Stimulation uncertainty reveals distinct mechanisms of sensation seeking and impulsivity.

Sensation-seeking is often described as a tendency to pursue novel and stimulating experiences, yet such options are often uncertain as well. This creates a central ambiguity where choices that appear to reflect attraction to stimulation may instead reflect tolerance of uncertain outcomes, or an interaction between the two. Across two experiments, we tested how expected stimulation and stimulation uncertainty shape reward-guided choice. A reanalysis of a previous operant sensation-seeking dataset suggests that stimulation uncertainty explained behaviour better than expected stimulation. Subsequently, we conducted a preregistered online experiment to investigate the joint effects of expected stimulation and stimulation uncertainty and to compare their respective associations with sensation-seeking and impulsivity. Our results indicate that higher sensation-seeking was associated with broader stochastic sampling and lower reward performance, but this was not reducible to random choice or uncertainty tolerance alone. Instead, uncertainty weighting depended on the value assigned to expected stimulation. This profile differed from impulsivity, suggesting that the two traits shape choice through distinct computational routes. By separating expected stimulation from uncertainty, these findings refine accounts of exploratory choice by showing that sensation-seeking shapes not only how much people sample uncertain options, but how stimulation value and uncertainty are jointly weighted during choice.