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Biol. Lett. (2006) 2, 412414
doi:10.1098/rsbl.2006.0509
Published online 27 June 2006
Cues of being watchedenhance cooperation ina real-world
settingMelissa Bateson*, Daniel Nettleand Gilbert Roberts
Evolution and Behaviour Research Group, School of Biology
andPsychology, University of Newcastle upon Tyne, Henry
WellcomeBuilding for Neuroecology, Framlington Place, Newcastle
upon TyneNE2 4HH, UK*Author for correspondence
([email protected]).
We examined the effect of an image of a pair ofeyes on
contributions to an honesty box used tocollect money for drinks in
a university coffeeroom. People paid nearly three times as muchfor
their drinks when eyes were displayed ratherthan a control image.
This finding provides thefirst evidence from a naturalistic setting
of theimportance of cues of being watched, and hencereputational
concerns, on human cooperativebehaviour.
Keywords: cooperative behaviour; altruism;reputation;
eyespots
1. INTRODUCTIONPeople tend to be generous, even toward
unrelatedindividuals (Fehr & Fischbacher 2003). This is
trueeven in situations where there is no prospect of
repeatinteraction, and hence no potential for direct recipro-city
(Gintis et al. 2003). A possible mechanismmaintaining generosity,
where direct reciprocity isabsent, is the motivation to maintain a
pro-socialreputation (Alexander 1987; Roberts 1998).Theoretical
models show that cooperation in sizeablegroups can, in theory, be
maintained where potentialpartners have information about a persons
pastbehaviour and use it in making decisions about intera-ction
(Nowak & Sigmund 1998; Panchanathan &Boyd 2004). In
indirect reciprocity models of thiskind, individuals with a history
of non-cooperationare shunned and thus pay a long-term cost for
theirbehaviour. Consistent with such models, laboratoryexperiments
have shown that people increase theirlevels of cooperation when
they know their behaviouris being observed by others, and also use
reputationalinformation in deciding how to interact with
others(Milinski et al. 2002a,b; Wedekind & Braithwaite2002;
Barclay 2004).
Recent studies have shown that even when subjectsare told they
are anonymous, they respond to subtlecues of being watched, such as
the presence of eye-likespots on the background of the computer on
which theycomplete the task (Haley & Fessler 2005; Burnham
&Hare in press). However, these studies were based onartificial
laboratory scenarios, and the effects of suchcues on naturally
occurring cooperative behaviourremain to be demonstrated. Here, we
investigatewhether subtle cues of being watched can
increasecontributions to a public good in a real-world setting
Received 14 April 2006Accepted 2 June 2006
412
where people have the option of contributing or not,using their
own money. Specifically, we test thehypothesis that participants
will contribute more moneyto an honesty box (also known as an
honour box) in thepresence of an image of a pair of eyes than in
thepresence of a control image of flowers.
2. MATERIAL AND METHODSParticipants came from a population of 48
members (25 femalesand 23 males) of the Division of Psychology at
the University ofNewcastle, who had the option to pay for tea and
coffee via anhonesty box. This system of payment for drinks had
been in placefor 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
mmhigh!210 mm wide) notice. The notice was displayed at eye
heighton a cupboard door located above a counter on which was
situatedthe honesty box and also the coffee and tea making
equipment; thefridge containing the milk was below the same
counter. The noticefeatured a 150!35 mm banner that alternated each
week betweenan image of a pair of eyes and an image of flowers
printed abovethe prices for tea, coffee and milk (30, 50 and 10
pence,respectively). A different image was used each week to
control forany effects attributable to a single image. The images
of eyes variedin the sex and head orientation, but were all chosen
such that theeyes 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 fortea and coffee; the most recent reminder was sent
approximatelyone month prior to the commencement of this study.
From theperspective of the participants, the only change introduced
at thestart of the experiment was the inclusion of the image banner
onthe notice. Participants were naive to the purposes of the
manipu-lation and none reported being aware of these. The layout of
thecoffee room is such that it is unlikely that anyone failing to
paywould be observed. Hence, contributions were effectively
anon-ymous, and participants could choose whether and how much
topay for their drinks.
Each week we recorded the total amount of money collected inthe
honesty box. Throughout the period of the study, supplies oftea,
coffee and milk were maintained to keep up with demand, andeach
week, the volume of milk consumed was recorded as the bestindex
available of total beverage consumption. We computed theratio of
money collected to the volume of milk consumed in eachweek to
control for weekly variation in consumption.
3. RESULTSThe ratio of money collected to milk consumed foreach
of the 10 weeks is shown in figure 1, along withthe image on the
banner for that week. Contributionlevels always increased with the
transition fromflowers to eyes, and decreased with the
transitionfrom eyes to flowers. A general linear model withfactors
image type (fixed) and week (covariate) fittedto log-transformed
data explained 63.8% of thevariance. There was a significant main
effect of imagetype (eyes versus flowers: F1,7Z11.551, pZ0.011)but
not week (F1,7Z0.074, pZ0.794). Theinteraction between image type
and week was omittedfrom the model because it was not significant.
Onaverage, people paid 2.76 times as much in the weekswith eyes
(meanGs.e.Z0.417G0.081 per litre) thanwith flowers (0.151G0.030 per
litre). There was noevidence that image type affected
consumption.
4. DISCUSSIONOur results show that an image of a pair of
eyesappearing to observe behaviour dramatically
increasescontribution to a public good in a real-world contextwhere
participants were behaving naturally and usingtheir own money.
q 2006 The Royal Society
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paid per litre of milk consumed
image
8
6
4
2
7
5
3
1
time(weeks)
eye weeksflower 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.
Eyes promote cooperation M. Bateson and others 413
Why does an image of a pair of eyes motivatecooperative
behaviour? While it is possible that theeyes were simply more
effective than the flowers atattracting peoples attention to the
notice, we do notbelieve that this is the explanation for our
findings.The participants had all been informed prior to
theexperiment that they were supposed to pay for theirdrinks.
Furthermore, the notice was positioned suchthat it was not possible
that anyone making drinkswould fail to see it, irrespective of the
imagedisplayed.
Instead, we believe that images of eyes motivatecooperative
behaviour because they induce a percep-tion in participants of
being watched. Althoughparticipants were not actually observed in
either ofour experimental conditions, the human perceptualsystem
contains neurons that respond selectively tostimuli involving faces
and eyes (Emery 2000; Haxbyet al. 2000), and it is therefore
possible that theimages exerted an automatic and unconscious
effecton the participants perception that they were beingwatched.
Our results therefore support the hypothesisthat reputational
concerns may be extremely powerfulin motivating cooperative
behaviour.
Our findings have practical interest for thosedesigning
honesty-based systems, or wishing to maxi-mize contributions to
public goods. They also havetheoretical implications. Faced with
the relative gen-erosity of human cooperation, even when
interactionsare explicitly anonymous and not repeated, somescholars
have argued that humans are not alwaysmaximizers of individual
self-interest (Camerer &Fehr 2006), but instead have been
shaped to bepro-social or other-regarding by a history of group
Biol. Lett. (2006)
selection (Gintis 2000; Gintis et al. 2003). A
simplerexplanation is simply that humans are stronglyattuned to
cues that generally indicate reputationalconsequences of behaviour
(Burnham & Johnson2005; Haley & Fessler 2005). If even very
weak,subconscious cues, such as the photocopied eyes usedin this
experiment, can strongly enhance cooperation,it is quite possible
that the cooperativeness observedin other studies results from the
presence in theexperimental environment of subtle cues evoking
thepsychology of being observed. The power of thesesubconscious
cues may be sufficient to override theexplicit instructions of the
experimenter to the effectthat behaviour is anonymous. If this
interpretation iscorrect, then the self-interested motive of
reputationmaintenance may be sufficient to explain cooperationin
the absence of direct return.
M.B. is funded by a Royal Society University ResearchFellowship.
We thank T. Burnham for sending us hisunpublished manuscripts.
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of being watched enhance cooperation in a real-world
settingIntroductionMaterial and methodsResultsDiscussionM.B. is
funded by a Royal Society University Research Fellowship. We thank
T. Burnham for sending us his unpublished manuscripts.head7
