Perceptual decision-making frequently requires making rapid, reliable choices upon encountering noisy sensory inputs. To better define the statistical processes underlying perceptual decision-making, we characterize the choices of human participants visualizing a system of nonequilibrium stationary physical dynamics and compare such choices to the performance of an optimal agent computing Wald’s sequential probability ratio test (SPRT). Participants viewed movies of a drifted Brownian particle and had to judge the motion as leftward or rightward.