EmotionMotivationalBrain.pdf

Biological Psychology 84 (2010) 437–450

Contents lists available at ScienceDirect

Biological Psychology

journal homepage: www.elsevier.com/locate/biopsycho

Review

Emotion and the motivational brain §

Peter J. Lang * , Margaret M. Bradley

CSEA, Box 112766, University of Florida, Gainesville, FL 32611, United States

ARTICLE INFO

ABSTRACT

Article history:

Received 26 May 2009

Accepted 20 October 2009

Available online 30 October 2009

Psychophysiological and neuroscience studies of emotional processing undertaken by investigators at

the University of Florida Laboratory of the Center for the Study of Emotion and Attention (CSEA) are

reviewed, with a focus on reﬂex reactions, neural structures and functional circuits that mediate

emotional expression. The theoretical view shared among the investigators is that expressed emotions

are founded on motivational circuits in the brain that developed early in evolutionary history to ensure

the survival of individuals and their progeny. These circuits react to appetitive and aversive

environmental and memorial cues, mediating appetitive and defensive reﬂexes that tune sensory

systems and mobilize the organism for action and underly negative and positive affects. The research

reviewed here assesses the reﬂex physiology of emotion, both autonomic and somatic, studying affects

evoked in picture perception, memory imagery, and in the context of tangible reward and punishment,

and using the electroencephalograph (EEG) and functional magnetic resonance imaging (fMRI), explores

the brain’s motivational circuits that determine human emotion.

Keywords:

Emotion

Neuroscience

fMRI

ERP

Picture

Imagery

Eye

Contents

Predator and prey: The defense cascade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

439

1.1.

A computer simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

439

1.2.

Autonomic responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

440

1.3.

The probe startle reﬂex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

441

1.4.

The brain in threat and reward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

441

The late positive potential and motivational relevance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

441

2.1.

Complexity or arousal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

441

2.2.

Attention and habituation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

442

3. What brain structures underlie the ERP late positive potential?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

442

Amygdala/visual cortex connections during picture viewing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

444

The brain begins at the eye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

444

Differences in brain circuit activation for pleasant and unpleasant cues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

446

6.1.

Looking at pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

446

6.2.

Emotional imagery and appetitive motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

448

Summary and conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

448

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

449

§ The experiments reviewed here were in the main accomplished at the NIMH

Center for the Study of Emotion and Attention at the University of Florida. Many

signiﬁcant contributors to the research reviewed here are now investigators at

other institutions, including Andreas L ¨w (Greifswald University, Germany), Dean

Sabatinelli (University of Georgia, USA), Maurizio Codispoti and Vera Ferrari

(University of Bologna, Italy), Harald Schupp (University of Konstanz, Germany),

Bruce Cuthbert (University of Minnesota, USA), Francesco Versace (MD Anderson

Cancer Center, USA), Tobias Flaisch (University of Konstanz, Germany), and Laura

Miccoli (Granada, Spain). We also take pleasure in acknowledging the contributions

of current Center investigators including Vincent Costa, Andreas Keil, and Lisa

McTeague. The research was supported in part by a National Institute of Mental

Health grant, P50 MH-72850.

* Corresponding author.

E-mail address: plang@phhp.uﬂ.edu (P.J. Lang).

The general thesis examined here is that experienced emotions

are founded on the activation of neural circuits that evolved in the

mammalian brain to ensure the survival of individuals and their

progeny. Primitively, these motive circuits were engaged by

external stimuli that are appetitive and potentially life sustaining,

or alternatively, represent threats to the organism’s survival. The

psychobiological consequences of this neural ﬁring are potentially

twofold: On the one hand, they engage sensory systems that

increase attention and facilitate perceptual processing, and on the

other, they initiate reﬂex responses that mobilize the organismand

prompt motor action.

doi: 10.1016/j.biopsycho.2009.10.007

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P.J. Lang, M.M. Bradley / Biological Psychology 84 (2010) 437–450

Fig. 1. Schematic diagram of the outputs of the basolateral nucleus of the amygdala to various target structures, and the subsequent outputs and targets of the amygdala’s

central nucleus (CeA) and the lateral basal nucleus of the stria terminalis (BNST: the ‘‘extended’’ amygdala). Known and possible functions of these connections are brieﬂy

described ( Davis and Lang, 2003 ).

Research with animals (e.g., Davis, 2000; Fanselow and Poulos,

2005; Kapp et al., 1994; LeDoux, 2003 ) has deﬁned the key neural

structures in this survival network (see Fig. 1 : Lang and Davis, 2006 ;

see also, Davis and Lang, 2003 ): The bilateral amygdalae – two small,

almond shaped bundles of nuclei in the temporal lobe – plays a

central role. Each amygdala receives input fromcortex and thalamus

(sensory) and hippocampus (memory), subsequently engaging

through the central nucleus and extended amygdala (bed nucleus

of the stria terminalis) a range of other brain centers that modulate

sensory processing (vigilance), increase related information proces-

sing, and activate autonomic and somatic structures that mediate

defensive or appetitive actions.

It is convenient to consider this survival circuit as organized

into two motivational systems, one defensive and associated with

reports of unpleasant affect and the other appetitive, associated

with pleasant affect. Konorski (1967) early conceived such a

motivational typology, keyed to the survival role of the body’s

many unconditioned reﬂexes. Exteroceptive reﬂexes were either

preservative (e.g., ingestion, copulation, nurture of progeny) or

protective (e.g., withdrawal from or rejection of noxious agents). He

further suggested that affective states were consistent with this

preservative/protective grouping: Preservative emotions include

such affects as sexual passion, joy, and nurturance; fear and anger

are protective affects. Dickinson and Dearing (1979) developed

Konorski’s distinction, renaming the two motivational systems,

aversive and attractive, with each again activated by a different, but

equally wide range of unconditioned stimuli, determining

perceptual-motor patterns and the course of learning. In this

general view, affective valence is determined by the dominant

motive system: the appetitive system (preservative/attractive)

prompts positive affect; the defense system (protective/aversive)

is the source of negative affect. Affective arousal reﬂects the

‘‘intensity’’ of motivational mobilization, determined originally by

degree of survival need and the imminence or probability of

nociception or appetitive consummation. In this regard, it is

pertinent that factor analyses of emotional/evaluative language

(since Osgood et al., 1957 ; see also, Russell and Mehrabian, 1977;

Bradley and Lang, 1994 ) have consistently found two main factors

accounting for the most variance among affect descriptors:

Emotional valence (positive/pleasant/appetitive vs. negative/aver-

sive/defensive) and arousal (intensity of activation). Thus, it would

appear that, despite the great number and diversity of emotional

words, the underlying structure of affective language appears to

reﬂect the dual motive system model—appetitive and defensive

neural circuits that vary in the vigor of their activation.

The defense system is ultimately a ﬁght or ﬂight circuit, but in

response to danger cues it also mediates behavioral ‘‘freezing’’

(hiding), increased vigilance, and counter-threat displays in animal

subjects. The appetitive system is activated variously in alimenta-

tion, sex, and nurturance of progeny. However, as will be seen,

although some reactions are uniquely appetitive or defensive, many

physiological and behavioral patterns are similar in both contexts of

arousal, and are mediated by the same neural structures.

The view to be elaborated here is that these survival circuits in

primitive cortex and the limbic brain are the stuff of human

motivation, and that motivational arousal is the foundation of

emotion. From this neuroscience perspective, human emotions can

be described as dispositions to action (e.g., anger > attack; sexual

desire > approach; fear > escape—see also Frijda, 1986 ). That is,

expressed emotions are grounded in motivational circuits that

feed back to sensory systems, heightening vigilance and informa-

tion gathering, and importantly, prompting reﬂexive autonomic

P.J. Lang, M.M. Bradley / Biological Psychology 84 (2010) 437–450

439

and motor responses that in evolutionary history acted directly to

counter

hypothesis is that reports of aversive arousal reﬂect an atavistic

distance parameter, and that the changes in physiology when

viewing unpleasant pictures reinstantiate reactions that in prey

animals changed as threatened confrontation became increas-

ingly imminent ( Lang et al., 1997 ). From this perspective it is

assumed that a human participant looking at an unpleasant/

aversive picture is viewing threat at a distance, analogous to a prey

animal (e.g., gazelle) apprehending a distant predator (e.g., a lion)

from afar. Increases in rated arousal might be associated with

progressive changes in reﬂex physiology that are similar to those

observed if a threatening event is increasingly imminent—the lion

approaches. That is, reports of emotional arousal indicate,

however imperfectly, the intensity of defense system activation

which then deploys different reﬂex responses for remote threats

(where confrontation is uncertain) than for an increasingly

imminent encounter. At a distance, perceptual processing and

information gathering dominate, but as the distance from a

threatening stimulus diminishes, organismmobilize increasingly

for coping action—the ﬁght/ﬂight imperative.

The aim of the ﬁrst research to be described here is to examine

changes in reaction patterns as motive cues appear to loom

progressively closer, as well as to consider possible differences

(and similarities) associated with cues that signal pleasant or

alternatively, unpleasant consequences (reward or punishment).

In a series of classic studies, Miller (1959) assessed behavioral

responses (latency and strength of response) in rodents conﬁned to

an alley maze, and deﬁned motivational gradients of approach to

food reward vs. avoidance of electric shock. His work showed

greater relative approach motivation when the animal was distant

from the reward, but that the strength of avoidance rapidly

superseded approach when the goal was proximal. More recently

Kahneman and Tversky (2000) have reported a similar advantage

for aversive motivation in human beings, showing that motivation

to avoid loss greatly exceeds motivation to gain new resources.

threats and escape punishment, or achieve needed

rewards.

In humans, affective percepts, thoughts, and images act as

motive cues that automatically engage the older limbic circuits and

reﬂex patterns. Of course, with evolution of the cerebrum came our

human metamorphic capacity to delay, modulate or inhibit overt

actions, providing for more ﬂexible and adaptive responses to

achieve survival’s aims. Nevertheless, the primitive physiology of

action preparation persists, mobilizing muscles and glands and

placing sensory systems on high alert—functions that are the

physiological manifestations of emotional expression.

This essay considers research undertaken from this perspective,

ﬁrst examining bodily, behavioral, and brain reactivity associated

with threatening or appetitive cues, as they vary in their proximity

to, and imminence of, punishment or reward. Subsequently, we

describe research with emotional pictures, assessing EEG event-

related potentials, eye tracking, and changes in pupil dilation that

co-vary with emotional arousal. Finally, we consider recent fMRI

research that delineates structural and network activation

differences for appetitive and aversive cues, and show a common

activation of the brain’s motivational circuits in emotional

perception and mental imagery.

1. Predator and prey: The defense cascade

In considering the mortal confrontations between predator and

prey, ethologists and comparative psychologists have deﬁned

characteristic response patterns that change systematically with

the proximity and probability of an encounter (e.g., Blanchard and

Blanchard, 1989; Campbell et al., 1997; Timberlake, 1993; Tinber-

gen, 1951 ). When one antagonist perceives the other, responses are

sequentially deployed that vary in function and emphasis with the

imminence of a physical confrontation: For prey, the sequence

enhances the probability that a threat will be survived; for the

predator, it optimizes the chance of a ﬁnal strike and capture. In

many ways the required responses (and their mediating brain

circuits) are broadly similar, consisting of augmented vigilance (a

risingdemand for attentional resources), accompaniedby increasing

physiological mobilization and a readiness for action (ﬁght/ﬂight or

strike/capture). In the natural environment, of course, the same

organism often plays both roles, foraging for rewards, but wary of

being attacked: A small bird ﬁshing formodest game risks the notice

of an eagle, a larger, more voracious species that views the ﬁsher and

its catch as its proper prey.

In a recent experiment ( L ¨w et al., 2008 ), we examined

anticipatory brain and reﬂex reactions in human beings in the

laboratory using a simulation that was modeled on features of the

predator–prey survival scenario, in which the participant acted

both parts. The research was prompted by previous data indicating

that viewing unpleasant, emotionally evocative pictures elicits

patterns of physiological reﬂex reactions that vary markedly (in

direction and amplitude) with evaluative reports of the intensity of

affective arousal (e.g., Lang et al., 1997 ). Thus, some autonomic

responses, such as skin conductance or pupil dilation, show a

monotonic increase with rated emotional arousal. Heart rate,

however, decreases with greater arousal, except when viewing

aversive pictures that prompt the reports of highest arousal (e.g., in

phobic reactions), which then show a dramatic tachycardia ( Hamm

et al., 1997 ). The probe startle reﬂex also shows directional

changes, initially inhibited and then increasingly potentiated with

greater rated arousal of individual aversive picture cues ( Bradley

et al., 2006; Cuthbert et al., 1996; Lang, 1995 ).

This directional variability within and between measures as

emotional intensity increases suggests that different defensive

functions are being served along the arousal continuum. One

1.1. A computer simulation

The predator/prey research environment took the form of a

computer simulation: Participants observed a continuous stream

of brieﬂy presented pictorial images (see Fig. 2 ). Most of these

images depicted motivationally neutral objects, animals, or people,

each replacing the other at a constant rate in a continuous ﬂow,

mimicking the serial humdrum of daily life. Occasionally, however,

a picture appeared that had motivational signiﬁcance: An offered

ﬁst-full of money or alternatively, an attacker’s hand pointing a

gun at the viewer. These motivationally relevant images were

sometimes repeated several times in a sequence, each time larger,

as if the gun or money were moving closer to the viewer. This

‘‘looming’’ sequence could continue for a few ‘‘foil’’ trials, ending

with naught but a return to the neutral image stream.

If, however, the image continued its approach, the player was

metaphorically in the predator–prey strike zone. At some point in

this region, the background of the picture (gun or money) changed

color, signaling the participant to press a reaction-time-key as

rapidly as possible. On money trials, a fast response resulted in a

reward of 1$; a slow response produced no gain and an image of

the money burning up. If reactions were slow on a threatening gun

trial, the gun appeared to ﬁre and 1$ was deducted from the

participant’s stake; with a timely response, however, she/he

escaped the potential loss and a steel door slammed shut, blocking

the gunner. As a control procedure, neutral pictures also some-

times appeared to loom, but, when their background color

changed, a key press (under no time pressure) only served to

continue the sequence of pictures.

The experimental task permitted the evaluation of both reﬂex

reactions and brain potentials as they are modulated by increasing

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Fig. 2. Diagram of the experimental design: A continuous stream of picture stimuli was presented throughout the experiment. Most of these pictures were emotionally

neutral in content (A). However, a ﬁst-full of money (B) or a gun aimed at the viewer (C) occasionally appeared in the stream. On response trials (D), the gun, themoney, or one

of the neutral images loomed increasingly larger for 6 or 7 repetitions. Participants were instructed to press a key at the end of this picture sequence, when the picture

background changed color (E). On gun trials a slow response resulted in a loss of $1; a fast response onmoney trials added $1 to the participant’s stake; all responses to neutral

cues were acknowledged without regard to latency. Money and gun pictures could also appear brieﬂy in the neutral stream—singly or in a short looming sequence of three

images. For these brief presentations, there was no subsequent response cue ( L ¨w et al., 2008 ).

temporal, proximity/probability of reward or of a punishing loss.

In humans, these measures are held to reﬂect modulation of

three coincident anticipatory processes: heightened attention to

motivationally signiﬁcant cues; mobilization of the body for

action, preparatory to avoiding a theft or achieving a reward;

and emotional arousal, evoked by the context of threat and

appetite.

1.2. Autonomic responses

As anticipated, skin conductance increased progressively during

both reward and punishment sequences. Its amplitude was already

somewhat heightened, compared to neutral cues, early in the

sequence when a ﬁnal confrontation was still uncertain. Then, as

shown for the gun cue in Fig. 3 – but also seen for reward – it rose

dramatically during the ﬁnal steps before the goal, when a fast

response would be required. Sweat gland activity is a well-known

indicator of general sympathetic activation (e.g., Wallin, 1981 ), and

associated with increased metabolism, visceral changes, and

modulation of sensory systems, as in pupil dilation (e.g., Janise,

1977 ). The other autonomic measure examined here, heart rate,

showed a modest initial increase (perhaps attributable to vagal

release); however, as a possible reward or the risk of loss became

more certain ( Fig. 3 ), heart rate decreased steadily in frequency to a

nadir on the penultimate approach cue. This deceleration was then

followed by an abrupt acceleration just prior to the ﬁnal response

signal for escape or capture.

Fig. 3. Heart rate and skin conductance change from pre-stimulus baseline values

(samples every 2 s) for the last three looming pictures prior to the ﬁnal gun

response signal ( L ¨w et al., 2008 ).

P.J. Lang, M.M. Bradley / Biological Psychology 84 (2010) 437–450

441

In preparing to seize a reward or escape a punishment, the two

branches of the autonomic nervous system are co-active: The

increase in sweat gland activity indicates progressively augmented

sympathetic arousal; in contrast, heart rate is mainly under

parasympathetic control, and decreases progressively with closer

proximity to the goal. This latter phenomenon has been widely

noted in biological studies of prey animals confronting a predator

( Campbell et al., 1997 ), and is coincident with relative immobility

(freezing) and an increasingly focused vigilance. In the context of

predator approach, it is described as ‘‘fear bradycardia’’ (and for the

predator/prey task, the deceleration was predictably, somewhat

greater for the gun cue). Nevertheless, within the strike zone, of

course, there is anticipatory parasympathetic release and a

sympathetic increase in rate accompanies the ﬁnal mobilization

for goal directed action. Interestingly, brief anticipatory increases in

rate can also be seen increasing over the immediately preceding

picture cues.

joy) directly to the underlying dynamic ﬂow of behavior that

changes differently across different physiological systems as an

anticipated reward or fear of loss passes from the possible to the

imminent.

1.4. The brain in threat and reward

In addition to autonomic and somatic reﬂex measures, the

electroencephalogram was recorded throughout the predator–

prey simulation, and event-related potentials were assessed at

each stage along the approach/avoidance gradients. Fig. 5 shows

the electroencephalographic event-related potential (ERP)

responses to each motivational cue (i.e., gun or money), at their

ﬁrst appearance in the continuing sequence of neutral pictures

(upper right panel). Emotional modulation of the ERP is essentially

the same as that found when pictures are presented for free

viewing (e.g. Cuthbert et al., 2000 ): A slow positive waveform is

apparent beginning around 300 ms and extending past 700 ms

that is reliably enhanced over centro-parietal sensors for emo-

tional pictures – either pleasant or unpleasant – that increases in

amplitude with increases in rated arousal. As illustrated in the left

panel, this late positive potential is dramatically enhanced for all

cues at the penultimate (presumably most activating) cue which

occurs just before a motor response is required.

Differences in the late positive potential for the looming gun

and money cues, compared to the neutral cue, are shown at the

bottom of Fig. 5 for each step in the looming sequence. It is of

interest that the initial heightened potential to motivational cues

shows some decrease early in the sequence, when the continuation

of the sequence is uncertain (1–3). Subsequently, however, the

amplitude of the late positive potential increases progressively,

peaking just before the cue that initiates action. Interestingly, the

late positive potential is signiﬁcantly larger for the gun cues (threat

of loss) than for money (a possible gain) at this ﬁnal stage,

consistent with Miller’s (1959) hypothesis that avoidance gradi-

ents are steeper than approach (relatively higher close to the goal,

cf. Cacioppo and Berntson, 1994 ), as well as with Kahneman and

Tversky’s (2000) view that motivation to avoid a loss is greater

than that to achieve a gain.

1.3. The probe startle reﬂex

In less complex animals, the startle response can be considered

an automatic escape reﬂex as with an abrupt movement overhead,

the sudden ﬂight of a ﬂy. Although this functional signiﬁcance has

been lost in humans, it is clear that startle reﬂex amplitude is

modulated by at least two factors: Hedonic content (most clearly, a

potentiated response in unpleasant perception) and focused

attention (prompting relative reﬂex inhibition).

During the predator–prey simulation, startle reactions were

tested at various stages of the approach/avoidance sequence,

including when viewing the initial cue, midway through the

sequence, and just prior to the response cue. As illustrated in Fig. 4 ,

the initial exposure to motivational cues (i.e., a distant threat or

reward) yielded the pattern observed in many studies—signiﬁcant

reﬂex potentiation when viewing the threat cue and a relative

inhibition for appetitive cues (e.g., Bradley et al., 2006; Lang et al.,

1990 ). However, as the distance to confrontation closed, reﬂex

magnitude is increasingly inhibited, reﬂecting effects of task-

focused attention and suppression of irrelevant action, facilitating

a ﬁnal functional response to the motive cue. From this

perspective, fear potentiated startle appears to be a premature

action trigger, subsequently suppressed when the exigencies of a

more efﬁcient survival response dominate.

The poetry of the predator–prey interaction can be described as

an orchestration of fear and desire. For a natural science of

emotion, however, it highlights the impossibility of marrying, in

the Jamesian sense, emotional language (fear, anxiety; longing,

2. The late positive potential and motivational relevance

The late positive potential evoked by picture stimuli is a reliable,

replicable index of their motivational relevance. Recording from

scalp electrodes and with the electroencephalograph (EEG) ampli-

ﬁers set for a long time constant (allowing one to see sustained brain

potentials), Cuthbert et al. (2000) observed an enhanced centro-

parietal positive signal that began around 300 ms after the onset of

anemotional picture andpersisted for almost the entire durationof a

6 s viewing interval (see Fig. 6 ). Its relationship to emotional arousal

was conﬁrmed in a second study inwhichwe found that this positive

potential was most enhanced for the pictures rated highest in

emotional arousal, regardless of whether they depicted appetitive

(e.g., erotica) or aversive (e.g., mutilated bodies) hedonic contents

( Schupp et al., 2004 ). The amplitude of the late positive potential

(LPP) not only correlated highly with reports of rated emotional

arousal but also co-variedwith sympathetic arousal, asmeasured by

electrodermal response amplitude.

2.1. Complexity or arousal

To conﬁrm that the late positive potential varies with motiva-

tional signiﬁcance, rather thanwith other physical characteristics of

these relatively complex visual stimuli, we varied the perceptual

composition of emotional and neutral pictures and presented either

simple ﬁgure-ground compositions ormore complex scenes in a free

Fig. 4. Average magnitude of the startle probe reﬂex for money, gun, and neutral

cues over the looming sequence. Probes were presented 1100 ms after picture

onset during pictures 1 and 3 (‘‘maybe’’ stage) and during either picture 5 or

picture 6 (‘‘imminent’’ stage). Mean t scores and their standard errors are shown

( L ¨ w et al., 2008 ).

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