Galin y Thorn (1993) Unmasking Pain

7/25/2019 Galin y Thorn (1993) Unmasking Pain

1/17

lournal

of

Social

an d

Clinical

Psychology,

Vol.

12,

No.

2,

1993,

pp.

182-197

UNMASKING

PAIN: DETECTION OF

DECEPTION

IN

FACIAL

EXPRESSIONS

KAREN E. GALIN

VA

Medical

Center,

Pittsburgh,

PA

BEVERLY

E.

THORN

University

of

Alabama

Trained

judges

66

college

students)

distinguished

facial

expressions

of

subjects

in

genuine

pain

hand

in

ic e

water ,

masked

pain, posed

pain,

or

no

pain. Judges

were

given

facial movement

training

based

on

Facia l Action

Coding

System)

plus

limited

feedback

training,

feedback

only training,

or

no

training.

All

judges,

regardless

of

training,

were more ur te

in

detecting

genuine

pain

in

subjects

demonstrating

low

pain

tolerance

than

in

subjects

with

high

tolerance. Relative to

no

training,

feedback

training

enhanced

accuracy

in

identifying

posed

and

genuine pain,

whereas facial action

training

plus

feedback enhanced

accuracy

in

identifying

posed

pain.

Results

suggest

judges

n be

provided

with

information

about

facial movements to

distinguish

between

genuine

and d isto rted

pain

displays.

Pain ssessment

represents

challenge

to clinicians.

The fundamental

difficulty

involves the

private

n ture of

pain,

which n

only

be

revealed

by

what

th e

suffering

person

says

or

does

Fordyce,

1983 .

Several researchers

have

attempted

to

identify

the

behaviors

reliably

associated

with

pain.

Keefe

and Block

1982)

investigated

number of

behav iors assoc ia ted with

low-back

pain,

including guarded

move

ment,

bracing, rubbing, sighing,

and

grimacing.

Other researchers

e.g.,

Craig,

Hyde,

Patrick,

1991;

Craig

Patrick,

1985;

LeResche

Dworkin, 1988;

Patrick,

Craig,

Prkachin, 1986;

Prkachin

Mercer,

1989

have

studied

specific

facial

expressions

characteristic

of

pain.

Investigations using

the

Facial Action

Coding

System

FACS;

Ekman

Friesen,

1969)

indicate that

circumscribed

subset of

facial actions is


2/17

PAIN

AND

FACIAL

EXPRESSIONS

183

associated

with

pain,

although

there

is

variability

in their

expression

cross

individuals

(Craig

et

al.,

1991 .

LeResche and Dworkin

(1988)

note

variability

ross

patients

in

the

frequency,

duration,

and inten

sity

of

facial

movements

in

response

to

painful

clinical

examinat ion.

Hyde (1986)

suggests

the

existence

of constellation of

AUs

(Action

Units),

any

one of

which

might

be

displayed

by

n

individual

in

pain

p.

98

rather

than

unitary

or

prototypic

pain expression.

Variability

in

the

expression

of

facia l ac tions

may

be

influenced

by

display

rules

and/or

secondary

gain.

Display

rules

(i.e.,

norms

for

managing

emotional

expressions)

may

serve to

intensify,

deintensify,

mask,

or

neutralize facial

expressions

of

pain

(Ekman

Friesen,

1978).

Similarly,

individuals who

receive

reinforcement

fo r their

pain

behav

iors

may

display

different

facial

expressions

than

individuals

for

whom

pain

has

only negative

consequences.

Attention

(Turk,

Meichen-

baum,

Genest,

1983)

and

insurance

compensation

(Fordyce,

1983)

n serve

s

potent

reinforcers

that

may shape pain expressions.

Little

research h as b een done

to

help

clinicians

identify

distortions of

th e

pain

experience,

such s

willfully

minimizing

pain

displays

(masking)

or

exaggeration

of such behav io rs

(posing).

Craig

et al.

1991

have identified the

facial

movements associated

with

simulated

and

masked,

s

well

s

genuine,

pain.

However,

it is unknown

whether

clinicians'

knowledge

of

deceptive

pain expressions

results in more

ccur te ssessments

This

question

w s

addressed

in

the

present

study.

STUDY

METHOD

Thirty

male

and

30

female

volunteers

underwent

Cold-Pressor

pain

(Wolf

Hardy,

1941),

whereby

th e

subject's

hand

is

immersed in w ter

maintained

t 0-4

degrees

Celsius.

Subjects

were asked to endure th e

discomfort s

long

s

they

could . Af te r

five

minutes,

th e

procedure

w s

discontinued.

Subjects

rated their

pain intensity using

Numer ic

Rating

Scale

(Scott

Huskisson,

1976 upon

immers ion

in

th e

w ter

and

upon

withdrawal .

The

scale w s vertical

line

with the numbers

0-100

spaced evenly along

its

length,

with

adjective

ancho rs no

pain,

just

noticeable

pain,

moderate

pain,

and

excruciating pain,

corresponding

to

th e

numbers

0, 10, 50,

and 100. The mount

of t ime


3/17

184

GALIN

A ND

THORN

focus

on facial

expressions.

Subjects

were

alone

in

the

room

but

were

informed

that

they

were

being

videotaped.

Participants'

facial

expressions

were

videotaped

in

four

conditions:

a

baseline

(the

subject placed

the h an d in

room

temperature

water

for

two

minutes);

b

genuine pain

(standard

cold-pressor

procedure);

c

masked

pain

(standard

cold-pressor

procedure

but

S

instructed

to

express

s little

discomfort

as

possible);

and

(d)

posed

pain

(baseline

procedure,

but S

asked to

pose

n

expression

of

pain).

The

m a sk ed and

posed

conditions

were counterbalanced for order

of

presentation

cross

subjects.

A

completely

counterbalanced

design

w s sacrificed to

ensure

that

the

genuine

pain

condition

represented

spontaneous

behavior

(Lanzetta,

Cartwright-Smith,

Kleck,

1976).

Videotapes

of

15

male

and

15

female

participants

were

selected

randomly

for

Tape

1. The

remaining segments

were

used

for

Tape

2.

The

videotapes

of th e

conditions were

edited

so that the

tapes

c o nta in ed fou r 20 second

segments

of each

subject,

one

segment

from

each of th e

baseline

posed pain,

masked

pain,

and

genuine

pain

conditions.

For the

genuine

an d m ask ed

conditions

th e

segment began

25

seconds

befo re the

subject

withdrew

their

hand

(either

because

they

quit

or because the 5 m inu te

ceiling

w s

reached).

T he 20 second

baseline

and

posed

segments

began

after one minute of

filming.

The

order of

the

segments

on th e stimulus

tape

w s

randomized

with th e

limiting

condition

that

no

more

than

two

segments

of the s me

subject

would be

presented

consecutively.

The

coders

were two

experienced

FACS

analysts

w ho were

blind

to

the

pain

conditions

appearing

in

each

segment.

Prior

to

coding

th e

videotapes,

they

demonstrated

their

expertise

in the

FACS

by

passing

th e final test

developed

by

Ekman and Friesen

1978 .

O ne coder

identified

th e

A U s

in

every segment

on

Tape

1

using

FACS. The other

coder scored

25

of th e data to

provide

a

reliability

me sure

Using

n

occurrence

agreement

formula

intercoder

reliability

w s

.83. Occur

rence

agreement

w s

defined as

agreements

of

occurrence divided

by

agreements

plus disagreements

of occurrence

multiplied

by

100.

RESULTS

Action Units

appearing

at least 17 t imes in

th e

videotape

segments

were

used

in the

analyses.

In

addition

A U s with similar

muscle movements


4/17

PAIN

A N D

FACIAL

EXPRESSIONS

185

differed

according

to

conditions;

brow

lower

F l,19

7.73,

p

.05;

cheeks

raise lids

tighten,

F

1,19

13.35,

p

.01;

lip

orner

pull,

F l,19

5.21,

p

.05;

dimpler-lips

stretch

F l,19

8.49,

p

.01;

lips

part,

F l,19

5.55,

p

.05;

lips

tighten,

F l,19

9.30,

p

.01;

jaw

drop,

F l,19

4.58,

p

.05;

eyes

closed-blink,

F 3,58

10.93,

p

.0001.

Significantly

more

brow

lower

cheek

raise lids

tighten,

lips

tighten,

and

eyes

close blink

occurred

in

th e

posed

condition. The

baseline,

genuine,

and

masked

cond itions d id not

differ

significantly

fro m each

other in

terms of

the

frequencies

of these

movements The

posed

and

genuine

conditions

yielded

significantly

more

lip

orner

pull

than

the

baseline condition.

The

ma sk ed c on d itio n

did

not

significantly

differ

from the

posed,

genuine,

or

baseline

conditions

in

the

frequency

of

lip

orner

pull.

Significantly

more

dimpler-lips

stretch

lips

part,

and

jaw

drop

also

occurred

in

th e

posed

c on ditio n th an

in

the

m asked and

baseline

condit ions.

The

genuine

cond ition d id

not

significantly

differ

from the

posed,

masked

or baseline conditions in terms of these

variables.

M e a n s

used

in

th e

pairwise

comparisons

are listed

in

Table

1.

Since

heterogeneity

of variance

w s

highest

in the

posed

condition

and

because

identification of differences

among

genuine

pain,

masked

pain,

and baseline w s

necessary

in

order

to

prepare

the

training

package

used

in

Study

2,

n additional

repeated

me sures

MANOVA

w s

performed

withou t

posed pain.

Cheeks

raise lids

tighten

F l,29

5.40,

p

.05 ,

lip

orner

pull F l,29

5.61,

p

.05 , dimpler-lips

stretch

F l,29

4.96,

p

.05 ,

and

lips

part F l,29

4.78,

p

.05

distinguished

among

th e conditions.

Lips

part

and

dimpler-lips

s tre tch occurred

significantly

more

often

in the

genuine

condition.

The

masked

and

baseline

conditions

did not differ

significantly

in

th e

frequency

of these

movements

In

addition

significantly

more cheeks raise lids

tighten

and

lip

orner

pull

occurred

in

th e

genuine

condition than in th e

baseline condition.

The m asked cond ition

yielded

a tre nd to w a rd more

lip

orner

pull

than

the baseline condition

p

10

Baseline

yielded

a

tren d to w ard

more

lips

tighten

than the m asked cond ition

p

.10 .

Means used in th e

pairwise

comparisons

re listed

in

Table

1.

DISCUSSION

A s

predicted,

a subset of action units

distinguished

among

th e

conditions

i.e.,

brow

lower

cheeks

raise

or

lids

tighten,

lips

tighten,


5/17

186

GALIN

AND

THORN

TABLE 1

Means fo r Pattern of

Action

Units

Function

of Condition

TUKEY

TUKEY

CONDITION

MEAN

SD

GROUPINGb

GROUPING^

Action Unit

4 Brow Lower

Posed

34

.70

A

Genuine

10 .36

B

A

Masked

03

18

B

A

No

pain

02

13

B

A

Action

Unit 6 7 Cheeks Raise Lids

Tighten

Posed

158

2 57

A

Genuine

.51

1 15

B

A

Masked

27

74

B

A B

No

pain

03

18

B

B

Action

Unit 12:

Lip

Corner

Pulld

Posed .37

66

A

Genuine

29 .53

A

A

M asked

20

45

A B

A B

No

pain

05

22

B

B

Action Unit 14 20:

Dimpler-Lips

Stretch

Posed

53

70

A

Genuine

34

63

A B

A

Masked 10

36

B B

No

pain

14 39

B

B

Action Unit

17

Chin

Raise

Posed

23 .54

A

Genuine

.07

25

A

A

Masked

.05

22

A

A

No

pain

05 22

A

A

Action Unit 23

Lips

ighten

Posed

36

66

A

No

pain

12 .38

B

A

Genuine .05

22

B

A

Masked

00 .00

B

A

Action

Unit 251

Lips

Part

Posed 54 89

A

Genuine

41 77

A B

A

Masked

17

46 B

B

No

pain

.15

45 B B

Action Uni t 26:

Jaw

Drop

Posed 46 .75

A

Genuine

24

63

A B

A

Masked

15

52

B

A

No

pain

12 42

B A

Ac tion Un it 43^15:

Eyes

Close Blink

Posed

5 30

3 09 A

Genuine

3 68 2 47

B A

Masked

3 81

3 01

B

A

No

pain

3 29

2 27

B A

Action

Unit

1 2 Inner

and

Outer

Brow

Raise

Posed

44

.89

A


6/17

PAIN

AND

FACIAL

EXPRESSIONS

187

TABLE

1.

Means for

Pattern o f Ac tio n Units s

Funct ion of Condition

continued

TUKEY

TUKEY

CONDITION

MEAN SD

GROUPINGb GROUP ING

Action

Unit

19:

Tongue

Out

Posed

.20 .55 A

Genuine .19

.57

A

A

No

pain

.07

.25

A

A

Masked

.03 18

A

A

Action Unit 24

Lip

Press

Posed

.27

.49 A

Masked

.20 .52 A

A

Genuine 10

.30

A A

No

pain

10

.36

A A

Action Uni t 41 :

Lids

Droop

Posed

.46

.45

A

Genuine 24

.81

A

A

Masked

.15

.56

A

A

No

pain

.12

.34

A

A

*SD

Standard

deviation.

bPost-hoc

Tukcy pairwise

comparisons

fo r

posed, genuine,

no

pain,

and masked conditions.

Mean s w ith th e

s me letter

re

not

significantly

different.

cPost-hoc

Tukcy pairwise comparisons

fo r

genuine,

no

pain,

a nd ma sk ed con ditio ns

only

Posed

condition

is

removed

from

analysis .

Means w ith the

s me letters re not

significantly

different

Comparisons

of

me ns

fo r

mask ed and no

pain

conditions

yield

trend toward

significance y

.10 .

stretch

and

lips part

than masked

pain

and baseline and

also

more

lip

corner

pull

and cheeks raise

or

lids

tighten

than baseline

in

analysis

with

genuine

pain,

masked

pain,

and baseline

only .

Although

there

is

overlap

in

th e facial

movements

associated with

pain

between this

and o th er

investigations,

variability

between

studies

is also

evident. For

example,

in

Craig

and

Patrick s

1985

experiment

and

in

th e

present study,

cheeks

raise-lids

tighten,

lip

corner

pull,

and

lips

part

occurred

more

frequently during

cold-pressor

exposure

than

during

baseline. On

the

other

hand,

upper

lip

raise,

jaw

drop,

and

eyes

close-blink

occurred

significantly

more often in

genuine

pain

than

baseline

in

only

th e

Craig

and

Patrick

1985

study.

It

is

possible

that th e

videotape

segments

selected for

coding

in

the

two

studies

resulted

in

th e differences

in

action units. The

present

study

used

segment

just prior

to

quit-point.

This

segment

w s

selected

because

our

observations

during

pilot

work

suggested

that

subjects


7/17

188

GALIN

AND

THORN

Patrick

1985)

because

we

wanted to

eliminate

other

expressions

concomitant with

pain,

such

s

startle

response

or

orienting

behavior

It is

also

possible

that th e

participants

w reness of the

videotaping

procedure

inhibited

their

expression

of

pain during

th e

genuine

condi

tion in

th e

present

experiment.

Kleck

et

al

(1976)

demonstrated that

individuals

con tro l th eir

facial

expressions

more

when

they

re

ob

served than w hen

they

re alone

Yet,

participants

in several other

investigations (e.g., Craig

et

al.,

1991;

Craig

Patrick

1985;

Patrick et

al.,

1986)

were also

in fo rmed tha t

they

were

being

videotaped

and

still

exhibited

variety

of

facial

movements

in

response

to

noxious

stimula

tion The

variat ions found

ross

experiments

suggest

that

facial ex

pressions

of

pain

re influenced

by

number of variables

On y

two

studies

have

compared

genuine

pain,

masked

pain,

posed

pain,

and

baseline

(the

present

study

and

Craig

et

al.,

1991

and

they

suggest

sim ilar conclusions about

the

facial

movements

associated with

simulation

In

both

studies

participants

were

capable

of

masking

expressions

of

pain,

and

they displayed

more

varied

and

intense

facial

activity

when

posing

pain

than

in

th e other conditions

Brow

lower

and

cheeks

raise

occurred

more

frequently

in

posed pain

than

genuine pain

in

both

studies

Thus

it

appears

that facial

expressions

of m ask ed and

posed pain

n be

described

using

FACS It

remains

unclear however

whether

observers

n

be trained

to

distinguish among genuine,

masked

and

posed

pain

displays.

STUDY 2

The

purpose

of

Study

2

w s to determine

whether

training,

using

either

repeated presentations

of

th e

taped

segments

of

th e different

pain

expressions

(masked,

posed, genuine)

or

using

those

constellations

of

facial

action units

found

to

distinguish

among

conditions

is more

useful

than

no

training

condition

in

improving

accuracy

in

detection

of

simulated

expressions

of

pain.

It

w s

expected

that

judges accuracy

in

distiguishing genuine,

masked

and

posed pain

on

pretraining

task

(Trial

1

would not differ

significantly

ross

groups

Groups

w h o receiv ed either facial move

ment

training

based on FACS

plus

lim ited feedback

training

or

feedback

only training

were

expected

to

improve

in

Trial

2,

with th e

greatest

increase

in

accuracy occurring

in th e facial

movement

training


8/17

PAIN

A ND

FACIAL

EXPRESSIONS

189

pain

than

other

pain

st tes It

w s

expected

that

judges

would be mor

ccur te

in

detecting genuine

and

masked

pain

in

subjects

w ho

demonstrate

low

pain

tolerance

because these

participants

w r

expected

to

be th e

most

expressive.

Subjects

in

th e

masked

condition

w ho had

low

pain intensity ratings

wh e n

they

withdrew

their

hands

from

th e w ter w r

expected

to be successful in

masking

their

discomfort,

and

thus

th e

judges

w r

expected

to believe that

they

w r

not

in

pain.

M E T H O D

Sixty-six

female

psychology

students

tested in

groups

of four

to

eight,

served

s

judges

in

Study

2.

They

v iew e d the

s m

videotape

used

in

Study

1.

Accuracy

in

labeling

the four conditions

genuine

pain,

masked

pain,

posed pain,

and

no

pain

on

th e

videotape

segments

served s th e

dependent

variable

Accuracy

w s determined

by

frequency

count

of the

number

of

videotape

segments correctly

identified

during

no

pain,

genuine

pain,

masked

pain,

and

posed pain.

Accuracy

w s calculated

separately

for th e 15 male and 15

female

faces

on the

videotape.

Thus

perfect

accuracy

would

yield

score of 15

correct

for each

condit ion and

gender,

and

c ha nc e le ve ls

of

accuracy

would

be

t 3 75

segments

labeled

correctly.

The

judges

w r

assigned

randomly

to

training group

control,

facial movement

training

plus

l imited feedback

training,

or feedback

only

training

and

trainer The

primary experimenter

Trainer 1

and

n

advanced

undergraduate

psychology

student

Trainer

2

served

s

th e

trainers Trainer

2

w s blind

to

the

hypotheses

of th e

study.

Each

trainer

presented

information

to

one half of th e

judges

in each

of th e

three

judging

conditions

First

all

judges

viewed

Tape

1

see

Study

1

without

audio

accompa

niment

Following

each of 120

segments,

judges

had five seconds to

indicate

whether

no

pain,

posed

pain,

masked

pain,

or

genuine pain

w s

portrayed.

Next

the

groups

received

either th e

control or on of th e

experimen

ta l interventions

Following

their

viewing

of

Tape

1,

control

group

judges

watched

videotapes

that

discussed

th e n ture

and

tre tment of

pain.

Judges

in th e

feedback

training group

viewed

Tape

1

again

120

total

segments

and

w r told

which

condition

no

pain,

posed,


9/17

190

GALIN

AND

THORN

expressions

characteristic of

genuine,

masked

and

posed

pain

as

derived

from

Study

1.

Specifically,

the

training

provided

to the facial

m o v e m e n t

training

group

had

three

components.

First,

th e

trainers

presented

detailed

descriptions

of the

changes

in

th e

face

associated

with

masked

posed,

and

genuine pain. Photographs

from the

FACS

manua l

were

used

to

il lus tr ate these

facial movements

Next

the

experimenter

taught

each

judge

to m ake

th e

movements

associated

with

masked

posed,

and

genuine

pain

on her own

face.

Finally,

th e

judges

viewed

segments

from

Tape

1,

during

which

they

w r

given

feedback

regarding

which

condition

w s

displayed.

In

order

that the

training

t ime

provided

to

all

groups

would be

equivalent,

th e to ta l number

of

segments

viewed

by

th e

facial movement

training

group

w s

limited

to

20.

Thus

subjects

in

th e

facial movement

training

group

w r

given

only

limited

feedback

compared

to Ss

in

th e

feedback

training

group.

Following

a

10 minute

recess

all

judges

viewed

Tape

2,

which

contained th e

videotape

segments

of th e

15

male

and

15

female

participants

from

Study

1

that

w r

not

included

on

Tape

1. After each

20 second

segment

on

Tape

2,

judges

had five seconds

to

indicate

whether no

pain,

posed,

masked

or

genuine

pain

w s

displayed.

RESULTS

ANALYSIS OF

VARIANCE

A 4 x

2

x

3

analysis

of

variance

ANOVA)

w s

used

to ss ss

th e effects

of condition

no

pain,

posed,

masked

and

genuine),

trial

1

and

2 ,

and

training group

control,

feedback

facial

movement)

on

judges

accu

racy

in

labeling

the

videotape

segments.

While

other variables

in th e

study gender

of face on

videotape

and

trainer)

did

interact in small

ways

w ith the

condition trial,

and

training

group

variables

relative

to

th e effects of

these

variables

th e

differences

w r

only

slight

and

th e

conclusions

did

not

change.

Therefore,

only

the

3-way

interaction

is

reported.

The

condit ion

x

trial

x

training

interaction

w s

significant,

F 6,387)

5.45,

p

genuine).

Feedback

trained Ss demonstrated a

pattern

of

accuracy

whereby

posed

>

genuine

masked

no

pain

in

Trial 2. Facial

Action trained

Ss

showed

a

pattern

of

accuracy whereby

no

pain

posed

>

masked

genuine

in

Trial 2.

As

hypothesized,

a

significant

main

effect

for condition

w s

found

F 3,387)

111.64,

p

.0001.

Judges

were

significantly

more accurate

in

labeling

the

posed

and no

pain segments

than

the m a sk ed an d

genuine

segments. They

were also

significantly

more accurate

in

labeling

th e

masked

segments

than

the

genuine

segments.

MULTIPLE

REGRESSION

It w s

expected

that

judges

would be

more accurate

in

detecting

genuine

an d m ask ed

pain

in

subjects

w ho

report

high

pain

intensity

at

quit-point

and demonstra te

lo w

pain

tolerance.

To test

this

hypothesis,

a

simultaneous

regression procedure

w s

used

to test the in te rac tion

between

final

pain

ratings

and

pain

tolerance.

The number of

judges

w ho

correctly

labe led the

segment

w s the

dependent

variable.

For th e

genuine

segments

in

Trial 1

Tape

1,

viewed

prior

to

training),

the

interaction

w s not

significant,

F 3,26

.05.

The test of


11/17

192

GALIN

AND

THORN

9

7

6

c

5

i

4

3

A

C

.sea

M35 rJ

Genune

Condition

6

5

r

2

4

i^

A

3 r

c

Baseline

Posed

rJlas^ ed

Genuine

Condition

Group

A

=

Control

group

Croup

B

=

Feedback

training gToup

Group

C

=

Facial

movement

training group

FIGURE 1. Mean

accuracy

as

a function

of

group,

condition,

and

trial.

F 3,26

=

.484. The test of the overa ll

mode l

was

significant,

with

an

R2

of

.300,

p

J

>rrJ

Documents

Galin y Thorn (1993) Unmasking Pain