Adamek, Markus

Abstract Decision-makers objectively commit to a definitive choice, yet at the subjective level, human decisions appear to be associated with a degree of certainty. Whether decisions are definitive—concluding in all-or-none choices, or whether the underlying representations are graded, has been unclear. To address this issue, we recorded neural signals directly from the brain while naive human subjects made perceptual decisions. The recordings revealed that each individual’s decisions formed within broadband gamma activity. The gamma activity was graded by decision evidence. Crucially, this analog, grading effect prevailed beyond the time of choice, instead of assuming a switch-like command. The effect was strongest in parietal and premotor cortex, brain regions traditionally implicated in decision-making. These data provide neural evidence for a graded nature of the decision process.