Do Children with Autism Spectrum Disorder Share Fairly and Reciprocally?
Journal of Autism and Developmental Disorders
Do Children with Autism Spectrum Disorder Share Fairly and Reciprocally?
Calum Hartley 0
Sophie Fisher 0
0 Sophie Fisher
1 Calum Hartley
This study investigated whether children with autism spectrum disorder (ASD) and typically developing children matched on receptive language share resources fairly and reciprocally. Children completed age-appropriate versions of the Ultimatum and Dictator Games with real stickers and an interactive partner. Both groups offered similar numbers of stickers (preferring equality over self-interest), offered more stickers in the Ultimatum Game, and verbally referenced 'fairness' at similar rates. However, children with ASD were significantly more likely to accept unfair offers and were significantly less likely to reciprocate the puppet's offers. Failure to reciprocate fair sharing may significantly impact on social cohesion and children's ability to build relationships. These important differences may be linked to broader deficits in social-cognitive development and potentially self-other understanding.
Autism spectrum disorder; Ultimatum Game; Dictator Game; Sharing; Reciprocity; Fairness
Sharing is a crucial foundation of human evolution
(Dunbar 1993; Winterhalder 2001)
and involves relinquishing
ownership or control of access to a commodity for someone
else’s benefit. For decades, behavioural economists have
examined the conflict between retaining valued possessions
and sharing with others via resource-exchange tasks. In the
Ultimatum Game, an individual is endowed with a desirable
resource and is required to offer a proportion to a partner
who has nothing. On acceptance, the resource is split as
proposed and both parties keep a share. On rejection, neither
party keeps any of the resource. Thus, the proposer must
strategically balance self-interest (i.e. the desire to retain
as much of the resource as possible) against their partner’s
interests. The Dictator Game follows the same format except
for one crucial difference: the partner must always accept
Department of Psychology, Lancaster University,
Lancaster LA1 4YF, UK
whatever share is offered. It is widely argued that players’
responses in these tasks are directed by socially-learned
norms concerning fairness
(Hoffman et al. 2008)
ability to infer the mental states of social partners via Theory
(ToM; Castelli et al. 2010; Takagishi et al. 2014)
Here, we explore whether children with autism spectrum
disorder (ASD)—a population characterised by impairments
in social interaction and Theory of Mind (APA 2013;
BaronCohen 1995)—show differences in resource sharing while
playing age-appropriate versions of the Ultimatum and
According to the economic model of rational self-interest,
proposers should always make the smallest possible offers,
and responders in the Ultimatum Game should accept any
offer greater than zero
. However, across
dozens of studies, typically developing (TD) adults
consistently offer 40–45% of the stake in the Ultimatum Game and
20–25% in the Dictator Game
(despite having the option to
offer less without fear of rejection; Camerer 2003; Henrich
et al. 2005; Rigdon 2003)
. The generosity of these average
offers reflects a general preference for fairness and
equality. Indeed, adults will usually reject offers they perceive
to be unfair, and failure to behave reciprocally elicits
punishment and negative affect in exchange partners
Gachter 2002; de Quervain et al. 2004)
. Lucas et al. (2008)
investigated whether TD children aged 4–5 years similarly
value fairness when sharing endowed commodities. This
was achieved by designing age-appropriate versions of the
Ultimatum and Dictator Games that employed stickers as a
resource (rather than money, tokens, or points), and stakes
were distributed immediately after each round (rather than
at the end of the task). The results showed that TD children
offered 47% and 40% of stakes in the Ultimatum Game and
Dictator Game respectively. Therefore, despite the natural
desire to retain one’s own resources, even young TD children
value fairness over self-interest in sharing contexts
Brownell et al. 2013; Castelli et al. 2014)
Many theorists have argued that children’s early-emerging
inclination to share equally (and reciprocate others’ sharing
behaviours) has adapted to promote cooperation and
diminish the impact of self-interests on social cohesion
(Hoffman et al. 2008)
. Upholding shared expectations concerning
fairness provides a foundation for positive and reciprocal
interactions, and establishes one’s reputation as a good
(which may be a stronger motivating factor in
typical development than greater material or instrumental
outcomes; Adamson et al. 2010; Dawson et al. 2004; Greene
et al. 2011; Hoffman et al. 2008)
. From 3-years, TD children
display strong adverse reactions when they are
disadvantaged by unequal distributions (despite showing little
willingness to share themselves; LoBue et al. 2011). By 4-years,
TD children can infer the emotions, needs, and interests of
social partners, and are able to differentiate these from their
(Wellman et al. 2001)
. At 5-years, they make explicit
verbal references to fairness, demonstrate a motivation to
engage in behaviour that benefits others, and show
generosity when sharing resources with partners
(Fehr et al. 2008;
Güroğlu et al. 2009; Lucas et al. 2008)
. Thus, TD children
may offer nearly half of a valued resource in the
Ultimatum Game because they can represent the perspective of the
responder and are aware that a lower offer may be construed
as “unfair”. In support of this reasoning, TD children with
superior ToM skills make higher mean offers and are more
likely to reject unfair offers in the Ultimatum Game
et al. 2010; Takagishi et al. 2010, 2014)
. Taken together, this
evidence suggests that TD children’s preference for sharing
fairly in resource-exchange tasks is driven by sensitivity to
social norms and awareness of others’ perspectives.
If the development of equal sharing is underpinned by
social norms and awareness of others’ mental states, we
may expect to observe qualitative differences in ASD.
Children with ASD show diminished social motivation and
experience difficulties interacting with others
Chevallier et al. 2012)
. Compared with TD children, those
with ASD spend less time engaged in social interactions
(Bauminger et al. 2008)
, are less likely to
(Aldridge et al. 2000; Carpenter et al. 2001; van
Ommeren et al. 2012)
, and are less likely to reciprocate
in naturalistic interactions
(Channon et al. 2001; Hadwin
et al. 1997; Wimpory et al. 2007; Joseph and
Tager-Flusberg 2004; Klin et al. 2006; Ozonoff and Miller 1995)
is also widely acknowledged that children with ASD have
fundamental impairments in intention reading and ToM
(Baron-Cohen 1995; Baron-Cohen et al. 1997; Charman
et al. 1997; D’Entremont and Yazbek 2007; Griffin 2002;
Hartley and Allen 2014, 2015; Hobson 2002; Mundy and
Willoughby 1996; Preissler and Carey 2005)
deficits result in reduced understanding and consideration of
others’ psychological states both separately and in relation
to one’s own interests. Theoretically, it is possible that
these social-cognitive difficulties impact children’s
preferences for fairness and reciprocity when sharing resources.
Indeed, it may be that sharing in children with ASD is
primarily motivated by instrumental outcomes, and is
influenced less by the behaviours and mental states of social
partners (Schmitz et al. 2015).
To date, few studies have investigated the sharing
behaviour of children with ASD using resource-exchange
Sally and Hill (2006)
, high-functioning children
with ASD aged 6–15 years played computerised versions
of the Ultimatum and Dictator Games, in which ‘points’
served as proxies for real resources. While children with
ASD made similar offers to TD controls in the Dictator
Game, the groups diverged in the more strategic
Ultimatum Game. Whereas most TD children shared the resource
equally, many children with ASD—particularly those who
failed a false belief test—tended to offer one or zero points
(out of ten). Furthermore, when offered 30% or less of the
total stake, children with ASD accepted on approximately
30% of trials, whereas TD controls accepted on just 11%.
In another study, Schmitz et al. (2015) tested “cognitively
able” children with ASD and TD controls aged 9–14 years
on a computerised version of the Dictator Game in which
they decided how to distribute coins between themselves
and an anonymous partner. Crucially, children could
choose either an equal distribution (1 point each) or an
unequal distribution that benefited either the participant
(2 vs 1) or the partner (1 vs 2). Although both populations
tended to select the equal split, children with ASD were
more likely to select unequal distributions of either type.
Paulus and Rosal-Grifoll (2016)
, 3–6 year old
children with ASD and TD controls matched on non-verbal
ability were tasked with sharing resources with partners
that were rich or poor. Unlike TD children who
consistently split the resources equally between parties, children
with ASD allocated most of the resources to the other
recipients and kept relatively little for themselves. The
findings from these three studies suggest that children with
ASD have a diminished aversion to inequity and are less
concerned about their own gains. Furthermore, their
sharing tends to maximize resources across parties,
accommodating both advantageous and disadvantageous inequality.
Atypical sharing behaviour and weaker preferences for
equality could have important implications for children’s
social relationships. Specifically, these characteristics may
place children with ASD at increased risk of bullying.
Recent estimates suggest that up to 87% of children with
ASD are bullied every week or month, placing them at
significantly higher risk than TD children
(Cappadocia et al.
2012; Wainscot et al. 2008)
. Due to their socially
incongruent behaviour and difficulties conforming to social norms,
children with ASD are often perceived as ‘different’ by their
(Humphrey and Lewis 2008; van Roekel et al. 2010)
This can impact their ability to develop friendships
(Bauminger and Kasari 2000; Chamberlain et al. 2007)
to feelings of isolation and increasing the likelihood of
(Bauminger et al. 2003; Hodges et al. 1999;
Humphrey and Symes 2011)
. If children with ASD are more
receptive to unfair social behaviour and less concerned about
their personal gain, this could significantly increase their
risk of exploitation or manipulation.
The objective of this study was to explore the sharing
behaviour of children with ASD and language-matched
TD controls via age-appropriate versions of the Ultimatum
Game and Dictator Game. In doing so, we advance the
literature in three important ways. Firstly, prior studies have relied
upon computer-based tasks that involve sharing “virtual
resources” with hypothetical or inanimate partners. Lucas
et al. (2008) point out that children may not understand that
points represent commodities, and may behave differently
when required to share tangible rewards with real partners.
Thus, we increased the stakes of sharing by endowing
children with attractive stickers (a valued resource often used to
reward and reinforce positive behaviour in both populations),
and instructing them to share with a pseudo-animate partner
(a puppet) in a face-to-face context. Secondly, we explored
how children’s offers are influenced by the offers of their
partner. Previous studies document children’s offers and
responses, but do not test the extent to which children with
ASD reciprocate fair or unfair offers. Exploring this
behaviour will provide an indication of children’s sensitivity to the
fairness norm and their ability to adapt to others’ behaviour.
Thirdly, the rationale underpinning the sharing behaviours of
children with ASD is currently unknown. We shed light on
this motivation by recording and analysing children’s verbal
justifications of their offers and responses when resources
are distributed. In addition, we conducted an ‘unexpected
contents’ false belief task to establish whether ToM relates
to sharing behaviour. Based on previous resource exchange
(Sally and Hill 2006; Schmitz et al. 2015)
evidence of reduced social reciprocity
(e.g. Klin et al. 2006)
we expected to observe a diminished preference for equality,
reduced reciprocation of fair offers, and fewer verbal
references to “fairness” in children with ASD. In comparison to
previous studies, we anticipated that the increasingly social
context and real-life rewards may heighten self-interest in
the ASD group.
Participants were 15 verbal children with ASD (13 male; M
age = 9.2 years, range 7.1–11.1 years) and 18 TD children
(12 male; M age = 4.3 years, range 3–6.1 years) recruited
from two specialist schools and one mainstream school in
Cheshire, UK. As cognitive development in ASD is often
delayed relative to chronological age
(Anderson et al. 2009)
Sally and Hill’s (2006)
approach of matching
samples on language comprehension rather than
chronological age (allowing us to assume with reasonable confidence
that participants in both groups could understand the task).
Samples were closely matched on receptive vocabulary as
measured by the British Picture Vocabulary Scale
ASD: M age equivalent: 5.1 years, SD: 1.67; TD: M age
equivalent: 4.83 years, SD: 1.59; Dunn et al. 1997)
every child with ASD had delayed linguistic development
in comparison to their chronological age, our sample is
representative of a significant proportion of the clinical
(Anderson et al. 2007)
. All children with ASD were
diagnosed by a qualified educational or clinical
psychologist, using standardised instruments
Diagnostic Observation Scale and Autism Diagnostic Interview—
Revised; Lord et al. 2002, 1994)
and expert judgement.
Diagnoses were confirmed via the Childhood Autism Rating
Scale (CARS; Schopler et al. 1980), which was completed
by each participant’s class teacher (ASD: M score = 31.78;
TD: M score = 15.42). Children with ASD were significantly
older (t(31) = 13.24, p < .001, d = 4.52), and had significantly
higher CARS scores (t(31) = 8.48, p < .001, d = 3.7) than
the TD children. The study was approved by the Lancaster
University Ethics Committee, and informed consent was
obtained from children’s caregivers prior to their
involvement in the research.
Following Lucas et al. (2008), brightly-coloured stickers
were used as trading items in the Ultimatum and Dictator
Games as they are desirable and often used as positive
reinforcers. Every child was presented with eight sets of eight
stickers (one set per trial of each game). The sticker sets
were different from one another in order to maintain interest
and motivation throughout each game (e.g. smiley faces,
animals, stars etc). However, within a set, stickers were
thematically similar (e.g. differently coloured stars) to reduce the
likelihood that children would develop strong preferences
for individual stickers that would impact their willingness
to trade. In line with previous studies of this nature, children
interacted with a human-looking hand puppet that matched
their gender (“Jack” or “Jill”) during the experimental tasks
(e.g. Kanngiesser and Hood 2014)
. Children were unlikely to
view the puppet as an authority figure, meaning their trading
decisions would not be influenced by unequal status.
For the Unexpected Contents Task, a Smarties tube was
emptied and filled with small colouring pencils. Three
pictures were created to facilitate the responding of children
with ASD if necessary (depicting a tube of Smarties,
colouring pencils, and a rainbow).
Participants were tested individually in their own schools
and were accompanied by a familiar adult. Children were
verbally praised for attention and good behaviour.
Participants completed three test sessions on different days. Session
1 consisted of the BPVS. Session 2 involved the Ultimatum
or Dictator Game (counterbalanced across participants).
Session 3 involved either the Ultimatum or Dictator Game
(whichever was not played in Session 2) followed by the
Unexpected Contents Task.
The Ultimatum Game consists of two roles: proposer and
responder. The roles alternated between the child and puppet
over four trials (e.g. the child was the proposer for trials 1
and 3). Half of the participants started in the proposer role,
while the other half started in the responder role. When in
the proposer role, the child was given eight stickers (per
trial) and instructed to give some to the puppet, with a one
sticker minimum offer. If the puppet accepted the offer, the
stickers were divided as proposed. If the puppet rejected,
neither player received any stickers. When in the responder
role, the child accepted or rejected an offer from the
puppet. Acceptance lead to both parties receiving stickers while
rejection meant neither party received any stickers. The
puppet offered one sticker (unfair offer) on one trial and four
stickers (fair offer) on another trial (order randomly
predetermined). The puppet accepted one of the child’s offers
and rejected the other (order randomly predetermined). After
making their offers, children were asked why they had made
this decision (“Why did you give Jack that number of
stickers?”). They were also asked how they felt about each of the
puppet’s offers (“Do you want that many stickers? Why?”).
This game followed the same procedure as the
Ultimatum Game, except the responder was unable to reject the
proposer’s offer. The proposer role alternated between the
child and puppet over four trials (e.g. the child was the
proposer for trials 1 and 3). Half of the participants started in
the proposer role, while the other half received the puppet’s
offer first. As the proposer, children were given eight
stickers (on each trial) and instructed to give some to the puppet,
with a one sticker minimum offer. They were informed that
the puppet had to accept their offer (e.g. “Jack has to take
the number of stickers you give him”). The puppet offered 1
sticker (unfair offer) on one trial and four stickers (fair offer)
on another trial (order randomly predetermined). Children
were asked to explain their offers, and describe how they felt
about the puppet’s offers.
Unexpected Contents Task
The puppet was hidden from view at the start of this task
(they were “sleepy and needed a nap”). Children were shown
a Smarties tube and asked what they thought was inside. The
tube was opened to reveal small coloured pencils instead of
Smarties. The pencils were placed back inside the Smarties
tube and the puppet “woke up”. Children were then asked
three questions in a random order: (a) “what does Jack/Jill
think is inside?”, (b) “what did you think was inside when
you first saw it?”, and (c) “what is really inside?” (a
memory check to identify children who were guessing or did not
understand). Children with ASD who had limited expressive
language responded to each question by pointing to one of
three colour pictures depicting a tube of Smarties, colour
pencils, and a rainbow (to control for guessing).
When children were in the proposer role, we recorded the
number of stickers they offered the puppet on each trial. In
the Ultimatum Game we recorded whether children accepted
or rejected each of the puppet’s offers and we also recorded
children’s verbal comments in both games.
On average, children with ASD offered 2.93 (SD: 1.22;
36.63% of the total stake) stickers on their first turn in
the proposer role, and 3.53 (SD: 1.77; 44.13%) stickers
on their second turn. By comparison, TD children offered
3.72 (SD: 2.22; 46.5%) stickers on their first turn as
proposer, and 3.06 (SD: 1.39; 38.25%) on the second. These
data were entered into a two (population: TD, ASD) × 2
(offer: first, second) mixed ANOVA, which revealed no
significant effects. Thus, an ASD diagnosis did not
significantly impact first or second offers made by children
in the Ultimatum Game.
We then tested whether children’s offers were influenced
by their starting role: proposer or responder. Data from each
population were entered into a 2 (order: child first, puppet
first) × 2 (offer: first offer, second offer) mixed ANOVA.
These analyses revealed no effects, suggesting that neither
group’s offers were influenced by whether the participant
started in the proposer or responder role. To assess whether
the populations differed when making initial offers without
a prior cue (e.g. a preceding offer from the puppet) we
conducted an independent samples t test. The results confirmed
that the first offers of TD children and children with ASD
who started in the proposer role did not significantly differ
in the Ultimatum Game.
While the analyses of children’s numerical offers have not
revealed any significant differences between populations, it
is important to note that they do not consider the influence of
the puppet’s behaviour. Reciprocity is a vital aspect of
sharing and we were interested to discover whether the fairness
of children’s offers was influenced by the fairness of the
puppet’s offers. When the puppet made a fair offer, TD children
responded with a fair offer 93% of the time, or an offer that
favoured themselves 7% of the time. When the puppet made
an unfair offer, TD children responded with a fair offer 36%
of the time, an offer that favoured themselves 64% of the
time, and never made offers that favoured the puppet. Thus,
the offers of TD children appear to be strongly mediated by
the puppet’s behaviour; when they received a fair or unfair
offer, they responded in kind on nearly 80% of trials. When
children with ASD received a fair offer from the puppet, they
responded with a fair offer 56% of the time, or an offer that
favoured themselves 44% of the time. When the puppet made
an unfair offer, children with ASD responded with a fair
offer 25% of the time, an offer that favoured themselves 42%
of the time, and an offer that favoured the puppet 33% of the
time. These frequencies suggest that the children with ASD
were less likely to reciprocate the puppet’s actions compared
to TD children; they reciprocated fair and unfair offers just
49% of the time.
We tested whether children with ASD were statistically
less likely to reciprocate the puppet’s offers in the
Ultimatum Game via a generalized linear mixed-effects model
(GLMM). The analysis modelled the probability (log odds)
of children reciprocating the puppet’s offer (yes/no),
considering variation across participants (random intercepts),
fixed effects of population (ASD/TD) and puppet’s offer
(fair/unfair), plus the interaction between these variables.
We conducted a sequence of GLMMs, entering fixed effects
simultaneously. Model 1 was a “null model” containing only
the random effect of participant ID. Model 2 added main
effects of population and puppet’s offer. Model 3 then added
the population × puppet’s offer interaction. We evaluated the
relative utility of each increasingly-complex model using
likelihood ratio tests. These indicated that inclusion of the
main effects in Model 2 yielded a significant improvement
in fit over the null model, χ2 (2) = 8.16, p = .017. Adding
the interaction afforded no further improvement. Therefore,
Model 2 provides the best fitting explanation of the observed
data (see Table 1). In support of our hypotheses, the results
show that children with ASD were significantly less likely
than TD controls to reciprocate the puppet’s offers in the
Ultimatum Game (49% vs 78.5%). However, across
populations, there was no difference in reciprocation rates for fair
or unfair offers made by the puppet.
Next, we explored how children responded to the puppet’s
fair and unfair offers. For each population, the relationship
between the puppet’s offers (fair offer, unfair offer) and
children’s responding (accept, reject) was measured via a
McNemar test. The responses of TD children were significantly
mediated by the fairness of the puppet’s offer, p< .001. They
accepted 94% of fair offers and 11% of unfair offers made by
the puppet. The responses of children with ASD were also
mediated by the fairness of the puppet’s offer, p= .016. They
accepted 100% of fair offers and 40% of unfair offers. These
data suggest that both groups were overwhelmingly biased
towards accepting the puppet’s offer of four stickers (likely
recognising it as fair), but the children with ASD were nearly
AIC Akaike information criterion; BIC Bayesian information criterion; logLik log-likelihood; Pr(>|z|), probability/statistical significance
30% more likely than the TD children to accept the puppet’s
unfair offer of one sticker. The significance of this difference
was tested by examining the relationship between population
(TD, ASD) and children’s responding (accept, reject) to fair
and unfair offers separately. For unfair offers, a chi square
test of independence revealed a borderline relationship, χ2
(1, N = 33) = 3.72, p = .054, φ = .34, suggesting that
children’s responding was mediated by their diagnostic group.
By contrast, there was no relationship between population
and children’s responding to fair offers. These results
suggest that the two populations have similar sensitivity and
response patterns when a partner shares fairly, but their
reactions differ when a partner shares unfairly.
On average, children with ASD offered 2.87 (SD: 1.55;
35.88% of the total stake) stickers on their first turn in the
proposer role, and 2.67 (SD: 1.4; 33.38%) stickers on their
second turn. By contrast, TD children offered 2.44 (SD:
1.25; 30.5%) stickers on their first turn as proposer, and 3.06
(SD: 1.31; 38.25%) on the second. As for the Ultimatum
Game, a 2 (population: TD, ASD) × 2 (offer: first, second)
mixed ANOVA revealed no main effects or interaction,
indicating no significant differences between the first and second
offers of either group. Similarly, a pair of 2 (order: child
first, puppet first)× 2 (offer: first offer, second offer) mixed
ANOVAs demonstrated that neither group was influenced
by starting role when making offers in the Dictator Game.
We then examined whether the populations differed when
making initial offers without a prior cue (e.g. a preceding
offer from the puppet). The results of the independent
samples t test indicated that the first offers of TD children and
children with ASD who started in the proposer role did not
significantly differ in the Dictator Game.
As above, we examined the reciprocity of children’s
offers. When the puppet made a fair offer, TD children
responded with a fair offer 75% of the time, an offer that
favoured themselves 19% of the time, or an offer that
favoured the puppet 6% of the time. When the puppet made
an unfair offer, TD children responded with an offer that
favoured themselves 100% of the time. As in the Ultimatum
Game, the offers of TD children were apparently influenced
by the puppet’s behaviour; they reciprocated fair and unfair
offers on 84% of trials. Opposite to the Ultimatum Game, TD
children were 25% more likely to reciprocate unfair offers
than fair offers. For children with ASD, when the puppet
made a fair offer, they responded with a fair offer 50% of the
time, an offer that favoured themselves 40% of the time, or
an offer that favoured the puppet 10% of the time. When the
puppet made an unfair offer, children with ASD responded
with a fair offer 10% of the time, an offer that favoured
themselves 80% of the time, and an offer that favoured the puppet
10% of the time. Thus, children with ASD reciprocated the
puppet’s offers on 65% of trials overall.
A GLMM was constructed to test whether children with
ASD were statistically less likely to reciprocate the puppet’s
offers in the Dictator Game. The analysis modelled the
probability (log odds) of children reciprocating the puppet’s offer
(yes/no), considering variation across participants (random
intercepts), fixed effects of population (ASD/TD) and
puppet’s offer (fair/unfair), plus the interaction between these
variables. We conducted a sequence of GLMMs, entering
fixed effects simultaneously. Model 1 was a “null model”
containing only the random effect of participant ID. Model
2 added main effects of population and puppet’s offer. Model
3 then added the population × puppet’s offer interaction.
Likelihood ratio tests were conducted to assess the relative
utility of each model. These showed that inclusion of the
main effects in Model 2 yielded a significant improvement
in fit over the null model, χ2 (2) = 8.47, p = .015. Adding
the interaction afforded no further improvement. Therefore,
Model 2 provides the best fitting explanation of the observed
data (see Table 2).
The results revealed a borderline effect of population,
suggesting that children with ASD tended to reciprocate the
puppet’s fair and unfair offers less frequently. There was also
a highly-significant effect of puppet’s offer; across
populations, children were significantly more likely to reciprocate
unfair offers (90%) than fair offers (62.5%). Viewed
alongside the opposing trend in the Ultimatum Game (74% fair vs
53% unfair), these results suggest that children moderated
AIC Akaike information criterion; BIC Bayesian information criterion; logLik log-likelihood; Pr(>|z|), probability/statistical significance
their reciprocity strategically overall. That is, they were
more likely to reciprocate fair or unfair sharing depending on
whether selfish behaviour could, or could not, be penalised
by the responder. However, in contrast to this general trend,
there was very little difference between reciprocation rates
for fair offers by children with ASD in the Dictator Game
and Ultimatum Game (50% vs 56%).
Ultimatum Game Versus Dictator Game
We assessed children’s strategic resource allocation by
making direct comparisons between offers on the Ultimatum and
Dictator Games. We began by testing the interaction between
diagnosis and game type by entering children’s offers into a
2 (population: TD, ASD) × 2 (game: ultimatum, dictator) × 2
(offer: first, second) mixed ANOVA. There was a significant
main effect of game, F(1, 31) = 8.58, MSE = 1.17, p = .006,
ηp2 = .22, indicating that both TD children and children with
ASD made larger average offers in the Ultimatum Game
(ASD M: 3.31; TD M: 3.39) than in the Dictator Game (ASD
M: 2.77; TD M: 2.75). These results show that both
populations adjusted the size of their offers in accord with the
different game rules. There was also a significant
population × game × offer interaction, F(1, 31) = 6.37, MSE = 1.39,
p = .017, ηp2 = .17. To establish the cause of the three-way
interaction, separate 2 (game) × 2 (offer) repeated measures
ANOVAs were conducted on the data for each population.
For children with ASD, there was a significant main effect
of game, F(1, 14) = 5.91, MSE = 0.55, p = .029, ηp2 = .3,
confirming that offers in the Ultimatum Game were greater than
offers in the Dictator Game. There was no effect of offer and
no interaction. For TD children, a significant main effect
of game was qualified by a significant game× offer
interaction, F(1, 17) = 4.4, MSE = 1.67, p = .05, ηp2 = .21, which
was explored via a series of Bonferroni-adjusted pairwise
tests. First offers in the Ultimatum Game (M: 3.72) were
significantly larger than first offers in the Dictator Game (M:
2.44), t(17) = 2.36, p = .03, d = .59. The difference between
second offers was not significant, nor were the differences
between first and second offers within either the Ultimatum
Game or Dictator Game.
The verbal responses provided by participants during the
Ultimatum and Dictator Games were transcribed and a
coding scheme was developed. Children’s comments were first
categorised based on context [(1) following their offer, (2)
in response to a fair offer from the puppet, (3) in response
to an unfair offer from the puppet] and then allocated to a
sub-category based on their content (see Table 3). The
purpose of this coding system was to identify whether children
with ASD and TD children differ in how they justify their
behaviour in different situations (e.g. by explicitly referring
to fairness at different frequencies). Every comment was
coded by the second experimenter and an independent rater
with relevant expertise. The second rater was blind to the
objectives of the study and the details of each child (e.g.
their age, population, background scores). Reliability of the
coding categories for each context was assessed via Cohen’s
Kappa, which was calculated based on the two raters’
categorical classifications. High inter-rater reliability was
achieved for all contexts (following child’s offer: κ = .88,
p < .01; response to fair offer: κ= 1.00, p < .01; response to
“Make him happy with that many”
“I want same amount, is really not fair”
unfair offer: κ = .86, p < .01). Disagreements in
classifications were resolved by consensus between the two raters.
Frequencies of response types made by TD children and
children with ASD are shown in Table 4. Chi square tests
of independence showed that response types in each
context were not mediated by population [following child’s
offer: χ2 (3, N = 64) = 2.30, p = .51; response to fair offer:
χ2 (2, N = 66) = .90, p = .64; response to unfair offer: χ2 (2,
N = 66) = 3.58, p = .17].
All children correctly answered the memory check correctly
(“what is really inside [the Smarties tub]?”). Children scored
0–2 based on how many Theory of Mind questions they
answered correctly. Mean scores for the children with ASD
and TD children were 0.59 and 1.33 respectively, a
significant difference, t(31) = 2.34, p = .026, d = .82. It is
noteworthy that 65% of the ASD group answered both Theory of
Mind questions incorrectly (compared with 28% of the TD
group), indicating their difficulty understanding their own
and others’ mental states.
The influence of children’s Theory of Mind task
performance on their offers in the Ultimatum/Dictator Games was
examined. Children were assigned to a ‘fail’ category if they
answered both unexpected contents test questions incorrectly
or a ‘pass’ category if they answered at least one test
question correctly (further sub-dividing participants based on
one or two correct answers would have resulted in
insufficient sample sizes). Children’s offers in the Ultimatum Game
and Dictator Game were entered into a pair of 2 (population:
TD, ASD) × 2 (Theory of Mind: pass, fail) × 2 (offer: first,
second) mixed ANOVAs. The analysis for the Ultimatum
Game revealed a significant Theory of Mind × offer
interaction, F(1, 29) = 4.78, MSE = 2.42, p = .037, ηp2 = .14,
which was explored using Bonferroni-adjusted pairwise
Table 4 Frequencies of qualitative response types made by TD
children and children with ASD in the Ultimatum and Dictator Games
tests. Children who failed both Theory of Mind test
questions made significantly smaller first offers (M= 2.57) than
those who passed at least one (M = 3.95), t(31) = 2.24,
p = .032, d = .82. However, the second offers made by the
pass and fail groups did not differ. The ‘fail’ group showed
an almost-significant tendency to make larger second offers
(M = 3.64) than first offers (M= 2.57), t(13) = 2.03, p = .06,
d = .55, while the ‘pass’ group showed a non-significant
trend in the opposite direction (first offer M= 3.95; second
offer M = 3.00; t(18) = 1.8, p = .09, d = .42). No other main
effects or interactions were significant.
The analysis for the Dictator Game revealed no main
effects or interactions. Taken together, these findings
indicate that Theory of Mind (rather than ASD) influences
children’s opening offers in the Ultimatum Game, but not the
relatively less strategic Dictator Game.
This study compared how children with ASD and
languagematched TD controls shared resources in age-appropriate
versions of the Ultimatum Game and Dictator Game. In
contrast to previous ASD research, children were required
to share real stickers—a tangible and desirable
commodity—with an interactive partner in a face-to-face context.
In addition to measuring their offers and responses, we also
examined children’s tendency to reciprocate the puppet’s
behaviour, and recorded their qualitative comments in a
variety of situations. The results revealed many similarities
in the way that TD children and children with ASD played
the resource exchange games; both groups indicated a
preference for equality over self-interest when making offers, they
offered more stickers in the Ultimatum Game than the
Dictator Game, and they explicitly referred to ‘fairness’ at similar
rates. However, we observed important between-group
differences in reciprocity that suggest ASD impacts children’s
ability to modify their sharing based on others’ behaviour.
When required to share stickers with a partner, Lucas
et al. (2008) found that TD children aged 4–5 years
demonstrated a preference for equality by offering 47% of their
stake in the Ultimatum Game and 40% in the Dictator Game.
In the present study, TD children aged 3–6 years offered
42% of their stake in the Ultimatum Game and 34% in the
Dictator Game. Surprisingly, children with ASD made very
similar average offers of 40% and 35% in the Ultimatum and
Dictator Games respectively. The two groups also explicitly
commented about fairness at similar rates when making and
responding to offers. These results support those of
and Hill (2006)
and oppose the theory that sharing in ASD
is increasingly governed by self-interest. Thus, despite the
natural desire to retain one’s own material possessions, the
offers of TD children and children with ASD do not align
with the economic model of rational self-interest
Many studies have posited that fair and reciprocal sharing
is underpinned by the ability to represent and understand
others’ intentions, emotions, and perspectives
et al. 2013; Castelli et al. 2014; Lucas et al. 2008; Schelling
. Although many children in the ASD group showed
impaired ToM (65% failed both questions in the false belief
task), this deficit did not influence the average value of their
offers. Our results showed that children across both
populations who failed both false belief questions tended to make
significantly smaller first offers in the Ultimatum Game than
peers who answered at least one question correctly. This may
suggest that children who are yet to develop ToM are less
concerned about making a positive impression at the start of
the interaction that would establish their reputation as a good
social partner. By contrast, children with more sophisticated
understanding of mental states may be increasingly mindful
that acting in their partner’s interests is likely to promote a
cooperative and cohesive interaction.
Although the average offer values did not differ between
populations, we observed several important indicators that
ASD affects children’s ability to evaluate the fairness of
others’ sharing behaviours and to reciprocate accordingly.
While both groups were heavily biased towards accepting
the puppet’s fair offers in the Ultimatum Game, children
with ASD were almost 30% more likely than TD children
to accept unfair offers. This finding replicates
Sally and Hill
, and aligns with previous observations that children
with ASD prefer resource allocations that maximise
benefits across parties
(Schmitz et al. 2015)
. One explanation
for this behaviour is that deficits in social-cognition
Chevallier et al. 2012)
cause children with ASD to be less
concerned about defending norms associated with reciprocal
and cooperative interaction. Consequently, these children
might be increasingly motivated by instrumental outcomes,
irrespective of whether they are personally advantaged or
(Paulus and Rosal-Grifoll 2016; Schmitz et al.
. To a child with ASD, accepting an unfair offer may be
favourable because it yields a greater physical reward than
rejection. Thus, the responses of children with ASD indicate
an approach to sharing that is characterized by reduced
interest in social-relational outcomes and diminished aversion to
inequity. By contrast, TD individuals almost always reject
unfair offers because of their strong preference for equality
and their desire to establish a mutually-beneficial and
(Fehr and Gachter 2002; Hoffman et al.
2008; Lucas et al. 2008)
Intriguingly, in the Ultimatum Game, children with ASD
were 37% less likely to reciprocate fair offers and 22% less
likely to reciprocate unfair offers. This significant
betweenpopulation difference clearly indicates that children with
ASD did not adapt their behaviour in accordance with the
puppet’s. Children with ASD also showed reduced
reciprocation in the Dictator Game, and both groups were
significantly more likely to reciprocate unfair offers than fair
offers in this context. It would appear that both groups
realised that the power imbalance enabled them to reciprocate
self-interest oriented behaviour without fear of consequence.
By contrast, both groups were more hesitant to reciprocate
unfair offers in the Ultimatum Game, presumably
recognising that the partner still needed to be appeased (despite
their selfish behaviour) in order to gain stickers. In this more
socially-strategic context, TD children reciprocated 93% of
the puppet’s fair offers, clearly indicating their adherence
to the cultural norm of fairness and their concern for
keeping the puppet “onside”. By contrast, children with ASD
demonstrated much lower, and highly similar, reciprocation
rates for fair offers in both the Ultimatum Game (56%) and
Dictator Game (50%). This striking finding highlights an
interesting conundrum: children with ASD may possess and
exercise an explicit notion of fairness (as indicated by their
offer values and comments), yet it does not appear to be
informed by others’ prosocial behaviour.
While children with ASD may learn a ‘fairness
heuristic’ that generally privileges equality
(Sally and Hill 2006)
we propose that fundamental deficits in social-cognition
and interaction may diminish the perceived importance of
reciprocal fairness. This is epitomised by their failure to
recognise the strategic importance of reciprocal fair sharing
in the Ultimatum Game. It is theorised that TD children’s
inclination to reciprocate fair behaviour serves to promote
cooperation, social cohesion, and foster mutually beneficial
(Hoffman et al. 2008)
. These positive
interpersonal outcomes may be less important to children with
ASD due to their reduced social motivation and impaired
ability to represent others’ mental states
1995; Chevallier et al. 2012)
. Alternatively, differences in
reciprocity when sharing may be related to impaired
selfunderstanding in ASD
(Frith 2003; Lind 2010)
. Typically, as
a child’s understanding of the self develops, so too does their
understanding of others
. Children with greater
self-understanding may be better able to reflect and act on
the needs of others by drawing comparisons with their own
situation and experiences
(Brownell et al. 2013)
deficits in self-concept development are well-documented in
ASD, including atypical use of first person pronouns
(Jordan 1996; Lee et al. 1994; Lind and Bowler 2009)
understanding of emotions
(Ben Shalom et al. 2006; Hill
et al. 2004; Silani et al. 2008; Williams and Happé 2010)
and impoverished memory for personal facts and events
(Bruck et al. 2007; Goddard et al. 2007)
these impairments in self-understanding may inhibit
children’s ability to behave reciprocally in a dynamic sharing
interaction. Future research is required to tease apart these
Importantly, reduced reciprocity and decreased
inequality aversion when sharing could severely impact children’s
ability to navigate the social world. The formation and
maintenance of positive social relationships requires
(Adamson et al. 2010; Hoffman et al.
, and failure to return prosocial behaviour could elicit
negative affect in peers and lead to marginalization
and Gachter 2002; de Quervain et al. 2004)
difficulties communicating and understanding others’
mental states may reduce the ability of children with ASD to
identify or appraise social feedback indicating how their
behaviour is being perceived
(Schroeder et al. 2014)
deficits may inhibit the ability of children with ASD to make
(Bauminger et al. 2008)
, which in turn exacerbates
their vulnerability to bullying
(van Roekel et al. 2010)
Worryingly, our results suggest that children with ASD
might be particularly susceptible to bullies exploiting their
lower concern for personal gain and their increased
tolerance of unfair behaviour. Moreover, their social naivety and
impaired understanding of others’ intentions may inhibit
children with ASD from even recognizing when they are
being bullied or unfairly manipulated
(Sofronoff et al. 2011;
van Roekel et al. 2010)
. These issues may be particularly
prominent for children with delayed language development,
such as those tested in our study (Zablotsky et al. 2014). We
advocate that anti-bullying interventions address these risks
by explicitly teaching children the importance of
reciprocating prosocial actions, highlighting cues that indicate they
are being treated unfairly, teaching prevention strategies,
and role-playing good sharing behaviours
Hebron 2015; Sofronoff et al. 2011)
Of course, we must address the limitations of this study.
Firstly, it is possible that the observed between-population
differences were related to general limitations in cognitive
functioning in the ASD sample, or differences in sharing
experience associated with chronological age (the ASD
group were significantly older than the TD controls). We
acknowledge that including a sample of children with
delayed intellectual development matched to children with
ASD on non-verbal intelligence and chronological age
would have eliminated this issue. However, this limitation
may be mitigated by (a) the fact that our TD participants
responded similarly to TD adults in previous studies
they offered approximately 40% of the stake in the
Ultimatum Game, and made significantly lower offers in the
Dictator Game; Camerer 2003)
, indicating maturity in how
they approached the two tasks, (b) TD children’s offers in
the Ultimatum and Dictator Games are not influenced by
variability in non-verbal intelligence
(Han et al. 2012)
and (c) offers made by young adults with Down Syndrome,
another population with general intellectual difficulties,
do not statistically differ from those of TD controls in
the Ultimatum Game (
Rêgo et al. 2017
). Secondly, the
Ultimatum and Dictator Games directly encouraged
children to share their endowed property with the puppet. It
is possible that children with ASD may behave differently
in naturalistic social situations that lack the structure and
scaffolding of our experimental tasks, or when required to
share different kinds of resources (e.g. attachment objects,
food, etc). Thus, it would be very interesting to
systematically investigate spontaneous sharing in children with
ASD and the conditions that are necessary to promote
this behaviour in naturalistic contexts
(see Brownell et al.
. It would also be valuable to explore how differences
in sharing behaviour in ASD directly relate to friendship
building and bullying. Thirdly, we acknowledge that
children’s behaviour within and across games may have been
influenced by their relatively unique history with the
puppet. The counterbalanced nature of turn orders within
games coupled with the puppet’s randomised responses
(irrespective of offer fairness) meant that the nature of the
interaction varied across participants. Indeed, children’s
behaviour in the second game may have been influenced
from the outset by the puppet’s actions in game one.
Although we have examined the relationship between the
child’s and puppet’s behaviour in our reciprocation
analyses, much larger sample sizes would be required to
identify how each variation of the interaction reliably impacts
In summary, our study has shown that children with ASD
and TD children offered similar numbers of stickers to a
puppet in age-appropriate versions of the classic Dictator
and Ultimatum Games. Both groups showed willingness to
share equally and neither prioritised self-interest. However,
children with ASD were significantly less likely to
reciprocate the puppet’s offers (especially in the Ultimatum Game).
In naturalistic contexts, failure to reciprocate fair sharing
may significantly impact on social cohesion and children’s
ability to build relationships (particularly in contexts that
depend on the goodwill of a partner). Children with ASD
were also much more likely to accept unfair offers,
indicating reduced aversion to inequality. We propose that these
important differences in sharing behaviour may be linked to
broader deficits in social-cognitive development and
potentially self-other understanding. These findings inform wider
understanding of social interaction deficits that
characterise ASD and further specify the nature of their difficulties
related to sharing in dynamic social interactions.
Acknowledgments We wish to thank the children, parents and staff
at Lisburne School, the Together Trust, and Mellor Primary School,
Author Contributions CH conceived of the study, participated in
its design, participated in the statistical analysis and interpretation
of data, and wrote the manuscript; SF participated in the design of
the study, collected data, and participated in the statistical analysis
and interpretation of data. Both authors read and approved the final
Compliance with Ethical Standards
Conflict of interest Hartley declares that he has no conflict of interest.
Fisher declares that she has no conflict of interest.
Ethics Approval All procedures performed in this study involving
human participants were in accordance with the ethical standards of
the institutional and national research committee and with the 1964
Helsinki declaration and its later amendments or comparable ethical
Informed Consent Informed consent was obtained from
parents/caregivers prior to children’s participation in this study.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://creativeco
mmons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give appropriate
credit to the original author(s) and the source, provide a link to the
Creative Commons license, and indicate if changes were made.
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