The neurophysiology underlying Hick’s law: A dissociation of forced-choice and free-choice decision-making

The present study investigated how agency and informational load interact to shape the neurophysiological architecture of human choice, thereby clarifying whether and when Hick's sequential-search law and Berlyne's conflict-based model best account for decision-making. Using EEG with a temporal signal decomposition approach and source localization, we contrasted forced-choice and free-choice conditions across set sizes (2, 4, 8 alternatives). Behaviorally, forced-choice produced steep set-size-dependent increases in reaction time and error rates consistent with Hick's law, whereas free-choice yielded faster responses with attenuated set-size effects, suggesting reliance on conflict-resolution strategies. Electrophysiologically, forced-choice amplified set-size effects at both early (N2) and late (P3) stages. N2 activity localized to the subcallosal ACC (BA 25) and response-related temporal-occipital-frontal networks (BA 18/19, 37/39, 8-10), consistent with sequential search and escalating competition costs. P3 responses in forced-choice further recruited fusiform, frontal, and parietal networks, reflecting incremental executive control demands. By contrast, free-choice predominantly engaged medial and frontopolar regions (BA 10), with larger and later N2 responses independent of set size and diffuse P3 activity, indicating evaluative monitoring and internally generated conflict resolution. Together, these findings suggest that externally constrained (forced) choices elicit neural dynamics aligned with Hick's law, whereas self-determined (free) choices preferentially recruit evaluative frontal regions in line with Berlyne's conflict framework. Importantly, the results imply that models of decision-making must explicitly account for agency, as paradigms restricted to forced-choice contexts may fail to capture the mechanisms governing everyday self-determined behavior.