reactions to noise probes under conditions <strong>of</strong> threat<br />
are consistent with <strong>the</strong> idea that <strong>the</strong>se are components <strong>of</strong> a<br />
common defensive startle response. Although <strong>the</strong> post-auricular<br />
<strong>reflex</strong> is likewise elicited by a sudden, loud noise, our data argue<br />
against <strong>the</strong> post-auricular <strong>reflex</strong> being a short latency component<br />
<strong>of</strong> <strong>the</strong> defensive startle <strong>reflex</strong> (Hackley, 1993). Indeed, <strong>the</strong>re is<br />
evidence that <strong>the</strong> post-auricular <strong>reflex</strong> may have a different<br />
circuitry than <strong>the</strong> startle <strong>reflex</strong> (Cassella & Davis, 1986; Hackley,<br />
1993), though more recent research with specific excitotoxic<br />
lesions in <strong>the</strong> circuitry <strong>of</strong> <strong>the</strong> pinna <strong>reflex</strong> in rats (ra<strong>the</strong>r than with<br />
general fiber-destroying electrolytic lesions; Cassella & Davis,<br />
1986) suggests that <strong>the</strong> circuitry for <strong>the</strong> post-auricular <strong>reflex</strong> may<br />
also include <strong>the</strong> nucleus reticularis pontis caudalis (Davis,<br />
Walker, & Yee, 1999; Li & Frost, 1996).<br />
Lang et al.’s (1990) motivational priming hypo<strong>the</strong>sis postulates<br />
that appetitive <strong>reflex</strong>es (salivation) would be facilitated<br />
during positive emotional states and inhibited during negative<br />
emotional states. In this regard, <strong>the</strong> post-auricular <strong>reflex</strong> behaved<br />
as an appetitive <strong>reflex</strong> in <strong>the</strong> current study, as it was potentiated<br />
during viewing <strong>of</strong> pleasant pictures and attenuated during<br />
viewing <strong>of</strong> unpleasant pictures. The fact that <strong>the</strong> post-auricular<br />
<strong>reflex</strong> increased during pleasant picture viewing indicates that<br />
some o<strong>the</strong>r mechanism (appetitive motor priming) operated<br />
against <strong>the</strong> influence <strong>of</strong> cross-modal sensory engagementFanalogous<br />
to <strong>the</strong> impact <strong>of</strong> defense system activation on <strong>the</strong> startle<br />
<strong>reflex</strong> during unpleasant pictures, which opposes <strong>the</strong> inhibitory<br />
influence <strong>of</strong> cross-modal attention in picture viewing (Cuthbert et<br />
al., 1996; Lang et al., 1997).<br />
In <strong>the</strong> case <strong>of</strong> <strong>the</strong> startle <strong>reflex</strong>, a specific neural mechanism<br />
has been identified to account for <strong>the</strong> facilitatory effect <strong>of</strong><br />
aversive foreground stimulationFnamely, an input from <strong>the</strong><br />
amygdala to <strong>the</strong> startle <strong>reflex</strong> circuit (Davis et al., 1982). A<br />
corresponding input from <strong>the</strong> brain’s appetitive system to <strong>the</strong><br />
post-auricular circuit could conceivably account for potentiation<br />
<strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> during pleasant foreground stimulation.<br />
Research on <strong>the</strong> neural circuitry <strong>of</strong> <strong>the</strong> pinna <strong>reflex</strong>, <strong>the</strong><br />
animal analogue <strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong>, indicates that <strong>the</strong><br />
motoneurons <strong>of</strong> <strong>the</strong> facial nerve that innervates <strong>the</strong> pinna receive<br />
additional input from <strong>the</strong> retrorubral nucleus (Li & Frost, 1996),<br />
a midbrain dopaminergic structure that has been associated with<br />
sensitivity to reward stimuli in rats (Waraczynski & Perkins,
Emotion and <strong>the</strong> post-auricular <strong>reflex</strong> 431<br />
2000) and with motor deficits arising from Parkinson’s disease in<br />
humans (Heim et al., 2002).<br />
An alternative possibility is that increased post-auricular<br />
reactivity reflects enhanced orienting to <strong>the</strong> noise probe stimulus.<br />
Indeed, <strong>the</strong>re is evidence that unexpected noises can evoke<br />
observable movement <strong>of</strong> <strong>the</strong> post-auricular (pinna) muscle in<br />
primates in whom this muscle serves more than a vestigial<br />
function. Naturalistic observations <strong>of</strong> Hanuman langurs, a lower<br />
primate species, have revealed that in adult males, loud and<br />
surprising sounds yield brief (i.e., 0.2–0.3 s) movements <strong>of</strong> both<br />
<strong>the</strong> pinna and <strong>the</strong> head in <strong>the</strong> direction <strong>of</strong> <strong>the</strong> noise (Trivedi &<br />
Mohnot, 2002), suggesting that <strong>the</strong> pinna <strong>reflex</strong> serves an<br />
orienting function in this primate species. It may be that states <strong>of</strong><br />
attentional engagement, such as those associated with viewing <strong>of</strong><br />
pleasurable pictures, facilitate this phasic <strong>reflex</strong>ive orienting<br />
reaction. However, because pleasant and unpleasant pictures<br />
engage more attention than neutral (Lang et al., 1990, 1997), <strong>the</strong><br />
predicted attentional pattern would have been one <strong>of</strong> <strong>postauricular</strong><br />
<strong>reflex</strong> inhibition for both affective categories compared<br />
to neutral. Fur<strong>the</strong>rmore, juveniles and females <strong>of</strong> this species<br />
exhibit greater short-duration pinna movements primarily<br />
during play, feeding, and foraging for food (Trivedi & Mohnot,<br />
2002), suggesting heightened responsiveness <strong>of</strong> this <strong>reflex</strong>ive<br />
system specifically during pleasurable activities.<br />
Never<strong>the</strong>less, <strong>the</strong>re is evidence that unpleasant pictures also<br />
engage attention (Lang et al., 1997), so it is possible that some<br />
types <strong>of</strong> aversive pictures might likewise facilitate <strong>the</strong> <strong>postauricular</strong><br />
<strong>reflex</strong>. The current study focused on threat and physical<br />
attack pictures that tend to be perceived as fearful. Modulatory<br />
Ames, K. A., Merritt, N. P., Stout, K., & Hetrick, W. P. (2003).<br />
Differential effects <strong>of</strong> affective <strong>modulation</strong> on orbicularis and <strong>postauricular</strong><br />
indices <strong>of</strong> startle. Psychophysiology, 40, S22.<br />
Anthony, B. J., & Graham, F. K. (1985). Blink <strong>reflex</strong> modification by<br />
selective attention: Evidence for <strong>the</strong> <strong>modulation</strong> <strong>of</strong> automatic<br />
processing. Biological Psychology, 21, 43–59.<br />
Benning, S. D., Patrick, C. J., Hicks, B., Blonigen, D., & Lang, A. R.<br />
(2001). Affective <strong>modulation</strong> <strong>of</strong> blink startle and post-auricular<br />
<strong>reflex</strong>es to noise probes. Psychophysiology, 38, S24.<br />
Bonnet, M., Bradley, M. M., Lang, P. J., & Requin, J. (1995).<br />
Modulation <strong>of</strong> spinal <strong>reflex</strong>es: Arousal, pleasure, action. Psychophysiology,<br />
32, 367–372.<br />
Bradley, M. M., Codispoti, M., Cuthbert, B. N., & Lang, P. J. (2001).<br />
Emotion and motivation I: Defensive and appetitive reactions in<br />
picture processing. Emotion, 1, 276–298.<br />
Bradley, M. M., Cuthbert, B. N., & Lang, P. J. (1993). Emotion, novelty,<br />
and <strong>the</strong> startle <strong>reflex</strong>: Habituation in humans. Behavioral Neuroscience,<br />
107, 970–980.<br />
Bradley, M. M., Drobes, D., & Lang, P. J. (1996). A probe for all<br />
reasons: Reflex and RTmeasures in perception. Psychophysiology, 33,<br />
S25.<br />
Braff, D. L., Geyer, M. A., & Swerdlow, N. R. (2001). Human studies <strong>of</strong><br />
prepulse inhibition <strong>of</strong> startle: Normal subjects, patient groups, and<br />
pharmacological studies. Psychopharmacology, 156, 234–258.<br />
Cassella, J. V., & Davis, M. (1986). Habituation, prepulse inhibition, fear<br />
conditioning, and drug <strong>modulation</strong> <strong>of</strong> <strong>the</strong> acoustically elicited pinna<br />
<strong>reflex</strong> in rats. Behavioral Neuroscience, 100, 39–44.<br />
Cassella, J. V., Harty, P. T., & Davis, M. (1986). Fear conditioning, prepulse<br />
inhibition and drug <strong>modulation</strong> <strong>of</strong> a short latency startle<br />
response measured electromyographically from neck muscles in <strong>the</strong><br />
rat. Physiology and Behavior, 36, 1187–1191.<br />
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REFERENCES<br />
effects may differ for o<strong>the</strong>r aversive contents, such as sadness,<br />
disgust, or mutilation pictures. It will also be important in future<br />
research to examine effects for o<strong>the</strong>r pleasurable picture contents<br />
(e.g., babies, animals, food). In addition, <strong>the</strong>re are o<strong>the</strong>r<br />
limitations <strong>of</strong> <strong>the</strong> current study that need to be addressed before<br />
firm conclusions can be advanced regarding <strong>the</strong> post-auricular<br />
<strong>reflex</strong> as an index <strong>of</strong> emotion. The current sample included only<br />
men; thus, it will be important to replicate <strong>the</strong>se findings in<br />
women. Fur<strong>the</strong>rmore, it will be important to assess <strong>modulation</strong><br />
<strong>of</strong> <strong>the</strong> post-auricular <strong>reflex</strong> in emotional processing tasks o<strong>the</strong>r<br />
than picture viewing. A key question is whe<strong>the</strong>r potentiation <strong>of</strong><br />
<strong>the</strong> post-auricular <strong>reflex</strong> would be observed in appetitive<br />
conditioning or reward anticipation contexts, as is true for<br />
startle in corresponding aversive paradigms (e.g., Hamm,<br />
Greenwald, Bradley, & Lang, 1993; Patrick & Berthot, 1995).<br />
Affirmative findings would lend support to <strong>the</strong> idea that <strong>the</strong> <strong>postauricular</strong><br />
<strong>reflex</strong> is primed during appetitive states. Finally, in light<br />
<strong>of</strong> recent data indicating that hedonic valence and approach–<br />
withdrawal aspects <strong>of</strong> emotion are dissociable, it would be<br />
informative to assess whe<strong>the</strong>r <strong>the</strong> post-auricular <strong>reflex</strong> is<br />
enhanced or inhibited during a negatively valent approach state<br />
(e.g., anger; Harmon-Jones & Sigelman, 2001).<br />
Notwithstanding <strong>the</strong>se limitations, <strong>the</strong> findings <strong>of</strong> our study<br />
are intriguing. They suggest that <strong>the</strong> post-auricular <strong>reflex</strong>, which<br />
is evoked by <strong>the</strong> same acoustic probe as <strong>the</strong> startle <strong>reflex</strong>, may<br />
provide an index <strong>of</strong> appetitive system activation. If so, this<br />
<strong>reflex</strong>ive measure could provide a valuable tool for studying basic<br />
appetitive processes and investigating deficiencies in positive<br />
affect associated with psychopathology.<br />
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(Received March 4, 2003; Accepted October 13, 2003)