The roles of stimulus and response uncertainty in forced-choice performance: an amendment to Hick/Hyman Law.

Hick/Hyman Law describes one of the core phenomena in the study of human information processing: mean response time is a linear function of average uncertainty. In the original work of Hick, (1952) and Hyman, (1953), along with many follow-up studies, uncertainty regarding the stimulus and uncertainty regarding the response were confounded such that the relative importance of these two factors remains mostly unknown. The present work first replicates Hick/Hyman Law with a new set of stimuli and then goes on to separately estimate the roles of stimulus and response uncertainty. The results demonstrate that, for a popular type of task-visual stimuli mapped to vocal responses-response uncertainty accounts for a majority of the effect. The results justify a revised expression of Hick/Hyman Law and place strong constraints on theoretical accounts of the law, as well as models of response selection in general.