Supplementary Materials
Supplementary Models 1–8 are provided to investigate the main effects of eye cues while
controlling for two demographic measures (gender and age), and for experimentally induced power.
Gender may significantly affect cooperative behavior, as there is evidence that gender differences
exist in cooperation and social preferences, but with contradictory results: sometimes men are more
other-regarding, while other times women are. A literature review in [1] suggests that these
inconsistencies are due to women’s choice behavior in economic games being more sensitive to
experimental cues. Concerning age, studies show older people tend to become more prosocial (see for
example [2,3]), hence we also include this control variable in our analyses (even though subjects were
students with little variability in age: the mean age in years was 21, with a standard deviation of 2.55).
In addition to testing the effect of watching eyes, the subjects’ state of power was manipulated in
this experiment. This paper focuses on the differential effect of eye cues with opposing valence. The
main effects of power on first and second mover cooperation are reported in detail in another
publication, which draws on a very different theoretical background. Power was manipulated with a
writing task adapted from previous research [4–6]. At the beginning of the experiment, half of the first
and second movers were randomly assigned to the high power condition and were asked to write about
an experience in which they had power over one or more others. The remaining participants were
assigned to the low power condition and were asked to write about an experience in which one or more
others had power over them.
Supplementary Models 1–4 show results from the analyses concerning trust, building on Models 3
and 4 reported in the main text. In Supplementary Models 1 and 2, which control for gender and age, 1
individual had a missing value for age, amounting to 360 observations (120 individuals times 3 rounds).
In Supplementary Models 3 and 4, which in addition control for induced power, an extra 10 individuals
were excluded from the analyses since priming was unsuccessful in these participants, leading to 330
observations (110 individuals). The results from these models show that the effect of unkind eyes on
first mover cooperation is robust when controlling for gender and age (β = 0.59, p = 0.012)
(Supplementary Model 2), and slightly less significant (β = 0.50, p = 0.054) above and beyond the effect
of power (β = −0.11, p = 0.014) in Supplementary Model 4.
Supplementary Models 5–8 show results from the analyses concerning reciprocity, building on
Models 9 and 10 reported in the main text. In Supplementary Models 7 and 8, an additional 6 individuals
were excluded because they had a missing value for power, resulting in 324 observations (108
individuals).
Table S1. Logistic regression estimates of the impact of SVO, eyes, kind eyes (K eyes), unkind eyes (UK
eyes), gender, age and power on trust.
TRUST
Gender
Age
Power
SVO
Eyes
K eyes
UK eyes
N
Wald chi-square
Supplementary
Model 1
−0.37 (0.27)
0.03 (0.06)
Supplementary
Model 2
−0.37 (0.27)
0.03 (0.06)
1.42 *** (0.27)
0.38 # (0.22)
1.42 *** (0.28)
360 (120 individuals)
32.94 ***
0.16 (0.28)
0.59 * (0.24)
360 (120 individuals)
36.99 ***
Supplementary
Model 3
−0.44 (0.29)
0.03 (0.06)
−0.11 * (0.05)
1.49 *** (0.29)
0.23 (0.24)
330 (110 individuals)
33.20 ***
Supplementary
Model 4
−0.44 (0.29)
0.03 (00.06)
−0.11 * (0.05)
1.51 *** (0.30)
−0.05 (0.30)
0.50 # (0.26)
330 (110 individuals)
36.20 ***
#, p < 0.1; *, p < 0.05; ***, p < 0.001 (two-tailed), robust standard errors in parenthesis.
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Table S2. Logistic regression estimates of the impact of SVO, eyes, kind eyes (K eyes), unkind eyes (UK
eyes), gender, age and power on reciprocity.
RECIPROCITY
Gender
Age
Power
SVO
Eyes
K eyes
UK eyes
N
Wald chi-square
Supplementary
Model 5
0.16 (0.31)
0.06 (0.05)
Supplementary
Model 6
0.16 (0.31)
0.06 (0.05)
0.96 ** (0.32)
−0.21 (0.20)
0.96 ** (0.32)
342 (114 individuals)
12.07 *
−0.15 (0.22)
−0.27 (0.23)
342 (114 individuals)
12.55 *
Supplementary
Model 7
0.20 (0.32)
0.07 (0.06)
−0.07 (0.05)
0.98 ** (0.34)
−0.17 (0.21)
324 (108 individuals)
16.10 **
Supplementary
Model 8
0.20 (0.32)
0.07 (0.06)
−0.07 (0.05)
0.98 ** (0.34)
−0.12 (0.23)
−0.21 (0.24)
324 (108 individuals)
16.68 *
*, p < 0.05’ **, p < 0.01 (two-tailed), robust standard errors in parenthesis.
Figure S1. A screenshot of the first mover decision. This screen is only an example of what the first mover
sees, as a different picture and matrix are displayed each round in random order. The experiment was
conducted with Dutch-speaking participants. Translation of the text in the lower right box: “You have
role 1. The choices you can make are represented in the matrix. Your decision is:
o
o
I choose L
I choose S”
Figure S2. A screenshot of the second mover decision. This screen is only an example, as a different
picture and matrix are displayed each round in random order. The experiment was conducted with
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Dutch-speaking participants. Translation of the text in the lower right box: “You have role 2. The choices
you can make are presented in the matrix. If the other player chose “L”, then your decision is:
o
o
I choose L
I choose S
If the other player chose “S”, then your decision is:
o
o
I choose L
I choose S”
References
1.
2.
3.
4.
5.
6.
Croson, R.; Gneezy, U. Gender Differences in Preferences. J. Econ. Lit. 2009, 47, 448–474.
Boone, C.; Declerck, C.; Kiyonari, T. Inducing Cooperative Behavior among Proselfs versus Prosocials: The
Moderating Role of Incentives and Trust. J. Confl. Resolut. 2010, 54, 799–824.
Van Lange, P.A.M.; Otten, W.; de Bruin, E.M.N.; Joireman, J.A. Development of prosocial, individualistic, and
competitive orientations: Theory and preliminary evidence. J. Personal. Soc. Psychol. 1997, 73, 733–746.
Galinsky 1986, A.D.; Gruenfeld, D.H.; Magee, J.C. From power to action. J. Personal. Soc. Psychol. 2003, 85, 453–
466.
Boksem, M.A. S.; Smolders, R.; De Cremer, D. Social power and approach-related neural activity. Soc. Cogn.
Affect. Neurosci. 2012, 7, 516–520.
Galinsky, A.D.; Magee, J.C.; Ena Inesi, M.; Gruenfeld, D.H.; Inesi, M.E.; Gruenfeld, D.H. Power and
perspectives not taken. Psychol. Sci. 2006, 17, 1068–1074.
Games
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