Time is a ubiquitous, defining feature of apparently simple decisions that we routinely face in daily life. These decisions include trading off speed against accuracy while taking a timed test, or stepping on the gas pedal rather than braking when the traffic light turns yellow. Keeping track of time is adaptive, because reward earned in many real-life scenarios depends on the temporal statistics of the environment. To that end, evolution appears to have favored a stopwatch-like mechanism that, with high accuracy but limited precision, allows many organisms to time intervals in the seconds-to-minutes range. Importantly, the subjective sense of time that results is sufficiently imprecise so that maximizing rewards while making decisions requires taking account of not only temporal accuracy, but also temporal uncertainty. In short, it requires optimal temporal risk assessment. With this project, the applicant aims to carry out an innovative, quantitative analysis of the temporal risk assessment capability that is fundamental to our daily functioning. He will specifically evaluate whether humans make optimal decisions and maximize rewards when confronted with their endogenous timing uncertainty, as well as experienced exogenous uncertainty. To that end, he proposes a number of experiments that impose different time constraints on the problem of reward maximization in scenarios that entail dissimilar everyday-like decisions. The results will lead to an in-depth characterization of human temporal risk assessment ability under multiple sources of uncertainty in terms of the degree to which it approaches optimality. This endeavor promises to open a new avenue for interval-timing and decision-making research, and to bridge the empirical and theoretical gap between them by incorporating the psychophysics of interval timing into the study of reward maximization. The results will have important implications for timing and decision-making deficits observed in neuropathology.