Perception is not exclusively determined by sensory input, being strongly shaped by expectations. Here, we manipulated target occurrence certainty—random (50%), probabilistic (63/75%), deterministic (100%)—to investigate how priors shape decision-making. Results revealed strong influence of expectations on decision-bias, with modulation increasing as priors attain predictive power. This influence was particularly evident in deterministic trials, where the prior’s absolute validity heightened performance. Notably, individuals exhibited wide variability in predictive strategies: some exhibited strong prior-driven choice (believers), while others relied more on sensory input (empiricists). Relative to empiricists , believers exhibited reduced midfrontal theta rhythm in probabilistic trials, indicating less monitoring for actual target occurrence, and higher motor beta desynchronization in deterministic trials, suggesting a shift toward motor strategy implementing prior-congruent action. Crucially, believers’ prior-driven approach conferred an advantage in deterministic conditions. These findings highlight priors’ impact on decision-making, emphasizing the interplay between monitoring and anticipatory mechanisms in leveraging expectations.