ArticlePDF Available

Human responses to unfairness with primary rewards and their biological limits

  • Carnegie Endowment for International Peace

Abstract and Figures

Humans bargaining over money tend to reject unfair offers, whilst chimpanzees bargaining over primary rewards of food do not show this same motivation to reject. Whether such reciprocal fairness represents a predominantly human motivation has generated considerable recent interest. We induced either moderate or severe thirst in humans using intravenous saline, and examined responses to unfairness in an Ultimatum Game with water. We ask if humans also reject unfair offers for primary rewards. Despite the induction of even severe thirst, our subjects rejected unfair offers. Further, our data provide tentative evidence that this fairness motivation was traded-off against the value of the primary reward to the individual, a trade-off determined by the subjective value of water rather than by an objective physiological metric of value. Our data demonstrate humans care about fairness during bargaining with primary rewards, but that subjective self-interest may limit this fairness motivation.
Content may be subject to copyright.
Human responses to unfairness with
primary rewards and their biological
Nicholas D. Wright, Karen Hodgson, Stephen M. Fleming, Mkael Symmonds, Marc Guitart-Masip
& Raymond J. Dolan
Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College, London, 12 Queen Square, London, WC1N
3BG, UK.
Humans bargaining over money tend to reject unfair offers, whilst chimpanzees bargaining over primary
rewards of food do not show this same motivation to reject. Whether such reciprocal fairness represents a
predominantly human motivation has generated considerable recent interest. We induced either moderate
or severe thirst in humans using intravenous saline, and examined responses to unfairness in an Ultimatum
Game with water. We ask if humans also reject unfair offers for primary rewards. Despite the induction of
even severe thirst, our subjects rejected unfair offers. Further, our data provide tentative evidence that this
fairness motivation was traded-off against the value of the primary reward to the individual, a trade-off
determined by the subjective value of water rather than by an objective physiological metric of value. Our
data demonstrate humans care about fairness during bargaining with primary rewards, but that subjective
self-interest may limit this fairness motivation.
In humans fairness has been studied extensively using games played for money
. The paradigmatic example is
the Ultimatum Game (UG)
where one player (the Proposer) is given an endowment (e.g. £10) and proposes a
division (e.g. keep £6/offer £4) to a second player (the Responder), who then accepts (both get the proposed
split) or rejects (both get nothing) the offer. In the UG with money humans typically reject low, ‘‘unfair’’, offers
even at cost to themselves
Here, we asked if thirsty humans in an UG instead make self-interest maximising
responses to unfair offers with a primary reward of water, and attempted to maximise our power to induce such
self-interested behaviour.
We sought to enhance our power to induce self-interested behaviour in two ways. Firstly, we physically
presented the water, which has been recently shown to increase food’s propensity to trigger appetitive responses
Secondly, we amplified this effect by inducing thirst. Such induction of thirst in humans is a non-trivial pro-
blem experimentally, for example requiring prolonged water deprivation under supervision (e.g. over at least
24 hours
); or extended heating and exercise as typically employed in military research
; or intravenous infusion
of hypertonic saline, which given the careful setup needed to prevent potential health risks has previously been
used to study the physiology of thirst in small numbers of subjects under clinical supervision
. Here we used an
intravenous saline infusion, as this method enabled a double-blind design allowing us to test UG choices in
individuals who were not in a deprived state (infusing isotonic saline similar to normal human osmolarity, so with
little impact on thirst), and also in individuals who received hypertonic saline that markedly increases blood
osmolarity (and thus thirst) and that might increase our power to induce self-interested behaviours.
This manipulation with primary rewards also enabled the possibility of providing insight into the nature of the
self-interested motivation in the UG, although we note that our experiment was not specifically designed to
address this subsidiary issue. Specifically, we probed whether objective need, subjective need, or both are traded-
off against a putative fairness motivation. Objective physiological need, for example the degree of energy deple-
tion, powerfully influences non-social value-based choice. This is seen even in organisms as simple as the
grasshopper, in which the value of stimuli is higher when learning about those stimuli originally occurred in a
lower than higher state of nutritional reserve
. However, when humans choose in an UG, even an increase in the
stakes equivalent to many months’ salary does not necessarily increase acceptances
. In contrast, subjective
motivations in the UG have been highlighted more recently in relation to a fairness motivation, with disruption to
2 May 2012
26 July 2012
23 August 2012
Correspondence and
requests for materials
should be addressed to
N.D.W. (n.wright@fil.
SCIENTIFIC REPORTS | 2 : 593 | DOI: 10.1038/srep00593 1
right dorsolateral Prefrontal Cortex (dlPFC) using Transcranial
Magnetic Stimulation (rTMS) leading to reduced rejections but leav-
ing subjective assessments of fairness unaffected
Finally, whilst in the UG with money humans typically reject low
, chimpanzees with a food primary reward behave solely as
self-interested maximisers in an UG and accept unfair offers
. Our
data help address one potential source of this discrepancy, although
we note a more complex picture emerges across different primate
species and tasks
, while other potential sources for this discre-
pancy may relate to inter-species differences in time horizon
In summary, we tested the behaviour of humans in an UG with
primary rewards, against the hypothesis that they would be rational
self-interest maximisers who would accept any offer. We sought to
maximise our chances of eliciting such self-interested behaviour by
physically presenting the water, and also by examining choice not
only in a non-deprived state (i.e. following isotonic infusion) but also
following a manipulation that might increase self-interested choices
(i.e. following hypertonic infusion). We also hoped to provide tent-
ative evidence concerning whether objective and subjective measures
of need might impact on a possible fairness motivation.
Thirst manipulation.As predicted, administering hypertonic saline
markedly altered objective and subjective measures relating to thirst.
Subjective thirst did not differ between treatments at t
tonic 2.561.9 and isotonic 2.561.7; t(19)50.057, P50.96, d50.02),
but differed at t
(7.361.6; 3.562.0; t(19)54.68, P,0.0005,
d52.06). Similarly, osmolarity at t
did not differ between
treatments (hypertonic 293 mOsmL
6s.d. 4; isotonic 29567;
t(19)51.27, P50.22, d50.57), but at t
was higher for the
hypertonic (31065) than isotonic group (29565; t(19)57.58,
Fairness influences choice.Our data show fairness influenced
responses in the UG despite the use of a primary reward. In an UG
with a primary reward of food, chimpanzees in a non-deprived state
accepted almost all offers, shown by only around 1 out of the 11
individuals tested rejecting a low offer similar to that presented
. However, our human subjects, who were also in a non-
deprived state (i.e. following isotonic infusion), showed the opposite
pattern with 8 of 11 individuals rejecting the unfair offer (binomial test
versus no influence of fairness, P,0.001). Furthermore, even
following the induction of severe thirst in the hypertonic group, we
still observed an effect of fairness with 5 of 10 individuals rejecting the
unfair offer (binomial test versus no influence of fairness, P,0.001).
There was no difference between groups (hypertonic versus isotonic)
in the proportion of rejections (likelihood ratio test between groups,
X251.16, P.0.25), as we discuss further below. When we compare
the frequency of rejections here with that previously reported for
similarly low monetary offer proportions (approximately 50–60%
rejections, see Methods for details), we find this was not significant
for either the isotonic or hypertonic group (likelihood ratio test P.0.3
in both groups).
Subjective and objective measures of self-interest.In addition to
our central question of whether humans were rational self-interested
maximisers with primary rewards, we next sought evidence that this
fairness motivation was traded-off against self-interest. When self-
interest was defined as subjective thirst, measured by a rating scale,
this was the case. Subjectively thirstier individuals at t
were more
likely to accept the unfair offered water, indicated by a main effect of
choice in a 2 choice (accept, reject) by 2 treatment (isotonic, hyper-
tonic) ANOVA with subjective thirst as the dependent variable
(main effects of choice F
59.37, P50.007, g
50.36; and treat-
ment F
519.53, P,0.0005, g
50.54; with no interaction,
50.15, P50.7, g
50.01). Further, our data revealed that the
degree to which hypertonic infusion increased subjective thirst was
related to choice. This was evident in a significant interaction of
choice (accept, reject) and treatment (isotonic, hypertonic) in an
ANOVA with change in subjective thirst as the dependent variable
(interaction F
57.19, P50.016, g
50.30; main effect of treat-
ment F
527.40, P,0.0001, g
50.62; no main effect of choice,
53.52, P50.078, g
50.17). This interaction was driven by the
degree to which hypertonic saline increased subjective thirst
(Fig. 1b).
However, our objective measure of thirst (blood osmolarity) was
not related to choice, either when used as the dependent variable or as
a covariate in the previous ANOVAs. Furthermore, there was no
difference between groups (hypertonic versus isotonic) in the pro-
portion of rejections (likelihood ratio test between groups, X
P.0.25). Thus, although our experiment was primarily designed to
ask whether humans behaved as rational self-interest maximisers in
an UG with primary reward, together these results present tentative
evidence that the primary driver of the self-interested motivation
here was subjective, rather than objective, thirst.
Humans’ closest relatives, chimpanzees, appear to be rational self-
interest maximisers who do not reject unfair offers in the canonical
fairness task, the UG, with primary rewards
. In contrast, here we
Figure 1
Change in subjective thirst and responses to unfairness. (a) All participants were assigned the Responder role in an UG and faced this
proposed division of water. They had received an intravenous infusion of either isotonic or hypertonic saline. (b) The change in subjective thirst induced
by the saline infusion is calculated by the difference in subjective thirst at baseline and at testing. In the hypertonic group the degree to which the infusion
increased subjective thirst was related to choice, such that a greater increase was seen in those who accepted (6.461.7) relative to those who rejected
(3.161.6; independent samples ttest, t
53.19, P50.013, d52.02). Error bars indicate s.e.m.
SCIENTIFIC REPORTS | 2 : 593 | DOI: 10.1038/srep00593 2
show that humans remain motivated by fairness even with primary
rewards and in a deprived state. Outside such a bargaining context,
capuchin monkeys have been reported to be more likely to reject a
cucumber slice after seeing that another capuchin has received a
more attractive grape
, although we note debate concerning these
; for a more general discussion of experiments on social
preferences in primates see the review by
. Further, in contrast to
that behaviour reported in capuchins
, humans tend not to reject
inequitable distributions of money when such rejection would have
no effect on the proposer’s payoffs, for example in a modification
of the UG where rejection does not alter the Proposer’s payoff
(an ‘‘Impunity game’’) the rate of rejections is markedly reduced
Taken together, such work across species and tasks has begun to
delineate the particular contexts in which particular species may
exhibit particular fairness-related behaviours. We do not suggest that
fairness-related behaviours are uniquely human, but that reciprocal
fairness (i.e. punishment of others’ unfair behaviours) even when
bargaining with primary rewards, may be particularly prominent
in humans.
In addition to our data examining responses to unfair offers with
primary rewards, recent work examining proposals has also shown
an influence of fairness in children making offers with sweets as
. Children given the opportunity to divide sweets between
themselves and others develop more egalitarian tendencies with age,
by the age of 7–8 they prefer resource allocations that remove advant-
ageous or disadvantageous inequality
. It would be interesting to
examine the response to unfair offers of sweets in children, although
this may require large subject numbers, deception or other such
methods. For example, in a recent study of 34 pairs of preschool
children only two responders faced a non-zero offer of ,4 out of
10 sweets, although none of 23 fair offers (even split or greater) were
Whilst our participants were not solely self-interested, neither
were they solely motivated by fairness, and instead they exhibited a
trade-off between these motivations. In terms of behavioural eco-
nomic theory, such a trade-off maps conceptually onto models where
choice is determined by utility functions containing both self and
other regarding components
. Previous work has suggested that a
subjective aspect of the fairness motivation can be dissociated from
choice, for example where TMS to right dlPFC reduces rejections but
does not alter subjective assessments of fairness in the UG
Whilst we acknowledge that our experiment was not designed to
make strong inferences regarding the nature of the self-interested
motivation, our data do provide tentative evidence that this self-
interested motivation may also be subjective in nature. With thirst,
objective measures of physiological need of water (e.g. blood osmo-
larity or sodium concentration) are closely monitored peripherally
and in the brain
to enable homeostasis. The subjective sensation of
thirst (e.g. individuals’ subjective reports of their thirst) is closely
related to such objective monitoring but is dissociable, for example
after drinking when thirsty, and involves a wide network of brain
This observation that this self-interested motivation may be sub-
jective in nature helps interpret previously discrepant results between
UG studies with money that tried to manipulate the self-interested
motivation. In previous work that manipulated individuals’ subject-
ive feeling of entitlement by having subjects ‘‘earn’’ the endowment
before an UG, this affected behaviour and led to lower (i.e. less fair)
offers in the UG
. However, other studies that increased the stakes of
the UG relative to individuals’ wealth, often in countries such as
Slovakia or Indonesia where the equivalent of many month’s salary
may be used experimentally, did not lead to a clear cut pattern of
more self-interested choices
. The former manipulation may
affect the subjective value of the self-interested motivation more than
simply raising the absolute amount of the stake. Further, our data
also shows that raising the stakes by increasing osmolarity (analog-
ous to reducing wealth) can matter, but only when these stakes
impact upon the individual’s subjective motivational state. In addi-
tion, it is known that culture can affect UG responses
, and unlike
previous high-stakes games with money, our method has the advant-
age of operationalising changes in ‘‘wealth’’ within a single country
and culture as a physiological need. Future work could usefully focus
on these aspects concerning the nature of the self-interested motiva-
tion using more subjects, perhaps also examining whether subjec-
tively thirsty individuals are also more likely to reject low monetary
Finally, a further interesting consideration here is the concept of
satisficing used in economics
and foraging theory
, where because
of constraints (e.g. information, time, other costs) a decision-maker
attempts to meet an acceptability threshold rather than choosing
optimally. Here this may have led to not bothering to drink the
62.5 ml of water (about 1/5
of a standard drink can). However,
we note there was no cost difference between drinking and not
drinking in the current experiment. Furthermore, individuals valued
even small amounts of water, as shown here by subjectively thirstier
individuals becoming more likely to consume this amount. Finally,
considerable previous work has shown that in thirsty individuals very
significantly smaller amounts of amounts of water than used here
reduce thirst
, are rated pleasantly
and modulate neural activity in
reward-related brain regions
In summary, our data demonstrate that humans care about being
treated fairly when bargaining with primary rewards, and, together
with a broader literature
, suggest that such reciprocal altruism
may be particularly prominent in humans. Our data also provide
tentative evidence that subjective self-interest may limit this fairness
Participants.21 healthy participants provided informed, written consent (11 male,
mean age 25 (range 20–32) years; 2 further participants did not complete testing) for a
study approved by University College London Ethics Committee. Note that including
gender as a factor in our analyses with respect to fairness or subjective measures of
thirst did not alter our findings below.
Thirst manipulation.On the testing day, participants were asked to refrain from
drinking after 08:00 am. They arrived at 09:00 am. We manipulated thirst using saline
administered via an intravenous line for 50 minutes, at a rate 0.15 ml/kg/min for
males and 0.12 ml/kg/min for females. The sessions lasted four to five hours
(including time for preparation beforehand and to ensure subject safety afterwards)
and experienced physicians were present throughout to ensure participant safety.
In a double-blind, randomised design. 11 participants received isotonic saline
(0.9% NaCl) similar to normal human osmolarity, with a minimal impact on thirst;
and 10 received hypertonic saline (5% NaCl) that markedly increases blood osmo-
larity and, as a consequence, thirst
. After infusion subjects performed one hour of
non-social tasks (not reported here); then the UG; and finally waited a further hour
without water. Participants were fully informed of this timetable at the start of each
testing day (only the UG was unexpected, as described below). The one hour wait
post-testing without water was in order to prevent the value of water being rendered
negligible if participants believed they would have immediate access to water after
At pre-infusion baseline (t
) and the time of testing (t
) we measured sub-
jective thirst (visual analogue scale from 0–10) and blood osmolarity (analysis by
freezing point depression osmometer). Participants completed a similar session 5–7
days before but without the UG (and receiving the alternative infusion), and were
unaware of the prospect of the UG until it was conducted.
Behavioural task.Three participants attended each session where they met and
interacted with each other, and were then tested in separate rooms. At time of testing,
, participants first received written instructions stating that two of the participants
(one Proposer and one Responder) would be randomly selected to play an UG, in this
case dividing 500 ml of water for immediate consu mption. Next, all participants were
informed they were the Responder. The experimenter then brought a covered tray,
removed the cover and left the room. For all participants the tray contained two
straight-sided 500 ml capacity glasses, one holding 62.5 ml (12.5%) with ‘‘they offer’’
written below, and the other holding 437.5 ml (87.5%) next to ‘‘they keep’’ (Fig. 1b).
Participants had 15 seconds to circle ‘‘accept’’ or ‘‘reject’’ on a piece of paper.
Participants who accepted then drank the 62.5 ml, and all participants waited one
further hour without water. Note that in the current study the number of participants
was limited by substantial difficulties and potential risks of IV saline administration,
and thus given the typically low rate of unfair offers made by Proposers in the UG
SCIENTIFIC REPORTS | 2 : 593 | DOI: 10.1038/srep00593 3
here we employed this deception to examine Responder behaviour in response to low
offers. Participants were informed that they would only play the UG once (i.e. it was
one-shot in nature) and would undertake no further tasks subsequently (i.e. during
this last post-testing wait period).
Analysis.Statistical tests were carried out using independent-samples t-tests or
independent analysis of variance (ANOVA) in SPSS 17.0; reported p-values are
two-tailed. Before implementing each parametric test we applied Levene’s test for
inhomogeneity of variance, and in no case found even trend level significance for
rejection of the null hypothesis. The Kolmogorov-Smirnov test of normality also did
not reach even trend level significance for rejection of the null hypothesis in either
group for either objective or subjective measures of thirst at either time point.
For the purpose of comparison with choice data from our task, we estimated an
average frequency of rejections of similarly low offers of money in human studies. We
used data from an extensive review of the UG literature (Table 2.3 in
) where we
averaged across all quoted rejection rates (not weighted by number of subjects and
collapsing over various manipulations). This revealed for offer proportions of
11–20% a mean rejection rate of 49% (mean of 39 entries), and for offer proportions of
1–10% a mean rejection rate of 59% (mean of 24 entries). This rejection rate accords
well with the author’s conclusion that offers below 20% are rejected about half the
1. Camerer, C. F. Behavioral game theory: Experiments in strategic interaction. 9,
(Princeton University Press Princeton, NJ: 2003).
2. Gu
¨th, W., Schmittberger, R. & Schwarze, B. An experimental analysis of
ultimatum bargaining. Journal of Economic Behavior & Organization 3, 367–388
3. Bushong, B., King, L. M., Camerer, C. F. & Rangel, A. Pavlovian Processes in
Consumer Choice: The Physical Presence of a Good Increases Willingness-to-
Pay. The American Economic Review 100, 1556–1571 (2010).
4. Szinnai, G., Schachinger, H., Arnaud, M. J., Linder, L. & Keller, U. Effect of water
deprivation on cognitive-motor performance in healthy men and women. Am. J.
Physiol. Regul. Integr. Comp. Physiol. 289, R275–280 (2005).
5. Cian, C., Barraud, P. A., Melin, B. & Raphel, C. Effects of fluid ingestion on
cognitive function after heat stress or exercise-induced dehydration. Int J
Psychophysiol 42, 243–251 (2001).
6. Engell, D. B. et al. Thirst and fluid intake following graded hypohydration levels in
humans. Physiology & Behavior 40, 229–236 (1987).
7. Gopinathan, P. M., Pichan, G. & Sharma, V. M. Role of dehydration in heat
stress-induced variations in mental performance. Arch. Environ. Health 43,
15–17 (1988).
8. Baylis, P. H. & Robertson, G. L. Plasma vasopressin respons e to hypertonic saline
infusion to assess posterior pituitary function. J R Soc Med 73, 255–260 (1980).
9. Denton, D. et al. Correlation of regional cerebral blood flow and change of plasma
sodium concentration during genesis and satiation of thirst. Proc Natl Acad Sci
USA96, 2532–2537 (1999).
10. Pompilio, L., Kacelnik, A. & Behmer, S. T. State-Dependent Learned Valuation
Drives Choice in an Invertebrate. Science 311, 1613–1615 (2006).
11. Cameron, L. A. Raising the stakes in the ultimatum game: Experimental evidence
from Indonesia. Economic Inquiry 37, 47–59 (1999).
12. Knoch, D., Pascual-Leone, A., Meyer, K., Treyer, V. & Fehr, E. Diminishing
Reciprocal Fairness by Disrupting the Right Prefrontal Cortex. Science 314,
829–832 (2006).
13. Jensen, K., Call, J. & Tomasello, M. Chimpanzees are rational maximizers in an
ultimatum game. Science 318, 107–109 (2007).
14. Brosnan, S. F. & de Waal, F. B. M. Monkeys reject unequal pay. Nature 425,
297–299 (2003).
15. Silk, J. B. Social preferences in primates. Neuroeconomics: decision making and the
brain (eds Glimcher PW, Camerer CF, Fehr E., Poldrack RA) 269–284 (2009).
16. Smith, P. & Silberberg, A. Rational maximizing by humans (<i>Homo
sapiens</i>) in an ultimatum game. Animal Cognition 13, 671–677 (2010).
17. Bra¨uer, J., Call, J. & Tomasello, M. Are apes inequity averse? New data on the
token-exchange paradigm. Am. J. Primatol. 71, 175–181 (2009).
18. Yamagishi, T. et al. The private rejection of unfair offers and emotional
commitment. Proc Natl Acad Sci U S A 106, 11520–11523 (2009).
19. Fehr, E., Bernhard, H. & Rockenbach, B. Egalitarianism in young children. Nature
454, 1079–1083 (2008).
20. Takagishi, H., Kameshima, S., Schug, J., Koizumi, M. & Yamagishi, T. Theory of
mind enhances preference for fairness. J Exp Child Psychol 105, 130–137 (2010).
21. Fehr, E. & Schmidt, K. M. A Theory Of Fairness, Competition, and Cooperation*.
Quarterly Journal of Economics 114, 817–868 (1999).
22. Egan, G. et al. Neural correlates of the emergence of consciousness of thirst. PNAS
100, 15241–15246 (2003).
23. List, J. A. & Cherry, T. L. Learning to accept in ultimatum games: Evidence from an
experimental design that generates low offers. Experimental Economics 3, 11–29
24. Slonim, R. & Roth, A. E. Learning in High Stakes Ultimatum Games: An
Experiment in the Slovak Republic. Econometrica 66, 569–596 (1998).
25. Henrich, J. P. Foundations of human sociality: economic experiments and
ethnographic evidence from fifteen small-scale societies. (Oxford University Press:
26. Simon, H. A. A Behavioral Model of Rational Choice. The Quarterly Journal of
Economics 69, 99–118 (1955).
27. Ward, D. The Role of Satisficing in Foraging Theory. Oikos 63, 312–317 (1992).
28. Denton, D. et al. Neuroimaging of genesis and satiation of thirst and an
interoceptor-driven theory of origins of primary consciousness. Proc. Natl. Acad.
Sci. U.S.A. 96, 5304–5309 (1999).
29. de Araujo, I. E. T., Kringelbach, M. L., Rolls, E. T. & McGlone, F. Human cortical
responses to water in the mouth, and the effects of thirst. J. Neurophysiol. 90,
1865–1876 (2003).
This work was supported by Wellcome Trust Programme Grant 078865/Z/05/Z to R.J.D.
The Wellcome Trust Centre for Neuroimaging is supported by core funding from the
Wellcome Trust 091593/Z/10/Z.
Author contributions
NDW and SMF originated the idea. NDW, KH, MS and MG collected the data. NDW
analysed the data. NDW and RJD wrote the manuscript, on which all autho rs commented.
Additional information
Competing financial interests: The authors declare no competing financial interests.
License: This work is licensed under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this
license, visit
How to cite this article: Wright, N.D. et al. Human responses to unfairness with primary
rewards and their biological limits. Sci. Rep. 2, 593; DOI:10.1038/srep00593 (2012).
SCIENTIFIC REPORTS | 2 : 593 | DOI: 10.1038/srep00593 4
... Does altruistic behavior occur in thirsty humans when water which serves for satisfying a primary, biological need, is the reward to be shared? Notably, most studies exploring sharing behavior have used money as reward to be shared ( [6], but see [7]). Little is known about how far their results generalise to other, primary rewards. ...
... This might explain why inequality aversion seems to be influencing behavior more when, instead of money, pain is to be divided amongst players [12]. Being better able to empathise with other thirsty people might equally lead to fairer behavior when it comes to sharing a primary reward [7,13]. Also, previous research suggests that in contrast to physical or emotional rewards, money decreases the need for social approval and, thus, also for cooperation with others ('Self-Reliance Theory' [14]). ...
Full-text available
Human social interactions in daily life involve sharing various types of rewards. Previous research evolving around issues of selfish versus altruistic behavior indicates that when individuals share rewards like money with powerless others, some are purely selfish while a substantial number shares evenly. It is, however, mostly unknown how they share primary rewards like water, compared to secondary rewards like money. We adopt the widely studied Dictator Game for comparing water to be divided among study participants with a monetary reward. We show that thirsty participants share water more often equally with powerless, anonymous others than they do money. This is the case even when they earned both types of rewards in a preceding task. Results indicate that altruistic behavior is more likely to occur when it comes to sharing primary rewards. The ecologically more valid scenario employed in this study provides initial evidence that the concept of a self-interested homo economicus might not apply to everyday social interactions involving rewards other than money.
... Homeostatic-appetitive (e.g., energy balance, thirst, and skin temperature) motivations are fundamental modulators on human cognition and behavior (e.g., Aarts, Dijksterhuis, & De Vries, 2001;Mogg, Bradley, Hyare, & Lee, 1998;Wright et al., 2012); ACT-R does not yet provide an architectural representation for this modulation. ACT-R/Φ provides a basic representation for these modifications by using the osmoreceptor, gi-lumen, and heatskin variables for thirst, hunger, and skin temperature (respectively). ...
... Though this method is admittedly crude, identification of particular physiological variables to tie to cognitive architecture changes is an important step; the ACT-R side of the connection will need to be expanded for more meaningful testing of the representations. It should be mentioned that most models built in ACT-R do not complete tasks over a time-period that would suitably leverage these motivations to display more autonomous behavior 13 ; though one may still begin to simulate other cognitive effects of these motivations (e.g., participating in a psychological experiment while thirsty; Wright et al., 2012). As previously noted, existing architectures like MicroPSI offer potential insights into ways one may add physiological representations to ACT-R by expanding current connections in ACT-R/Φ. ...
Full-text available
Adding a physiological representation to a cognitive architecture offers an attractive approach to modeling the effects of stress on cognition. We introduce ACT-R/Φ, an extended version of the ACT-R cognitive architecture that includes an integrative model of physiology. The extension allows the representation of how physiology and cognition interact. This substrate was used to represent potential effects of a startle response and task-based stress during a mental arithmetic (subtraction) task. We compare predictions from two models loaded into the new hybrid architecture to models previously developed within ACT-R. General behavior differed between models in that the ACT-R/Φ models had dynamic declarative memory noise over the course of the task based on varying epinephrine levels. They attempted more subtractions but were less accurate; this more closely matched human performance than the previous ACT-R models. Using ACT-R/Φ allows a more tractable integration of current physiological and cognitive perspectives on stress. ACT-R/Φ also permits further exploration of the interaction between cognition and physiology, and the emergent effects on behavior caused by the interaction among physiological subsystems. This extension is useful for anyone exploring how the human mind can occur in and be influenced by the physical universe.
... Subjects can become more risk-seeking in terms of patch choice and predation risk 30 . With a few important exceptions (for examples, see refs 59,60 ), most behavioural neuroscience decision-making studies have taken the view, typically implicitly, that individuals are not constrained by energy or homeostatic challenges. Indeed, it is rare for subjects even to be able to run out of experimentally provided money. ...
Modern decision neuroscience offers a powerful and broad account of human behaviour using computational techniques that link psychological and neuroscientific approaches to the ways that individuals can generate near-optimal choices in complex controlled environments. However, until recently, relatively little attention has been paid to the extent to which the structure of experimental environments relates to natural scenarios, and the survival problems that individuals have evolved to solve. This situation not only risks leaving decision-theoretic accounts ungrounded but also makes various aspects of the solutions, such as hard-wired or Pavlovian policies, difficult to interpret in the natural world. Here, we suggest importing concepts, paradigms and approaches from the fields of ethology and behavioural ecology, which concentrate on the contextual and functional correlates of decisions made about foraging and escape and address these lacunae.
... Several studies have explored the extent to which fairness concerns are crossculturally universal Wright et al., 2012; though see criticisms of some methods in Dana, Cain, & Dawes, 2006;List, 2007;Winking & Mizer, 2013), and the extent to which they vary. For example, studied dictator game behavior across 15 diverse populations, from the nomadic and foraging Hadza in Tanzania, to wageworkers in Missouri. ...
This volume brings together cutting-edge research from emerging and senior scholars alike representing a variety of disciplines that bears on human preferences for fairness, equity and justice. Despite predictions derived from evolutionary and economic theories that individuals will behave in the service of maximizing their own utility and survival, humans not only behave cooperatively, but in many instances, truly altruistically, giving to unrelated others at a cost to themselves. Humans also seem preoccupied like no other species with issues of fairness, equity and justice. But what exactly is fair and how are norms of fairness maintained? How should we decide, and how do we decide, between equity and efficiency? How does the idea of fairness translate across cultures? What is the relationship between human evolution and the development of morality? The collected chapters shed light on these questions and more to advance our understanding of these uniquely human concerns. Structured on an increasing scale, this volume begins by exploring issues of fairness, equity, and justice in a micro scale, such as the neural basis of fairness, and then progresses by considering these issues in individual, family, and finally cultural and societal arenas. Importantly, contributors are drawn from fields as diverse as anthropology, neuroscience, behavioral economics, bioethics, and psychology. Thus, the chapters provide added value and insights when read collectively, with the ultimate goal of enhancing the distinct disciplines as they investigate similar research questions about prosociality. In addition, particular attention is given to experimental research approaches and policy implications for some of society's most pressing issues, such as allocation of scarce medical resources and moral development of children. Thought-provoking and informative, Interdisciplinary Perspectives on Fairness, Equity, and Justice is a valuable read for public policy makers, anthropologists, ethicists, psychologists, neuroscientists, and all those interested in these questions about the essence of human nature.
... Social science literature suggests that citizens are more willing to comply with laws they consider fair (Tyler 1990, Levi 1997, Clayton 2000, Fehr and Falk 2002, May 2004, Wright et al. 2012, Olive 2014). There is a substantial literature around environmental justice that highlights the link between what individuals perceive as just and what individuals are willing to obey or voluntarily perform for environmental purposes. ...
Full-text available
The United States and the Canadian province of Ontario have enacted endangered species laws that regulate private land. The rationale for this is that the vast majority of endangered species in the two countries rely on private lands for survival. However, from a landowner perspective the law is deemed unfair. This paper presents analysis from 141 interviews with landowners in three U.S. states and Ontario. In recognition of distributive justice claims, both the U.S. government and the Ontario government have enacted programs aimed at increasing financial incentives for participation and compliance with the law. However, the law is still perceived as unfair. The central argument of this paper is that future amendments and new policies for endangered species should confront two other forms of environmental justice: procedural justice and justice-as-recognition. Landowners in both countries expressed not only concerns about compensation, but also a deep desire to be included in the protection and recovery process, as well as to be recognized by government and society as good stewards of the land. The paper concludes by stating that future policy amendments need to address justice-as-recognition if endangered species conservation on private lands is to be considered fair by landowners.
... Players either receive money if the responder accepts the offer or receive nothing if the responder chooses to decline the offer (Güth et al., 1982). Behaviorally, responders routinely reject substantial offers at a cost to themselves if the offers are unfair (Camerer and Thaler, 1995), irrespective of the stake size (Lisa, 1999;Munier and Zaharia, 2002), anonymity (Bolton and Zwick, 1995), the bargaining domain (Berger et al., 2012;Wright et al., 2012), or their cultural backgrounds (Henrich et al., 2006). Neuroscience studies using the UG showed that unfair offers were associated with increased activity in the anterior insula (Sanfey et al., 2003;Tabibnia et al., 2008) and that rejections of unfair offers were associated with reward-related brain regions such as the dorsal striatum (Osumi et al., 2010;Crockett et al., 2013;Wu et al., 2014). ...
Full-text available
Empirical evidence indicates that people are inequity averse. However, it is unclear whether and how suffering unfairness impacts subsequent behavior. We investigated the consequences of unfair treatment in subsequent interactions with new interaction partners and the associated neural mechanisms. Participants were experimentally manipulated to experience fair or unfair treatment in the ultimatum game (UG), and subsequently, they were given the opportunity to retaliate in the dictator game (DG) in their interactions with players who had not played a role in the previous fair or unfair treatment. The results showed that participants dictated less money to unrelated partners after frequently receiving unfair offers in the previous UG (vs. frequently receiving fair offers in the previous UG), but only when they were first exposed to unfair UG/DG. Stronger activation in the right dorsal anterior insula was found during receiving unfair offers and during the subsequent offer-considering phase. The regional homogeneity (ReHo), a measure of the local synchronization of neighboring voxels in resting-state brain activity, in the left ventral anterior insula and left superior temporal pole was positively correlated with the behavior change. These findings suggest that unfair treatment may encourage a spread of unfairness, and that the anterior insula may be not only engaged in signaling social norm violations, but also recruited in guiding subsequent adaptive behaviors.
Though computational cognitive architectures have been used to study several processes associated with human behavior, the study of integration of affect and emotion in these processes has been relatively sparse. Theory from affective science and affective neuroscience can be used to systematically integrate affect into cognitive architectures, particularly in areas where cognitive system behavior is known to be associated with physiological structure and behavior. I introduce a unified theory and model of human behavior that integrates physiology and primal affect with cognitive processes in a cognitive architecture. This new architecture gives a more tractable, mechanistic way to simulate affect-cognition interactions to provide specific, quantitative predictions. It considers affect as a lower-level, functional process that interacts with cognitive processes (e.g., declarative memory) to result in emotional behavior. This formulation makes it more straightforward to connect these affective representations with other related moderating processes that may not specifically be considered as emotional (e.g., thirst or stress). An improved understanding of the architecture that constrains our behavior gives us a better opportunity to comprehend why we behave the way we do and how we can use this knowledge to recognize and construct a more ideal internal and external environment.
The goal of this chapter is to explore the developmental origins of fairness. To do so, it first describes the relationship between fairness in particular and moral psychology in general. Recent evolutionary accounts of moral psychology have placed a particular emphasis on fairness, due to its importance in governing cooperative interactions between non-kin. Applying this account to development can explain otherwise peculiar features of how fairness emerges over childhood, most notably a “knowledge-behavior gap” in which children understand many features of fairness before they are motivated to behave in compliance with those features. Specifically, merely evaluating others is low-cost and has clear benefits even in infancy (e.g., it influences who we choose to learn from), but costly prosocial behavior is typically beneficial only at later ages, when a reputation for fairness becomes increasingly important for being included rather than shunned for mutually beneficial interactions with others.
A runaway train is racing toward five men who are tied to the track. Unless the train is stopped, it will inevitably kill all five men. You are standing on a footbridge looking down on the unfolding disaster. However, a fat man, a stranger, is standing next to you: if you push him off the bridge, he will topple onto the line and, although he will die, his chunky body will stop the train, saving five lives. Would you kill the fat man?. The question may seem bizarre. But it's one variation of a puzzle that has baffled moral philosophers for almost half a century and that more recently has come to preoccupy neuroscientists, psychologists, and other thinkers as well. In this book, David Edmonds, coauthor of the best-selling Wittgenstein's Poker, tells the riveting story of why and how philosophers have struggled with this ethical dilemma, sometimes called the trolley problem. In the process, he provides an entertaining and informative tour through the history of moral philosophy. Most people feel it's wrong to kill the fat man. But why? After all, in taking one life you could save five. As Edmonds shows, answering the question is far more complex--and important--than it first appears. In fact, how we answer it tells us a great deal about right and wrong.
Full-text available
Although conservation efforts have sometimes succeeded in meeting environmental goals at the expense of equity considerations, the changing context of conservation and a growing body of evidence increasingly suggest that equity considerations should be integrated into conservation planning and implementation. However, this approach is often perceived to be at odds with the prevailing focus on economic efficiency that characterizes many payment for ecosystem services (PES) schemes. Drawing from examples across the literature, we show how the equity impacts of PES can create positive and negative feedbacks that influence ecological outcomes. We caution against equity-blind PES, which overlooks these relationships as a result of a primary and narrow focus on economic efficiency. We call for further analysis and better engagement between the social and ecological science communities to understand the relationships and trade-offs among efficiency, equity, and ecological outcomes.
Full-text available
Human social interaction is strongly shaped by other-regarding preferences. These preferences are key for a unique aspect of human sociality – large scale cooperation with genetic strangers – but little is known about their developmental roots. We show here that young children’s other-regarding preferences assume a particular form – inequality aversion – that develops strongly between the ages of 3 and 8. At age 3-4, the overwhelming majority of children behave selfishly, while the vast majority at age 7-8 prefers resource allocations that remove advantageous or disadvantageous inequality. Moreover, inequality aversion is strongly shaped by parochialism, a preference for favouring the members of one’s own social group. These results indicate that human egalitarianism and parochialism have deep developmental roots, and the simultaneous emergence of altruistic sharing and parochialism during childhood is intriguing in view of recent evolutionary theories which predict that the same evolutionary process jointly drives both human altruism and parochialism.
Full-text available
The concept of satisficing, as developed by Simon (1955), has been much mis-represented in the ecological literature, both by its opponents and proponents. Satisficing consists of two related concepts, namely: (1) satisfying a minimum requirement, and 2) choosing among a subset of behaviors when information-processing or time constraints limit the ability of a decision-maker to make an optimal decision. The second aspect of satisficing offers interesting prospects for alternatives to optimal models. Examples of the uses of satisficing are provided for predator search and parental behavior.
Full-text available
This book is the result of a collaborative effort by eleven anthropologists and six economists, and questions the motives that underlie the ways that humans interact socially, and whether these are the same for all societies, and are part of our nature, or are influenced by our environments. Over the past decade, research in experimental economics has emphatically falsified the textbook representation of Homo economicus, with hundreds of experiments that have suggested that people care not only about their own material payoffs but also about such things as fairness, equity, and reciprocity. However, this research has left fundamental questions unanswered: are such social preferences stable components of human nature; or, are they modulated by economic, social, and cultural environments? Until now, experimental research could not address this question because virtually all subjects had been university students, and while there are cultural differences among student populations throughout the world, these differences are small compared with the full range of human social and cultural environments. A vast amount of ethnographic and historical research suggests that people's motives are influenced by economic, social, and cultural environments, yet such methods can only yield circumstantial evidence about human motives. In combining ethnographic and experimental approaches to fill this gap, this book breaks new ground in reporting the results of a large cross-cultural study aimed at determining the sources of social (non-selfish) preferences that underlie the diversity of human sociality. The same experiments that provided evidence for social preferences among university students were performed in fifteen small-scale societies exhibiting a wide variety of social, economic, and cultural conditions by experienced field researchers who had also done long-term ethnographic field work in these societies. The results, which are given in chs. 4 to 14, demonstrated no society in which experimental behaviour is consistent with the canonical model of self-interest, and showed that variation in behaviour is far greater than previously thought, and that the differences between societies in market integration and the importance of cooperation explain a substantial portion of the variation found (which individual-level economic and demographic variables could not). The results also trace the extent to which experimental play mirrors the patterns of interaction found in everyday life. The book has three introductory chapters that include a succinct but substantive introduction to the use of game theory as an analytical tool, and to its use in the social sciences for the rigorous testing of hypotheses about fundamental aspects of social behaviour outside artificially constructed laboratories, and an overview and summary of the results of the fifteen case studies.
Game theory, the formalized study of strategy, began in the 1940s by asking how emotionless geniuses should play games, but ignored until recently how average people with emotions and limited foresight actually play games. This book marks the first substantial and authoritative effort to close this gap. Colin Camerer, one of the field's leading figures, uses psychological principles and hundreds of experiments to develop mathematical theories of reciprocity, limited strategizing, and learning, which help predict what real people and companies do in strategic situations. Unifying a wealth of information from ongoing studies in strategic behavior, he takes the experimental science of behavioral economics a major step forward. He does so in lucid, friendly prose. Behavioral game theory has three ingredients that come clearly into focus in this book: mathematical theories of how moral obligation and vengeance affect the way people bargain and trust each other; a theory of how limits in the brain constrain the number of steps of "I think he thinks . . ." reasoning people naturally do; and a theory of how people learn from experience to make better strategic decisions. Strategic interactions that can be explained by behavioral game theory include bargaining, games of bluffing as in sports and poker, strikes, how conventions help coordinate a joint activity, price competition and patent races, and building up reputations for trustworthiness or ruthlessness in business or life.
Differences in the deployment of altruism in human and non-human primate groups raise two different questions in this article. This article considers some of the factors that may limit the extent of cooperation in non-human primate groups. In particular, it focuses on the evidence for the features that are associated with altruistic behaviour in humans: the capacity for empathy, the existence of moral sentiments, and the concern for the welfare of others. The article also defines cooperation as equivalent to the biological definition of altruism, and uses these terms interchangeably. It distinguishes between empathy and sympathy. The definition of empathy corresponds to Stephanie Preston and Frans de Waal's concept of 'cognitive empathy'. While one often conflates empathy and sympathy, the two can be uncoupled. Thus, empathy is a necessary, but not sufficient, condition for sympathy.
To investigate the nature of social preferences in primates, researchers have recently devised a series of experiments in which animals are presented with opportunities to provide benefits to others at little or no cost to themselves. The choices that they make in these experiments provide insight about their social preferences. Although the discrepancy between the results obtained in experiments that were designed to examine chimps' social preferences may seem like an unfortunate complication, it provides with an important opportunity. If one can work out the reasons why the results of these experiments differ, one may gain deeper insights about the complexity and nature of chimps' social preferences. For example, the presence of food rewards might compete with selfish motives about food. If that is the case, then the chimps who were indifferent in the Silk/Jensen/Vonk experiments might behave prosocially in the protocol used by Warneken and his colleagues, and vice versa.
Introduction, 99. — I. Some general features of rational choice, 100.— II. The essential simplifications, 103. — III. Existence and uniqueness of solutions, 111. — IV. Further comments on dynamics, 113. — V. Conclusion, 114. — Appendix, 115.
Game theory, the formalized study of strategy, began in the 1940s by asking how emotionless geniuses should play games, but ignored until recently how average people with emotions and limited foresight actually play games. This book marks the first substantial and authoritative effort to close this gap. Colin Camerer, one of the field's leading figures, uses psychological principles and hundreds of experiments to develop mathematical theories of reciprocity, limited strategizing, and learning, which help predict what real people and companies do in strategic situations. Unifying a wealth of information from ongoing studies in strategic behavior, he takes the experimental science of behavioral economics a major step forward. He does so in lucid, friendly prose. Behavioral game theory has three ingredients that come clearly into focus in this book: mathematical theories of how moral obligation and vengeance affect the way people bargain and trust each other; a theory of how limits in the brain constrain the number of steps of "I think he thinks . . ." reasoning people naturally do; and a theory of how people learn from experience to make better strategic decisions. Strategic interactions that can be explained by behavioral game theory include bargaining, games of bluffing as in sports and poker, strikes, how conventions help coordinate a joint activity, price competition and patent races, and building up reputations for trustworthiness or ruthlessness in business or life. While there are many books on standard game theory that address the way ideally rational actors operate, Behavioral Game Theory stands alone in blending experimental evidence and psychology in a mathematical theory of normal strategic behavior. It is must reading for anyone who seeks a more complete understanding of strategic thinking, from professional economists to scholars and students of economics, management studies, psychology, political science, anthropology, and biology.
Introduction, 99.--I. Some general features of rational choice, 100.--II. The essential simplifications, 103.--III. Existence and uniqueness of solutions, 111.--IV. Further comments on dynamics, 113.--V. Conclusion, 114.--Appendix, 115.