Emotional specificity of startle potentiation during the

early stages of picture viewing

JAMES STANLEYand ROBERT G. KNIGHTDepartment of Psychology, University of Otago, Dunedin, New Zealand

Abstract

Potentiation of the startle blink reflex shortly after picture onset has only been reported in a sample of high animal-fear

participants during fear-evoking stimuli. The experiment tested the emotional specificity of startle reflex modification

at early (300 ms) and late (2–5 s) stages of picture viewing in an unselected sample (n5 55). Participants viewed two

negative picture categories, threat and disgust contents, in addition to neutral and positive pictures. Blink potentiation

occurred for threat contents at both probe times, relative to neutral responses. Disgust contents only potentiated blinks

relative to positive content responses. These results are inconsistent with a basic, prepulse interpretation of early startle

modification and suggest that affective modification can be observed shortly after picture onset, depending on the

specific emotional content of the picture.

Descriptors: Emotion, Startle, Reflex modification, Time course, Prepulse inhibition, Blink reflex

The startle reflex is reliably potentiated when elicited several

seconds after the onset of an emotionally negative picture stim-

ulus (e.g., Vrana, Spence, & Lang, 1988; for an in-depth review,

see Bradley, Cuthbert, & Lang, 1999). At shorter picture-to-

probe onset latencies (o500ms), startle blink modification dur-

ing negative-content pictures has shown either reflex inhibition

relative to neutral content startle (Bradley, Cuthbert, & Lang,

1993; Bradley & Lang, 2001; Levenston, Patrick, Bradley, &

Lang, 2000) or no difference between negative and neutral con-

tent responding (Codispoti, Bradley, & Lang, 2001). The results

of these studies testing the time course of emotional processing

are consistent with findings from the field of prepulse modifica-

tion of the startle reflex. The presentation of a prepulse (usually

an acoustic tone) immediately prior to elicitation of the startle

reflex sets in motion inhibitory mechanisms designed to protect

the processing of the initial stimulus from external influence

(Graham, 1992)Fin this case, protecting the prepulse stimulus

from the subsequent startle probe. The observed dampening of

the elicited reflex is referred to as prepulse inhibition (PPI).

Presentation of an acoustic tone prepulse between 30 and

500ms prior to startle elicitation leads to significant startle blink

inhibition, relative to no-prepulse startle instances (Anthony,

1985; Norris & Blumenthal, 1996). At longer latencies (e.g.,

800ms in Norris & Blumenthal, 1996), prepulse presentation has

no effect on blink magnitude; in experiments using affective pic-

tures as prepulse, startle reflex magnitude at probe latencies

longer than 800ms depends on the emotional valenceFpositive,

neutral, or negativeFof the picture (Bradley et al., 1993; Bradley

& Lang, 2001; Levenston et al., 2000). The reflex inhibition ob-

served for both negative and positive picture stimuli at probe

times earlier than 800ms has been interpreted as evidence for PPI

caused by the onset of a motivationally relevant stimulus (Brad-

ley et al., 1993).

In comparison, a sample of snake/spider aversive individuals

showed significant potentiation of the startle blink reflex as early

as 300ms after picture onset for their feared snake or spider

stimuli (Globisch, Hamm, Esteves, & Ohman, 1999). Low-fear

participants in this study showed no significant blink potentiat-

ion for these picture contents, regardless of the delay between

picture onset and startle probe presentation. These effects were

independent of the length of the picture presentation period (ei-

ther 6 s or 150ms, as a between-subjects manipulation), leading

the authors to conclude that ‘‘fear responses can be activated very

rapidly and with minimal stimulus input’’ (Globisch et al., 1999,

p. 73; Ohman, 1993).

Two other studies have reported blink potentiation at 250ms

for negative relative to positive pictures (Vanman, Boehmelt,

Dawson, & Schell, 1996, Experiment 2; Vanman, Dawson, &

Brennan, 1998). These experiments are somewhat confounded

by the absence of a neutral picture condition to test whether this

difference is due to startle potentiation for negative pictures, in-

hibition for positive pictures, or both. Participants also previewed

the pictures prior to the startle elicitation study, which the authors

concede may speed up subsequent processing of the pictures’

This researchwas completed in partial fulfillment of requirements for a

Doctor of Philosophy degree by James Stanley, under the supervision of

Robert G. Knight. The article was prepared with the aid of an Otago

University BridgingGrant to the first author. Aspects of this researchwere

previously presented at the Annual Meeting of the Society for Psycho-

physiological Research, October 2002, in Washington D.C. We acknowl-

edge the suggestions of three anonymous reviewers for improving this

article. James Stanley is now at the University of Birmingham, England.

Address reprint requests to: James Stanley, School of Psychology,

Birmingham University, Edgbaston, Birmingham, B15 2TT, United

Kingdom; e-mail: jstanley@psy.otago.ac.nz.

Psychophysiology, 41 (2004), 935–940. Blackwell Publishing Inc. Printed in the USA.Copyright r 2004 Society for Psychophysiological ResearchDOI: 10.1111/j.1469-8986.2004.00242.x

935

emotional content (Vanman et al., 1996). In the absence of such

previewing, no modification was observed at 250ms (Vanman et

al., 1996, Experiment 1). These observations of differential startle

for negative and positive contents at early probe times (Globisch et

al., 1999; Vanman et al., 1996, Experiment 2; Vanman et al., 1998)

appear inconsistent with a basic prepulse interpretation of early

picture processing and startle modification.

Hawk and Cook (2000) suggested that differential modifica-

tion for positive and negative pictures at short picture-to-probe

onset latencies may be due to PPI mechanisms being dampened

during viewing of negative pictures. This hypothesis was tested

by an experimental design combining the PPI and emotional

modification paradigms: While participants viewed a series of

affective pictures, an acoustic prepulse was presented 120ms be-

fore startle elicitation (between 3 and 5.5 s after picture onset).

Although the prepulse successfully inhibited startle, the results

indicated that the degree of PPI was consistent across positive,

neutral, and negative picture contents. Bradley and Lang (2001)

proposed that startle modification at the early stages of picture

viewing would depend on both reflex-inhibiting processes initi-

ated by the onset of a motivationally relevant picture, and emo-

tional reflex modification engendered by the picture’s valence

content. For negative picture contents, startle blink modification

will be influenced by both reflex-inhibiting attentional demands

and reflex-augmenting emotional processes, the latter being de-

pendent on the degree of stimulus aversiveness. It appears likely

from the above evidence that the differential startle modification

observed between positive and negative pictures at 250–300ms

(Globisch et al., 1999; Vanman et al., 1996, Experiment 2; Van-

man et al., 1998) is due to the activation of aversive startle po-

tentiation circuits rather than differences in PPI mechanisms

during negative and positive valence categories. The two-process

hypothesis thus provides a reasonable explanation of how the

highly aversive negative stimuli used in Globisch et al. (1999)

produced significant blink potentiation by 300ms.

There are two further important differences between Globisch

et al. (1999) and those experiments showing no blink potentiation

at 300ms (Bradley et al., 1993; Bradley & Lang, 2001; Codispoti

et al., 2001; Levenston et al., 2000). First, the use of a highly

fearful participant sample in Globisch et al. suggests that early

startle potentiation by negative emotional content may be specific

to high-fear individuals only, rather than specific to highly aversive

stimuli. Second, Globisch et al. used only threatening stimuli in

their negative picture category, whereas in the other studies cited

the negative condition consists of a variety of negative stimuli. The

following section considers whether startle modification differs

between certain categories of negative picture stimuli.

Emotional Specificity of Startle Potentiation

A central premise of the affective startlemodification paradigm is

that the systems responsible for these modification processes are

organized by the simple distinction of appetitive and aversive

drive systems (Lang, Bradley, & Cuthbert, 1998). This implies

that discrete emotions within each system (e.g., fear, anger, and

disgust as negative emotions) should produce similar effects on

the startle reflex, provided these foregrounds are of similar in-

tensity (level of emotional arousal).

Testing this hypothesis with negative emotional photographic

stimuli has revealed a more complex pattern of startle modifica-

tion. Balaban and Taussig (1994) included both fear- and dis-

gust-eliciting picture stimuli in their experimental design, but only

observed blink potentiation for fear contents. Lethbridge, Sim-

mons, and Allen (2002) reported no startle modification for pic-

ture contents depicting socially aversive (i.e., non-physical) events.

Levenston et al. (2000) tested startle modification in male

prison inmates, dividing negative contents into physical threat

and ‘‘victim’’ stimuli (photographs of injury or assault between

actors). Threat contents produced greater magnitude startle

blinks than victim contents (C. J. Patrick, personal communi-

cation, April 9, 2003). Preliminary results from undergraduate

female participants have also supported this finding (Bernat,

Patrick, Benning, Blonigen, & Hicks, 2002).

In some experiments, differences in stimulus intensity between

emotional categories can better explain startle modification ef-

fects. Two studies (Bradley, Codispoti, Cuthbert, & Lang, 2001;

Bradley, Codispoti, Sabatinelli, & Lang, 2001) reported increas-

ing blink magnitude across eight specific negative categories, oc-

curring in parallel with increases in the subjective arousal ratings

for these categories (in ascending order of arousal: pollution,

loss, illness, contamination, accidents, mutilation, animal attack,

and human attack). Yartz and Hawk (2002) tested two disgust

picture categories (one with pictures including blood or injury,

the other non-blood disgusting images) alongside positive, neu-

tral, and fear stimuli. For female participants, blink magnitude

during the disgust categories (considered together) was greater

than blink magnitude during fear stimuli (Yartz & Hawk, 2002),

although the disgust-blood category was rated as more arousing

than the other negative categories.

One observation across all of these studies is that physical

threat and fear stimuli potentiate startle more consistently than

other negative contents, and this effect cannot be entirely attrib-

uted to differences in stimulus intensity.

Experimental Design and Hypotheses

The following study explores the possibility that between-study

differences in early startle modification can be attributed to the

types of emotional stimuli included in the negative picture cat-

egory. In addition to positive and neutral pictures, participants in

the current study viewed two categories of negative stimuli, dis-

gust and threat contents, while the startle reflexwas elicited either

300ms after picture onset (early probe time condition) or be-

tween 2 and 5 s after picture onset (late probe time).

Through the testing of an unselected sample of participants,

we hypothesized that early startle potentiation will be observed

for the threat content stimuli only. At the late probe time we

predicted that both negative picture contents would potentiate

startle relative to neutral and positive content trials.

Preliminary evidence from an unselected sample (Stanley,

2003) suggested that startle potentiation occurs for some threat

contents by 300ms. The threat contents used here include human

and animal threat content pictures. Pictures of spiders and snakes

were excluded from the threat condition (a) to allow generali-

zation of the findings of Globisch et al. (1999) to a wider range of

threat stimuli and (b) because previously collected subjective

ratings of pleasantness and arousal indicated that snake and spi-

der pictures were more sensitive than other negative stimuli to

individual differences in fearfulness (Stanley, 2003).

Method

Participants

An unselected sample of 55 University of Otago students

(32 female) completed the experiment, including 30 first-year

936 J. Stanley and R.G. Knight

psychology students who received course credit for participating.

An on-campus student job placement center provided the re-

maining 25 participants, who received NZ$10 for taking part.

Participant age ranged from 18 to 44 years, with a median of 19

years and a mean of 20.95 years.

Four participants did not complete the experiment, due to

computer failure (n5 1), absence of blink responding during the

habituation session (n5 2), and withdrawing from the study

halfway through the experiment (n5 1). The data analysis sec-

tion includes the exclusion criteria used for analyses of blink and

SCR magnitude. From the pool of those who completed the

experiment, 48 participants (30 female) contributed data to the

blink magnitude analyses and 43 participants (25 female) con-

tributed to the SCR analyses.

Picture Stimuli

Twenty-four pictures were selected from the International Af-

fective Picture System (IAPS; Lang, Bradley, & Cuthbert, 1999)

to comprise positive, neutral, and negative emotional conditions.

The negative picture condition consisted of two distinct catego-

ries of pictures: The ‘‘threat’’ category included pictures of hu-

man and animal (excluding snakes and spiders) threat directed

toward the viewer, such as a gun pointed at the screen. The

‘‘disgust’’ category primarily included pictures of mutilated bod-

ies, as well as other pictures chosen to elicit feelings of disgust

(e.g., human feces, dead animals). Picture selection for the two

negative categories included identifying pictures that met the

above descriptions, and then matching stimuli between these

categories on the basis of valence and arousal ratings, collected

using the Self-Assessment Manikin (Hodes, Cook, & Lang,

1985), from an independent sample of 88 participants (64 female)

from the University of Otago. Pictures were selected for the

neutral and positive categories on the basis of having been used in

previously published studies.1 Table 1 reports the means of va-

lence and arousal ratings for the different picture categories from

the sample of 88 participants, as well as the range ofmean ratings

for pictures in each category. A further 36 pictures (14 positive,

14 neutral, 8 negative) were presented as filler material; startle

probes were never presented on these trials. Participants there-

fore viewed a total of 20 pictures from each valence group during

the experiment.

Stimulus Presentation

A custom-designed program (Jones, 2000) controlled both pic-

ture and probe presentation through a Pentium III computer.

The program displayed each picture for 6 s on a 40-cm monitor

(60-Hz refresh rate) positioned 1.2m from the participant; in-

tertrial intervals (ITIs) were randomized, ranging from 15 to 21 s

duration. Startle probe presentation consisted of a 50-ms burst of

white noise at 95 dB (A) with near-instantaneous rise time, pre-

sented binaurally over headphones.

Experimental Design

Startle probe presentation occurred during picture viewing on all

six pictures in each emotional category. Half of these startle

probes occurred 300ms after picture onset (early probe time),

with the other half occurring at random time points between 2

and 5 s after picture onset (late probe time). Means (and SE) of

timings for the late probe instances in each emotional category

were as follows: positive, 3407.9ms (56.8); neutral, 3547.2ms

(71.4); disgust, 3430.4ms (86); threat, 3557.6ms (67.6).

Each emotional category/probe time condition thus consisted

of data from three pictures. Startle was also elicited during one

intertrial interval in each block. The picture set was divided into

five blocks of 12 pictures each, with the provisions that within

each block no two adjacent pictures contained the same valence

content (positive, neutral, negative), and that in each block the

number of pictures from each emotional category (threat, dis-

gust, neutral, positive) and number of early/late probe instances

were equal. There were two possible assignments of probes to

specific pictures in each block, so that a picture was probed at the

early time for one version of that block and in the late interval for

the second version of that block. Block presentation order also

varied, so that there were a total of eight groups for probe as-

signment/block order, counterbalanced across participants.

Physiological Recordings

The disposable electrodes used for recording blink EMG activity

fromorbicularis oculi had a 1.5 � 1.5 cm conductive surface area

(Blue Sensor BRS-50-K), preventing placement with an inter-

electrode distance of 1 cm (as recommended by Fridlund & Ca-

cioppo, 1986). The experimenter consistently used a slightly

wider interelectrode distance of approximately 2 cm (center to

center), with the negative lead electrode centered 1.5 cm below

the eyelid in line with the pupil of the left eye and the positive lead

electrode placed lateral and superior to the first electrode; the

ground electrode was placed on the forehead, below the hairline.

A PowerLab signal processor controlled by the MacLab

Chart program recorded both EMG and SCR signals (recording

software and MacLab hardware designed by ADInstruments).

The raw EMG signal was recorded at 1,000 samples per second,

and filtered off-line with a 28–500Hz bandpass (van Boxtel,

Boelhouwer, & Bos, 1998) prior to rectification and smoothing

with a 10-ms time constant. For the skin conductance recordings,

bright-plated, dry-operation electrodes (i.e., requiring no con-

ductive paste; ADInstruments) were attached to the medial

phalanges of the participant’s index and ring fingers on his or her

nondominant hand, and this signal was digitized at 400 samples

per second. The stimulus presentation computer produced sig-

nalsmarking onset and offset of the picture stimulus and onset of

the startle probe stimulus. Data sampling began 2 s prior to pic-

ture onset and ended 4 s after picture offset.

Calculation of blink response magnitude consisted of iden-

tifying the peak rectified EMGamplitude in a 20–150mswindow

Emotional specificity of early startle potentiation 937

Table 1. Mean Valence and Arousal Ratings for Startled Pictures

by Emotional Category

Dimension Positive Neutral Disgust Threat

ValenceMean 7.69 5.45 2.25 3.08Range 7.1–8.2 5.1–5.9 1.6–3.4 2.7–3.7

ArousalMean 3.81 1.95 5.4 5.34Range 2.4–6.1 1.2–3 3.6–6.5 3.6–6.5

Note: Reported ratings were collected during an earlier study.

1The IAPS numbers for the pictures on which startle was elicited areas follows: threat condition: 1300, 1301, 6244, 6250, 6260, and 6300;disgust condition: 3140, 3150, 3170, 9008, 9140, and 9400; neutral con-dition: 2840, 5740, 7006, 7182, 7503, and 7830; positive condition: 1460,2040, 2530, 7350, and 8030; additional pleasant pictures were 4210 formen and 4520 for women.

following startle probe presentation, and then subtracting the

mean rectified EMG level for the 20-ms period immediately prior

to probe presentation. The SCRmagnitude calculation identified

the largest change in SC amplitude occurring between 1 and 4.5 s

after picture onset. SCR magnitudes were only calculated for

pictures on which startle was elicited, due to the limited selection

of pictures and the specific experimental hypotheses.

These SCR conditions therefore roughly correspond to the

early and late probe time categories: In the ‘‘probe’’ condition,

startle was elicited almost simultaneously with picture onset (i.e.,

the early probe time); for the ‘‘no-probe’’ condition, responses

were only included for late probe time instances when startle was

elicited at least 3.5 s after picture onset (and thus not likely to

influence measurement of SCRs to the picture stimulus in the 1–

4.5 s time window for SCR measurement).

Transformations of blink and SCRdatawere performed prior

to analysis to render the data more suitable for assessing differ-

ences in responding to the within-subjects factors.2 The blink

magnitude transformation converted the uncorrected data into a

T score distribution (mean of 50, standard deviation of 10). The

blink standardization procedure included data from all startle

instances (during picture and ITI trials). Range correction of the

SCR magnitude data (Lykken & Venables, 1971) transformed

each picture’s SCR magnitude to a proportion of the range of

SCRmagnitudes elicited in that participant (range being equal to

the maximal SCR shown minus the minimal SCR shown).

Procedure

Once the participant entered the laboratory, the experimenter

explained that the procedure involved viewing a series of neg-

ative, neutral, and positive emotional pictures, and that the par-

ticipant was to view each picture for its entire time on-screen.

They werewarned that loud noises could be presented at any time

during picture presentation and occasionally during ITIs, but

that these stimuli could be ignored. Participants provided written

informed consent at this stage.

The participants then washed their hands with soap to ensure

accurate SCR measurement. After cleaning the EMG electrode

sites with an ethanol pad and applying OmniPrep skin prepa-

ration paste (D. O.Weaver), the experimenter attached the EMG

and SCR electrodes (details listed above). At this stage the par-

ticipant received three startle probe presentations (15-s ITI) to

ensure that blink responses were observable and relatively noise

free on the EMG record. Presentation of the five picture blocks

followed, and in the short break between blocks (approximately

1min) the experimenter checked that the participant was still

comfortable and wished to continue the experiment. Following

presentation of the five picture blocks, the experimenter removed

the electrodes, debriefed the participant on the experimental hy-

potheses, and thanked them for their assistance. The entire pro-

cedure lasted approximately 40min.

Data Analysis

Exclusion criteria involved identifying those participants who

showed infrequent or no responding to the startle probe. For

blink magnitude analyses, data from a participant were excluded

if they showed an absence of blink responding on all three pos-

sible startle instances in any emotional category/probe time con-

dition (smaller than 10 mVmagnitude in the raw data; this criteria

correctly identified non-blinks with this recording setup). Data

from a participant were included in the SCR analyses provided at

least one nonzero response was available in each emotional cat-

egory/probe presentation condition.

For the analysis of blink magnitude, emotional category

and probe time were within-subjects factors, with gender as

a between-subjects factor. Greenhouse–Geisser corrections

were applied to main effects or interactions involving emotion-

al category, and the correction epsilon (e) values are re-

ported where appropriate. Planned contrasts for significant

effects involving emotional category compared each negative

category separately against neutral and positive responses. To

control for possible Type 1 errors, the alpha level for each test

was set to .0125 (.05 overall alpha, divided by four contrasts).

Contrasts between the two negative categories were not

performed, as the primary experimental hypothesis related to

how these contents modified startle relative to neutral/positive

contents.

A similar strategy was used for SCR magnitude, with emo-

tional category and probe presentation aswithin-subjects factors,

and gender also included. Planned contrasts again followed up

significant effects involving emotional category (with a reduced

alpha level of .0125). The nature of these contrasts differed

slightly from those used for the blink analysis.

Results

Blink Magnitude

In the analysis of blink magnitude by emotional category,

gender was not significant as a main effect, F(1,46)5 0.56,

p5 .46, nor was it involved in significant interactions with

emotional category, Fs(3,138)o1; subsequent analyses excluded

this factor.

Late probe time blinks (M5 51.35, SE5 0.43T units) were

greater in magnitude than early probe time blinks (M5 48.05,

SE5 0.44T units), indicated by a significant main effect

for probe time, F(1,47)5 15.96, po.001. Blink magnitude also

varied on the basis of foreground emotional category,

F(3,141)5 9.76, po.001, e5 .96. Emotional category did not

interact with probe time, F(3,141)5 0.73, p5 .526, e5 .94. Fig-

ure 1 presents means and standard errors of blink magnitude by

emotional category at each probe time. Table 2 presents raw blink

magnitude data for each emotional category and ITI blinks.

Averaged over both probe times, blinks during threat con-

tents were of greater magnitude than neutral or positive blinks,

Fs(1,47)5 17.92 and 23.02, both pso.001.

Disgust content blinks were significantly larger than positive

content blinks, F(1,47)5 7.26, po.001, but did not differ from

neutral content blinks, F(1,47)5 2.72, p5 .106.

SCR Magnitude

To check that arousal was equated in the threat and disgust cat-

egories, a planned comparison was performed on the SCR data

from no-probe trials (see Table 3), and this indicated that there

was no significant difference in SCR magnitude between these

938 J. Stanley and R.G. Knight

2Blink magnitude data were transformed to correct for the fact thatsome participants had greater rawmagnitude blink responses (on averageover emotional categories) than other participants. Thirty-two of the 48participants included in the analysis had a mean blink magnitude of lessthan 60mV; 10 participants had mean magnitudes of between 70 and160mV. Because response variance increases with average magnitude(r5 .78), the decision was made to standardize these data. The maineffect of emotional category was still significant with the raw data,F(3,141)5 7.73, po.001, e5 .86, and the ordering of the cell means forthe Emotional Category � Probe Time conditions was the same with thetwo data sets.

two negative categories, F(1,41)5 .42, p5 .521. The affective

condition SCRs were of greater magnitude than neutral SCRs,

F(1,41)5 8.9, p5 .005.

The main effect of gender on SCR magnitude approached

significance, F(1,41)5 3.04, p5 .089. On average over emo-

tional category, SCRs elicited on trials with a 300-ms probe

were greater in magnitude (M5 0.41, SE5 0.026 of partici-

pant response range) than SCRs on trials with no probe

(M5 0.1, SE5 0.014 of participant response range), F(1,41)5

160.07, po.001. The magnitude of SCRs also depended on pic-

ture emotional category, F(3,123)5 5.65, p5 .002, e5 .85.

Emotional category did not interact with gender, F(3,123)5

1.09, p5 .35, nor with probe presentation, F(3,123)5 1.32,

p5 .273, e5 .9.

Averaged across the two probe presentation conditions, SCR

magnitudes did not differ between threat and positive contents,

F(1,41)5 2.36, p5 .132, or between disgust and positive con-

tents, F(1,41)5 0.11, p5 .739. The contrast between threat and

disgust content SCRs fell just outside of the corrected alpha level,

F(1,41)5 5.86, p5 .02. As the planned comparison reported

above indicated that there was no significant difference between

these categories for the no-probe trials, an exploratory compar-

ison was performed on the probe data, which indicated that

SCRs were of greater magnitude during threat relative to disgust

pictures (see Table 3) when startle was elicited 300ms after pic-

ture onset, F(1,41)5 7.77, p5 .008.

A final test indicated greater SCR magnitude for the three

affective conditions (threat, disgust, positive) compared to neu-

tral responses, F(1,41)5 17.98, po.001.

Discussion

Blink responses for threat contents were potentiated relative to

neutral and positive content blinks. For disgust contents, blinks

were potentiated relative to positive contents only. These effects

were consistent across the 300-ms and late-interval responses.

The early potentiation observed for threat contents replicates

the findings of Globisch et al. (1999), extending their result to an

unselected sample with the use of a different selection of pictures.

Disgust content blinks were not significantly different from

neutral at either early or late probe times (in a manner similar to

the negative condition in Codispoti et al., 2001).

These results are inconsistent with the prediction, based on

simple tone prepulse studies, that blink responses to interesting

picture stimuli will be inhibited at early probe times. Instead, the

results are consistent with the prediction of Globisch et al. (1999)

that threatening picture contents will activate defensive mecha-

nisms early in the picture viewing period. This could occur as an

outcome of Bradley and Lang’s (2001) two-process account of

early startle modification, where the net effect of prepulse inhi-

bition and affective potentiation will determine the degree of

startle modification for negative contents. This interpretation

suggests that the highly arousing threat contents in this study and

in Globisch et al. (1999) activated blink potentiation circuits to a

degree surpassing the effects of prepulse inhibition. Disgust con-

tent blinks did not differ from neutral at the early probe time,

which could potentially indicate (a) some aversive activation

from the picture content, but not enough to surpass attentional

inhibition or (b) a lack of any aversive/attentional modifica-

tionFin other words, the pictures failing to produce emotional

processing that differed from neutral. Both possibilities can be

addressed through the stimulus arousal/intensity dimension.

Participants did not provide ratings of the pictures in this exper-

iment, leaving the SCR magnitude data as the sole measure of

stimulus intensity. For trials in which SCRs were not influenced

by the startle probe, these data suggested that arousal levels were

equivalent in the two negative conditions, and augmented rela-

tive to neutral content SCRs. For trials on which startle was

elicited almost simultaneously with picture onset, SCR magni-

tude was much greater for the threat compared to the disgust

condition. From the no-probe results, it appears unlikely that the

disgust contents produced no emotional activation, and thematch-

ing of arousal between the two negative categories suggests that a

factor other than stimulus intensity is responsible for the differ-

ences in blink magnitude between threat and disgust contents.

It is possible that the differences in blink modification reflect

other stimulus characteristics unrelated to emotional content

(e.g., visual complexity). One limitation to this study was the

relatively small number of pictures used for each of the categories

(six pictures per category), which leaves the possibility open that

these differences in stimulus characteristics may have influenced

Emotional specificity of early startle potentiation 939

Table 2. Raw Blink Magnitude (in Microvolts) Means and

Standard Errors for Each Emotional Category and ITI Instances

Positive Neutral Disgust Threat ITI

Mean 50.01 52.27 55.85 58.43 57.89(SE ) (4.81) (5.44) (5.87) (5.55) (5.88)

Table 3. Standardized SCR Magnitude (Proportion of Range)

Means and Standard Errors for Each Emotional Category, Divided

by Probe Presentation

Probe condition Positive Neutral Disgust Threat ITI

No probe 0.12 0.06 0.1 0.12 N/A(SE ) (0.02) (0.01) (0.02) (0.03)Probe 0.40 0.36 0.41 0.48 0.35(SE ) (0.03) (0.03) (0.03) (0.03) (0.03)

Early Late40

45

50

55

60

Positive Neutral Disgust Threat

Probe Time

Blin

k M

agni

tude

(T

-sco

re)

Figure 1. Mean standardized blink magnitude by emotional category, at

the early and late probe times. Error bars indicate one standard error.

Dotted line represents mean level of ITI responses.

the pattern of responses. The small picture sets were largely due

to the experimental hypotheses regarding the emotional specifi-

city of each category, and replication with a larger number of

exemplars and/or a different picture set will strengthen the va-

lidity of these conclusions.

This experiment showed that early startle potentiation is not

limited to preselected, highly fearful participants (cf. Globisch

et al., 1999), with threat content pictures successfully potentia-

ting startle within 300ms of picture onset. Subsequent studies

should assess whether the observed early startle modification

differences between threat and disgust content stimuli reflect

arousal differences between these categories in the present study,

or a more qualitative difference in the processing of these two

picture contents.

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(Received August 7, 2003; Accepted July 1, 2004)

940 J. Stanley and R.G. Knight