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Encoding of emotional facial expressions in direct and incidental tasks:Two event-related potential studiesMichela Balconi a; Claudio Lucchiari b

a Department of Psychology, Catholic University of Milan, b Department of Neurology, NeurologicalNational Hospital “C. Besta”, Milan, Italy

To cite this Article Balconi, Michela and Lucchiari, Claudio(2007) 'Encoding of emotional facial expressions in direct andincidental tasks: Two event-related potential studies ', Australian Journal of Psychology, 59: 1, 13 — 23To link to this Article: DOI: 10.1080/00049530600941784URL: http://dx.doi.org/10.1080/00049530600941784

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Encoding of emotional facial expressions in direct and incidental tasks:Two event-related potential studies*

MICHELA BALCONI1 & CLAUDIO LUCCHIARI2

1Department of Psychology, Catholic University of Milan and 2Department of Neurology, Neurological National Hospital

‘‘C. Besta’’, Milan, Italy

AbstractEmotional face encoding process was explored through electroencephalographic measures (event-related potentials [ERPs]).Previous studies have demonstrated an emotion-specific cognitive process in face comprehension. However, the effectof emotional significance of the stimuli (type of emotion) and task (direct or indirect task) on the ERP is uncertain.In Experiment 1 (indirect task) ERP correlates of 21 subjects were recorded when they viewed emotional (anger, sadness andhappiness) or neutral facial stimuli. An emotion-specific cortical variation was found, a negative deflection at approximately200 ms after simulus (N2 effect). This effect was sensitive to the emotional valence of faces, because it differentiated higharousal emotions (i.e., anger) from low arousal emotions (i.e., sadness). Moreover, a specific cortical site (posterior) wasactivated by emotional faces but not by neutral faces. In Experiment 2 (direct task), the authors investigated whetherencoding for emotional faces relies on a single neural system irrespective of the task, or whether it is supported by multiple,task-specific systems. Differences in the cortical distribution (posterior for incidental task; central and posterior for directtask) and lateralisation (right-distribution for the negative emotions in direct task) of N2 on the scalp were observed in thedifferent tasks. This indicates that distinct task-specific cortical responses to emotional focus can be detected with ERPmethodology.

Facial expressions of emotions are social and com-

municative tools. Because humans use facial expres-

sions to interpret the intentions of others, they play

an important role in daily interactions (Darwin,

1872). The existence of a specific process to encode

emotional features has been well documented by the

cognitive model of face processing proposed by

Bruce and Young (1986, 1998). This model

supposes that there are seven distinct types of

information that can be derived from the face, such

as structural, expression and identity information.

These types of information, which differ in terms of

the cognitive and functional subprocesses impli-

cated, are represented as ‘‘codes’’. In line with this

model, event-related potential (ERP) studies in

humans have provided evidence for the early

emergence of emotional encoding and its distinc-

tiveness from other cognitive processes.

The aim of the present study was to investigate

the encoding processes of emotional faces, taking

into consideration these main points: (a) an accurate

description of encoding process of emotional faces,

through ERP measures; and (b) exploring the effect

of a range of emotional expressions on ERPs, as a

function of their salience. There are three principal

ways in which electrophysiological measures can

inform the neural (hence cognitive) processes that

support operations of face comprehension. They can

provide information about the time course of cogni-

tive processes implicated; whether qualitatively dis-

tinct processes are engaged as a function of type of

stimulus (type of emotion); and the extent to which

such processes are engaged as a result of different

encoding procedures (Balconi, 2003; Rugg & Coles,

1995). From that perspective, evidence that emo-

tional faces elicit specific patterns of brain activity

could be construed as support for the claim that a

dedicated cognitive process exists.

An increasing range of research studies have analy-

sed the cognitive and neuropsychological features

Correspondence: Dr M. Balconi, Department of Psychology, Catholic University of Milan, L.go Gemelli, 1 20123 Milan, Italy.

E-mail: michela.balconi@unicatt.it

*Accepted under the previous Editorial Board.

Australian Journal of Psychology, Vol. 59, No. 1, May 2007, pp. 13 – 23.

ISSN 0004-9530 print/ISSN 1742-9536 online ª The Australian Psychological Society Ltd

Published by Taylor & Francis

DOI: 10.1080/00049530600941784

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of face comprehension (Posamentier & Abdi, 2003;

Russell, 1994). Although some studies have ex-

plored the later endogenous components (Holmes,

Vuilleumier, & Eimer, 2003; Streit, Wolwer,

Brinkmeyer, Ihl, & Gaebel, 2000), there is also

evidence that emotional processing can be differ-

entiated in earlier time windows. A very early positive

peak was observed at approximately 100 ms after

stimulus, the P1 effect, related to emotional valence

of the facial stimulus, which might demonstrate that

emotional perception of faces can take place pre-

attentively and automatically (Pizzagalli, Regard, &

Lehmann, 1999).

In addition, recent ERP studies found an early

posterior negativity (peaking at around 230 – 270 ms),

reflecting facilitated processing of emotional stimuli

(Schupp, Junghoper, Weiker, & Hamm, 2003). In

fact, it was demonstrated that emotional faces (fear

and happiness) elicited a larger negativity at approxi-

mately 270 ms than neutral faces over the posterior

temporal areas (Marinkovic & Halgren, 1998; Sato,

Takanori, Sakiko, & Michikazu, 2001; Vanderploeg,

Brown, & Marsh, 1987). Another study investigated

the influence of facial expressions and blurred faces on

ERP measures, without any differences between

conditions (emotional vs. blurred faces) at 120 and

170 ms after stimulus onset, but with significant

differences in amplitude between 180 and 300 ms

(Balconi & Lucchiari, 2005; Streit et al., 2000).

Nevertheless, in spite of these consistent results, other

studies found that N200 did not supply evidence in

favour of differential processing for facial expressions

(Carretie & Iglesias, 1995), and this ERP effect was

considered as independent from facial expression

analysis (Herrmann et al., 2002).

The first interpretation supposed that N2 could be

a cognitive marker of the complexity and relevance

of the facial stimulus (Carretie & Iglesias, 1995).

Nevertheless, some authors stated that this position

is in contrast with a large part of the experimental

evidence (Marinkovic & Halgren, 1998; Sato et al.,

2001). Consequently, a second hypothesis pointed

out the emotional specificity of N2, because it is

thought to be an index of the emotional encoding of

facial stimuli, and it may signal different semantic or

functional value of the emotional expressions

(Balconi & Pozzoli, 2003a; Posamentier & Abdi,

2003). Thus, some fundamental questions remain to

be answered.

First, the cognitive nature of this ERP variation

must be clarified, taking into consideration the

specificity of N200 for emotional facial expression

encoding. The comparison of facial expressions

with a neutral condition (neutral facial expression)

becomes crucial, in order to characterise the emo-

tional significance of this early peak variation.

Moreover, spatial localisation of the N200 effect is

unclear. Previous research found a more posterior

distribution of the peak, and specifically it was

localised in the temporo-occipital sites of the scalp

(Sato et al., 2001). Nevertheless, some studies have

found a different cortical distribution of the peak,

such as the central or anterior localisation. Therefore,

we chose to analyse ERP profile, in terms of brain

distribution of the N200.

A second main question of the current study

relates to the effect of type of emotions on ERP

correlates. Recent neuropsychological and neuro-

imaging data have been interpreted as indicating

that emotional perception, and specifically percep-

tion of facial expressions, is organised in a modular

fashion, with distinct neural circuitry subserving in-

dividual emotions (Adolphs, Tranel, & Damasio,

2003; Batty & Taylor, 2003; Calder, Keane, Manes,

Anton, & Young, 2000). However, few studies have

examined the range of basic emotions or distin-

guished possible differential cortical activation as a

function of the emotions. Some of them analysed

face-specific brain potentials but they did not explore

exhaustively the emotional content of faces and its

effect on ERPs (Eimer, 2000; Eimer & McCarthy,

1999). In some cases only a limited number of

emotions were considered, usually comparing one

positive and one negative emotion, such as sadness

and happiness (Herrmann et al., 2002).

Moreover, findings of previous research have noted

a modulation of late deflections of ERP as a func-

tion of ‘‘motivational significance’’ (Lang, Bradley, &

Cuthbert, 1997). Specifically, greater magnitude of

ERP deflection characterises the response to emo-

tionally salient stimuli (unpleasant compared to

neutral) (Palomba, Angrilli, & Mini, 1997; Schupp

et al., 2000). This effect has been theoretically related

to motivated attention, in which motivationally

relevant stimuli naturally arouse and direct atten-

tional resources (Hamm, Schupp, & Weike, 2003;

Keil et al., 2002; Lang et al., 1997). How can we

explain these effects of motivation and salience of

emotional facial expressions on ERPs? As suggested

by the functional model, each emotional expression

represents the subject’s response to a particular kind

of significant event – a particular kind of harm or

benefit – that drives coping activity (Frjida, 1994;

Hamm et al., 2003; Moffat & Frijda, 2000). Thus, an

important question of the present study is whether the

salience value of facial expressions could have an

effect on stimulus elaboration, and whether this could

be shown by ERP variations. We hypothesise that, if

the ERP variations are useful markers of cognitive

processes underlying emotion encoding, significant

differences should be found between the two cate-

gories of high/low arousal emotions. As suggested by

the functional model, we expected that subjects could

be more engaged by a high-threat negative expression

14 M. Balconi & C. Lucchiari

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(i.e., anger) than a low-threat positive emotion

(happiness), and that they might have a more intense

emotional reaction while viewing a negative high-

arousal (highly salient) than a negative low-arousal

emotion (Lang, Nelson, & Collins, 1990; Wild,

Erb, & Bartels, 2001).

Experiment 1

Method

Participants. Twenty-one subjects (11 male, age

range 21 – 25 years, M¼ 23.32 years; SD¼ 0.58

years), students of psychology at the Catholic

University of Milan, took part in the research. They

all were right-handed, with normal or corrected to

normal visual acuity and all denied any history of

neurological or mental abnormalities. They were

recruited for a cognitive task of stimulus encoding

but were not aware that the investigation of

emotional variables was the real purpose of the

experiment. The subjects gave their overt consent to

participate in the experiment (they were neither paid

nor did they receive course credits). The Ethics

Committee approved the study.

Materials and procedure. Stimulus materials were

taken from the set of pictures of Ekman and Friesen

(1976). They were black and white pictures

(116 15 cm) of a young male and female actor

(opportunely randomised across the emotions),

presenting respectively a happy, sad, angry, or

neutral face. The neutral faces did not present a

specific emotional expression. The items are iden-

tical in terms of lighting and angle. Pictures were

presented in a random order in the center of a

computer monitor placed approximately 80 cm from

the subject, with a visual horizontal angle of 48 and

a vertical angle of 68 (STIM 4.2 software). An

interstimulus fixation point was projected at the

center of the screen (a white point on a black

background). Each stimulus was presented for

500 ms on the monitor with an interstimulus interval

(ISI) of 1500 ms. Every type of emotional expression

was applied 20 times, resulting in a total of 80 trials.

After a brief introduction to the laboratory, the

subjects were seated in a sound-attenuated, electri-

cally shielded room and they were asked not to blink

during the task. The subject was told to observe the

stimuli carefully, but they were not asked to judge

the emotional content of faces. However, in this

experiment we used an incidental task (gender

decision task). A motor response (by stimpad) to

the features of the stimulus was required (button

response was counterbalanced). Prior to recording

ERPs, the subject was familiarised with the overall

procedure (training session), where every subject

saw in a random order all the emotional stimuli

presented in the successive experimental session

(a block of 16 trials, each type of expression repeated

four times).

Stimulus evaluation task. All the subjects were sub-

sequently asked (after the experimental phase) to

analyse the facial expressions and to express the

degree of their own emotional involvement for each

emotion. In order to rate the emotional valence of

face and the emotional reaction to a single ex-

pression, the subjects were asked to identify each

expression (categorisation of face), to evaluate its

pertinence (category pertinence), and to quantify the

strength of experienced emotions (Balconi & Pozzoli,

2003a; Lang, Greenwald, Bradley, & Hamm, 1993).

They correctly recognised the emotional valence

of the stimuli (correct identification 94.52%; for

neutral expression the definition was: ‘‘no emotion’’)

and they evaluated each expression as highly

pertinent with its emotional category (5-point Likert

scale; fear M¼ 4.73, SD¼ 0.60; happiness M¼ 4.40,

SD¼ 0.51, sadness M¼ 4.25, SD¼ 0.32; neutral

M¼ 4.12, SD¼ 0.83). Moreover, they evaluated on

a 5-point Likert-like scale as more emotionally

involving, the negative high-threat emotion (fear,

M¼ 4.55, SD¼ 0.62) than happiness (M¼ 2.15,

SD¼ 0.68), sadness (M¼ 2.50, SD¼ 0.37) and

neutral (M¼ 1.01, SD¼ 0.80). The statistical sig-

nificance of the difference between the four facial

expressions was tested on univariate analysis of

variance (ANOVA); for the main factor of emotion,

F(3,20)¼ 13.52, p¼ 0.001, Z2¼ .53. A post hoc

comparison (ANOVA for planned contrasts) showed

different responses between anger and happiness,

F(1,20)¼ 9.52, p¼ 0.001, Z2¼ .44, and sadness,

F(1,20)¼ 7.73, p¼ 0.001, Z2¼ .36. Finally, the three

expressions were rated more highly than the neutral

expression, anger F(1,20)¼ 14.12, p¼ 0.001, Z2¼ .50;

happiness F(1,20)¼ 9.02, p¼ 0.001, Z2¼ .40; and

sadness F(1,20)¼ 10.51, p¼ 0.001, Z2¼ .46. Type I

errors associated with inhomogeneity of variance were

controlled by decreasing the degrees of freedom using

the Greenhouse-Geiser epsilon.

Registration and ERP measures. The electroencepha-

logram (EEG) was recorded with a 64-channel DC

amplifer (SYNAMPS system) and acquisition soft-

ware (NEUROSCAN 4.2) at 32 electrode sites

(International 10-20 system, Jasper, 1958) with

reference electrodes at the mastoids, and mounted

in a stretch-lycra electrode cup (high-density regis-

tration). Electroculograms (EOG) were recorded

from electrodes lateral and superior to the left eye.

The signal (sampled at 256 Hz) was amplified and

processed on-line with a pass-band from .01 to

50 Hz and was recorded in continuous mode.

Encoding of emotional facial expression 15

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Impedance was controlled and maintained below

5 KO. Twelve of the registered sites were considered

for the statistical analysis (four central: Fz, Cz, Pz,

Oz; eight lateral: F3, F4, T3, T4, P3, P4, O1, O2).

An averaged waveform (off-line) was obtained from

approximately 20 artefact-free (trials450 mV in

amplitude were excluded from the averaging

process) individual target stimuli for each type of

emotion. The EEG signals were visually scored on a

high-resolution computer monitor and portions of

the data that contained eye movements, muscle

movements, or other sources of artefact were

removed. The percentage of the rejected epochs

was low (5%). Peak amplitude measurement was

quantified relative to 100 ms before stimulus (epoch

duration: –100/900 ms).

Results

Component windows were defined based on grand

average ERP waveforms across all type of emotion

and electrodes. To evaluate differences in ERP

response the data analysis was focused within the

time window 200 – 300 ms after stimulus. The time-

window reference is a common procedure that

allowed us to measure the average variation around

a peak (Rugg & Coles, 1995). In order to analyse

early ERP effects in face encoding, we focalised this

temporal range and we did not consider successive

peak variations. The morphological analysis of waves

confirmed the existence of a consistent ERP negative

deflection (N200) at this time, whereas some succes-

sive deflections (e.g., P300) were not consistently

present.

Two dependent variables, the peak value (calcu-

lated from baseline to peak amplitude) and the

latency of the peak (the time of emergence of the

peak), were entered into three-way repeated-measure

ANOVAs, using the following repeated factors:

type of stimuli (4)6 site (4)6 lateralisation (2).

To assess lateralisation, a lateral electrode factor

(F4, T4, P4, O2 vs. F3, T3, P3, O1) was created.

The site effect (anterior/central/parietal/occipital)

was analysed by means of four separate electrodes

(Fz vs. Cz vs. Pz vs. Oz).

The repeated-measure ANOVA applied to peak

amplitude showed a significant main effect for

type, F(3,20)¼ 18.20, p¼ 0.001, Z2¼ .54, and site,

F(3,20)¼ 13.31, p¼ 0.001, Z2¼ .50, but not for

lateralisation, F(1,20)¼ 1.07, p¼ 0.22, Z2¼ .16.

Table I shows the mean values for each emotion

and electrode site.

The two- and three-way interactions were not

statistically significant. As shown in Figure 1, a peak

at approximately 220 ms (223 ms) is observable for

all of the emotional expressions.

In order to compare different facial expressions, an

ANOVA for planned contrasts was applied for type of

expression. From the analysis it was observed that

happiness, sadness and neutral expressions had a

more positive peak than anger (anger/happiness

comparison: F(1,20)¼ 9.02, p¼ 0.001, Z2¼ .44;

anger/sadness: F(1,20)¼ 10.12, p¼ 0.001, Z2¼ .48;

anger/neutral: F(1,20)¼ 13.53, p¼ 0.001, Z2¼ .55).

In contrast, no differences were found between

happiness and sadness, but they both were differen-

tiated from the neutral face, as shown by the com-

parison happiness/neutral, F(1,20)¼ 7.71, p¼ 0.001,

Z2¼ .40, and sadness/neutral, F(1,20)¼ 6.98,

p¼ 0.001, Z2¼ .37. Second, the planned contrast

analysis applied to the simple effect of site showed

that the negative deflection was higher at the posterior

(Pz) than anterior (Fz), F(1,20)¼ 10.34, p¼ 0.001,

Z2¼ .48, and central (Cz) sites, F(1,20)¼ 6.42,

p¼ 0.001, Z2¼ .39. Figure 2 shows the cortical distri-

bution of N2 as a function of the four sites.

A second repeated measure ANOVA was applied

to the latency dependent measure. No main effect

was significant to the analysis (type: F(3,20)¼ 0.92,

p¼ 0.53, Z2¼ .10; site: F(2,20)¼ 1.30, p¼ 0.29,

Z2¼ .13; lateralisation: F(1,20)¼ 1.02, p¼ 0.26,

Z2¼ .11), nor were their two- and three-way inter-

actions. Therefore, the peak latency was quite similar

in each emotion and in all sites of the scalp.

Table I. Mean values of N2 ERP for each emotion and electrode site (incidental task)

Electrode sites

Fz Cz Pz Oz Right Left

Amplitude (volt)

M SD M SD M SD M SD M SD M SD

Happiness 2.28 .29 2.30 .64 2.28 .61 2.26 .48 2.18 .37 2.26 .44

Sadness 2.14 .37 2.39 .61 2.51 .80 2.40 .56 2.53 .47 2.10 .69

Anger 2.63 .49 2.50 .33 3.40 .55 2.89 .42 2.78 .22 2.42 .73

Neutral 2.04 .40 2.08 .34 2.23 .41 2.10 .69 2.05 .59 2.03 .44

Total mean 2.27 .38 2.31 .48 2.50 .58 2.41 .53 2.38 .41 2.20 .57

Notes. ERP¼ event-related potential. The amplitude values reported are negative.

16 M. Balconi & C. Lucchiari

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Discussion

Our data support the view that emotion discrimina-

tion occurs at the first stage of stimulus processing,

with a latency of approximately 220 ms from stimulus

onset, and that the N2 deflection is affected by

emotional significance of faces (Streit et al., 2000).

First, because all of the emotional expressions were

differentiated from the neutral expression, N2 can

represent an ERP marker of emotional facial exp-

ressions, and not a generic cue of facial stimulus

elaboration. Thus, our data indicate that this compo-

nent reflects specific emotional processing. When the

emotional content of faces is varied (i.e., emotional or

neutral), N2 reacts more to the emotional valence of

the stimulus.

The second main and new result of this research is

that N2 is different among the four facial stimuli in

terms of peak amplitude variation. The different ERP

profiles found as a function of the emotional content

of the stimulus may indicate the sensitivity of this

negative-wave variation to the ‘‘semantic’’ value of

facial expressions (Jung et al., 2000). A more negative

peak is produced by anger than by happiness and

sadness. In contrast, very similar potentials, with

identical early latency and amplitude, were observed

for happy and sad expressions, differentiated from the

negative high-arousal emotion (anger). The results

allowed us to extend the range of emotions and to

explore in detail the functional value of ERPs applied

to facial expressions. Two main parameters seem to

affect the ERP profile: the high/low arousal of the

stimuli (related to their threatening significance) and

the type of emotional expression.

Specifically, negative emotions (such as anger) may

induce a stronger reaction than positive emotions

(such as happiness), with a more intense emotional

response, and emotional intensity may increase

Figure 2. Waveforms of grand-averaged event-related potential (ERP; all expressions) for the cortical sites

Figure 1. Waveforms of the grand-averaged event-related potential (ERP; all electrodes) for the facial stimuli

Encoding of emotional facial expression 17

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while viewing a negative high-threat emotion but

decrease while viewing a negative low-threat emotion

(Lang et al., 1990; Yee & Miller, 1987). This

assumption is strengthened by the finding of the

subject behavioral responses: anger elicited negative

intense feelings, whereas happiness and sadness were

less involving. This would suggest that effects due to

emotional arousal should be greater for unpleasant

salient stimuli, which were rated as slightly more

arousing than less relevant stimuli. Negative, relevant

emotions appear to be prominent as a human

safeguard (Lang et al., 1990). Specifically, they facili-

tate the survival of the species; and the immediate and

appropriate response to emotionally salient (threat-

related) stimuli confers an ‘‘adaptive’’ value on them

(Ellsworth & Scherer, 2003). For example, anger is

related to negative feeling and high attention. This

appraisal produces specific physiological and cogni-

tive reactions.

Experiment 2

The aim of the second experiment was to assess the

effect of an explicit judgement task on neural

responses to facial expressions when multiple emo-

tions were considered within a single experiment.

Previous studies have shown a consistent difference

in face-encoding process based on type of task

(direct vs. incidental task) (Critchley et al., 2000;

Gorno-Tempini, Pradelli, Serafini, Baraldi, & Porro,

2001; Rossion et al., 1999; Winston, O’Doherty, &

Dolan, 2003). Specifically, consistent variations were

observed between an explicit and an implicit task,

where the first includes the request of a direct

elaboration of a specific feature of the stimulus (i.e.,

emotion) and the second does not require a direct

encoding but only an incidental processing (Critchley

et al., 2000). A task effect was observed for words,

objects, and faces. In particular, a significant effect of

face encoding on several cortical and subcortical

regions was modulated by task type and by facial

expressions (Adolphs, 2002; Calder, Lawrence, &

Young, 2001). Nevertheless, the stimulus material

used included only a few emotions (normally

two emotional expressions) (Gorno-Tempini et al.,

2001).

We reasoned that, in contrast to the incidental

encoding condition examined in Experiment 1,

direct encoding would require participants to attend

more closely to emotional features of the stimuli, and

to engage in more evaluative operations in compre-

hending facial expressions. Second, different cortical

wave variations in terms of wave morphology or wave

distribution might indicate that there exists a

qualitative rather than a quantitative difference in

the neural activity underlying the ERP effects in the

two tasks.

Method

Participants. Twenty subjects (different from

Experiment 1), students of psychology at the Catholic

University of Milan, took part in the research. They

all were right-handed and with normal or corrected to

normal visual acuity (12 male, age range 21 – 25 years,

M¼ 23.13 years; SD¼ 0.34 years) and all denied any

history of neurological or mental abnormalities. They

gave informed consent and were neither paid nor did

they receive course credits. The Ethics Committee

approved the study.

Materials and procedure. The same procedure adop-

ted in Experiment 1 was used, as well as the stimulus

material. The main variation was the experimental

task. In order to assess the neural correlates of making

judgments concerning the emotional content of faces,

our design incorporated a direct task, in which

subjects made an emotional judgment concerning

each expression (expression recognition) (Winston

et al., 2003). Prior to recording ERPs, the subjects

were familiarised with the overall procedure, where

every subject saw in random order all the emotional

stimuli presented in the successive experimental

session (16 trials).

Stimulus evaluation task. All the subjects were

subsequently asked to analyse the facial expressions

in a post-experimental phase (for details see Experi-

ment 1). The subjects were asked to identify each

expression, to evaluate their pertinence, and to

quantify the strength of experienced emotions. They

correctly recognised the emotional valence of the

stimuli (correct identification 96.51%; and a judg-

ment of ‘‘no emotion’’ for neutral face,) and evalu-

ated each expression as pertinent (anger M¼ 4.62

SD¼ 0.98; happiness M¼ 4.22 SD¼ 0.83; sadness

M¼ 4.17 SD¼ 0.47; neutral M¼ 4.16 SD¼ 0.63).

Finally, they evaluated as more emotionally involving

and threatening, the negative emotion of anger

(M¼ 4.63 SD¼ 0.72) than happiness (M¼ 2.30

SD¼ 62), sadness (M¼ 2.15 SD¼ .83), and neutral

(M¼ 1.77 SD¼ 0.61). The repeated-measure

ANOVA showed a significant main effect for type of

emotion, F(3,19)¼ 14.32, p¼ 0.001, Z2¼ .53, and the

successive post hoc comparison (ANOVA for con-

trasts) found different responses between anger and the

other emotions (happiness F(1,19)¼ 8.15, p¼ 0.001,

Z2¼ .45; sadness F(1,19)¼8.93, p¼ 0.001, Z2¼ .43).

Neutral expression was differentiated from the other

three emotions (anger F(1,19)¼16.70, p¼ 0.001,

Z2¼ .47, happiness F(1,19)¼15.32, p¼ 0.01, Z2¼.43, sadness F(1,19)¼ 14.25, p¼ 0.03, Z2¼ .42).

EEG registration parameters. EEG was recorded in

the same manner as Experiment 1 (32 electrodes in

18 M. Balconi & C. Lucchiari

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an electrocap, international 10-20 system) with

acquisition software NEUROSCAN 4.2. Only 4%

of the epochs was rejected due to artefacts.

Results

Component windows were defined based on grand

average ERP wave forms across all type of emotion

and electrodes. The time window 200 – 300 ms after

stimulus was used to analyse peak variations, because

morphological investigation of the wave profiles

showed a peak variation analogous to that observed

in Experiment 1, within the same time interval. The

variables were entered into three-way repeated

measure ANOVAs, using as repeated factors

Type of emotion (4)6Site (4)6Lateralisation (2).

Table II shows the mean values as a function of

emotion and electrode sites.

The type of emotion was significant in distinguish-

ing peak variation, F(3,19)¼ 19.35, p¼ 0.001,

Z2¼ .61, as well as site, F(3,19)¼ 7.70, p¼ 0.001,

Z2¼ .40, and there was a Type6Lateralisation

interaction, F(3,19)¼ 8.93, p¼ 0.001, Z2¼ .44.

The contrast analysis indicated differences between

anger and happiness, F(1,19)¼ 13.29, p¼ 0.001,

Z2¼ .47, and anger and sadness, F(1,19)¼ 14.66,

p¼ 0.001, Z2¼ .50. Moreover, all the emotions were

differentiated from the neutral face: anger F(1,19)¼12.45, p¼ 0.001, Z2¼ .47; happiness F(1,19)¼ 10.47,

p¼ 0.001, Z2¼ .44; and sadness F(1,19)¼ 9.53,

p¼ 0.001, Z2¼ .42. The site main effect showed

a more central (Cz), F(1,19)¼ 9.03, p¼ 0.001,

Z2¼ .45, and posterior (Pz), F(1,19)¼ 10.04,

p¼ 0.001, Z2¼ .49, distribution of the peak than

anterior (Fz) position (Figure 3).

Finally, the post hoc comparison for Type6Lateralisation effect a more right distribution of the

peak for the negative expressions of anger,

F(1,19)¼ 8.70, p¼ 0.001, Z2¼ .42, and sadness,

F(1,19)¼ 6.93, p¼ 0.001, Z2¼ .36, compared with

happiness. The same trend was found for the negative

emotions of anger, F(1,19)¼ 9.04, P¼ 0.001,

Z2¼ .47, and sadness, F(1,19)¼ 8.80, P¼ 0.001,

Z2¼ .44, compared with neutral face. Figure 4

presents the topographical maps of the scalp for each

emotion.

Latency was entered as the dependent variable in a

successive repeated-measure ANOVA. The analysis

Table II. Mean values of N2 ERP for each emotion and electrode site (direct task)

Electrode sites

Fz Cz Pz Oz Right Left

Amplitude (volt)

M SD M SD M SD M SD M SD M SD

Happiness 2.08 .33 2.49 .69 2.53 .58 2.39 .40 2.24 .28 2.37 .66

Sadness 1.89 .28 2.70 .72 2.68 .53 2.65 .32 2.92 .43 2.45 .73

Anger 2.39 .41 2.90 .62 3.10 .28 2.93 .57 3.21 .23 2.83 .45

Neutral 2.03 .56 2.25 .91 2.25 .30 2.28 .48 2.15 .20 2.06 .39

Total mean 2.09 .39 2.58 .73 2.67 .42 2.56 .44 2.63 .28 2.42 .55

Notes. ERP¼ event-related potential. The amplitude values reported are negative.

Figure 3. Waveforms of grand-averaged event-related potential (ERP; all expressions) for the cortical sites

Encoding of emotional facial expression 19

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did not find a significant main effect for either type,

site or lateralisation effects.

Direct/incidental task comparison (Experiment 1

and 2). A direct comparison between the two types

of task (direct and incidental) was conducted by a

mixed design ANOVA (Type6Site6Lateralisa-

tion6Task), applied to both peak and latency-

dependent measures. The first ANOVA showed a main

effect for type, F(3,39)¼ 13.05, p¼ 0.001,Z2¼ .48, and

site, F(3,39)¼ 9.32, p¼ 0.001, Z2¼ .42, but not for

task, F(1,39)¼ 1.15, p¼ 0.18, Z2¼ .12, or lateralisa-

tion, F(1,39)¼ 1.17, p¼ 0.23, Z2¼ .10. For the inter-

action effects, Task6Site was significant, F(6,39)¼9.03, p¼ 0.001, Z2¼ .45, as well as Type6Task6Lateralisation, F(3,39)¼ 9.14, p¼ 0.001, Z2¼ .48.

Specifically, in addition to the type effect, the post

hoc comparisons showed a more posterior (Pz),

F(1,39)¼ 5.23, p¼ 0.02, Z2¼ .34, and central (Cz),

F(1,39)¼ 14.24, p¼ 0.001, Z2¼ .49, site of N2 for the

direct task than the incidental task. In contrast, N2 at

the frontal site was similar for the direct and incidental

tasks, F(1,39)¼ 0.73, p¼ 0.32, Z2¼ .09. Moreover, a

more right distribution of the N2 was found for anger

and sadness than for happiness: F(1,39)¼ 10.32,

p¼ 0.001, Z2¼ .46; F(1,39)¼8.08, p¼ 0.001, Z2¼.42, respectively; and neutral faces: F(1,39)¼ 14.67,

p¼ 0.001, Z2¼ .52; F(1,39)¼11.12, p¼ 0.001,

Z2¼ .48; respectively) in direct task. In contrast, no

differences in N2 were found in the incidental task

condition between the left and right sides.

The latency measure was entered in a successive

mixed-design ANOVA. No specific main or interac-

tion effect was significant.

Discussion

The present experiment allowed us to identify some

main effects due to different types of task. First,

we can state the existence of a specific cortical

module devoted to emotional feature analysis, that

is, a specific module for emotional configuration.

Second, we can state that this cortical effect is

activated independently from type of task, because it

was observed in the same form for both the direct

and the indirect conditions. From a morphological

point of view, we showed that the direct task

produces an analogous peak variation to the inci-

dental task, represented by the N200 ERP effect.

We can explain this result by stating that the

emotional encoding is an automatic process, devoted

to extrapolate the emotional meaning from facial

expressions regardless of the type of task (Balconi &

Pozzoli, 2003b). This supposition is compatible with

a model in which simple perception of emotional

faces entailed activation of specific recognition

processes, indexed by the N2 ERP effect (Winston

et al., 2003). Nevertheless, consequent to a direct

comparison between the two types of task, some

consistent differences were found for N2 as a func-

tion of direct and incidental elaboration of the

stimulus, mainly related to the cortical distribution

of the negative deflection. Whereas in the incidental

task N2 was mainly posteriorly distributed, in the

direct elaboration of faces a central localisation was

observed in addition to the posterior (parietal) one.

These differences are in line with previous studies

that found a central larger effect for a direct semantic

task. We can explain this topographical difference by

supposing that encoding in the two tasks may have

engaged neurophysiologically equivalent activity in

differently located neural generators. Alternatively,

encoding in the two tasks may have engaged neuro-

physiologically distinct activity in a different set of

generator populations. While the present data do not

allow a selection between these two possibilities, they

do allow the conclusion that ERP encoding in a

direct task is not simply a stronger version of ERP

encoding in an incidental task, because our findings

suggest that emotional encoding is supported by

multiple neural systems.

A striking finding of this research was the effect of

the emotion category on N2. The peak amplitude

variations as a function of emotions follow the

same direction for the two tasks. The fact that

the motivational features of faces can affect both

Figure 4. Topography of event-related potential maps for each emotion (coronal section, left view)

20 M. Balconi & C. Lucchiari

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the implicit and explicit comprehension of emotions

allows us to suppose that an underlying main factor,

such as arousal, may act in emotion comprehension

and that this factor plays a major role in determining

the cognitive significance of the stimulus. Moreover,

the study indicates that subjects can discriminate

between types of facial emotions even when facial

emotion perception is not task relevant, concomitant

with the idea that facial expression is processed

automatically (Blair, Morris, Frith, Perrett, & Dolan,

1999; Dolan et al., 1996; Vuilleumier, Armony,

Driver, & Dolan, 2001).

Finally, an interesting effect was the lateralisation

observed as a function of type of emotional expres-

sion in the direct task. N200 peak amplitude was

higher to the right than the left side for the negative

expressions (anger and sadness) compared with the

positive emotion (happiness). This needs to be

explored further in the future, because N2 may turn

out to be a marker of the left – right processing

dichotomy in relation to the type of emotion. In this

regard, future research must consider the lateralisa-

tion effect more closely, through a more direct

comparison between the processes of production

and recognition of facial expressions.

General discussion

In the present study we investigated the processes of

encoding of emotional facial stimuli in two different

conditions of elaboration: direct and incidental

tasks. The elaboration of emotional facial expres-

sions appears indexed by a specific ERP effect, the

N2 effect. The emotional specificity of N2 is

underlined by the major differences observed

between emotional and neutral stimuli. In line with

the Bruce and Young (1998) model, we postulate

that a specific neural mechanism could exist for the

processing of facial expressions of emotion. In

addition, N2 can be considered a marker of the

specific emotional content because it was observed

to vary in amplitude as a function of type of

emotion, and more specifically of motivational

significance for the subject. The peak increases as

the subject appears more emotionally aroused and

attentively involved by the stimulus. Recent re-

search emphasises that motivational relevance is a

primary determinant of selective attention: somatic,

autonomic, and cortical events associated with

orienting are automatically activated by more

emotionally arousing representations in a variety of

paradigms, independently from instructional direc-

tion and from task condition, because the relevance

of the stimulus is pre-task or ‘‘intrinsic’’ (Lang

et al., 1997). From this perspective, the significance

of emotional expression for the subject, in terms

of low/high-threat power and relevance, should

influence both the physiological (i.e., arousal) and

the cognitive level (mental processes and attentional

effort), and has an important effect on ERP

correlates (Balconi & Pozzoli, 2003a; Frijda, 1986;

Keil et al., 2002; Lang et al., 1993; Schorr, 2001;

Wild et al., 2001).

The absence of differences in the cortical distribu-

tion of the peak related to type of emotion is a fact

that must be considered here. Whereas the idea of

the right hemisphere advantage in facial identity

recognition has been extended to facial expression

processing, our study did not find a clear superiority

of one hemisphere in the encoding of emotional

faces. However, it should be noted that recent data

exist indicating that the right dominance in facial

expression recognition is modulated by variables

such as the task requirements, which can modify the

right-hemisphere advantage. Therefore, the laterali-

sation of ERP is a major aspect to be considered in

relation to task manipulation.

We can summarise the task effect for encoding

processing of face into two main points: the cortical

distribution of the N2 on the scalp and the

lateralisation of the peak deflection. We observed a

more posterior and central localisation of N2 for

direct compared to incidental conditions. It follows

that at least one aspect of the cognitive operations

associated with emotional encoding in the two tasks

could differ. Either the cognitive processes that

enable the encoding, the type of information the

processes act upon, or both, differ depending on the

type of task.

A second result related to task manipulation is a

right lateralisation effect observed for negative

emotions in comparison with positive and neutral

emotions for the direct task, but not for the

incidental task. A specific right lateralisation for

negative emotions was found when the subjects had

to be attentive to the emotional content of faces. A

considerable number of studies have investigated the

lateralisation of emotional processing. According to

the ‘‘right hemisphere hypothesis’’, the right hemis-

phere plays a superior role in emotional processing,

such as recognition of both positive and negative

emotions (Borod et al., 1998 ). An alternative view

(the ‘‘valence hypothesis’’) is that the right hemi-

sphere primarily mediates negative rather than

positive emotions. Our data seem to be better

explained by the valence model of lateralisation,

but it is not clear why this effect was found

exclusively in the direct task condition. It is possible

that this localisation effect is a consequence of

differences in attentional effort in processing the

stimuli. That is, in a direct task negative and positive

emotions may be more clearly distinct, with a related

activation of right side of the scalp only for the

emotional face evaluated as negative.

Encoding of emotional facial expression 21

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