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Journ al of Personal ity and Socia l Psychology Copyright 1990 by the Am erica n Psychologica l Associa tion, Inc .

1990, Vol , 58, No. 2 , 330-341 0022-3514/90/$00.75

A p p r o a c h W i th d r a w a l a n d C e re br al A s y m m e t ry :

Em ot iona l E xpress ion and Bra in Phys io logy I

Richard J Davidson

U n i v er s it y o f W i s c o n s i n - - M a d i s o n

Clifford D Saron and Joseph A Senulis

U n i v er s it y o f W i s c o n s i n - - M a d i s o n

Paul Ekman

H u m a n I n t e r a c ti o n L a b o r a t o r y

U n ive r s i ty o f C a l i fo rn ia , S a n Fra n c i s c o

Wallace V Friesen

U n i v e r s it y o f C a l i f o r n i a , S a n F r a n c i s c o

In this experiment, w e combined the measurement of observable facial behavior with s imultaneous

measures o f brain electrical activity to assess patterns o f hemispheric activation in different regions

during the experience of happiness and disgust. Disgust was found to be associated with right-s ided

activation in the frontal and anterior tem poral regions compared with the happy condition. Happi-

ness was accompanied by left-s ided activation in the anterior tem poral region compared with disgust.

No differences n asym metry were found between emotions in the central and p arietal regions. When

data aggregated across positive films were compared to aggregate negative film data , no reliable

differences in brain activity were found. These finding s illustrate the utility of using facial behavior

to verify the presence o f emotion, are consis tent with the notion of emotion-specific physiological

patterning, and underscore the importance of anterior cerebral asymm etries for emotions associated

with approach and withdrawal.

T h i s a n d t h e a c c o m p a n y i n g r e p o r t ( E k m a n , D a v i d so n , &

F r i e se n , 1 9 9 0 ) r e p r e s e n t t h e c o n v e r g e n c e o f t w o i n d e p e n d e n t

y e t o v e r la p p i n g l in e s o f r e s e ar c h . O n e i s t h e o r y a n d e v i d e n c e

f r o m E k m a n ' s l a b o r a t o r y , w h i c h , f r o m a n e v o l u t i o n a r y p e r -

s p e c t ive , t a ke s th e p o s i t i o n th a t e a c h e mo t io n i s c h a ra c t e r i ze d

b y u n i q u e p a t t e r n s o f e x p re s si v e b e h a v i o r a n d p h y s i o lo g i c a l a c -

t iv i ty ( e. g. , E kma n , 1 9 7 7, 1 9 8 4) . T h e s e c o n d i s r e s e a rc h f ro m

D a v i d s o n ' s l a b o r a t o r y o n c e r e b r a l a s y m m e t r y a n d e m o t i o n ,

w h i c h i n d i c a te s t h e d i f fe r e n ti a l i n v o l v e m e n t o f t h e t w o c e r e b r a l

h e m i s p h e r e s i n t h e c o n t r o l o f c e r t a i n p o s it i ve a n d n e g a t i v e e m o -

t io n s (e .g ., D a v id s o n , 1 9 8 4 a , 1 9 8 4 b , 1 9 8 7 ; D a v id s o n & T o ma r -

ken, 1989).

P s y e h o p h y s io l o g i c a l S pe c i fi c it y a n d E m o t i o n

T h e d e g r e e t o w h i c h d i ff e r e n t e m o t i o n s a r e a c c o m p a n i e d b y

u n iq u e p a t t e rn s o f p h y s io lo g ic a l a c t iv i ty is a qu e s t io n a s o ld a s

t h e s t u d y o f e m o t i o n i t se lf . T w o d i a m e t r i c a l l y o p p o s e d p o s i t i o n s

o n t h i s i s s u e h a v e b e e n a d v a n c e d , w i t h a r d e n t s u p p o r t e r s o f

e a c h v iew . C o g n i t ive th e o r i s t s ( e. g. , Ma n d le r , 1 9 7 5 ; S c h a c h te r

& S ing e r, 1 9 62 ) , fo l lo w in g C a n n o n ( 1 9 2 7 ) , h a ve c l a im e d th a t

d i f f er e n t e m o t i o n s a r e a c c o m p a n i e d b y t h e s a m e p a t t e r n o f u n -

d i f f e re n t i a t e d p h y s io lo g ic a l a ro u s a l . T h e s e c o n d p o s i t i o n , c o n -

This research was supported b y grants from the N ational Institute of

Mental Health (MH 40747 and MH 43454) and the Graduate School

of the University of W isconsin to Richard J . Davidson and by Research

Scientist Award MH 06092 from the N ational Institute of Mental

Health to Paul Ekman.

We wish to thank Andrew Tomarken for valuable comm ents on an

earlier draft o f his artic le , and Linda Kinney, Barry Cohen, Barry Go r-

don, and Andrea Straus for assis tance with the d ata analysis .

Correspondence concerning this artic le should be addressed to Rich-

ard J . Davidson, Department of Psychology,University of Wisconsin,

1202 West Johnson Street, Madison, W isconsin 53706.

330

s i st e n t w i t h t h e t h e o r e t ic a l w r i t in g s o f D a r w i n ( 1 8 7 2 / 1 9 5 5 ) a n d

J a m e s ( 1 8 9 0) , a s se r t s t h a t d i f f e r e n t e m o t i o n s a r e a c c o m p a n i e d

b y u n iqu e p a t t e rn s o f p h y s io lo g ic a l a c t iv i ty (e .g ., A x , 1 9 5 3) . E k-

m a n ( 1 9 8 4 ) h a s s p e c if i ca l ly s ug g e s te d t h a t u n i q u e c e n t r a l o r a u -

t o n o m i c p a t t e r n s w i ll d i f f er e n t ia t e a m o n g t h e p r i m a r y e m o -

t io n s o f h a p p in e s s , s a d n e s s , a n g er , f e ar , d i s g u s t , a n d s u rp r i s e .

T h e r e a r e n o w d a t a a v a il a b le t h a t a r e b e g i n n i n g t o i l l u m i n a t e

t h i s d e b at e . E k m a n a n d h i s c o l l ea g u e s ( E k m a n , L e v e n s o n , &

Fr ie s e n , 1 9 8 3 ; L e ve n s o n , E km a n , & F r i e s e n , i n p re s s ) h a ve u n -

c o v e r e d e v i d e n c e f o r u n i q u e p a t t e r n s o f a u t o n o m i c a c t iv i t y t h a t

d i f f e re n t i a t e a m o n g th e n e g a t ive e m o t io n s o f fe a r, a n g er , d i sg u s t ,

a n d s a d n e s s , a n d d i f f e re n c e s b e tw e e n th e s e n e g a t ive e mo t io n s

a n d h a p p in e s s . O th e r i n ve s t ig a to r s h a ve a l s o r e p o r t e d r e l i a b le

d i f f e re n t i a ti o n a m o n g s o m e n e g a t iv e e m o t i o n s o n t h e b a s i s o f

me a s u re s o f a u to n o m ic p h y s io lo g y ( e. g. , S c h w a r tz , We inb e rg e r,

& Singer, 1981).

T o d a te , t h e re h a s b e e n l i t t l e r e s e a rc h th a t h a s e xp lo re d th e

h y p o t h e s i s o f d i st i n ct i v e c e n t r a l n e r v o u s s y s t e m p a t t e r n s t h a t

d i f f er e n t ia t e a m o n g t h e p r i m a r y e m o t i o n s . A n u m b e r o f e l e-

m e n t a r y c i r c u i ts f o r c e r t a i n c o n s t e ll a t io n s o f e m o t i o n a l b e h a v -

io r h a ve b e e n d e s c r ib e d (s e e P a p e z , 1 9 3 7 , a n d M a c L e a n , 1 9 4 9 ,

f o r e a r ly a n a l ys e s o f th i s p r o b l e m a n d P a n k s e p p , 1 9 8 2 , fo r a

m o r e m o d e r n v i e w ) , a l t h o u g h t h e d e g r e e t o w h i c h t h e s e m a p

o n t o d i s c r e t e e m o t i o n s i n h u m a n s i s n o t e n t i r e l y cl ea r. B e c a u s e

u n iqu e e xp re s s ive s ig n a l s a n d s u b j e c t ive e xp e r i e n c e c h a ra c t e r -

i z e e a c h o f t he s e p r i m a r y e m o t i o n s , o n e w o u l d e x p e ct t h e m t o

b e a s s o c ia t e d w i th d i s t in c t ive , i n va r i a n t p a t t e rn s o f c e n t r a l n e r -

v o u s s y s t e m a c t i v it y a t s o m e l e ve l o f t h e n e u r a x is . O n e i m p o r -

t a n t g o a l o f t h e p r e s e n t r e s e a r c h i s t o a d v a n c e k n o w l e d g e r e-

g a r d i n g t h i s u n e x p l o r e d t o p ic .

C e r e b ra l A s y m m e t r y , A p p r o a c h - W i t h d r a w a l ,

a n d E m o t i o n

I t i s t h e s e c o n d b o d y o f r e s e a r c h t h a t p r o v i d e s a u s e f u l t h e o -

re t i c a l g u id e fo r s p e ci f i c h y p o th e s e s a b o u t t h e d i s t in c t ive c e n t ra l



B R A IN A SY MMETR Y A N D A PPR O A C H -WI TH D R A WA L 331

n e r v o u s s y s t e m a c t i v it y f o r s o m e o f t h e e m o t i o n s . D a v i d s o n a n d

o t he r s ha ve a m a s s e d a va r i e t y o f e v i de nc e ove r t he pa s t l 0 ye a r s

t h a t i n d i c a t e s t h a t t h e a n t e r i o r r e g i o n s o f th e t w o h e m i s p h e r e s

o f t he b r a i n ( f r on t a l a nd a n t e r i o r t e m por a l ) a r e d i f fe r e n t i al l y

i nvo l ve d i n c e r t a i n pos i t ive a nd ne ga t i ve e m ot i on s ( s ee r e v ie w s

by D a v i ds on , 1984a , 1984b ; D a v i ds on Tom a r ke n , 1989 ;

K i n s b o u r n e B e m p o r a d , 1 9 8 4 ; L e v e n t h a l T o m a r k e n , 1 9 8 6 ;

S i l be r m a n We i nga r t ne r , 1986 ; Tuc ke r F r e de r i c k , 1989) .

D a v i d s on ( 1984a , 1987) , f o l l ow i ng a n e a r l y s ugge s t i on o f K i ns -

b o u r n e ' s ( 1 9 7 8 ) c o n c e r n i n g th e r e l a ti o n b e t w e e n a p p r o a c h b e -

ha v i o r a nd t he l e f t he m i s phe r e , ha s t he o r i z e d t ha t t he f unda -

m e n t a l c o n t i n u u m a l o n g w h i c h t h e a n t e r i o r c o r t ic a l r e g io n s a r e

l a t e r a li z e d i s a pp r oa c h - w i t hd r a w a l , w i t h t he l e ft a n t e r i o r r e g i on

s u b s e r v in g a n a p p r o a c h s y s t e m a n d t h e h o m o l o g o u s r ig h t h e m i -

s phe r e r e g i on s ubs e r v i ng a w i t hd r a w a l s ys t e m . D a v i ds on ha s

f u r t h e r a r g u e d t h a t t o t h e d e g r ee t h a t a p p r o a c h a n d w i t h d r a w a l

a r e c o m p o n e n t s o f d i f fe r e n t e m o t i o n s , s u c h e m o t i o n s s h o u l d

d i f f er e n t ia l l y a c t iva t e t he a n t e r i o r r e g i ons o f t he t w o c e r e b r a l

he m i s phe r e s . Fo r e xa m pl e , s e ve r a l e m o t i on t he o r i s t s (e .g ., Ek -

m a n Fr i e s e n , 1975 ; P l u t c h i k , 1980) ha ve no t e d t ha t bo t h f e a r

a n d d i s g u st o f t e n i n c l u d e b e h a v i o r a l c o m p o n e n t s o f w it h -

d r a w a l , a l t hough i n s om e w ha t d i f f e r e n t f a s h i ons . Fo r f e a r , Ek -

m a n p r o p o s e s t h a t w i t h d r a w a l e n t a il s e s c a p i n g f r o m t h e t h r e a t -

e n i ng s t i m u l us , w he r e a s i n d i s gus t t he w i t hd r a w a l e n t a i ls t e r m i -

na t i ng t he i npu t , w he t he r i t be o l f a c t o r y , o r a l , o r v i s ua l .

t n t h i s e x p e r im e n t , w e s o u g h t t o e x a m i n e t h e p a t t e rn o f b r a in

e l e c t ri c a l a c t i v i ty de r i ve d f r om m ul t i p l e s c a l p l oc i du r i n g t he s e

t w o w i t hd r a w a l e m ot i ons , f e a r a nd d i s gus t . The b r a i n a c t i v i t y

d u r i n g t he s e e m o t io n s w a s to b e c o m p a r e d t o a n a p p r o a c h e m o -

t i on , ha pp i ne s s , a nd a ba s e l ine c ond i t i on . W e us e d s ho r t , 1 - m i n

pos i t i ve a nd ne ga t i ve f i l m c l i p s t o a r ous e t he s e d i f f e r e n t e m o-

t iona l s ta tes .

M e t h o d o l o g i c a l D e s i d e r a t a f o r P s y c h o p h y s i o l o g i c a l

R e s e a rc h o n E m o t i o n

B e l ow w e no t e e i gh t c ha r a c t e r i s t i c s t ha t i de a l ly s hou l d b e i n -

c o r p o r a t e d i n t o a l l r e s e a r c h on t he b i o l og i c a l s ubs t r a t e s o f hu -

m a n e m o t i o n a n d t h a t a p p ly t o s t u di es o f b o t h a u t o n o m i c a n d

c e n t r a l n e r v o u s s y s t e m c o m p o n e n t s o f e m o t i o n . W e t h e n i l lu s -

t r a t e how t he p r e s e n t r e s e a r c h c o n f o r m s t o t he s e de si de r a t a.

1. E mo tion m ust b e actually e lic ited.

A l t ho ugh t h i s r e qu i r e -

m e n t m a y s e e m t r iv i al , m a n y e x p e r i m e n t s t h a t p u r p o r t t o s t u d y

e m o t i o n m a y n o t a c t u a l l y i n v o l v e t h e p r o d u c t i o n o f e m o t i o n i n

s u b je c ts . S o m e s t u d ie s f o c u s m o r e o n t h e p e r c e p t i o n o f e m o -

t i o n a l i n f o r m a t i o n , w h e r e a s o t h e r s e x a m i n e t h e l a n g u a g e t h a t

i s u s e d t o d e s c r i be e m ot i on . I f t he goa l o f t he r e s e a r c h i s t o

c h a r a c t e r iz e t h e p s y c h o p h y s i o l o g y o f e m o t i o n , t h e n t h e r e m u s t

be e v i de nc e , a pa r t f r om t he de pe nd e n t v a r i a b l e o f i n t e re s t , t ha t

e m o t i o n w a s a c t u a ll y p r o d u c e d .

2 . Adequate procedures m us t be used to ver if y the presence o f

the in tended emot ion .

O n e o f th e n o t e w o r t h y c h a r a c t e ri s ti c s o f

e m o t i o n i s t h e l a c k o f a n i s o m o r p h i c r e l a t io n b e t w e e n a n e l ic i to r

a nd a pa r t i c u l a r e m ot i on ( s e e Ek m a n , 1984) . I n o t he r w or ds , the

s a m e e l ic i to r w i ll o f t e n p r o d u c e a n a r r a y o f d if f e re n t e m o t i o n s

a c r os s s ub j e c ts . E ve n i n r e s pons e t o e l i c it o r s t ha t a r e s pe c i fi c a ll y

c hos e n t o t a r ge t a pa r t i c u l a r d i s c r e t e e m ot i on , s ub j e c t s t yp i c a l l y

w i l l r e po r t a r a nge o f d i ff e r e n t e m ot i on s i f g i ve n t he op po r t un i t y

( e.g. , Ek m a n , F r i e s e n , A nc o l i , 1980) . Som e t i m e s t he s e o t he r

e m ot i ons a r e e xp e r i e nc e d a t d i f f e r e n t po i n t s i n t i m e ove r t he

c ou r s e o f a n e l i c i ti ng e ve n t a nd , a t o t he r t i m e s , e m o t i on s m i gh t

be p r oduc e d i n b l e nds , w i t h d i f f e r e n t e m ot i ons e xpe r i e nc e d s i -

m u l t a n e o us l y . W h a t e v e r t h e t i m e c o u r s e o f th e d i f f e re n t e m o -

t i ons , w e be l i e ve t ha t t he u s e o f s e l f -r e po r t i s i n s u f fi c i e n t t o ve r -

i f y t he p r e s e n c e o f t he e m ot i on i n t e nde d by t he i nve s t iga t o r , i f

a s e l f - r e po r t i n s t r um e n t a s ks on l y a bou t t he t a r ge t e d e m ot i on .

Suc h a m e a s u r e w i l l no t be s e nsi ti ve t o t he pos s i b i l it y t ha t o t he r

e m o t i o n s m i g h t h a v e b e e n e x p e r i e n c e d i n a d d i t i o n t o t h e t a r g e t

e m o t i o n .

W e b e l ie v e t h a t o n e o f t h e m a j o r m e t h o d o l o g i c a l i n a d e q u a -

c i e s in p r e v i o u s p s y c h o p h y s i o lo g i c a l r e s e a rc h o n e m o t i o n h a s

be e n t he f a i l u r e t o ve r i fy w i t h p r e c i s i on t ha t t he i n t e nde d e m o-

t ion w as e l i c i ted in ev ery subjec t . Typ ica l ly , it i s only the inves t i -

g a t o r ' s p r e s u m p t i o n t h a t s u p p o r t s t h e p o s s ib i li ty t h a t t h e e m o -

t i o n e l ic i to r p r o d u c e d t h e i n t e n d e d e m o t i o n . T h e p h y s i o lo g y i n

r e s pons e t o t he e l i c i t o r i s u s ua l l y e xa m i ne d w i t hou t r e ga r d t o

ve r i f y i ng t he i nve s t i ga t o r ' s p r e s um pt i on .

3. E poch s o f di f ferent discrete em otions mu st be separable .

G i ve n t he l i ke l i hood t ha t a ny g i ve n e l i c i t o r w i l l p r oduc e m or e

t ha n one e m ot i on t h a t m a y c ha nge s e que n t i a l ly ove r t i m e , i t is

i m pe r a t i ve t o i de n t i f y s e pa r a t e e poc hs du r i ng w h i c h d i f f e r e n t

d i s c r e t e e m ot i on s a r e p r e s e n t . O n l y i n t h i s w a y c a n t he phy s i o l -

o g y th a t a c c o m p a n i e s d i ff e r en t e m o t i o n s b e c o m p a r e d . N o t e

t ha t t h i s r e qu i r e m e n t ne c e s s i ta t e s a m e t hod , s uc h a s t he a na lys i s

o f f a c ia l be ha v io r , t ha t p r ov i de s a c o n t i nu ous o r ne a r - c on t i nu -

o u s m e a s u r e o f e m o t i o n a l s ta te . U s i n g s u c h a m e a s u r e , a n i n -

ve s t i ga t o r c a n t he n e x t r a c t , pos t hoc , t hos e pe r i ods du r i ng

w hi c h d i f f e r e n t d i s c r e t e e m ot i ons w e r e p r e s e n t . B e c a us e m os t

phys i o l og i c a l st ud i e s a gg r e ga t e da t a ove r the e n t i r e l e ng t h o f t he

e l i c i t i ng s t i m u l us , e m o t i ons o t he r t ha n t he i n t e nde d one w ou l d

c on t r i bu t e t o t he phys i o l og i c a l c ha nge s obs e r ve d . P r e v i ous f a i l-

u r e s t o f i nd phys i o l og i c a l d i f f e r e n t ia t i on a m on g e m ot i on s m a y ,

a t l e a s t in pa r t , be a t t r i bu t a b l e t o t he f a i l u r e t o c om pa r e d i ff e r-

e n t d i s c r e t e e m ot i ons . Mos t i nve s t i ga t o r s unw i t t i ng l y c om pa r e

b e t w e e n t w o o r m o r e b l e n d s o f e m o t i o n .

4 . Behav iora l and physiologica l measures o f emot ion mu s t

be appropriate ly synchronized.

I f a c o n t i n u o u s b e h a v i o ra l m e a -

s u r e o f e m o t i on i s u s e d t o f l a g e poc hs du r i ng w h i c h d i f f e re n t

d i s c r e t e e m ot i on s a r e p r e s e n t , t he be ha v i o r a l a nd p hys i o l og i c a l

d a t a s t r e a m s m u s t b e a c c u r a t e l y s y n c h r o n i z e d . T h i s n e c e s s i -

t a te s t h e u s e o f c o m m o n , s i m u l t a n e o u sl y p r o d u c e d s i g n a ls o n

t h e v i d e o t a p e r e c o r d a n d t h e c o m p u t e r i n w h i c h t h e p h y s io l o g i-

c a l da t a a r e s t o r e d .

5. The physiological mea sures chosen for s tud y mu st have a

suJ~iciently as t t im e constant to re flect br ie fper iods o f emot ion .

G i ve n t he r e l a t ive l y f le e t ing na t u r e o f e m ot i on , w i t h m o s t e p i -

sodes l as t ing less than 4 s (Ekman, 1984) , i t i s c lear tha t only

t hos e phys i o l og i c a l p r oc e s s e s t ha t ha ve a r e l a t i ve l y f a s t t i m e

c ons t a n t a r e l og i c a l c a nd i da t e s t o e xa m i ne t he phys i o l og i c a l

s ubs t r at e s . C e r t a i n l y , o t he r a f f e c ti ve phe no m e na r e l a t e d t o e m o-

t i on , s uc h a s m o od , ha ve l onge r du r a t i ons a n d w ou l d t he r e f o r e

be e xpe c t e d t o i nvo l ve o t he r phys i o l og i c a l s y s t e m s w hos e r e -

s p o n s e p r o p e r ti e s a r e m o r e e n d u r i n g .

6. At leas t two emotions and a basel ine condit ion must be

compared. M a n y e x p e r i m e n t s o n t h e p s y c h o p h y s i o lo g y o f e m o -

t i on , i nc l ud i ng s om e o f ou r ow n p r e v i ous s t ud i e s (e .g ., D a v i d -

s on , Sc hw a r t z , Sa r on , B e nn e t t , G o l e m a n , 1979) , ha ve on l y

i n c l u d e d t w o e m o t i o n c o n d i t i o n s. T h e p r o b l e m w i t h t h is s t r at -

e g y is t h a t n o n o n e m o t i o n r e f e r e n c e c o n d i t i o n is i n c lu d e d .

T h u s , i t w o u l d b e i m p o s s i b l e t o c o n c l u d e w h i c h , i f a n y , o f t h e

e m ot i on c ond i t i ons w ou l d d i f f e r f r om a ba s e l i ne pe r i od . I n a

s t udy i nv o l v i ng a c om pa r i s o n o f t w o e m ot i ons , i t is pos s ib l e



3 3 2 D A V I D S O N , E K M A N , S A R O N , S E N U L IS , F R I E S E N

t h a t t h e t w o c o n d i t i o n s c o u l d d i f f e r f r o m e a c h o t h e r , b u t n o t

f r o m a b a s e l i n e c o n d i t i o n . I t i s a ls o p o s s i b l e t h a t o n l y o n e o f th e

e m o t i o n c o n d i t i o n s w o u l d d i f f e r f r o m b a s e l in e . I n s t u d i e s t h a t

c o m p a r e o n l y o n e e m o t i o n c o n d i t i o n w i t h a b a s el i ne , i t is i m -

p o s s i b l e t o c o n c l u d e w h e t h e r t h e p h y s i o l o g i c a l c h a n g e s o b -

s e r v e d d u r i n g t h e e m o t i o n p e r i o d a r e u n i q u e t o t h a t s p e c i f ic

e m o t i o n o r a r e n o n s p e c i f i c c h a n g e s a s s o c i a t e d w i t h a n y e m o -

t i o n . F o r t h is r e a s o n , a t l e a st tw o e m o t i o n c o n d i t i o n s a n d a b a s e -

l i n e a r e r e q u i r e d .

7 The intensity of the e lic i ted emotion mu st be matched

among conditions

W h e n t w o o r m o r e e m o t io n s a r e c o m p a r e d ,

i t i s i m p e r a t i v e t o m a t c h t h e i n t e n s i t y o f e m o t i o n s o t h a t d i f f e r-

e n c e s i n i n t e n s i t y d o n o t c o n f o u n d t h e e m o t i o n - s p e c i f i c c o m -

p a r is o n s . M a n y i n v e s ti g a to r s w h o h a v e c o m p a r e d t w o o r m o r e

e m o t i o n s h a v e n o t u s e d a n y p r o c e d u r e t o m a t c h t h e i n te n s i ty

o f t h e e l ic i t ed e m o t i o n s ( e .g . , S c h w a r t z e t a l ., 1 9 8 1 ). I f t w o e m o -

t i o n s d i ff e r i n s o m e p a r a m e t e r o f p h y s i o lo g y , b u t a l s o d i f f e r i n

i n te n s i ty , i t i s n o t p o s s i b l e t o d i s e n t a n g l e w h e t h e r t h e p h y s i o l o g -

i c a l d i f fe r e n c e s a r e s i m p l y a f u n c t i o n o f t h e i n t e n s i ty o f e m o -

t i o n - r e l a t e d a c t i v a t io n p e r s e , o r r a t h e r a r e a s s o c i a t e d w i t h t h e

s p e c if i c e m o t i o n t h a t w a s e l i c it e d .

8 The data m ust be of su~icient duration fo r each emotion

under study

P r e c i s e l y wh a t c o n s t i t u t e s a s u f fi c i e n t d u r a t i o n w i l l

v a r y a s a f u n c t i o n o f t h e p h y s i o l o g ic a l m e a s u r e s o f in t e r e st . I f

s t a b l e e s t i m a t e s o f p h y s i o lo g i c a l a c t iv i t y a r e t o b e o b t a i n e d , a

c e r t a in m i n i m u m a m o u n t o f a rt i fa c t -f r e e d a ta i s r eq u i r ed .

W i t h i n - s u b j e c t a g g r e g a t i o n i s p e r f o r m e d t o a r r i v e a t a s i n g l e

i n d e x o f a p a r t i c u l a r p h y s i o l o g i c a l v a r i a b l e f o r a c e r t a i n e m o -

t i o n a l s t a t e f o r e a c h s u b j e c t. F o r e x a m p l e , i f p h y s i o l o g ic a l a c t iv -

i t y d u r i n g s m i l i n g w a s o f in t e r e s t, a l l in s t a n c e s o f t h e a r t i f a c t -

f r e e p h y s io l o g y d u r i n g t h e t a r g e t s m i l e s w o u l d b e e x t r a c t e d , a n -

a l y z e d , a n d t h e n a ~ g gr eg a te d f o r e a c h s u b j e c t . I f t h e d e p e n d e n t

m e a s u r e w a s t h e e le c t ro e n c e p h al o g ra m ( E E G ) , a m i n i m u m o f

a p p r o x i m a t e l y 1 0 s ( a c r o s s a ll i n s ta n c e s o f t h e t a r g e t e m o t i o n )

w o u l d b e r e q u i r e d t o o b t a i n a s t a b l e e s t i m a t e o f s p e c t r a l p o w e r

( D a v i d s o n , 1 98 8 ). N o t e t h a t a l t h o u g h 1 0 t o t a l s e c o n d s a r e r e -

q u i r e d , e a c h i n d i v i d u a l e p o c h o f s m i l i n g c a n b e q u i t e b r i e f , a s

s h o r t a s 1 s p e r e x p r e s s i o n p e r i o d .

T h e s t u d y r e p o r t e d h e r e w a s d e s ig n e d t o a c c o m m o d a t e e a c h

o f t h e se e i g h t m e t h o d o l o g i c a l d e s i d e r a t a . S h o r t f i l m c l i p s w e r e

u s e d t o e l i c i t e m o t i o n . T h e s e c l i p s h a v e b e e n u s e d e x t e n s i v e l y

i n p r e v i o u s e m o t i o n r e s e a r c h a n d h a v e b e e n f o u n d t o e l i c it b o t h

s e l f - r e p o r t a n d f a c i a l s i g n s o f p o s i t iv e a n d n e g a t i v e e m o t i o n t h a t

a r e c o m p a r a b l e i n i n t e n s i t y ( e .g . , E k m a n e t a l. , 1 9 8 0) . T o v e r i f y

t h e p r e s en c e o f t h e t ar g e t e m o t i o n , w e u s e d a c o m b i n a t i o n o f

f a c i al b e h a v i o r a n d s e l f - r e p o r t c ri t e r ia . T h e f a c i al b e h a v i o r w a s

u s e d t o f l ag t h e o n s e t a n d o f f se t o f d i f f e r e n t f a ci a l s ig n s o f e m o -

t i o n . W e u s e d s e l f - r e p o r t c r i t e r i a t o e n s u r e t h a t s u b j e c t s w e r e

r e p o r t i n g e m o t i o n s w h o s e v a l e n c e w a s c o n s i s t e n t w i t h t h e f il m

c l ip u s e d a n d t o e n s u r e t h a t t h e i n t e n s i t y o f t h e r e p o r t e d p o s i t i v e

a n d n e g a t i v e a f f e c t w a s m a t c h e d . W e e x t r a c t e d h a p p y e p o c h s

f r o m p o s i t i v e f i l m c l i p s a n d d i s g u s t e p o c h s f r o m t h e n e g a t i v e

f i lm c l ip s . W e h a d e x p e c t e d t o b e a b l e t o a l s o e x t r a c t f e a r e p -

o c h s , b u t h a p p y a n d d i s g u s t w e r e t h e o n l y f a c ia l e x p r e s s i o n s t h a t

o c c u r r e d w i t h s u f f ic i e n t fr e q u e n c y .

T h e E E G m e a s u r e s w e r e p re c i se l y s y n c h r o n i z e d w i t h t h e f a-

c i a l b e h a v i o r b y h a v i n g th e s a m e t ri g g e r s p r o d u c e e v e n t m a r k s

o n t h e v i d e o r e c o r d a n d t h e c o m p u t e r d a t a b a s e s i m u l t a ne o u s ly .

T h e u s e o f E E G , a n d t h e a n a ly t i c m e t h o d e m p l o y e d t o q u a n t if y

t h e E E G , e n s u r e d t h a t a s u f f i c i e n t l y a c c u r a t e t i m e r e s o l u t i o n

w a s a c h ie v e d . C h u n k s o f E E G 1 . 02 s i n d u r a t i o n s e r v e d a s t h e

e p o c h l e n g t h f o r a n a l y s is . T h e s e c h u n k s w e r e o v e r l a p p e d b y

7 5 . T h e a n a l y s i s e p o c h s t a r t e d a t t h e p r e c i s e t i m e o f t h e o n s e t

o f th e f a c ia l e x p r es s io n . O u r s t u d y c o m p a r e d t h r e e p e r i o d s - -

h a p p y e x p r e s s i o n s , d i s g u s t e x p r e s s i o n s , a n d b a s e l i n e - - t h u s e n -

a b l in g u s t o s p e c i fy b o t h t h e d e g r e e t o w h i c h E E G s d u r i n g e a c h

e x p r e s s i o n t y p e d i f f e r e d f r o m e a c h o t h e r a n d f r o m a r e s t i n g

b a s e l in e . F i n a l ly , w e r e q u i r e d a m i n i m u m o f l 0 s o f a r t i f a c t -f r e e

E E G d u r i n g e a c h e x p r e s s i o n t y p e ( a g g r e g a t e d a c r o s s m u l t i p l e

i n s t a n c e s o f t h e e x p r e s s i o n ) t o u s e a s u b j e c t ' s d a t a f o r t h a t e x -

p r e ss i o n. T h i s e n s u r e d t h a t a s u f fi c ie n t a m o u n t o f E E G w a s

a v a i l a b le t o c o m p u t e s t a b l e e s t i m a t e s o f s p e c t r a l p o w e r ( s e e

M o c k s & G a s s e r, 1 98 4 ). F i n a ll y , w e i n c l u d e d a c o n t r o l p r o c e -

d u r e t o e v a l u a t e t h e e f f ic a c y o f o u r e l a b o r a t e d a t a e x t r a c t i o n

p r o c e d u r e . E E G w a s a n al y z e d in a m a n n e r s i m i l a r t o w h a t i s

t y p i c a l ly d o n e i n s t u d i e s o n t h e p s y c h o p h y s i o l o g y o f e m o t i o n .

D a t a f r o m b o t h p o s it iv e fi l m s w e r e a g g re g a t ed a n d c o m p a r e d

w i t h t h e d a t a f r o m t h e t w o n e g a t i v e fi l m s , ir r e s p e c ti v e o f f a c ia l

b e h a v i o r . W e p r e d i c t e d l i t t l e d i f f e r e n c e i n a n t e r i o r a s y m m e t r y

b e t w e e n t h e p o s i t i v e a n d n e g a t i v e f i l m c o n d i t i o n s b e c a u s e t h e

d a t a f o r t h is c o m p a r i s o n a r e a g g r e g a t e d a c r o s s a ll n o n f a c i a l a n d

f a c ia l e x p r e s s io n p e r i o d s , i n c l u d i n g t h o s e t h a t a r e i n c o n s i s t e n t

w i t h t h e t a r g e t e m o t i o n .

T o s u m m a r i z e , t h e g o a l o f t h is s t u d y w a s to c o m p a r e e p o c h s

o f b r a i n a c t i v it y c o i n c i d e n t w i t h t h e e x p r e s s i o n o f d i f f e re n t

e m o t i o n s . F a c i a l si g n s o f h a p p i n e s s a n d d i s g u s t o c c u r r e d w i t h

s u f f ic i e n t f r e q u e n c y t o c o m p a r e E E G a c t i v i t y c o i n c i d e n t w i t h

e a c h . W e r e c o r d e d E E G o v e r t h e l e ft a n d r i g h t h e m i s p h e r e s i n

t h e f r o n t a l, a n t e r i o r t e m p o r a l , c e n t r a l , a n d p a r i e t a l r e g i o n s a n d

v i d e o t a p e d s u b j e c t s u n o b t r u s i v e l y w h i l e t h e y w a t c h e d s h o r t

e m o t i o n a l f i lm c l ip s . W e s p e c i fi c a ll y p r e d i c t e d t h a t a c t i v a t i o n

a s y m m e t r y w o u l d d i ff e r en t ia t e b e t w e e n h a p p y a n d d i sg u s t

e m o t i o n s i n t h e fr o n t a l a n d a n t e r i o r t e m p o r a l r e g i o n s . T h e c e n -

t r a l a n d p a r i e t a l r e g i o n s w e r e a s s u m e d t o b e r e l a t iv e l y u n i n -

v o l v e d i n t h e g e n e r a t i o n o f e m o t i o n . B r a i n e l e c t ri c a l a c ti v i t y

w a s m e a s u r e d f r o m t h e s e s it e s t o s e r v e as a c o m p a r i s o n w i t h

t h e m o r e a n t e r i o r s i t e s a n d t o e v a l u a t e t h e d e g r e e t o w h i c h t h e

v a l e n c e - d e p e n d e n t a s y m m e t r i e s w e r e s p e c if i c t o t h e a n t e r i o r r e -

g i o n s .

T h e f o ll o w i n g s p e ci f ic h y p o t h e s e s w e r e t e s te d i n t h i s e x p e r i -

m e n t :

Hypothesis 1

E E G a s y m m e t r y f r o m t h e e n ti r e f i lm p e r io d ,

i n d e p e n d e n t o f fa c i a l b e h a v i o r , w i l l n o t d i s c r i m i n a t e b e t w e e n

p o s i t iv e a n d n e g a t i v e f i lm c o n d i t io n s .

Hypothesis 2

F r o n t a l a n d a n t e r i o r t e m p o r a l a c t i v a t i o n

a s y m m e t r y w i ll d i s c r im i n a t e b e t w e e n h a p p i n e s s a n d d i sg u st .

S p e c i f i c a l l y , d i s g u s t w i l l b e a s s o c i a t e d w i t h g r e a t e r r i g h t - s i d e d

a n t e r i o r a c t i v a t i o n c o m p a r e d w i t h h a p p i n e s s . C o n v e r s e l y , h a p -

p i n e s s w i l l b e a s s o c i a t e d w i t h m o r e i e f ~ o s i d ~ a c t i v a t i o n c o m -

p a r e d w i t h d i s g u st . W e s p e c i fi c a ll y o f f e r n o p r e d i c t i o n s r e g a r d -

i n g b e t w e e n - h e m i s p h e r e d i f f e r e n ce s w i t h i n e m o t i o n c o n d i t i o n s .

T h e r a t i o n a l e f o r n o t m a k i n g s u c h p r e d i c t i o n s i s b a s e d o n t h e

f a c t t h a t s u b s t a n t i a l i n d i v i d u a l d i f f e r e n c e s i n b a s e l i n e a s y m m e -

t r y e x is t, u p o n w h i c h a r e s u p e r i m p o s e d t a s k -d e p e n d e n t

c h a n g e s ( s ee D a v i d s o n & T o m a r k e n , 1 9 8 9 , f o r a r e v ie w ) . T h u s ,

f o r a s u b j ec t w i t h t o n i c e x t r e m e r i g h t f r o n t a l a c t i v a t io n , w e

w o u l d n o t n e c e s s a r i l y e x p e c t t h a t h a p p i n e s s w o u l d b e a s s o c i -

a t e d w i t h a b s o l u t e l e f t f r o n t a l a c t i v a t i o n ( i . e . , g r e a t e r a c t i v a t i o n

i n t h e l e ft c o m p a r e d w i t h t h e r i g h t f r o n t a l le a d ) . H o w e v e r , w e

w o u l d s t i l l p r e d i c t t h e b e t w e e n - c o n d i t i o n , w i t h i n - h e m i s p h e r e

d i f f e re n c e s d e s c r i b e d a b o v e .

Hypothesis 3

B o t h d i s g u s t a n d h a p p i n e s s w i l l b e d i s c r i m i -



B R A I N A S Y M M E T R Y A N D A P P R O AC H - W IT H D R A W A L

n a t e d f r o m b a s e l i n e o n m e a s u r e s o f a n t e r i o r a c ti v a t io n a s y m -

m e t r y . W e s p e c i f ic a l ly p r e d i c t e d t h a t d i s g u s t w o u l d b e a s s o c i-

a t e d w i t h a s i g n i f i c a n t i n c r e a s e i n r i g h t - s i d e d a n t e r i o r a c t i v a t i o n

c o m p a r e d w i t h b a s e l i n e a n d t h a t h a p p i n e s s w o u l d b e a c c o m p a -

n i e d b y a s i g n i f i c a n t i n c r e a s e i n l e f t- s i d e d a n t e r i o r a c t i v a t i o n

c o m p a r e d w i t h b a s e li n e .

M e t h o d

Subjects

A t o t a l o f 3 7 r i g h t - h a n d e d ( a s se s se d w i t h t h e E d i n b u r g h H a n d e d n e s s

Inve n tory ; O ldf ie ld , 1971) wom e n be tw e e n the a ge s of 17 a nd 41 ye a r s

we re te s te d . The sa m p le wa s re s t r i c te d to r ight -h a nde d subje c t s be c a use

he m isphe r ic spe c ia l i z a t ion i s kn ow n to d i f f e r in l e f t -ha nde d subje c t s . Of

t h e s e 3 7 s u b j e c ts , 2 6 h a d a t l e a s t o n e i n s t a n c e e a c h o f a h a p p y a n d d i s -

gus t e xpre s s ion du r ing th e pos i t ive a nd ne ga t ive f i lm c l ips . Of the se 26 ,

17 ha d a t l e a s t one ins ta nc e of e a c h of the se e xpre s s ions tha t we re a c -

c o m p a n i e d b y a r t i f ac t - f re e E E G ( E E G w a s s c o r e d f o r a r t i f a c t p r i o r t o

a ny a na lys i s ; s e e be low) . Two of the se 17 subje c t s we re e l im ina te d be -

c a u s e o f f a i l u re to m e e t t h e d u r a t i o n c r i t e r i a , w h i c h w a s a m i n i m u m o f

1 0 t o t al s e c o n d s o f a r t i fa c t - fr e e E E G d u r i n g e a c h e x p r e s s io n t y p e . F o u r

othe r subje c t s we re e l im ina te d be c a use the y r e por te d ne ga t ive a f f e c t

( i .e . , fear , sadness , disgust , or anger) a t a level of 3 or more on a 0-8-

p o i n t s c a le d u r i n g a t l e a s t o n e o f t h e p o s i t iv e f il m s f r o m w h i c h t h e h a p p y

e xpre s s ions we re e x t r a c te d . We we re thus l e f t w i th a f ina l s a m ple o f 11

subje c t s . The pe rc e nta ge of subje c t s who we re e xc lude d i s s im i la r to

p r e v i o u s s t u d ie s i n w h i c h E E G d a t a w e r e e x t ra c t e d d u r i n g f a c i al e x p r es -

s ion pe r iods (Fox & Da vid son, 1988).

Procedure

S u b j e c t s w er e t e s te d i n d i v i du a l ly . P r i o r t o c o m m e n c e m e n t o f t h e

s tu d y , s u b j e c ts w e r e t o l d t h a t t h e e x p e r i m e n t w a s c o n c e r n e d w i t h s u b j e c -

t ive a nd phys io logic a l r e a c t ions to sho r t e m o t ion a l f i lm c l ips. Af te r s ign-

i n g a c o n s e n t f o r m t h a t i n d i c a t e d t h a t f i l m c l i p s d e s i g n e d t o e l i ci t b o t h

p o s i ti v e a n d n e g a t iv e e m o t i o n w o u l d b e p r e s e n t e d , a n e x p e r i m e n t e r a p -

p l i e d e le c t ro d e s f o r th e m e a s u r e m e n t o f t h e E E G . T h e s u b j e c t w as t o l d

t h a t n o i n t e r c o m e x i s te d b e t w e e n t h e r o o m s a n d t h a t i f t h e s u b je c t

n e e d e d t o s p e a k w i t h t h e e x p e r i m e n t e r f o r a n y r e a s o n d u r i n g t h e s e s -

s i o n , s h e co u l d p r e s s a b u t t o n m o u n t e d o n o n e a r m o f t h e c h a i r t h a t

w o u l d r i n g a s i g n a l i n t h e c o n t r o l r o o m , a t w h i c h p o i n t t h e e x p e r i m e n t e r

would e n te r . We spe c i f i c a l ly de s igne d the s i tua t ion in th i s f a sh ion to

m a x i m i z e t h e d e g r e e t o w h i c h s u b j e c t s p e r c e iv e d t h e m s e l v e s to b e v i e w -

ing the f i lm cl ips pr iva te ly , w i th l i t t le e xp e r im e nte r c onta c t .

T o f u r t h e r i n c r e as e t h e d e g r e e t o w h i c h s u b j e c ts b e l ie v e d t h a t t h e y

w e r e n o t b e i n g o b s e r v e d d u r i n g t h e f i l m v i e w i n g p e r i o d s , t h e r o o m w a s

d a r k e n e d a t t h e t i m e t h e e x p e r i m e n t e r d e p a rt e d . T h e s u b j e c t w a s t o l d

t h a t t h e p u r p o s e o f t h e d a r k e n e d r o o m w a s t o m i m i c a m o v i e t he a t er .

Two sm a l l r e d l igh t s provide d low- le ve l a m bie nt i l lum ina t ion , whic h

w a s r e q u i re d f o r s u b j e c ts t o v i e w t h e n u m b e r p a d o n w h i c h t h e i r r a t i n g s

we re m a de ( se e be low) .

T h e e x p e r i m e n t e r a n s w e r e d a n y g e n e r a l q u e s t i o n s t h a t t h e s u b j e c t

h a d a n d e x p l a i n e d t h a t t h e r e m a i n d e r o f t h e i n s t r u c t i o n s w o u l d b e p r e -

se nte d on the r e a r -pro je c t ion sc re e n towa rd whic h the y f a c e d . Ins t ruc -

t ions we re pre se nte d in a s e l f -pa c e d fa sh ion . A sc re e nfu l of ins t ruc t io ns

w a s p re s e n t e d a t a ti m e , a t th e b o t t o m o f w h i c h w a s t h e p h r a s e p r e s s

t o c o n t i n u e . T h e s u b j e c t s a d v a n c e d t h r o u g h a l l o f t h e i n s t r u c t io n s a t

the i r own pa c e .

The e x pe r im e nt be ga n wi th b a se l ine r e c ord ings of physio logy, a f t e r

whic h th e f i lm c l ips we re pre se nte d . Fol lowing the pre se n ta t ion of the

f i lm c l ips , a nothe r s e t of ba se l ine t r i a l s wa s pre se nte d . E a c h se t o f ba se -

l i n e p e r i o d s c o n s i s t e d o f t h e p r e s e n t a t i o n o f o n e e y e s - o p en a n d o n e e ye s-

c lose d t r i a l, e a c h 30 s in dura t io n . T he o rde r in whic h the se t r i a l s we re

p r e s e n t e d w a s c o u n t e r b a l a n c e d w i t h i n a n d b e t w e e n s u b je c t s. T h e o n s e t

a n d o f f se t o f t h e b a s e l i n e t r ia l s w e re m a r k e d b y t h e p r e s e n t a t i o n o f t o n e

pips .

Emotion Arousing Stimu li

The re we re f ive fi lm t r i a l s , e a c h c om p r i s ing a d i f f e re nt shor t f i lm of

a p p r o x i m a t e l y 6 0 s i n d u r a t i o n . T h e f i rs t c l i p w a s u s e d t o a c c l i m a t e

s u b j e c ts t o t h e p r o c e d u r e . T h e n e x t t w o w e r e in t e n d e d t o e v o k e p o s it i v e

e m o t i o n s , a n d t h e l a s t tw o w e r e d e s ig n e d t o e v o k e n e g a t iv e e m o t i o n s .

Pr ior r e se a rc h w i th the se f i lm s (Ekm a n e t a l. , 1980; Ekm a n & Fr ie se n ,

1 9 74 ) h a d f o u n d t h a t s u b j e c ts r e p o r t e d s t r o n g f e e li n g s o f a m u s e m e n t

a n d h a p p i n e s s a n d s h o w e d s m i l i n g e x p r e ss i o n s d u r i n g t h e p o s i t i ve f i lm s .

Fe e l ings of f e ar , sa dne ss , d i sgus t , a nd p a in a nd a va r ie ty of ne ga t ive e m o-

t iona l e xpre s s ions oc c ur re d in r e sp onse to the ne ga t ive fi lm s .

A l l the f i lm s we re s i le n t a nd in c o lor . S i l e n t f i lm s we re de s i r a b le for

o u r p u r p o s e s b e c a u s e d i f f e r e n t a u d i t o r y p a t t e r n s m i g h t c o n c e i v a b l y

e l i c i t d i f f e re nt pa t t e rns of he m isphe r ic a c t iva t ion so le ly a s a func t ion of

the a c ous t i c va r ia t ion a m o ng the c l ips ( e. g ., Ca rm o n & N a c hson , 1973).

On e o f the pos i t ive fi lm s showe d a pupp y p la y ing w i th f lowe rs . The se c -

o n d w a s a c l i p o f m o n k e y s p l a y i n g a n d a g o r i l l a t a k i n g a b a t h i n t h e

z oo. Th e orde r in w hic h the two pos i t ive f i lm c l ips we re pre se nte d wa s

c ounte rba la nc e d a c ros s subje c t s .

The two negative f i lm c l ips a lways fol lowed the posi t ive c l ips . The

r a t i o n a l e f o r t h i s w a s b a s e d o n b o t h p r e v i o u s w o r k b y E k m a n e t a l .

( 1 9 8 0 ) a n d o u r o w n p i l o t w o rk , w h i c h i n d i c a t e d t h a t t h e n e g a t i v e af f ec t

e l i c i t e d by the ne ga t ive f i lm s t e nde d to pe r s i s t longe r tha n the pos i t ive

a f fe c t e l i c i t e d by the pos i t ive f ilm s . I f we ha d c ou nte rb a la nc e d the orde r

of pos i t ive a nd ne ga t ive fi lm s , the pe r s i s t ing ne ga t ive m ood would ha ve

in te r f e re d w i th the in te nde d e f f e ct of the pos i t ive f i lm s , de c re a s ing the

n u m b e r o f p o s i ti v e e m o t i o n a l e x p r e s si o n s t h a t w o u l d h a v e o c c u r r e d i n

re sponse to the se c l ips . Th e ne ga t ive f i lm c l ips we re t a ke n f rom t r a in in g

m o v i e s u s e d i n t h e t e a c h i n g o f n u r s e s . O n e c l i p d e p i c t e d a l e g a m p u t a -

t i o n a n d t h e o t h e r w a s t h e s c e n e o f a t h i r d - d e g r e e b u r n v i c t im . B o t h

w e r e q u it e g r u es o m e . T h e o r d e r i n w h i c h t h e a m p u t a t i o n a n d b u r n c l i p s

we re pre se nte d wa s c ounte rb a la nc e d a c ros s subje c t s .

F i lm s we re pre se nte d w i th a L a fa ye t te Mode l 925 A na lys t f i lm pro je c -

t o r, w h i c h g e n e r a t e d a f r a m e c o u n t p u l s e f o r a u t o m a t e d c o n t r o l . D i g i ta l

logic c oun te d the se pul se s for pre c i se t im in g of f i lm onse t a n d of f se t.

Subjective Ratings o f Em otion

A f t e r e a c h o f t h e b a s e l in e a n d f i lm t r i a l s , s u b je c t s r a te d t h e e m o t i o n s

t h e y h a d e x p e r i e n c e d d u r i n g t h e p r e c e d i n g t r i a l o n a s e r i e s o f u n i p o l a r

sc a le s . Se pa ra te s c a le s we re inc lude d for in te re s t , ha ppine s s , a m use -

m e n t , c ont e ntm e nt , e xc i t e m e nt , f e ar , s a dne ss , a nge r, d i sgus t , pa in , a nd

a r o u s al . T h e i n s t r u c t i o n s i n f o r m e d t h e s u b j e c t t h a t z e r o r e p r e s e n t e d n o

e m o t i o n a n d 8 t h e m o s t i n t e n s e f e el i n g o f t h a t e m o t i o n . T h e s e r a t i n g

s c a le s w e re p r o j e c t e d o n e a t a t i m e o n t h e r e a r p r o j e c t i o n s c r e e n . T h e

s u b j e c ts e n t e r e d t h e i r r a t i n g b y p r e s s in g a n u m b e r o n t h e i r k e y p a d .

For the subje c t s who we re r e ta ine d in the a na lyse s ( s e e a bove ) , the

i n t en s i ty o f a m u s e m e n t ( th e d o m i n a n t e m o t i o n r e p o r t e d d u r i n g t h e

pos i t ive c l ips ) du r ing th e pos i t ive c lips a nd d i sgus t du r ing th e ne ga t ive

c l ips wa s c om pa ra b le . In a dd i t ion , the re we re no d i f f e re nc e s in the in-

t e n s i ty o f a n y o f t h e r a t e d e m o t i o n s b e t w e e n t h e s u b j e c t s w h o w e r e r e-

t a i n e d f o r t h e E E G a n a l y si s a n d t h o s e w h o w e r e e x cl u d e d . T a b l e 1 p re -

s e n t s th e m e a n r a t i n g s o f t h e p o s i t i v e a n d n e g a ti v e e m o t i o n s i n r e s p o n s e

to the po s i t ive a nd ne ga t ive f i lm c l ips for the subje c t s who we re r e ta ine d

a nd tho se who we re e xc lude d .

Video Recordings

D u r i n g e a c h o f t h e f i l m c l i p s, s u b j e c t s w e r e v i d e o t a p e d u n o b t r u s i v e l y

t h r o u g h a w i r e m e s h s c r e e n t h a t s e r v e d a s t h e b o r d e r o f t h e r e a r p r o j e c -

t i o n s c r e en . T h e c a m e r a ( G . E . S i te G u a r d I I ) w a s m o u n t e d i n t h e p r o j e c -

t i o n r o o m , w h i c h w a s a d j a c e n t t o t h e s u b j e c t r o o m , a l o n g w i t h t h e f i lm

proje c tor . The c a m e ra wa s a bsolu te ly invi s ib le to the subje c t , a nd no t

o n e s u b j e c t s u s p e c te d t h a t s h e w a s b e i n g v i d e o t a p e d . A f t e r t h e e x p e r i-



4

D A V I D S O N , E K M A N , S A R O N , S E N U L I S , F R I E S E N

T a b l e 1

Rat ings o f Emo t ional In t ens it y or Subject s Re ta ined and Exc luded

I n t e r e s t A m u s e m e n t C o n t e n t m e n t E x c i t e m e n t H a p p i n e s s F e a r S a d n e s s P a i n D i s g u s t A n g e r

Posi t ive f i lm c l ips

S u b j e c t s i n c l u d e d

(n = 11)

M 5 .60 5 .60 3 .95 2 .65 4 .45 0 .40 1 . 8 0 .45 0 .75 1 .00

SD

1.29 1.60 1.91 1.60 2.14 0.88 1.06 0.83 0.95 1.29

Subje c t s e xc lude d

(n = 15)

M 5 .50 6 .05 3 .68 2 .73 4 .68 0 .50 1 .35 0 .18 0 .95 0 .86

SD 1.92 1.44 1.93 1.69 1.85 1.02 1.83 0.3 4 1.42 1.43

Ne ga t ive f i lm c l ips

S u b j e c t s i n c l u d e d

(n = 11)

M 5 .00 1 .35 0 .25 2 .40 0 .25 4 .10 2 .90 4 .50 5 .70 3 .00

SD

2.07 1 .63 0 .54 2 .23 0 .79 2 .65 2 .29 3 .16 2 .98 2 .59

Subje c t s e xc lude d

(n = 15)

M 5 .52 1 .55 0 .45 2 .15 0 .50 4 .45 3 .30 3 .80 6 .70 3 .60

SD

2.38 1.64 1.42 2.47 1.41 2.53 2.79 2.82 2.53 2.97

Note T h i s t a b l e i l l u s t r at e s m e a n i n t e n s i t y ( a n d s t a n d a r d d e v i a t i o n ) o f s e l f- r e p o r te d e m o t i o n ( o n a 0 - 8 s c a le ) i n r e s p o n s e t o t h e t w o p o s i t i v e a n d t w o

ne ga t ive f i lm c l ips . For e a c h subje c t , a m e a n for e a c h e m ot ion for the pos i t ive f ilm s wa s c re a te d by a ve ra ging the r a t ings a c ros s the two pos i t ive f ilm

c l ips a nd a m e a n for e a c h e m o t ion for the ne ga t ive fi lm s wa s c re a te d by a ve ra ging the r a t ings a c ros s the two ne ga t ive f ilm s . The sub je c t s inc lude d

w e r e t h o s e o n w h o m t h e E E G a n a l y se s a r e b a s ed . T h e e x c l u d e d s u b j e c t s a r e t h o s e w h o w e r e r e m o v e d a s a f u n c t i o n o f e xc es si ve a r t i f a ct d u r i n g h a p p y

or d i sgus t e xpre s s ions or be c a use the y r e por te d e xce ss ive ne ga t ive a ff e c t du r ing the pos i t ive f ilm s ( see t e x t ) .

m e n t w a s c o m p l e t e d , s u b j e c t s w er e t h o r o u g h l y d e b r i e fe d , a n d w r i t t e n

c onse nt wa s r e que s te d to use the i r v ide ota pe s for s c ie n t i f i c purpose s .

T h e s u b j e c t w a s to l d t h a t i f s h e d i d n o t w i s h f o r t h e t a p e t o b e u s e d , i t

w o u l d b e e r as e d . N o s u b j e c t d e c l i n e d o u r r e q u e s t t o u s e h e r t a p e .

A t t h e t i m e t h e v i d e o r e c o r d i n g w a s m a d e , a v i d e o s t o p w a t c h ( F o r a

V T G - 2 2 ) m a r k e d t h e t i m e t h a t h a d e l ap s e d s in c e t h e c o m m e n c e m e n t

o f t h e e x p e r i m e n t o n t h e v i d e o t a p e . I n a d d i t i o n , t h e b e g i n n i n g a n d e n d

o f e a c h n e w c o n d i t i o n ( b o t h b a s e l i n e a n d f i l m ) w e r e m a r k e d b y a u t o -

m a t i c a ll y c h a n g i n g t h e d i g it s o n t h e v i d e o c l o c k f r o m b l a c k t o w h i t e a n d

b a c k . T h e t r ig g e r u s e d t o c h a n g e t h e v i d e o s t o p w a t ch f r o m b l a c k t o

w h i t e a n d b a c k a l so w a s s en t t o a P D P I 1 / 3 4 A c o m p u t e r t o s i g n a l t h e

onse t a n d of f se t of a ll e xpe r im e nta l t r i a l s . Us ing th i s sys te m , we we re

a ble to pre c i se ly sync hro niz e the v ide o a nd phys io logic a l da ta s t r e a m s .

E E G R e c o r d i n g P ro c e d u re

T h e E E G w a s r e c o r d e d f r o m t h e l e f t a n d r i g h t f r o n t al , c e n t ra l , a n t e -

r ior t e m po ra l , a n d pa r ie ta l r e g ions (F3 , F4 , C3, C4, T 3, T4, P3 , 1"4) a l l

r e fe r r e d to ve r te x (Cz ) us ing a lyc ra s t r e tc ha ble c a p (E le c t ro-Ca p) . J A l l

i m p e d a n c e s w er e b e l o w 5 K o h m s . T h e E E G w a s a m p l i f i e d w i t h a G r a s s

M o d e l 7 p o l y g r a p h a n d M o d e l 7 P 5 A a m p l i f i er s a n d t h e n l o w - pa s s fi l-

t e r e d a t 4 4 H z (48 d b/oc ta ve ro l l -of f s ) to p re ve nt a l i a s ing . The f i l te r e d ,

a m p l i f i ed s i g n a ls w e r e t h e n l e d i n t o t h e A / D c o n v e r t e r o f t h e P D P 1 1 /

3 4 A c o m p u t e r s y s te m . T h e E E G w a s s am p l e d a t 1 2 5 sa m p l e s p e r se c -

o n d . T h e E E G w a s c a li b r a t e d b y i n p u t t i n g b e f o r e a n d a f t e r e a c h s u b j ec t

a s e r ie s o f 2 5 a n d 5 0 z V s i n e wa ve s a t l 0 H z . T h e c o m p u t e r u s e d t h e s e

k n o w n s i g n a l s to c a l i b r a te e a c h o f t h e c h a n n e l s .

D a t a A n a l y s i s

Scoring acia l behavior

A l l o f t h e o b s e r v a b l e f ac i a l a ct i v i ty s h o w n b y

e a c h s u b j e c t d u r i n g t h e p o s i t iv e a n d n e g a t iv e f i lm s w a s m e a s u r e d w i t h

E k m a n a n d F r i e s e n 's (1 9 7 6 , 1 9 7 8 ) F a c ia l A c t io n C o d i n g S y s t e m

( FA C S ). U s i n g t h i s i n f o r m a t i o n , t h e o n s e t a n d o f f se t ti m e s o f e a c h e m o -

t i o n a l e x p r e s s io n w e r e d e t e r m i n e d . I n t e r c o d e r r e l ia b i l it y h a s b e e n e s -

t a b l i s h e d f o r th i s s c o r i n g p r o c e d u r e i n a n u m b e r o f l a b o r a t o r i e s (c f.

Ekm a n & Fr ie se n , 1976; Ek m a n e t a l ., 1980; Ekm a n, Fr ie se n , & O 'Sul -

l iva n , 1988; Ekm a n, Fr ie se n , & Sim ons , 1985; Fox & Da vidso n, 1988;

Kra u se & Ste im e r , 1988; Ruc h, 1987; S te ine r , 1986) . Se e the a c c om pa -

nying a r t i c le (Ekm a n e t a l ., 1990) for a ddi t iona l de ta i l c onc e rn in g the

s c o r i n g o f f a c ia l b e h a v i o r a n d t h e r e l i a b i li t y o f t h e m e a s u r e m e n t p r o c e -

dure .

F A C S s c o r i n g r e v ea l e d t h a t t h e t w o t y p e s o f f a c i a l a c t io n s t h a t o c -

c u r r e d w i t h t h e m o s t f r e q u e n c y w e r e h a p p y e x p r e s si o n s i n r e s p o n s e t o

the pos i t ive f ilm c l ips a nd d i sgus t e xpre s s ions in r e spon se to the ne ga t ive

f i lm c l i p s . T h e t y p e o f h a p p y e x p r e s s io n u s e d i n t h i s a n a l y s i s w as t h e

" f e l t s m i l e " ( E k m a n & F r i e s e n , 1 9 8 2 ), w h i c h h a s s i n c e b e e n t e r m e d

D u c h e n n e ' s s m i l e ( se e E k m a n e t a l ., 1 9 88 ). I n a n u m b e r o f s tu d i e s,

E k m a n a n d h i s c o l le a g u e s h a v e f o u n d t h a t o n l y t h e f re q u e n c y a n d d u r a -

t ion of th i s sm i le , r a the r tha n o the r type s o f sm i le s, i s s igni f i c a nt ly c or re -

l a te d w i th s e l f - r e por t s of ha ppin e s s (e .g . , Ekm a n & Fr ie se n , 1982; Ek-

m a n e t a l . , 1988) . For e a c h subje c t , the onse t a nd of f se t of e a c h ha pp y

a nd d i sgus t e xpre s s ion we re ide nt i f i e d by FACS. The se t im e s we re the n

i n p u t i n t o t h e c o m p u t e r s o t h a t E E G c o i n c i d e n t w i t h th e s e ex p r e s si o n s

c o u l d b e e x t r a c t e d .

Artifact editing of E EG All EEG re c ords we re v i sua l ly s c ore d for

a r t if a c t. A l l e y e m o v e m e n t a n d m u s c l e a r t i fa c t s w e re r e m o v e d f r o m t h e

d a t a p r i o r t o a n a ly s i s. I f a rt i f a c t w as p r e s e n t o n a n y c h a n n e l , d a t a f r o m

all

c h a n n e l s w e r e re m o v e d s o t h a t t h e E E G d a t a w e r e al w ay s t a k e n f r o m

c o i n c i d e n t p o i n t s i n t i m e .

EEG analysis T h e r e w e r e t h r e e m a j o r s e ts o f E E G d a t a t h a t f o r m e d

the ba s i s of ou r a na lyse s . The f i r s t s et wa s de r ive d f rom th e pos i t ive f ilm

c l i p s d u r i n g t h o s e p e r i o d s w h e n h a p p y e x p r e s s io n s w e re p r e s e n t a n d

f r o m t h e n e g a t i v e f il m c l i p s d u r i n g t h o s e p e r i o d s w h e n d i s g u s t ex p r e s -

s i o n s w er e p r e s en t . T h e s e c o n d s e t w a s b a s e d o n t h e e n t i r e d u r a t i o n s o f

the pos i t ive a nd ne ga t ive f i lm c l ips , re spe ct ive ly . For th i s a na lys i s , EEG

wa s a ggre ga te d for a l l a r t i f a c t- f r e e pe r iods , in de pe nde n t of f a c ia l e xpre s -

s i o n , t o f o r m o n e s e t o f d a t a f o r t h e p o s i t iv e f i lm c l i p s a n d o n e f o r t h e

ne ga t ive f i lm c l ips . The th i r d da t a s e t c ons i s te d of the e ye s -ope n ba se l ine

J Ve r te x wa s use d a s a r e fe re nc e be c a use o f the e x te ns ive use of th i s

r e c o r d i n g m o n t a g e i n E E G s t u d i e s o f d if f e re n t i al h e m i s p h e r i c a c t iv a t i o n

(see Davids on, 1988, for a review).



B R A I N A S Y M M E T R Y A N D A P P R O A C H - W I TH D R A W A L

335

condit ion, averaged across the pre- a nd postf ilm tr ials . We considered

the eyes -open base l ine co nd i t ion the m os t app ropr ia te fo r compar i son

with the f i lms because subjects ha d their eyes open du ring the f i lm pre-

sentations.

For the da ta dur ing fac ia l s igns o f happ iness and d i sgus t , the onse t

and offset t ime s of these facial expressions were entered into th e com -

pute r a long wi th the t imes dur ing which a r t i f ac t was no t p resen t . Th e

com pute r then ext rac ted those por t ions o f the EE G reco rd tha t were

1.02 s or longer in d urat io n for analysis that corresponded to th e overlap

of these two c r i t e r i a . For the ana lyses o f the en t i re f i lm per iod an d the

base l ine tr i a l s , chunks o f 2 .05 s were ext rac ted fo r ana lys is . Chunk s o f

EEG (1 .02- o r 2 .05-s pe r iods) were ext rac ted using a Ham ming window.

T h e p u r p o s e o f t h e H a m m i n g w i nd o w i s t o m i n i m i ze s p u r i o u s f re -

quencies in the est imates o f spectra l power. Ch unk s were overlapped by

75% to coun te rac t the a t t enua ting e f fec t o f the Ha mm ing window and

to improve the t empora l r eso lu t ion o f the measure (see Dum ermu th &

Mo linari , 1987, and Davidson, 1988, for a discussion of these metho d-

o log ica l i ssues) . A Fas t Four ie r T ransform (FFT ) was app l ied to each

c h u n k o f E E G . T h e F F T i s a n a l g o r it h m t h a t d e c o m p os es a n y c o m p l e x

waveform in to i t s under ly ing s ine wave componen ts . Wh en app l ied to

E E G , t h e F F T p e r m i t s th e c o m p u t a t i o n o f t h e a m o u n t o f p ow e r a t

different frequencies. Power values from al l chunks within an epoch

were averaged (see Dum ermu th and Mol ina r i , 1987 , fo r an extens ive

overview of th i s da ta -ana ly t icprocedure).

The dependent measures th at were extracted from this analysis were

power dens ity ( in V2/Hz) in the a lpha (8 -13 Hz) and be ta (13-20 Hz)

bands . These da ta were log t rans formed to norm al ize the i r d i s t r ibu t ion

because pow er values are posi t ively skewed (see Davidson, 1988, for a

review of methodological issues in EE G asy m me try research). Pow er in

the a lph a band is inversely related to act ivation (e.g., Lindsley & Wicke,

1974) and has been the measure mos t cons is ten t ly ob ta ined in s tud ies

of EEG a symm et ry (Davidson , 1988) . Alp ha power has been found to

be m ore re l i ab ly re la ted to t a sk pe r fo rmance com pared wi th power in

o ther f requency bands , when the t a sks tha t a re co mp ared a re ca re fu lly

matched on psychomet r ic p rop er t i e s (Davidson , Chapm an, C hapm an,

& Henriques, in press). We therefore expected tha t the em otion cond i-

t ions would re l i ab lydiffer on m easures of alph a power asymm etry. Beta

power was exam ined in l igh t o f some suggest ions tha t a lpha an d b e ta

power ma y reflect different com pon ents o f activat ion (e.g., Ray & Cole,

1985). However, on th e basis o f our ow n previous f indings, we expected

the m os t cons is ten t d i f ferences in asy mm et ry to be fou nd fo r the a lph a

band.

R e s u l t s

Hypothesis 1: EE G from the entire fi lm period independent

of facial behavior will not discriminate between positive a nd

negative ilm conditions. F o r t h i s a n a l y s i s , a l l a r t i f a c t - f r e e E E G

d u r i n g e a c h o f th e t w o p o s i ti v e a n d t w o n e g a t i v e fi l m s w as a n a -

l y z e d. E E G p o w e r d u r i n g e a c h o f t h e t w o p o s i ti v e f i lm s a n d e a c h

o f t h e t w o n e g a t i v e f i l m s w a s s e p a r a t e l y a v e r a g e d , t o p r o v i d e

c o m p o s i t e p o s i t i v e a n d n e g a t i v e d a t a s e t s f o r e a c h s u b j e c t . R e -

p e a t e d m e a s u r e s a n a l y s e s o f v a r i a n c e ( A NO V A S)w e r e c o m p u t e d

s e p a r a t e l y o n t h e d a t a f r o m e a c h o f t h e f o u r r e g i o n s : f r o n t al ,

a n t e r i o r t e m p o r a l , c e n t r a l , a n d p a r i e t a l . T h e f a c to r s w e r e c o n d i -

t i o n ( p o s i t i v e - n e g a t i v e f i l m s ) a n d h e m i s p h e r e ( l e f t - r i g h t ) . E v i -

d e n c e o f a d i f fe r e n c e i n a s y m m e t r y b e t w e e n t h e c o n d i t i o n s

w o u l d b e r e v e a l e d i n a s i g n i fi c a n t C o n d i t i o n × H e m i s p h e r e i n -

t e r a c ti o n . F o r m e a s u r e s o f a l p h a p o w er , th i s i n t e r a c t i o n d i d n o t

r e a c h s i g n i f i c a n c e f o r a n y r e g i o n . T h e h i g h e s t F v a l u e w a s f o r

t h e c e n t r a l le a d s , w h e r e t h e C o n d i t i o n × H e m i s p h e r e i n t e r a c -

t i o n w a s F ( I , 6 ) = 2 . 5 9 , p > . 1 5 . A l l o t h e r F v a l u e s f o r t h i s

i n t e r a c t i o n w e r e b e l o w 1 . 5. N o m a i n e f f e c t s f o r h e m i s p h e r e

w e r e o b t a i n e d f o r a n y r e g i o n . T h e o n l y c o n d i t i o n m a i n e f fe c t

w a s f o u n d f o r t h e c e n t r a l l e a d s , w h e r e t h e n e g a t i v e fi l m s w e r e

a s s o c i a t e d w i t h l e s s a l p h a p o w e r c o m p a r e d . w it h t h e p o s i t i v e

f i lm s , F ( I , 6 ) = 5 1 . 8 1 , p < . 0 0 1 .

O n m e a s u r e s o f b e t a p o w er , th e r e w e r e a l s o n o s i g n i f i ca n t

C o n d i t i o n X H e m i s p h e r e i n t e r a c ti o n s . T h e h i g h e s t F v a l u e w as

f o r t h e c e n t r a l le a d s , w h e r e t h e C o n d i t i o n x H e m i s p h e r e i n t e r -

a c t i o n w a s F ( 1 , 8 ) = 1 . 22 . A l l o t h e r F v a l u e s w e r e b e l o w 1 .0 .

T h e r e w e r e n o s i g n i f i c a n t m a i n e f f ec t s i n a n y o f th e s e a n a l y s e s .

T h e s e a n a l y s e s o n t h e e n t i r e f i l m p e r i o d i n d i c a t e t h a t w h e n

a v e r a g e d a c r o s s t h e w h o l e f i l m p e r i o d , p o s i t i v e a n d n e g a t i v e fi l m

c l i p s d o n o t p r o d u c e a n y r e l i a b l e d i f fe r e n c e s i n E E G a s y m m e -

t r y i n e i t h e r th e a l p h a o r b e t a b a n d s .

Hypothesis 2: Anterior asym metry will discriminate between

happy an d disgust conditions. W e p r e d i c t e d t h a t t h e d i s g u s t

c o n d i t i o n w o u l d b e a s s o c i a t e d w i t h m o r e r i g h t -s i d e d a n d l e ss

l e f t- s i d ed fr o n t a l a n d a n t e r i o r t e m p o r a l a c t i v a t i o n c o m p a r e d

w i t h t h e h a p p y c o n d i t io n . F o r t h e s e a n a ly s e s E E G d u r i n g f a c ia l

s i gn s o f h a p p i n e s s a n d d i s g u s t w a s c o m p a r e d i n A N O VA Sw i t h

c o n d i t i o n ( h a p p y - - d i s g u s t ) a n d h e m i s p h e r e a s f a c to r s . T h e s e A N -

O VA S w e r e p e r f o r m e d o n E E G p o w e r i n t h e a l p h a a n d b e t a

b a n d s , s e p a r a t e l y b y r e g i o n . T h e a l p h a d a t a w i l l b e p r e s e n t e d

firs t .

T h e C o n d i t i o n X H e m i s p h e r e i n t e r a c t i o n f o r t h e f r o n t a l re -

g i o n w a s h i g h l y s i g n i f i c a n t, F ( 1 , 9 ) = 3 2 . 1 0 , p < . 0 0 0 5 . A s c a n

b e s e e n f r o m F i g u r e 1 , t h e d i s g u s t c o n d i t i o n w a s a s s o c i a te d w i t h

l e s s a l p h a p o w e r ( i .e . , m o r e a c t i v a t i o n ) i n t h e r i g h t f r o n t a l r e -

g i o n c o m p a r e d w i t h t h e h a p p y c o n d i t i o n ( p < . 01 ). W h e n i n d i -

v i d u a l s u b j e c t d a t a w e r e e x a m i n e d , w e f o u n d t h a t 1 00 % o f t h e

s u b j e c t s sh o w e d m o r e r i g h t - s i d e d f r o n t a l a c t i v a t io n d u r i n g d i s -

g u s t v e r s us h a p p i n e s s . W i t h i n t h e d i s g u s t c o n d i t i o n , t h e r e w a s

s i g n i f i c a n t ly l e s s r i g h t a l p h a p o w e r c o m p a r e d w i t h l e f t f r o n t a l

a l p h a p o w e r ( p < . 0 1) . A l t h o u g h t h e h a p p y c o n d i t i o n w a s a s so -

c i a t e d w i t h l e s s l e f t f r o n t a l a l p h a p o w e r t h a n t h e d i s g u s t c o n d i -

t i o n , t h i s d i f f e r e n c e fa i l e d t o r e a c h s i g n i f ic a n c e . I n a d d i t i o n ,

t h e r e w a s n o s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e h e m i s p h e r e s

w i t h i n t h e h a p p y c o n d i t i o n . N o m a i n e f f e ct s w e r e o b t a i n e d o n

m e a s u r e s o f f r o n t a l a l p h a p o w e r i n t h i s a n a l y si s .

H y p o t h e s i s 2 a l s o p r e d i c t e d t h e s a m e i n t e r a c t io n f o r t h e a n t e -

r i o r t e m p o r a l r e g i o n . T h e A N O V A o n a l p h a p o w e r i n t h i s r e g i o n

r e v e a l e d a s i g n i f ic a n t C o n d i t i o n x H e m i s p h e r e i n t e r a c t i o n , F ( I ,

9 ) = 6 . 3 2 , p = . 0 3 . T h e s e d a t a a r e d i s p l a y e d i n F i g u r e 2 . 2 A s

w e h a d h y p o t h e s i z e d , t h e d i s g u s t c o n d i t io n w a s a s s o c i a t e d w i t h

m o r e r i g h t - s id e d a c t iv a t i o n ( le s s a l p h a p o w e r ) t h a n t h e h a p p y

c o n d i t i o n ( p < . 0 1) a n d t h e h a p p y c o n d i t i o n w a s a s s o c ia t e d w i t h

m o r e l e f t - s i d e d a c t i v a t i o n t h a n t h e d i s g u s t c o n d i t i o n ( p < . 0 5 ).

I n a d d i t i o n , w i t h i n t h e h a p p y c o n d i t i o n , t h e r e w a s l e ss l e ft - t h a n

r i g h t - si d e d a l p h a p o w e r ( p < . 01 ) . A l p h a p o w e r d i d n o t d i f f e r

s i g n i f i c a n t l y b e t w e e n t h e t w o h e m i s p h e r e s i n t h e d i s g u s t c o n d i -

t i o n . W h e n i n d i v i d u a l s u b j e c t d a t a w e r e e x a m i n e d , w e f o u n d

t h a t 7 0 % o f t h e s u b j e c t s s h o w e d m o r e r e l a t i v e r i g h t - s i d e d a n t e -

r i o r t e m p o r a l a c t i v a ti o n d u r i n g t h e d i s g u s t c o m p a r e d w i t h t h e

h a p p y c o n d i t i o n .

T h e s a m e a n a l y s e s a s d e s c r i b e d a b o v e f o r t h e f r o n t a l a n d a n -

t e r i o r te m p o r a l a l p h a d a t a w e r e a ls o p e r f o r m e d o n b e t a p o w er .

C o n s i s t e n t w i t h o u r p r e v i o u s w o r k o n c o g n i ti v e a s y m m e t r i e s

( D a v i d s o n e t a l. , i n p r e s s ) , n o s i g n i f i c a n t C o n d i t i o n X H e m i -

2 As can be seen f rom F igure 2 , the sca le o f power dens i ty in the an te -

r ior tem pora l region is different from th at displayed for the frontal re-

gion in Figu re I . This difference between regions in absolute pow er is

expected. The frontal region typical lydisplays the leas t overal l am oun t

of alph a power (e .g., Ingvar, Sjolund, & Ard o, 1976).



6

DAVIDSON, EKMAN, SARON, SENULIS, FRIESEN

Frontal lpha Power

Figure 1 Mean log-transformed alp ha power in uVZ/Hz) for the left and right frontal regions F3 and F4)

during the h appy and disgust facial expression conditions. More negative numbers in dicate less alpha

power. The negative numbers a re a function o f the log transformation. Lower numbers i.e., mo re negative)

are associated with increased activation.)

sphere in teract ion was found for ei ther f rontal , F I , 9) = 0 .33,

or anter ior temporal , F 1 , 9) = 0 .21, beta power . In addi t ion,

no main effects were obtain ed in these analyses.

EE G was recorded f rom the cent ral and par ie tal regions to

ascer tain the degree to which the asymmetr ies associated wi th

emot ion were speci f ic to the anter ior regions. The Condi t ion

happy-d i sgus t ) × Hemi sphe re i n t e r ac t i on for a l pha power da t a

from the cent ral and par ietal regions fai led to reach signi f i -

cance : centr al , F I, 8) = 3.6, p < .10; par ietal , F I, 9) = 3.16,

p > . 10. These sam e analyses were perform ed on beta power

and again showed no signi f icant Condi t ion X Hemisp here in ter-

action: centr al , F 1, 8) = 0.96; p arie tal , 17 1, 9) = 2.33, p > . 15.

Thus, for act ivat ion measures base d on alpha power , in both

the f rontal and anter ior tempo ral regions, the d isgust condi t ion

produces s igni f icant increases in r ight -s ided act ivat ion com-

pared wi t h t he happy cond i t i on . In t he an t e r i o r t empora l r e -

nterior Temporal lpha Pow er

Figure 2 Mean log-transformed alpha power in uVZ/Hz) for the left and right anterio r temp oral regions

T3 and T4) during the hap py and disgust facial expression conditions. Lower numbers a re associated with

increased activation.)



B R A IN A S Y MME T R Y A N D A P P R OA C H -WIT H D R A WA L 3 3 7

T a b l e

Means of Left and Right Frontal Log Alpha Power

for the Baseline and Disgust Conditions

Condit ion Left Righ t

Baseline - . 168 - . 163

Disgust - .40 3 - .80 0

Note.The baseline means are th e average of the pre- and postfilm eyes-

open baseline periods. The negative sign of the num bers is due to the log

transform ation. Lower num bers are indicative of increased activation.

g i o n , b u t n o t i n t h e f r o n t a l r e g i o n , t h e h a p p y c o n d i t i o n i s a s so c i -

a t e d w i t h m o r e l e f t - s i d e d a c t i v a t i o n c o m p a r e d w i t h t h e d i s g u s t

c o n d i t i o n . N o d i f f e re n c e s i n e i t h e r a l p h a o r b e t a p o w e r a s y m -

m e t r y b e t w e e n t h e h a p p y a n d d i s g u s t c o n d i t i o n s w e r e f o u n d i n

t h e c e n t r a l o r p a r i e t a l r e g i o n s .

Hypothesis 3: Both disgust and happiness will be discrimi

nated from baseline on measures of anterior asymmetry. T h i s

h y p o t h e s i s p r e d i c t e d t h a t t h e d i s g u s t c o n d i t i o n w o u l d b e a s s o c i -

a t e d w i t h a s i g n i f ic a n t i n c r e a s e i n r i g h t - s i d e d a n t e r i o r a c t i v a t io n

c o m p a r e d w i t h b a s e l i n e a n d t h a t h a p p i n e s s w o u l d b e a c c o m p a -

n i e d b y a s i g n i f ic a n t i n c r e a s e i n l e f t - s i d e d a n t e r i o r a c t i v a t io n

c o m p a r e d w i t h b a s e l i n e . T o t e s t th i s h y p o t h e s i s, w e c o m p a r e d

e a c h e m o t i o n c o n d i t i o n w i t h b a s e l i n e ( av e r ag e o f p r e - a n d p o s t -

f i lm b a s e l in e s ) i n a s e r i e s o f 2 × 2 A N O V A Sw i t h c o n d i t i o n ( b a s e -

l i n e -- d i s g u st o r b a s e l i n e - h a p p y ) a n d h e m i s p h e r e a s f a c t o r s o n

b o t h a l p h a a n d b e t a p o w e r d a t a .

W h e n d i s g u s t w a s c o m p a r e d w i t h b a s e l i n e i n th e f r o n t a l r e -

g i o n , a s i g n if i c a n t C o n d i t i o n × H e m i s p h e r e i n t e r a c t i o n w a s o b -

t a in e d , F (1 , 9 ) = 6 . 5 5 , p < . 0 4 . T h i s i n t e ra c t io n w a s a fu n c t io n

o f t h e d i s g u s t c o n d i t i o n p r o d u c i n g s i g n i f ic a n t l y l e ss f r o n t a l a l -

p h a p o w e r i n t h e ri g h t h e m i s p h e r e c o m p a r e d w i t h b a s e l i n e ( p <

. 0 01 ) . N o d i f f e r en c e b e t w e e n t h e b a s e l i n e a n d d i s g u s t c o n d i -

t i o n s w a s f o u n d i n l e f t f r o n t a l a l p h a p o w e r. T h e r e l e v a n t m e a n s

a r e p r e s e n t e d i n T a b l e 2 . W h e n i n d i v i d u a l s u b j e c t d a t a w e r e

e x a m i n e d , w e f o u n d t h a t 8 0 o f t h e su b j e c t s s h o w e d m o r e r e l a -

t i v e ri g h t - s i d e d f r o n t a l a c t i v a t i o n d u r i n g t h e d i s g u s t c o n d i t i o n

c o m p a r e d w i t h b a s e l i n e .

T h e c o m p a r i s o n o f t h e b a s e l i n e a n d d i s g u s t c o n d i t i o n s f o r t h e

a n t e r i o r t e m p o r a l r e g i o n f a i l e d t o r e v e a l a s i g n i f i c a n t C o n d i -

t i o n × H e m i s p h e r e i n t e r a c t i o n , F ( I , 9 ) = 1 .8 9 .

T o a s c e r t a i n w h e t h e r t h e d i f f e r en c e b e t w e e n t h e b a s e l i n e a n d

d i s g u s t c o n d i t i o n i n a l p h a p o w e r a s y m m e t r y i n t h e f r o n t a l r e -

g i o n w a s a s p e c i f i c r e g i o n a l e f f e c t , w e c o m p u t e d C o n d i t i o n

( b a s e li n e - -d i s g u s t) × H e m i s p h e r e A N O VA S o n t h e c e n t r a l a n d

p a r i e t a l d a t a . T h e C o n d i t i o n × H e m i s p h e r e i n t e r a c t i o n w a s n o t

s ig n i f i c a n t fo r e i th e r t h e c e n t ra l , F (1 , 8 ) = 1 . 38 , o r p a r i e t a l , F (1 ,

9 ) = 4 .00 , p = .08 , reg ions .

W e c o m p a r e d t h e b a s e l i ne a n d d i s g u s t c o n d i t io n s o n m e a -

s u r e s o f b e t a p ow e r . T h e C o n d i t i o n × H e m i s p h e r e i n t e r a c t i o n

fa i l e d to r e a c h s ig n i f i c a n c e fo r b o t h th e f ro n ta l , F (1 , 9 ) = 0 . 9 1 ,

a n d a n te r io r t e m p o ra l , F (1 , 9 ) = 3 . 9 8 , p = . 0 8 , r e g io n s . T h u s ,

o n l y i n t h e f r o n t a l r e g i o n a n d o n l y f o r a l p h a p o w e r w a s d i s g u s t

a s s o c ia t e d w i th s ig n i f i c a n t ly m o re r ig h t - s id e d a c t iv a t io n ( i . e .,

l e ss a l p h a p o w e r ) c o m p a r e d w i t h b a s e l i n e.

W e n e x t c o m p a r e d t h e h a p p y c o n d i t i o n w i t h b a s el i n e. T h e

C o n d i t i o n × H e m i s p h e r e i n t e r a c t i o n f o r t h e a l p h a p o w e r d a t a

i n t h e f r o n t a l a n d a n t e r i o r t e m p o r a l r e g i o n s w a s n o t s i g n if i c an t :

f ro n ta l , F (1 , 9 ) < 1 ; a n te r io r t e m p o ra l , F (1 , 9 ) = 1 . 1 3, p > . 3 0.

W h e n t h e s e a n a l y s e s w e r e p e r f o r m e d o n m e a s u r e s o f b e t a

p o w e r, t h e C o n d i t i o n × H e m i s p h e r e i n t e r a c t i o n s w e r e a g a i n n o t

s ig n i f i c a n t : f ro n ta l , F (1 , 9 ) < 1 ; a n te r io r t e m p o ra l , F ( I , 9 ) < 1 .

T h e s e f i n d i n g s i n d i c a t e t h a t t h e h a p p y a n d b a s e l i n e c o n d i t i o n s

d o n o t d i ff e r o n m e a s u r e s o f a n t e r i o r a s y m m e t r y c o m p u t e d o n

t h e b a s i s o f a l p h a o r b e t a p o w er .

D i s c u s s i o n

T h e f i n d i n gs f r o m t h i s s t u d y p r o v i d e s u p p o r t f o r t h e p r o p o s a l

t h a t p a t t e r n s o f b r a i n p h y s i o l o g y d u r i n g t h e a r o u s a l o f a f fe c t a r e

e m o t i o n s p e ci f ic r a t h e r t h a n u n d i f f e r e n t i a te d . M o r e s p e ci f ic a ll y ,

t h is s t u d y i s co n s i st e n t w i th a n a p p r o a c h - w i t h d r a w a l m o d e l o f

l a t e ra l i z a t io n fo r a f f e c t . T h e f in d in g s in d ic a t e d th a t a c t iv a t io n

a s y m m e t r y i n t h e a n t e r i o r c o r t i c a l r e g i o n s d i f f e r e n t i at e s b e -

t w e e n p o s i t i v e a n d n e g a t iv e e m o t i o n s t h a t h a v e b e e n a s s o c i a t e d

w i t h a p p r o a c h a n d w i t h d r a w a l . F i n a l ly , t h e m a n n e r i n w h i c h

t h i s s t u d y w a s c o n d u c t e d a n d t h e p a t t e r n o f r es u l t s t h a t e m e r g e d

h a v e i m p o r t a n t m e t h o d o l o g i c a l i m p l i c a t i o n s f o r p h y s i o l o g i c a l

s t u d i e s o f e m o t i o n . W e f i r s t w i l l d is c u s s th e m e t h o d o l o g i c a l i m -

p l i c a t i o n s a n d l i m i t a t i o n s o f t h i s r e s e a r c h a n d t h e n c o n s i d e r t h e

s u b s ta n t iv e th e o re t i c a l i s s u e s o n w h ic h th e s e f in d in g s b e a r .

Methodological Implications and Limitations

T h e f i n d i n gs f r o m t h i s s t u d y i n d i c a t e t h a t w h e n d a t a a r e a v e r -

a g e d a c ro s s th e e n t i r e f i lm p e r io d , p o s i t i v e a n d n e g a t iv e f ilm

c o n d i t i o n s a r e n o t r e l i a b l y d i s t i n g u i s h e d o n t h e b a s i s o f E E G

a s y m m e t r y . T h e m a n n e r i n w h i c h t h e d a t a f r o m t h e e n t i re f i lm

p e r i o d a r e a n a l y z e d i s t h e t y p i c a l s t ra t e g y u s e d i n t h e s t u d y o f

p h y s i o l o g i c a l r e s p o n s e s t o e m o t i o n e l i c it o r s . I n t h i s t y p e o f a n a l -

y s is , n o p r o c e d u r e s a r e u s e d t o v e r i f y t h a t t h e i n t e n d e d e m o t i o n

w a s a c t u a l l y p r o d u c e d i n t h e s u b j e ct . W h e n a n i n d i v i d u a l is e x -

p o s e d t o a n e l i c i t o r s u c h a s a f i l m , t h e r e a r e p e r i o d s d u r i n g t h e

p r e s e n t a t i o n o f t h e s t i m u l u s w h e n l i t tl e o r n o e m o t i o n i s p r e s e n t

a s w e ll a s p e r i o d s d u r i n g w h i c h e m o t i o n s i n c o n s i s t e n t w i t h t h e

t a r g e t e m o t i o n a r e p r o d u c e d . T h e d i f f er e n c e i n t h e o u t c o m e o f

t h e a n a l y s e s f r o m d a t a e x t r a c t e d o n t h e b a s i s o f f a c i a l s i g n s o f

e m o t i o n i s c o n s i d e r a b l e . W h e n f a c ia l c r i te r i a a r e u s e d t o v e r i f y

t h e p r e s e n c e o f t h e t a r g e t e m o t i o n a n d t o s p e c i fy o n s et a n d o f f-

s e t ti m e s f o r d a t a e x t r a c t i o n , d i f f e r e nc e s i n a s y m m e t r y e m e r g e

t h a t d i s t i n g u i s h b e t w e e n d i s g u s t a n d e i t h e r h a p p y o r b a s e l i n e

c o n d i t io n s .

I n t h e s e a r c h f o r p h y s i o l o g i c a l d i f f e r e n t i a t io n a m o n g e m o -

t i o n s, i t i s i m p e r a t i v e t o v e r if y t h e p r e s e n c e o f t h e t a r g e t e m o -

t i o n u s i n g b o t h s e l f - r e p o r t a n d b e h a v i o r a l c r i t e r ia . O n e a d v a n -

t a g e o f u s i n g f a c i a l b e h a v i o r t o f l a g p o r t i o n s o f t h e p h y s i o l o g i c a l

r e c o r d t o b e e x t r a c t e d f o r a n a l y s i s i s t h a t o n s e t a n d o f f s e t t i m e s

f o r a n e m o t i o n c o n d i t i o n c a n b e r e a d i l y s p e ci f i ed . T h i s w o u l d

n o t b e p o s s i b l e u s i n g c o n v e n t i o n a l s e l f - r e p o r t m e t h o d s .

O n e l i m i t a t i o n o f t h e u s e o f f a c ia l a c ti o n t o f la g o n s e t a n d

o f fs e t t i m e s i s t h e c u r r e n t l a c k o f k n o w l e d g e c o n c e r n i n g t h e s ig -

n i f i c a n ce o f t h e se t i m e m a r k e r s . I t i s n o t c e r t a i n w h e t h e r t h e

o n s e t o f t h e f a c i a l e x p r e s s i o n d e n o t e s t h e o n s e t o f a n e m o t i o n a l

e x p e r i e n c e , o r w h e t h e r e m o t i o n a l e x p e r i e n c e m a y b e g i n p r i o r

t o t h e o n s e t o f e m o t i o n a l e x p r e s si o n . P e r h a p s e ve n m o r e p r o b -

l e m a t i c i s t h e s ig n i f i c a n c e o f f a c i a l e x p re s s io n o f f s e t. I t m a y b e

t h a t f a c i a l a c t i o n r e t u r n s t o b a s e l i n e a f t e r a c e r t a i n p e r i o d o f

t i m e h a s e l a p s e d s o l e l y a s a f u n c t i o n o f m u s c u l a r f a t i g u e.

W h e t h e r t h e r e t u r n o f t h e f a c e t o a n e u t r a l e x p r e s s i o n i n s u c h a

s i t u a t i o n a l s o s i gn i f ie s t h e a t t e n u a t i o n o f e m o t i o n i s n o t c u r -



33 8 DAVIDSON, EKMA N, SAR ON , SENULIS, FRIESEN

r e n t l y k n o w n . W e a t t e m p t e d t o e x a m i n e b r a i n a c t iv i ty b e f o re

a nd a f t e r fa c i a l s i gns o f e m ot i on . H ow e ver , w e w e r e una b l e t o

e x t r a c t a s u f f i c i en t du r a t i on o f a r t if a c t - f r e e pe r i ods t ha t w e r e

t e m por a l l y i s o l a t e d f r om a d j a c e n t e xp r e s s i ons . I t i s c l e a r t ha t

f u t u r e s t u d ie s m u s t b e g i n t o u n r a v e l t h e c o m p l e x t e m p o r a l r e -

la t ions am on g express ive , phys io logica l , an d subjec t ive s igns of

e m o t i o n . U n t i l b a s ic r e s e a r c h o f t h is n a t u r e i s p e r f o r m e d , t h e

d y n a m i c r e l at io n s a m o n g t h e s u b c o m p o n e n t s o f t he e m o t i o n

pa c k a ge r e m a i n e lu s ive .

I n t h i s s tu d y , w e c o m p u t e d m e a s u r e s o f a c t iv a t io n b a s e d o n

b o t h a l p h a a n d b e t a p o w er . A s w e h a d e x p e c t e d , th e e m o t i o n

c o n d i t io n s w e r e d i s c r im i n a t e d o n l y o n m e a s u r e s o f a l p h a

pow er . We be l ie ve t ha t m a n y o f t he p r e v i ous s t ud i e s i n t he c og -

n i ti v e E E G a s y m m e t r y l i t e ra t u r e t h a t h a v e f o u n d t a s k - d e p e n -

de n t c ha nge s i n be t a a c t i v i ty s u f f e r f r om t w o s i gn i f ic a n t f la w s:

( a ) t he f a i l u r e t o m a t c h t he c ogn i t i ve t a s ks t ha t w e r e u s e d on

ba s i c p s yc hom e t r i c c ha r a c t e r i s t i c s , a nd ( b ) t he f a i l u r e t o c on -

v i n c i n g l y r e m o v e m u s c l e a r t i f a c t f r o m t h e E E G . T h e l a t t e r

p r o b l e m i s v e r y si g n if ic a n t b e c a u se t h e f r e q u e n c y s p e c t r u m o f

EE G a nd m us c l e a c t i v i t y ove r l a p in t he be t a r a nge . I n t h i s s t udy ,

t he pos i t i ve a nd ne ga t i ve fi l m c l ip s w e r e c a r e f u l ly m a t c he d a nd

c a r e w a s t a k e n t o r e m o v e a l l m u s c le a n d m o v e m e n t - r e la t e d a r t i -

f a c t f r o m t h e E E G . W h e n s i m i la r c o n t r o l s a r e e x e rc i se d i n c o g -

n i t i ve s t ud i e s , i t i s a l s o a s ym m e t r i e s i n a l pha pow e r , no t be t a

pow er , t ha t be s t d i s c r i m i n a t e be t w e e n ve r ba l a nd s pa t i a l c ogn i -

t ive t asks (D avid son e t a l . , in press) .

The r e w e r e t h r e e s pe c i f ic m e t hodo l og i c a l l i m i t a t i ons o f t h i s

s t udy t ha t de s e r ve e m p ha s i s . T he f i r st c on c e r ns t he f a c t t ha t t he

pos i t ive a nd ne ga t i ve f i l m c li p s w e r e no t c oun t e r b a l a nc e d . T he

pos i t i ve c l i p s a l w a ys p r e c e de d t he ne ga t i ve d i p s . We c hos e t o

p r e s e n t t h e c l i p s i n t h i s o r d e r b e c a u s e o f o u r c o n c e r n w i t h c a r r y -

ove r e ff ec ts . A l t hou gh i t is t r ue t ha t t he m a n ne r i n w h i c h w e

s e le c te d t h e e p o c h s f o r a n a ly s i s w o u l d g u a r a n t e e t h a t E E G w a s

e x t r a c t e d d u r i ng a d i s c r e t e f ac i a l e xp r e s s i on o f e m ot i on , w e e x -

pe c t e d t h a t i f t he ne ga t i ve f il m s w e r e p r e s e n t e d f ir st , t he ne g a -

t iv e m o o d p r o d u c e d b y t h e n e g a ti v e f il m c l ip s w o u l d c a r r y o v e r

a nd de c r e a s e t he i nc i de nc e o f f a c ia l e xp r e s s ions o f ha pp i ne s s .

W h e n t h e se s a m e f i lm c l i p s w e re u s e d i n p r e v i o u s r e s e a r c h , t h e

pos i t ive c l ips were a lways presen ted f i r s t (E km an e t a l ., 1980).

N e ve r t he le s s , i t is pos s i b le t ha t t he d i f f e r e nc e s in a n t e r i o r E EG

a s y m m e t r y b e t w e e n h a p p i n e s s a n d d i s g u s t m a y b e a f u n c t i o n

o f t he o r de r i n w h i c h t he s e c l ip s w e r e p re s e n t e d . Sub j e c t s m i gh t

ha ve be e n m or e f a t i gue d l a t e r i n t he s e s s i on , w i t h t he f a t i gue

a f f e c ti ng t he t h r e s ho l d f o r c ha nge i n c e r t a i n b r a i n r e g i ons m or e

t ha n o t he r s . We c ons i de r t h i s e xp l a na t i on un l i ke l y be c a us e i n

t h e c o m p a r i s o n b e t w e e n t h e h a p p y a n d d i s g u s t c o n d i t i o n s i n

a n t e r i o r a s y m m e t r y , t h e r e w e r e n o m a i n e f fe c ts f o r c o n d i ti o n

a c r os s he m i s phe r e . I f s ub j e c t s w e r e m or e f a t i gue d du r i ng t he

d i s g us t c o m p a r e d w i t h t h e h a p p y c o n d i t io n , w e w o u l d h a v e e x -

pe c t e d ove r a ll d if f e r e nc e s in b r a i n a c t i va t ion . M or e ove r , t he f a c t

t ha t t he d i s gus t c ond i t i on w a s f ound t o d i f f e r f r om ba s e l i ne i n

f r o n ta l a s y m m e t r y c a n n o t b e a t t r i b u t e d t o s h i ft s o v er t h e c o u r s e

o f t he s e s s i on i n ba s e l i ne a c t i v i ty be c a us e t he b a s e l i ne da t a u s e d

i n t he a na l ys e s w e r e t he a ve r a ge o f t he p r e - a nd pos t f i l m ba s e -

l i ne s . Thus , t he ba s e l i ne t r i a l s c a m e f r om bo t h t he be g i nn i ng

a nd e nd o f t he s e s si on . N e ve r the l e s s, i n f u t u r e s t ud i e s , t he pos i -

t ive a nd ne ga t i ve f il m c l i p s c ou l d be p r e s e n t e d o n s e pa r a t e da ys ,

w i t h t h e d a y o n w h i c h e a c h t y p e i s p r e s e n t e d c o u n t e r b a l a n c e d .

T h e s e c o n d m e t h o d o l o g i c a l l i m i t a ti o n o f t h is s t u d y i s th e

m a n n e r i n w h i c h i n t e n s i t y w a s m a t c h e d f o r t h e p o s i t i v e a n d

ne ga t i ve fi lm s . W e e s ta b l i s he d t h a t s e l f - r e po r t s i n r e s po ns e t o

these f i lm c l ips are equ ated in in tens i ty . However, the se l f - repo r t

da t a p r e s um a b l y r e f le c t the s ub j e c t s ' a gg r e ga t i on ove r t he e n t i r e

l e n g th o f t h e f i lm c l ip . T h i s p r o c e d u r e d o e s n o t e n s u r e t h a t t h e

s pe c i fi c e xp r e s s i on pe r i ods t ha t w e r e e x t r a c t e d f o r a na lys i s w e r e

m a t c he d on i n t e ns i t y . I t i s no t e ve n c l e a r how s uc h i n t e ns i t y

m a t c h i n g s h o u l d b e a c c o m p l i s h e d . I t m a y b e p o s s ib l e i n f u t u r e

r e s e a r c h t o ha ve s ub j e c t s r e t r o s pe c t i ve l y r e v i ew a s p l i t- s c r e e n

i m a ge o f t he i r f a c ia l be ha v i o r a nd t he f i lm c l i p a nd ha ve t he m

m a k e r a t in g s o f t h o s e m o m e n t s d u r i n g w h i c h t h e t a rg e t e x p re s -

s i ons w e r e p r e s e n t . I t s hou l d be no t e d t ha t E km a n e t a l . ( 1980)

e xa m i n e d t he r e l a t i on be t w e e n a m e a s u r e o f f a c ia l e xp r e s s i on

i n t e ns i t y a nd s e l f - r e po r t s o f e m ot i on a l i n t e ns i t y i n r e s pons e t o

t he s a m e c l i p s u s e d i n t h i s s t udy . Ekm a n e t a l . r e po r t e d a s i g -

n i f i c a n t c o r r e l a t i on be t w e e n t he s e m e a s u r e s , s ugge s t ing tha t

w he n s ub j e c t s r a t e i n t e ns i t y i n r e s pons e t o t he s e pa r t i c u l a r

d i ps , t he i r r a t i ngs r e f l e c t t he i n t e ns i t y o f t he i r f a c ia l e xp r e s -

sions.

The t h i r d l i m i t a t i on t ha t de s e r ve s m e n t i on i s t he s ubs t a n t i a l

s ub j e c t a t tr i t i on t ha t w a s p r e s e n t . T h i r t y pe r c e n t o f t he o r i g i na l

s a m p l e w a s e l im i na t e d i n i ti a l ly a s a f unc t i on o f no t s how i ng a t

l ea s t o n e i n s t a n c e e a c h o f a h a p p y a n d d i s g u st e x p r e ss i o n d u r i n g

t he pos i t i ve a nd ne ga t i ve f i l m d i ps . Th i s f i gu r e i s c om pa r a b l e

t o w ha t ha s be e n p r e v i ous l y r e po r t e d u s i ng t he i de n t i c a l f i l m

c l i p s ( Ek m a n e t a l. , 1980). M os t o f t he r e m a i n i ng s ub j e c t s w ho

w e r e e l i m i na t e d w e r e r e m o ve d be c a us e o f e xce ss ive a r t i f a c t i n

t h e E E G . W e u n f o r t t i n a t e l y d i d n o t r e c o r d t h e e l e c t r o o c u l o -

g r a m ( E O G ) o n o u r c o m p u t e r a n d t h e r ef o re c o u l d n o t u s e a n

a u t o m a t e d e y e - m ove m e n t c o r r e c t i on a l go r i t hm ( e.g. , G a s se r,

S r oka , & Moc k s , 1986 ; G r a t t o n , C o l e s , & D onc h i n , 1983) .

H ow e ve r , s uc h a p r oc e dur e w ou l d on l y ha ve r e c ove r e d a s m a l l

n u m b e r o f r e c o r d s b e c a u s e m o s t o f t h e a r ti f a c t w a s m o v e m e n t

r e l a t e d . We s hou l d no t e t ha t t he d i f f e r e nc e s i n s e l f - r e po r t e d

e m o t i o n b e t w e e n t h e s u b j e ct s w h o w e r e re t a i n e d a n d t h o s e w h o

w e r e r e m o ve d ( a f t e r t he i n i t ia l c u t m a de on t he ba s i s o f the p r e s -

e nc e o f t he t a r ge t f a c i a l e xp r e s si ons ) w e r e s l i gh t a nd nons i gn i f i-

c a n t . T h e s u b je c ts w h o w e r e r e m o v e d r a t e d t h e i n t e n s it y o f t h e

t a r g et e m o t i o n s s l ig h tl y m o r e e x t r e m e l y t h a n t h e s u b j e c ts w h o

w e r e r e t a i ne d . T hus , i f a ny t h i ng , t he a r t i f a c t r e je c t i on p r oc e -

du r e a c t ua l l y b i a s e d t he f i na l s a m p l e i n t he d i r e c t i on o f l es s

i n t e n se e m o t i o n a l r e s p o n se s . O n e s t ra t e g y w e a t t e m p t e d i n t h e

p i l o t e x p e r i m e n t a t i o n p r i o r t o t h e c o n d u c t o f t h i s s tu d y w a s t o

i n s t r uc t s ub j e c t s t o r e m a i n ve r y s ti ll du r i ng t he p r e s e n t a t i on o f

t h e f i lm c l ip s , t o r e d u c e t h e a m o u n t o f m o v e m e n t - r e la t e d a r t i-

f a ct . A l t h o u g h t h e p r o v i s i o n o f s u c h a n i n s t r u c t i o n d i d s u c c e e d

i n r e d u c i n g m o v e m e n t a r t i f a c t , i t a l s o h a d t h e u n f o r t u n a t e

e f f ec t o f d r a m a t i c a l l y r e du c i ng f a c i a l be ha v i o r i n r e s pons e t o t h e

f i lm c l ip s . We t hus e l i m i na t e d t h i s i n s t r uc t i on , be l i e v ing t ha t w e

w ou l d a c t ua l l y ob t a i n m or e u s a b l e da t a w i t hou t i t . I t i s c l e a r

t ha t r e s e a r c h o f t h i s k i nd r e qu i r e s a ve r y s ubs t a n t i a l s a m p l e s i z e

s o t ha t s ub j e c t l o s s due t o a r t i f a c t i s to l e r a b l e . A v e r y l a rge s a m -

p l e w ou l d a l s o f a c i li t a te t he s t udy o f the t e m por a l r e l a t i on be -

t w e e n c ha nge s i n b r a i n a c t i v i ty a nd f a c i a l be ha v i o r . I n t h i s s t udy ,

w e w e r e p re v e n t e d f r o m p e r f o r m i n g s u c h a n a l y s e s b e c a u s e o f

t he pa uc i t y o f a va i l ab l e da t a .

Physiological Di f ferentiation m on g Em ot ions

A s n o t e d i n t h e i n t r o d u c t i o n , t h e r e i s in c r e a s i n g s u p p o r t f o r

t he no t i on t h a t e m o t i ons d i f f er i n t he i r unde r l y i ng phys i o l og i c a l

p a t t e r n s . E k m a n ( 1 9 8 4 ) p r e d i c t e d t h a t s u c h d i f f e r e n t i a t i o n

w o u l d b e f o u n d i n b o t h t h e a u t o n o m i c a n d c e n t r a l n e r v o u s s y s-



B R A IN A SY MMETR Y A N D A PPR O A C H -WI TH D R A WA L 339

t e m s . E k m a n , L e v e n s o n , a n d t h e i r c o l l e a g u e s ( E k m a n e t a l . ,

1 9 8 3; L e v e n s o n e t a l. , i n p r e ss ) h a v e o b t a i n e d r o b u s t a u t o n o m i c

d i f f e r e n t i a t i on be t w e e n pos i t i ve a nd ne ga t i ve e m ot i ons a nd

a m o n g f o u r n e g a ti v e e m o t i o n s .

A l t h o u g h t h e d a t a p r e s e n t e d i n t h i s r e p o r t o n l y i n v o lv e t w o

e m o t i ons , t he e v i de nc e i s ne ve r t he l es s c ons i s t e n t w i t h t he ge n -

e r a l no t i on o f phys i o l og i c a l d i f f e re n t i a t ion . Th e de g r e e t o w h i c h

E E G a s y m m e t r y w i ll d is t in g u i s h a m o n g d i f f e re n t e m o t i o n s is

c u r r e n t l y no t know n . H ow e ve r , a s no t e d a bove , w e w ou l d p r e -

d i c t t ha t t o t he de g r e e t ha t a n e m ot i on i s a s s oc i a t e d w i t h e i t he r

a pp r oa c h o r w i t hd r a w a l , i t s hou l d be a s s oc i a t e d w i t h l e f t- ve rs us

r i gh t - s ide d a n t e r i o r a c t iva t i on . Thus , a c c o r d i ng t o t h is m od e l ,

t w o e m ot i ons t ha t a r e e a c h a s s oc i a t e d w i t h w i t hd r a w a l ( s uc h

a s f e a r a nd d i s gus t ) s hou l d bo t h be a s s oc i a t e d w i t h r i gh t - s i de d

a n t e r i o r a c t i va t i on . I t s hou l d be n o t e d t ha t t h i s v i e w i s no t i n -

cons i s tent wi th the no t ion of psychop hys io logica l speci fici ty .

T w o e m o t i o n s t h a t a r e s i m i la r i n a n t e r i o r a c t i v a ti o n a s y m m e t r y

s h o u l d d i ff e r i n s o m e o t h e r m e a s u r e o f c e n t ra l n e r v o u s s y s t e m

f unc t i on . Fo r e xa m pl e , a nu m be r o f w or ke r s (e .g ., G a r c i a ,

Q u i c k , & Whi t e , 1984) ha ve no t e d t ha t d i s gus t i s a s s oc i a t e d

w i t h he i gh t e ne d s e ns i ti v i ty t o t he pe r c e p t u a l a t t r i bu t e s o f the

e l i c i t i ng s t i m u l us . We w ou l d t he r e f o r e e xpe c t m or e ne u r a l a c -

t i v it y i n c i r c u i t s t ha t m e d i a t e c e r t a i n pe r c e p t ua l p r oc e s s e s du r -

i ng d i sgus t c om pa r e d w i t h f ea r.

Cerebral Asymmetry and Approach Withdrawal

T h e f in d i n gs f r o m t h i s s t u d y p r o v i d e s u p p o r t f o r th e h y p o t h e -

s is t ha t ne ga t i ve a ff e c t a s s oc i a t e d w i t h w i t hd r a w a l i s a c c om pa -

n i e d by r i gh t - s ide d a n t e r i o r a c t i va ti on . I n bo t h f r on t a l a nd a n t e -

r i o r t e m por a l r e g i ons , t he d i s gus t c ond i t i on p r oduc e s s i gn i f i -

c a n t l y m o r e r i g h t - s i d e d a c t i v a t i o n c o m p a r e d w i t h t h e h a p p y

c ond i t i on . I n a d d i t i on , i n t he f r on t a l r e g i on , t he d i s gus t c ond i -

t i o n p r o d u c e d m o r e r i g h t- s id e d a c t i v at i o n c o m p a r e d w i t h b a s e-

l ine.

W e p r ed i c t e d t h a t t h e h a p p y c o n d i ti o n w o u l d p r o d u c e m o r e

l e f t - s i de d a c t i va t i on c om pa r e d w i t h bo t h t he d i s gus t c ond i t i on

a nd ba s e l i ne . I n the a n t e r i o r t e m p or a l r e g i on , t he ha ppy c ond i -

t i on d i d p r oduc e s i gn i f i c a n t l y m or e l e f t - s i de d a c t i va t i on c om -

pa r e d w i t h d i s gus t . H ow eve r, t he r e w a s no d i f f e re nc e i n a s ym -

m e t r y b e t w e e n t h e h a p p y a n d b a s e l i n e c o n d i t io n s i n a n y b r a i n

r e g io n . T h e r e f o re , o n e c o m p o n e n t o f H y p o t h e s i s 3 w a s n o t c o n -

f i r m e d b y ou r r e s u lt s .

D a v i d s o n ( 1 9 8 4 a ) h a s p r o p o s e d t h a t t h e f u n d a m e n t a l b a s i s o f

t h e a n t e r i o r a s y m m e t r y a s s o c i a t e d w i t h e m o t i o n i s a p p r o a c h -

w i t hd r a w a l . To the e x t e n t t ha t a pos i t ive e m o t i on i s a c c o m p a -

n i e d by a p p r oa c h , he w ou l d e xpe c t i t t o be a s s oc i a t e d w i t h l e f t

ante r ior ac t iva t ion . However , not a l l form s of pos i t ive af fec t in-

c l u d e a n a p p r o a c h c o m p o n e n t . E k m a n a n d F r i e s e n (1 9 8 2 ) p r o -

p o s e d t h a t t h e h a p p i n e s s e x p r e ss i o n c o d e d i n t h is s t u d y c a n

m a r k a nu m be r o f ra t he r d i f f e re n t pos i ti ve a f fe c t ive s ta t e s i n -

c l u d i n g a m u s e m e n t a s w e ll a s s e v e ra l f o r m s o f h a p p in e s s . T h e

p r i m a r y pos i t i ve e m ot i on e l i c i t e d by t he pos i t i ve f i l m c l i p s i n

t h is s t u d y w a s a m u s e m e n t . A l t h o u g h s o m e t y p e s o f a m u s e m e n t

m a y i nvo l ve t he a c t i va t i on o f a pp r oa c h be ha v i o r, w e be l ie ve t ha t

i n t h is s t u dy , i n w h i c h a m u s e m e n t w a s a r o u s e d b y w a t c h i n g a

f il m o f m o n k e y s a n d g o r il la s p l a y in g , t h e t e n d e n c y t o a p p r o a c h

w a s w e a k o r none x i s t e n t . W e bel i eve t h i s is t he r e a s on f o r ou r

f a i lu r e t o f i nd l e ft a n t e r i o r a c t i va t i on r e l a t ive t o ba s e l i ne du r i n g

t he ha p py c on d i t i on . O t he r f o r m s o f pos it i ve a f f e ct a r e a s soc i -

a t e d w i th u n a m b i g u o u s a p p r o a c h , s u c h a s t h e r e a c ti o n o f m a n y

1 0 - m o n t h - o l d i n f a n t s t o t h e a d v a n c e o f th e i r m o t h e r s . I n f a n t s

i n th i s s i t ua t i on o f t e n r e a c h o u t t ow a r d t he m o t he r a s s he d r a w s

ne a r e r, s how i ng a c l e a r be ha v i o r a l m a n i f e s t a t i on o f a pp r oa c h .

I n t h i s s i t ua t i on , e v i de nc e o f s t rong l e f t f r on t a l a c t i va t ion r e l a-

t ive t o ba s e l ine ha s be e n f ou nd ( Fox & D a v i ds on , 1987, 1988) .

I t w o u l d b e e s s e n t i a l t o e x a m i n e E E G a s y m m e t r y d u r i n g

s u c h a p p r o a c h h a p p i n e s s a n d c o m p a r e i t i n t h e s a m e s u b je c ts

t o o t h e r n o n a p p r o a c h f o r m s o f p o si ti v e af fe c t, s u c h a s s o m e

f o r m s o f a m u s e m e n t , i n o r d e r t o e v a l u a te t h i s h y p o t h es i s. O n e

m a j o r m e t hodo l og i c a l p r ob l e m i n e va l ua t i ng t h i s hypo t he s i s i s

t h e n e e d t o o b t a i n a n i n d e p e n d e n t m e a s u r e o f a p p r o a c h t e n -

de nc y . I n a du l t s , i t m a y be pos s i b le t o ob t a i n a n i nde x o f t h i s

c ons t r uc t w i t h a s e l f - r e po r t i nve n t o r y . Me a s u r e m e n t o f e l e c t r o -

m y o g r a p h i c a c ti v it y i n t h e f o r e a r m o r l e g m i g h t a l s o p r o v id e a

us e f u l i nde x . I t w ou l d be i de a l t o i nc l ude bo t h s e l f - r e po r t a nd

e l e c t r om yogr a ph i c m e a s u r e s i n t he s a m e s ub j e c t s t o e s t a b l i s h

c ons t r uc t va li di ty . I n i n f a n t s, a p p r oa c h t e nd e nc i e s a r e t yp i c a l l y

qu i t e ove r t a nd a r e e a s i l y m e a s u r e d . I n t he Fox a nd D a v i ds on

( 1 9 8 8 ) s t u d y , m o s t i n f a n t s i n t h e m o t h e r a p p r o a c h c o n d i t i o n

l i te r a ll y r e a c he d ou t t ow a r d t he i r m o t he r s .

I t i s e s s e n t i a l t o no t e t ha t t he r a t i ona l e p r e s e n t e d a bove i s

a dm i t t e d l y pos t hoc , a nd o t he r a lt e r na t ive i n t e r p r e t a t i ons o f ou r

da t a a r e pos s i b l e . Fo r e xa m pl e , i t m i gh t be a r gue d t ha t t he r i gh t -

s i de d a c t i va ti on obs e r ve d du r i n g d i s gus t r e f le c t s t he a r ous a l o f

em ot io n per se and i s not a speci f ic s ign o f negat ive affec t . I t i s

c l e a r t ha t s ub j e c ts a r e r e po r t i ng pos i t i ve e m ot i on i n r e s pons e t o

the pos i t ive f i lm c l ips and tha t such pos i t ive emot ion i s s igni f i -

c a n t l y c o r r e l a t e d w i t h t he du r a t i on o f f a c ia l s igns o f fe l t ha pp i -

ness ( see Ekman e t a l . , 1990) . However , r ight - s ided ac t iva t ion

w a s no t f ou nd du r i n g t h i s c ond i t ion . T h i s f i nd ing a r gue s a ga i ns t

t he s ugge s t i on t ha t r i gh t - s i de d a n t e r i o r a c t i va t i on i s i nde x i ng

t he a r ous a l o f e m ot i on pe r s e.

O n e q u e s t i o n r a is e d b y t h e a p p r o a c h - w i t h d r a w a l i n t e rp r e t a -

t i o n o f o u r d a t a is w h e t h e r t h e a n t e r i o r a s y m m e t r y i s re f le c ti n g

e m o t i o n o r a p p r o a c h - w i t h d r a w a l p e r s e. W e b e li ev e t h a t c e r -

t a i n e m o t i o n s i n c lu d e h a r d - w i r e d a p p r o a c h o r w i th d r a w a l

t e nde nc i e s . Fo r e xa m pl e , bo t h f e a r a nd d i s gus t i nc l ude a w i t h -

d r a w a l c o m p o n e n t , w h e r e a s c e r t a in f o r m s o f a n g e r a n d h a p p i -

n e s s i n c l u d e a n a p p r o a c h c o m p o n e n t . S u p e r i m p o s e d o n t h e s e

h a r d - w i r e d a c t i o n t e n d e n c ie s a r e l e a rn e d c o m p o n e n t s t h a t c a n

a c c e n t ua t e , a t t e nua t e , o r e ve n r e p l a c e the a pp r oa c h o r w i t h -

d r a w a l pa t t e r ns . Fo r e xa m pl e , s om e i nd i v i dua l s l e a r n t o a p -

p r oa c h s i t ua t i ons t he y f e a r . A nge r i s a n e m ot i on t ha t i s s om e -

t i m e s a s s oc i a t e d w i t h a pp r oa c h a nd a t o t he r t i m e s a s s oc i a t e d

w i t h w i t hd r a w a l . I n f u t u r e r e s e a r c h i t w il l be i n s t r uc t i ve t o c om -

p a r e i n s t a n c es o f t h e s a m e e m o t i o n w h e n i t i s a c c o m p a n i e d b y

a pp r oa c h ve r s us w i t hd r a w a l s o t ha t t he r e l a ti ve c on t r i bu t i ons

t o a n t e r i o r a s y m m e t r y o f th e e m o t i o n p e r s e a n d t h e a c t i o n

t e nde nc i e s w i t h w h i c h i t is a s s oc i a t e d c a n be s ys t e m a t i c a l l y d is -

e n t a ng l e d .

A c t i va t i on a s ym m e t r y i n t he c e n t r a l a nd pa r i e t a l r e g i ons

f a i le d t o d i f f e re n t i a t e be t w e e n t he h a ppy a nd d i s gus t c ond i t ions .

Th i s f i nd i ng , i n c on j unc t i on w i t h t he f r on t a l a nd a n t e r i o r t e m -

p o r a l d i f fe r en c e s, u n d e r s c o r e s t h e i m p o r t a n c e o f a s y m m e t r y i n

t he s e a n t e r i o r c o r t i c a l z one s f o r e m ot i on . B o t h t he f r on t a l a nd

a n t e r i o r t e m por a l r e g i ons ha ve e x t e ns i ve a na t om i c a l r e c i p r oc -

i t y w i t h l i m b i c c i r c u i t s t ha t ha ve be e n d i r e c t l y i m p l i c a t e d i n t he

c on t r o l o f e m ot i on ( e. g. , Mye rs , 1972 ; N a u t a , 1971) . Mor e ove r ,

a n u m b e r o f r e c e n t st u d ie s t h a t h a v e u s e d t h e a p p r o p r i a t e p r o -

c e du r e s f o r m e a s u r i ng e i t he r a c t iva t i on o r ne u r oc he m i c a l a c t iv -

i t y i n t he s e s ubc o r t i c a l r e g i ons i n hum a ns ha ve unc ove r e d



34

DAVIDSON, EKMA N, SAR ON, SENULIS, FRIESEN

a s y m m e t r i e s r el a t ed t o e m o t i o n a n d c o g n i t i o n ( e .g ., R e i m a n ,

Raic hle , Buf fer , Hers covi tch , Rob ins , 1984; Rey nold s , 1983).

M a n y i n v e s t i g a t o r s h a v e p r o p o s e d a n i m p o r t a n t r o l e f o r t h e

f r on t a l a nd a n t e r i o r t e m por a l c o r t i c a l r e g i ons i n e m ot i o n ( e .g .,

R o l l s, 1986). T he l a c k o f a d i f f e re nc e i n pa r i e t a l a s ym m e t r y

be t w e e n t he ha ppy a nd t he d i s gus t pe r i ods s ugge s t s t ha t t he s e

c ond i t i ons d i d n o t d i f f e r i n t he c ogn i t i ve p r oc e s s e s t ha t a r e m e -

d i a t e d b y t h i s b r a i n r e g i o n . T h e d a t a f r o m t h i s s tu d y a l s o i n d i -

c a t e t h a t c e n t ra l a s y m m e t r y d o e s n o t d i s ti n g u i sh b e t w e e n h a p -

p i ne s s a nd d i s gus t. I f t he d i f f e re nc e be t w e e n t he s e c ond i t i ons

h a d b e e n a s s o c i a t e d w i t h a s y m m e t r i e s i n m o t o r c o n t r o l , w e

w ou l d ha ve e xpe c t e d t he c e n t r a l r e g i on t o r e l i a b l y d i s t i ngu i s h

be t w e e n t he m . The f a c t t ha t i t d i d no t s ugge s t s t ha t t he d i f f e r -

e n c e b e t w e e n t h es e c o n d i t io n s i s in a p r o c e s s o t h e r th a n m o t o r

a s y m m e t r i e s p e r s e .

A l t hough t h i s a r t i c l e ha s t r e a t e d e m ot i on a c r os s i nd i v i dua l s

a s a n i nde pe nde n t va r i a b l e , w e be l i e ve t ha t t he a pp r oa c h ha s

i m p o r t a n t i m p l i c a t io n s f o r t h e s t u d y o f i n d i v id u a l d i f f er e n c es i n

e m o t i ona l r e a c t iv i t y . Th e t a s k - de p e nde n t d i f f e re nc e s i n a n t e r i o r

E E G a s y m m e t r y t h a t w e d e m o n s t r a t e d i n t h i s s tu d y a r e s u p e r-

i m p os e d on w i de - r a ng i ng i nd i v i dua l d i f f e re nc e s in t he d i r e c t i on

a n d m a g n i t u d e o f a s y m m e t r y i n t h i s re g i o n . S u c h i n d i v id u a l

d i ff e re n c e s i n a c t iv a t io n a s y m m e t r y h a v e b e e n n o t e d b y a n u m -

ber of inves t iga tors (e .g. , Glass , 1987; Levy, 1983) . Individ ual

d i ff e re n c e s i n E E G m e a s u r e s o f a c ti v a ti o n a s y m m e t r y h a v e

b e e n f o u n d t o b e st a b le ov e r t i m e (e .g ., A m o c h a e v S a l a m y ,

1979 ; Eh r l i c hm a n Wi e ne r , 1979). I n s e ve r al r e c e n t s t ud i e s,

w e ha ve de m ons t r a t e d t ha t i nd i v i dua l d i f f e r e nc e s i n a n t e r i o r

E E G a s y m m e t r y a r e r e l a te d t o e m o t i o n a l r e a c ti v it y a n d v u l n e r -

a b i li ty t o p s y c h o p a t h o l o g y i n b o t h i n f a n ts a n d a d u l t s ( D a v i d s o n

Fox , 1989 ; Tom a r ke n , D a v i ds on , H e nr i que s , 1989 ; s e e D a -

v i ds on Tom a r ke n , 1989 , f o r a r ev ie w ). We ha ve i n t e r p r e t e d

s u c h i n d i v i d u a l d i f f e r e n c e s i n a n t e r i o r a s y m m e t r y t o m a r k a

t h r e s ho l d f o r t he e xpe r i e nc e o f c e r t a i n pos i t i ve a nd ne ga t i ve

e m ot i ons .

A c e n t r a l p u r p o s e o f t h is s t u d y w a s t o e x a m i n e d i f f e re n c e s

i n a n t e r i o r a s y m m e t r y be t w e e n a w i t hd r a w a l - r e l a t e d ne ga t ive

e m o t i o n a n d a n a p p r o a c h - r e l a t e d p o s i t i v e e m o t i o n . T h e d a t a

s t ro n g l y s u p p o r t e d o u r h y p o t h e s i z e d d i f fe r e n ce i n a s y m m e t r y

b e t w e e n t h e se c o n d i t i o n s i n b o t h t h e f r o n t a l a n d a n t e r i o r t e m -

por a l r e g i ons . The s t udy w a s a l s o de s i gne d t o i l lu s t r a t e t he u s e

o f a m u l t i p ro c e s s r e s e ar c h p a r a d i g m i n th e s t u d y o f t h e p s y c h o -

p h y s i o lo g y o f e m o t i o n . U s i n g s u c h a p a r a d i g m , w e d e m o n -

s t r a t e d t he i m por t a nc e o f r i go r ous ve r i f ic a t i on c r i te r i a t o e s t a b -

l is h t h a t t h e i n t e n d e d e m o t i o n w a s a c t u a l ly p r o d u c e d . T h e a c -

c o m p a n y i n g r e p o r t ( E k m a n e t a l. , 1 9 9 0 ) o f o u r j o i n t r e s e a r c h

s h o w s t h e i m p o r t a n c e o f d i s ti n g u i sh i n g a m o n g d i f f e re n t f o r m s

o f s m i li n g i f o n e i s t o s e p a r a t e m o m e n t s o f e n j o y m e n t f r o m

ot he r e xpe r i e nc e s . I t a l s o unde r s c o r e s t he s i gn i fi c a nc e o f c e r e -

b r a l a s y m m e t r y f o r t h e s t u d y o f e m o t i o n a n d p r o v i d e s a s e c o n d

e x a m p l e o f t h e u t i li t y o f c o m b i n i n g m e a s u r e s o f b r a in a c t iv i ty

a nd f a c i a l e xp r e s s i on i n e m ot i on r e s e a r c h .

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