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Biol. Lett. (2006) 2, 412–414
doi:10.1098/rsbl.2006.0509
Published online 27 June 2006
Cues of being watched
enhance cooperation in
a real-world setting
Melissa Bateson
*
, Daniel Nettle
and Gilbert Roberts
Evolution and Behaviour Research Group, School of Biology and
Psychology, University of Newcastle upon Tyne, Henry Wellcome
Building for Neuroecology, Framlington Place, Newcastle upon Tyne
NE2 4HH, UK
*Author for correspondence (melissa.bateson@ncl.ac.uk).
We examined the effect of an image of a pair of
eyes on contributions to an honesty box used to
collect money for drinks in a university coffee
room. People paid nearly three times as much
for their drinks when eyes were displayed rather
than a control image. This finding provides the
first evidence from a naturalistic setting of the
importance of cues of being watched, and hence
reputational concerns, on human cooperative
behaviour.
Keywords: cooperative behaviour; altruism;
reputation; eyespots
1. INTRODUCTION
People tend to be generous, even toward unrelated
individuals (Fehr & Fischbacher 2003). This is true
even in situations where there is no prospect of repeat
interaction, and hence no potential for direct recipro-
city (Gintis et al.2003). A possible mechanism
maintaining generosity, where direct reciprocity is
absent, is the motivation to maintain a pro-social
reputation (Alexander 1987; Roberts 1998).
Theoretical models show that cooperation in sizeable
groups can, in theory, be maintained where potential
partners have information about a person’s past
behaviour and use it in making decisions about intera-
ction (Nowak & Sigmund 1998; Panchanathan &
Boyd 2004). In indirect reciprocity models of this
kind, individuals with a history of non-cooperation
are shunned and thus pay a long-term cost for their
behaviour. Consistent with such models, laboratory
experiments have shown that people increase their
levels of cooperation when they know their behaviour
is being observed by others, and also use reputational
information in deciding how to interact with others
(Milinski et al. 2002a,b; Wedekind & Braithwaite
2002; Barclay 2004).
Recent studies have shown that even when subjects
are told they are anonymous, they respond to subtle
cues of being watched, such as the presence of eye-like
spots on the background of the computer on which they
complete the task (Haley & Fessler 2005; Burnham &
Hare in press). However, these studies were based on
artificial laboratory scenarios, and the effects of such
cues on naturally occurring cooperative behaviour
remain to be demonstrated. Here, we investigate
whether subtle cues of being watched can increase
contributions to a public good in a real-world setting
where people have the option of contributing or not,
using their own money. Specifically, we test the
hypothesis that participants will contribute more money
to an honesty box (also known as an honour box) in the
presence of an image of a pair of eyes than in the
presence of a control image of flowers.
2. MATERIAL AND METHODS
Participants came from a population of 48 members (25 females
and 23 males) of the Division of Psychology at the University of
Newcastle, who had the option to pay for tea and coffee via an
honesty box. This system of payment for drinks had been in place
for several years prior to the commencement of the current study.
Instructions for payment remained constant throughout the experi-
ment, and were posted on a black and white A5-sized (148 mm
high!210 mm wide) notice. The notice was displayed at eye height
on a cupboard door located above a counter on which was situated
the honesty box and also the coffee and tea making equipment; the
fridge containing the milk was below the same counter. The notice
featured a 150!35 mm banner that alternated each week between
an image of a pair of eyes and an image of flowers printed above
the prices for tea, coffee and milk (30, 50 and 10 pence,
respectively). A different image was used each week to control for
any effects attributable to a single image. The images of eyes varied
in the sex and head orientation, but were all chosen such that the
eyes were looking directly at the observer. In addition to the notice,
all members of the department were informed by email approxi-
mately every six months about the arrangements for payment for
tea and coffee; the most recent reminder was sent approximately
one month prior to the commencement of this study. From the
perspective of the participants, the only change introduced at the
start of the experiment was the inclusion of the image banner on
the notice. Participants were naive to the purposes of the manipu-
lation and none reported being aware of these. The layout of the
coffee room is such that it is unlikely that anyone failing to pay
would be observed. Hence, contributions were effectively anon-
ymous, and participants could choose whether and how much to
pay for their drinks.
Each week we recorded the total amount of money collected in
the honesty box. Throughout the period of the study, supplies of
tea, coffee and milk were maintained to keep up with demand, and
each week, the volume of milk consumed was recorded as the best
index available of total beverage consumption. We computed the
ratio of money collected to the volume of milk consumed in each
week to control for weekly variation in consumption.
3. RESULTS
The ratio of money collected to milk consumed for
each of the 10 weeks is shown in figure 1, along with
the image on the banner for that week. Contribution
levels always increased with the transition from
flowers to eyes, and decreased with the transition
from eyes to flowers. A general linear model with
factors image type (fixed) and week (covariate) fitted
to log-transformed data explained 63.8% of the
variance. There was a significant main effect of image
type (eyes versus flowers: F
1,7
Z11.551, pZ0.011)
but not week (F
1,7
Z 0.074, p Z 0.794). The
interaction between image type and week was omitted
from the model because it was not significant. On
average, people paid 2.76 times as much in the weeks
with eyes (meanGs.e.Z0.417G0.081 £ per litre) than
with flowers (0.151G0.030 £ per litre). There was no
evidence that image type affected consumption.
4. DISCUSSION
Our results show that an image of a pair of eyes
appearing to observe behaviour dramatically increases
contribution to a public good in a real-world context
where participants were behaving naturally and using
their own money.
Received 14 April 2006
Accepted 2 June 2006
412 q 2006 The Royal Society
Why does an image of a pair of eyes motivate
cooperative behaviour? While it is possible that the
eyes were simply more effective than the flowers at
attracting people’s attention to the notice, we do not
believe that this is the explanation for our findings.
The participants had all been informed prior to the
experiment that they were supposed to pay for their
drinks. Furthermore, the notice was positioned such
that it was not possible that anyone making drinks
would fail to see it, irrespective of the image
displayed.
Instead, we believe that images of eyes motivate
cooperative behaviour because they induce a percep-
tion in participants of being watched. Although
participants were not actually observed in either of
our experimental conditions, the human perceptual
system contains neurons that respond selectively to
stimuli involving faces and eyes (Emery 2000; Haxby
et al. 2000), and it is therefore possible that the
images exerted an automatic and unconscious effect
on the participants’ perception that they were being
watched. Our results therefore support the hypothesis
that reputational concerns may be extremely powerful
in motivating cooperative behaviour.
Our findings have practical interest for those
designing honesty-based systems, or wishing to maxi-
mize contributions to public goods. They also have
theoretical implications. Faced with the relative gen-
erosity of human cooperation, even when interactions
are explicitly anonymous and not repeated, some
scholars have argued that humans are not always
maximizers of individual self-interest (Camerer &
Fehr 2006), but instead have been shaped to be
pro-social or other-regarding by a history of group
selection (Gintis 2000; Gintis et al. 2003). A simpler
explanation is simply that humans are strongly
attuned to cues that generally indicate reputational
consequences of behaviour (Burnham & Johnson
2005; Haley & Fessler 2005). If even very weak,
subconscious cues, such as the photocopied eyes used
in this experiment, can strongly enhance cooperation,
it is quite possible that the cooperativeness observed
in other studies results from the presence in the
experimental environment of subtle cues evoking the
psychology of being observed. The power of these
subconscious cues may be sufficient to override the
explicit instructions of the experimenter to the effect
that behaviour is anonymous. If this interpretation is
correct, then the self-interested motive of reputation
maintenance may be sufficient to explain cooperation
in the absence of direct return.
M.B. is funded by a Royal Society University Research
Fellowship. We thank T. Burnham for sending us his
unpublished manuscripts.
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£
p
aid
p
er litre of milk consumed
image
8
6
4
2
7
5
3
1
time
(weeks)
eye weeks
flower weeks
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7
9
10
Figure 1. Pounds paid per litre of milk consumed as a function of week and image type.
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414 M. Bateson and others Eyes promote cooperation
Biol. Lett. (2006)
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