Time-based reward maximization.

Humans and animals time intervals from seconds to minutes with high accuracy but limited precision. Consequently, time-based decisions are inevitably subjected to our endogenous timing uncertainty, and thus require temporal risk assessment. In this study, we tested temporal risk assessment ability of humans when participants had to withhold each subsequent response for a minimum duration to earn reward and each response reset the trial time. Premature responses were not penalized in Experiment 1 but were penalized in Experiment 2. Participants tried to maximize reward within a fixed session time (over eight sessions) by pressing a key. No instructions were provided regarding the task rules/parameters. We evaluated empirical performance within the framework of optimality that was based on the level of endogenous timing uncertainty and the payoff structure. Participants nearly tracked the optimal target inter-response times (IRTs) that changed as a function of the level of timing uncertainty and maximized the reward rate in both experiments. Acquisition of optimal target IRT was rapid and abrupt without any further improvement or worsening. These results constitute an example of optimal temporal risk assessment performance in a task that required finding the optimal trade-off between the 'speed' (timing) and 'accuracy' (reward probability) of timed responses for reward maximization.