Neural correlates of changing stimulus–response probabilities in speeded choice reactions

Introduction: In two-choice reaction-time tasks with unequally probable response signals, people respond faster and more accurately to the high- than to the low-probability alternative. Exploiting the development and adaptation of such response biases over time, we aimed to delineate brain areas associated with predictive motor coding. Methods: We used fMRI to measure brain activity in 20 healthy volunteers while making speeded responses to arrows pointing to either the left or right side with different and previously unknown probabilities across different blocks. In the middle of some blocks, these probabilitie…