Data from: Social disappointment and partner presence affect long-tailed macaque refusal behaviour in an "inequity aversion" experiment

Protest in response to unequal reward distribution is thought to have
played a central role in the evolution of human cooperation. Some animals
refuse food and become demotivated when rewarded more poorly than a
conspecific, and this has been taken as evidence that non-human animals,
like humans, protest in the face of inequity. An alternative explanation -
social disappointment – shifts the cause of this discontent away from the
unequal reward, to the human experimenter who could – but elects not to –
treat the subject well. This study investigates whether social
disappointment could explain frustration behaviour in long-tailed
macaques, Macaca fascicularis. We tested 12 monkeys in a novel `inequity
aversion’ paradigm. Subjects had to pull a lever and were rewarded with
low-value food; in half of the trials, a partner worked alongside the
subjects receiving high-value food. Rewards were distributed either by a
human or a machine. In line with the social disappointment hypothesis,
monkeys rewarded by the human refused food more often than monkeys
rewarded by the machine. Our study extends previous findings in
chimpanzees and suggests that social disappointment plus social
facilitation or food competition effects drive food refusal patterns.