13th International Conference on Social Dilemmas
Kyoto, 20-24th August, 2009
Detecting defectors when
they have incentives to
manipulate their impressions.
Toko Kiyonari (Aoyama Gakuin University)
J. Schug, M. Shinada, T. Takahashi, &T. Yamagishi
(Hokkaido University)
Do people discriminate
cooperators from defectors?
The human capacity of cheater
detection is of great significance in
Evolutionary psychology.
Human evolved sensitivity to cues of
cheaters and cooperators (e.g.,
Cosmides & Tooby, 1992).
There is evidence suggesting that people
can visually discriminate defectors from
cooperators.
 Brown, Palameta, and Moore (2003) found a significant
altruist detection effect in response to video taped
storytelling.
 Verplaetse, Vanneste, Braeckman (2007) show that
participants could discriminate defectors from
cooperators when they saw event-related pictures
taken during the decision-making moment of a proper
round.
 Frank, Gilovich, and Regan (1993) found that
participants were able to predict individual behavior in a
one-shot PD when they had a 30-min "get-acquainted"
meeting before the game.
Purpose
Except for Frank's (1988) study in which
participants could make promises for their game
behavior, however, these results were obtained
only in situations where defectors had no
incentives to deceive others.
 In this study, we examine if
participants can successfully tell
cooperators from defectors when
defectors have incentives to conceal
or disguise their facial or verbal
expressions.
Summary of methods
The first-player of a “semi-sequential” PD game made a
cooperation-defection decision, and was given an
opportunity to send a video-taped message to the secondplayer before the second-player made his or her decision.
The second-player saw the video message (with no
sound), but was not informed of the first-player’s actual
choice, and then made a decision.
The second-player also judged if the first-player
cooperated or defected before actually making a decision
(First Study).
Different groups of judges saw the same video (without
sound) or transcripts of the verbal messages (without
visual presentations) and judged if the first-players
cooperated or defected (Second Study).
Summary Findings
In a situation where defectors had an incentive to
conceal or disguise their facial and verbal expressions,
Second-players were not able to discriminate
defectors from cooperators in the PD game.
However, they were able to identify “hardcore defectors” who defected both in PD
and Stag Hunt (one type of coordination
game) games.
And yet, another group of judges (third
party) were unable to detect even hard-core
defectors.
Flow of the experiment: 1st-players~
#1: They answered a Pre-exp. questionnaire (Trust, SVO, Machiavellianism) .
#2: A video tape was taken while they were reading a tale of “The country
mouse and the city mouse” written by Aesop.
#3: Their saliva- sample was taken-1.
#4:They played a “semi-sequential” Prisoners’
Dilemma (PD) Game as a 1st-player
#5: They answered a Post-exp. questionnaire-1
#6: They took a video message to their potential partner.
#7: Their saliva sample was taken-2
#8: They answered a Post-exp. questionnaire-2
#9:They played a Stag Hunt (SH) Game as a 1st-player.
#10: They answered a Post-exp. questionnaire-3&4
Fin.
1st-Players
Mon Tue Wed Thur
PD
SH
Fri
1st-Players
Mon Tue Wed Thur
Fri
Sat
Sun
2nd-Players
PD
PD
SH
SH
Incentive structure of the PD game
Partner
K
Partner
\1200
L
YOU
S
P
Partner
\1800
Exchange rate
$1 ≈ \ 94
€1 ≈ \134
₤1 ≈ \156
You
\1200
You
\0
Partner
Partner
\600
\0
You
\1800
You
\600
In this game, the first-player made the decision between L (i.e., cooperate) and S
(i.e., defect), and then the second-player made the same decision without
knowing the choice of the first-player (as in the simultaneously played game).
The first-players knew their partner would participate in this experiment later
approximately within a week. Thus their reward would be paid as their partner has
made their decision.
Sending a video message
➢After the decision in a PD, the first-players were
given a chance to send a video message (30
seconds long) to the second-player. They were
told that the second-player would make his/her
decision after seeing the video.
➢When the first players made the C-D decision,
they did not know that they would have this
opportunity to send a message.
➢They were informed that the video tape of their
message may be presented to their partner
either with or without voices.
1st-Players
Mon Tue Wed Thur
PD
SH
Fri
Incentive structure of SH game
Partner
M
Partner
\700
T
YOU
Q
X
Partner
\500
You
\700
You
\100
Partner
Partner
\500
\100
You
\500
You
\500
The SH is a coordination game (e.g., Skyrms, 2004) where
cooperation is the best choice insofar as the other
cooperates as well.
The first-player was not given a chance to give a video message.
Flow of the experiment: 2nd-player~
#1: They answered a Pre-exp.questionnaire (Trust, SVO,
Machiavellianism) .
#2: The 2nd-player watched video messages of 1014 1st-players, and judged whether each of them
cooperated or defected.
Then, they played the game as second-players.
#3: They answered a Post-exp. questionnaire-1.
#4: They played a Stag Hunt (SH) Game as a 2ndplayer.
#5: They answered a Post-exp. questionnaire-2.
#6: They participated in a detection experiment of fake or not-fake smile.
#7: They answered a Post-exp. questionnaire-3.
Fin.
1st-Players
Mon Tue Wed Thur
Fri
Sat
Sun
2nd-Players
PD
SH
PD with video messages
You
K
P
\1200
\1800
L
\1200
\0
Partner
\0
\600
S
\1800
\600
•Each second-player was shown
video clips of 10-14 first-players,
without sound, and decided
whether to cooperate (K) or defect
(P) with each of these first players,
on the assumption that he/she
would be paid for the outcome of
the game with one randomly
chosen partner.
In addition, the second-player was asked to predict if
each of the first-players cooperated or defected
before their decision.
PD with video messages
Did the person choose “L” (cooperation) or “S” (defection)?
I am going to choose “K” (cooperation) or “P” (defection) with
this person.
1st-Players
Mon Tue Wed Thur
Fri
Sat
Sun
2nd-Players
PD
SH
Incentive structure of SH game
You
M
You
\700
T
Partner
Q
X
You
\500
Partner
\700
Partner
\100
You
You
\500
\100
Partner
\500
Partner
\500
The second-player did not see the video face of
the first-player.
Participants
First Study
 Seventy-nine participants played the role of firstplayers in a “semi-sequential” PD and SH
games, and 79 participants played the role of
second-players in those games.
 They played with partners of the same sex.
 Six were eliminated from today’s report because
they received different manipulations .
Second Study
 Thirty participants from another university
judged all 73 video tapes of the first players.
1st-players’ choices
• Twenty-six out of 73 (35.6%) first-players
cooperated in the PD.
• Thirty-seven out of 73 (50.7%) first-players
cooperated in the SH.
• Thirty-one out of 73 (42.5%) defected in both
games.  Hard-core defector
• No sex difference in PD cooperation (M:34.2%
vs. F:37.5%).
• No sex difference in SH cooperation (M:56.1%
vs. F:43.8%).
Basic results
The first-players who actually cooperated in
PD were judged to have cooperated, on
average, by 54.6% of the second-players who
saw their videos.
The first-players who actually defected in PD
were judged to have cooperated, on average,
by 49.9% of the second-players who saw their
videos.
Degree of being judged as a cooperator
Cooperators
Defectors
54.6% > 49.9%, t(71)=.99, p=.32
However, in this study, the second-players saw different
numbers of cooperators and defectors , thus we need to use
adjusted judgment score for the analysis.
First-players were judged only by the secondplayers in the same group.
Numbers of cooperators in each video set:
Group 1: 6/10, Group 2: 2/10, Group 3: 4/10, Group 4: 2/11,
Group 5: 7/12 (6 were eliminated from today’s report),
Group 6: 7/12, Group 7: 4/14
Adjusted Judgment Score:
Individual first player’s deviation score adjusted
for the group mean (deviation of cooperation
judgment for each target from mean cooperation
judgment )
Regression Analysis 1:
Dependent variable: Adjusted judgment score
If the actual behaviors in PD and SH predicted the judgment, i.e.,
If the judgment reflects actual behaviors.
Actual Behavior in PD
Judgment
Actual Behavior in SH
Model 1
Intercept
Actual behavior (PD)
Actual behavior (SH)
b
-0.034
0.006
0.063
t
-1.14
0.12
1.37
p
0.260
0.902
0.174
Controlling for some individual differences
Model 2
Intercept
Actual behavior (PD)
Actual behavior (SH)
Encode
Activity
Prosocial
b
-0.131
0.046
0.081
-0.050
0.040
-0.002
t
-0.90
0.89
1.80
-2.32
2.14
-0.41
p
0.373
0.379
0.079
0.023
0.036
0.682
Encode: self-report encode ability
Activity: self-report willingness to get new acquaintances actively and behave socially to anyone
Prosocial: Degree of pro-sociality (Social Value Orientation)
Regression Analysis 2:
Dependent variable: Adjusted judgment score
We then examined whether the first- player was a hard-core defector or not predict the
judgment.
Model 1
Intercept
Hard-core D
b
0.033
-0.078
t
1.24
-1.90
p
0.220
0.062
Model 2
Intercept
Hard-core D
Encode
Activity
Prosocial
b
-0.047
-0.119
-0.050
0.0429
-0.001
t
-0.33
-2.85
-2.38
2.32
-0.18
p
0.743
0.006
0.020
0.023
0.860
Encode: self-report encode ability
Activity: self-report willingness to get new acquaintances actively and behave
socially to anyone
Prosocial: Degree of pro-sociality (Social Value Orientation)
The second-players’ judgment reflected the actual behavior of the first
player—whether the first player was a hard-core defector or not.
When the third-party was the judge…
Thirty raters from another university judged each
of the 73 first players if the video taped person
cooperated or defected.
Defectors in PD game were judged that they had cooperated, on
average, by 16.68 out of 30 raters.
Cooperators in PD game were judged that they had cooperated,
on average, by 16.85 out of 30 raters.
They couldn’t discriminate cooperators and defectors in the PD game.
PD game
How many raters
judged the target
as a cooperator?
Defectors
Cooperators
(N=47)
(N=26)
16.68
(sd=5.45)
16.85
(sd=5.80)
When the third-party was the judge…
They couldn’t discriminate cooperators and defectors in the SH game.
Stag Hunt Game
How many out of
30 raters?
Defectors
(N=36)
Cooperators
(N=37)
16.69
(sd=4.77)
16.78
(sd=6.25)
When judges didn’t have monetary incentive to discriminate
between cheaters and cooperators, the third-party judges could
not detect even hard-core defectors.
How many out of
30 raters?
Hard-core
Defectors
(N=42)
Else
(N= 31)
16.76
(sd=5.96)
16.71
(sd=5.00)
Did the third-party judges see
differences in the cooperators’ and
defectors’ messages?
Thirty raters judged each first player’s transcribed
message on the following criteria.
Criterion: The message implies that the message
sender has cooperated Yes/No
Criterion: The message sender equivocates if
he/she has cooperated or defected Yes/No
Criterion: The message sender is trying to
communicate that he/she has cooperated Yes/No
Criterion: The message is a lie if the message
sender has actually defected  Yes/No
Are cooperators’ messages rated differently
from defectors’ messages by 30 raters?
How many raters checked
“YES” on average?
Defectors’
message
Cooperators’
message
7.98
11.11
ns.
11.34
11.12
ns.
The message sender is trying to
communicate that he/she has
cooperated
8.34
11.42
ns.
The message would be a lie if the
message sender had actually
defected
7.51
9.42
ns.
Criterion
The message implies that the
message sender cooperated
The message sender sent a
message which could be
interpreted either way
Did the third-party judges see differences in the cooperators’
and defectors’ messages
30 raters read the first player’s message, and judged
whether he/she cooperated or defected (or unsure)
More judges correctly rated actual cooperators as cooperators
(M = 9.85) than as defectors (M=6.54), though the difference
was not significant (t(25)=1.34, p=.19).
13.38 raters selected “unsure”
More judges correctly rated the actual defectors as defectors
(M = 9.74) than cooperators (M=7.30), though the difference
was not significant (t(46)=1.17, p=.25).
12.87 raters selected “unsure”
The difference between differences was marginally significant
(t(71)=1.71, p=.0911).
These results suggest that the contents of the verbal messages
may be used to discriminate cooperators from defectors, but they
may not be an efficient means of cooperator/cheater detection.
Conclusion
When the players have incentives to hide intentions or
manipulate impressions, even motivated judges (whose
monetary gain depended on the accuracy of cheater/
cooperator detection) could not distinguish defectors
from cooperators either in PD or SH game.
However, they seem to be able to discriminate hardcore defectors from others.
Yet, when judges had no monetary incentives to detect
targets’ choice, they couldn’t detect even hard-core
defectors. The content of the messages were also not
sufficient help to tell defectors from cooperators.
s
Conclusion
Needless to say, more controlled judgment experiment
is required to conclude…
As a final remark…
Majority of our cooperators didn’t broadcast their
cooperation. This may or may not be based on Japanese
culture. We will see…
Thank you!
Personality traits items
Activity (alpha=.83):
I seek to make new acquaintances.
(積極的に新しい知り合いを増やしていきたい)
It is important to make new acquaintances for enhancing my future chances.
(自分の可能性を広げるために、新しい知り合い作りは重要だ)
I think gaining acquaintances is useful for my future in many respects.
(知り合いを増やすことは、なにかにつけて将来自分の役に立つと思う)
For succeeding in one’s life, it is necessary to jump at anywhere even no one knows you.
(人生で成功するためには、知らない人しかいないところにでも、積極的に出て行く必要がある)
I want to behave socially to anyone.
(誰に対しても社交的に振る舞いたい)
One should present his/her positive aspects to others.
(自分の良いところは積極的に他人にアピールすべきだ)
Encode (alpha=.70):
I am good at accurately telling my own feelings to others.
(自分の気持ちを正確に相手に伝える)
I am good at leading conversation.
(会話をうまくすすめる)
I can express my own feelings easily.
(感情を素直にあらあす)
I am good at using body language to explain my thoughts and feelings.
(身振りや手振りをうまく使って表現できる)
Correlations between items and behavior
Trust
Caution
Prosocial
Individual
Machiavellian
Activity
Encode
Altruism
Scale
Adjusted
estC
PD
r=.15
r= -.17
r=.42
r= -.41
r=.32
r= -.22
r=.20
r=.07
r=.10
D=0, C=1
p=.22
p=.14
p=.0002
p=.0003
p=.0056
p=.07
p=.09
p=.57
p=.42
SH
r=.20
r= -.10
r=.15
r= -.19
r=.14
r= -.11
r=.23
r=.07
r=.19
D=0, C=1
p=.08
p=.39
p=.21
p=.10
p=.24
p=.36
p=.047
p=.54
p=.11
Hard-core
r= -.20
r=.11
r=-.17
r=.20
r=-.12
r=.19
r= -.22
r= -.004
r= -.22
p=.09
p=.34
p=.15
p=.09
p=.31
p=.11
p=.059
p=.97
p=.0617
D=1
Did predictions based on messages differ from
cooperators and defectors?
Thirty raters judged each transcribed message whether the target cooperated or
defected based on verbal meanings in each message.
Defectors
Cooperators
How many raters judged the
target “cooperated”
7.30
(sd=8.10)
9.85
(sd=9.10)
ns.
How many raters judged the
target “defected”
9.74
(sd=8.37)
6.54
(sd=5.21)
p=.0479
How many raters judged the
target is “hard to judge”
(because of no information
about the decision)
12.87
(sd=8.10)
13.38
(sd=7.97)
ns.
These suggest that at least some of defectors probably tried to
manipulate their impression during their message video.
Furthermore, at least some of cooperators’ message were
misinterpreted and judged as defectors…
Adjusted judgment score for cooperation
Second Player's Judgment
First Choice
P2_1
Player in PD
P1_1
P1_2
P1_3
P1_4
P1_5
P1_6
P1_7
P1_8
P1_9
P1_10
D
C
D
D
C
D
C
C
C
C
Average
1
1
1
1
1
1
0
0
0
0
0.6
P2_2
P2_3
P2_4
P2_5
P2_6
P2_7
P2_8
P2_9
P2_10
0
1
1
1
1
1
1
1
1
0
0.8
0
0
0
0
1
1
0
0
0
0
0.2
1
0
0
1
0
1
0
1
0
0
0.4
1
1
1
1
1
1
1
1
1
1
1.0
0
1
1
1
1
1
0
0
1
0
0.6
0
1
0
1
1
1
0
1
0
1
0.6
1
1
0
0
0
0
1
0
1
0
0.4
1
1
0
0
1
1
0
0
1
0
0.5
0
1
0
0
1
0
0
0
1
0
0.3
Proportion Deviation
to be
from
judged C Average
0.5
-0.04
0.4
-0.14
0.6
0.06
0.8
0.26
0.8
0.17
0.4
-0.23
0.6
-0.03
0.2
-0.43
0.7
0.07
0.7
0.07
0.54
0.035
Defectors in PD (n=47): -0.012 (sd=0.177)
Cooperators in PD (n=26): 0.023 (sd=0.178), t(71)=.82, p=0.415
Defectors in SH (n=36): -0.033 (sd=0.155)
Cooperators in SH (n=37): 0.0325 (sd=0.193), t(71)=1.61, p=0.112
Hardcore Defectors (n=31): -0.045 (sd=0.158)
Rest of participants (n=42): 0.0338 (sd=0.188), t(71)=1.90. p=0.0617