Monkeys can learn and remember order of items in a list sans rewards

A new study has revealed that for monkeys, learning and remembering the correct order of things may well be its own reward.  As is the case with humans, knowing and remembering that “A” comes before “B”, “B” comes before “C”, and therefore “A” also comes before “C”, may be a critical factor in monkey’s survival (such as finding the best pathways to food and water, remembering behavioral patterns of predators, or surviving social hierarchies).

Previous studies have demonstrated the ability to learn and recall rank order in monkeys, but some scientists have been skeptical of the conclusions, arguing that monkeys only learned to do the feat because of the rewards they were given in the studies and may not engage in such higher order thinking naturally. This recent study debunked that belief because the researchers used only a variable reward system, mixing up the reward distribution so that it was not directly tied to positive responses in the cognitive tests.

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Study overview

The researchers designed experimental sessions in which four Rhesus macaque monkeys completed as many as 600 trials to determine the order of seven images in a list. Images included a hot air balloon, an ear of corn and a zebra. Monkeys couldn’t rely on rewards to guide their choices. In some sessions, animals usually received a larger reward for correctly identifying which of two images came later in the list and a smaller reward for an incorrect response. In other sessions, incorrect responses usually yielded a larger reward than correct responses. Rewards consisted of larger or smaller gulps of water delivered through tubes to the moderately thirsty primates.

Monkeys consistently learned list orders in both reward conditions, making relatively few errors by the end of the sessions. Giving rewards for correct responses produced slightly faster list learning, the team found. (source)

Journal Reference:  G. Jensen et al. Reward associations do not explain transitive inference performance in monkeys. Science Advances. Published online July 31, 2019. doi:10.1126/sciadv.aaw2089.