A state-transition-free, delayed-feedback task elicits heterogeneous human responses

Abstract Humans and nonhuman animals learn to perform actions by associating actions with outcomes. In everyday life, outcomes sometimes occur only after a delay, and at an unexpected moment. The ability to connect actions and delayed outcomes has received less attention than performance in tasks where rewards follow the most recent state and action. Here, we investigated humans’ ability to link actions and outcomes which occurred after an intervening cognitive task. We prepared a total of six visual stimuli for use in three types of trials: A vs B, where choosing A immediately led to reward and choosing B was never rewarded, C vs D, where neither choice was immediately rewarded but choice of C led to reward in a later E vs F trial, and E vs F, where neither stimulus was associated with reward but a reward was given based on choice of C in a previous trial. The quasi-random trial sequence meant that the next trial type was independent of choice in the current trial, ensuring a state-transition-free task structure. Results showed that some individuals learned to choose C, thereby receiving a delayed reward. We also observed large individual differences in participants’ explicit and implicit understanding of the link between action and delayed outcome, choice bias with no causal relationship but with close proximity to reward, and persistence of choice that actually reduced reward rates. Our results offer new insights into the ability to cognitively link actions and outcomes following a time lag.