Animals (including us) conjure model-based structures from random events

Superstitious learning is usually thought to be accounted for by conditioned association, but Jin et al. now show that monkeys can develop more complex cognitive structures independent of reinforcement:  

Significance

Past studies on learning and decision-making usually rely on the assumption that the task is learnable. However, humans and other animals often infer spurious relationships from coincidental associations, and it is unknown if this could be achieved without reward conditioning. Here, we exposed monkeys to sets of images that had a hidden hierarchical order and to unordered sets that lacked an underlying structure. Monkeys treated the unordered sets as if they had a hierarchical order even under reward schedules that incentivized random choices. The results cannot be explained by simple associative mechanisms that account for other types of spurious learning, suggesting that when presented with random events animals conjure elaborate model-based structures.

Abstract

Humans and other animals often infer spurious associations among unrelated events. However, such superstitious learning is usually accounted for by conditioned associations, raising the question of whether an animal could develop more complex cognitive structures independent of reinforcement. Here, we tasked monkeys with discovering the serial order of two pictorial sets: a “learnable” set in which the stimuli were implicitly ordered and monkeys were rewarded for choosing the higher-rank stimulus and an “unlearnable” set in which stimuli were unordered and feedback was random regardless of the choice. We replicated prior results that monkeys reliably learned the implicit order of the learnable set. Surprisingly, the monkeys behaved as though some ordering also existed in the unlearnable set, showing consistent choice preference that transferred to novel untrained pairs in this set, even under a preference-discouraging reward schedule that gave rewards more frequently to the stimulus that was selected less often. In simulations, a model-free reinforcement learning algorithm (Q-learning) displayed a degree of consistent ordering among the unlearnable set but, unlike the monkeys, failed to do so under the preference-discouraging reward schedule. Our results suggest that monkeys infer abstract structures from objectively random events using heuristics that extend beyond stimulus–outcome conditional learning to more cognitive model-based learning mechanisms.