Failure of the race model accounting for inhibition in a stop signal selective task of upper and lower limb

Inhibitory control of movement is essential for interacting with a continuously changing environment. This function has been largely investigated by using the Stop-Signal Task (SST), that requires to execute a movement when a Go signal is presented, and to refrain it as a Stop signal suddenly appears in a minority of trials. While SST and the related theoretical model (race model) have been successfully used to study the behavioural and physiological aspects of motor inhibition for single effectors, it is still poorly investigated how it accounts for inhibition of actions in which more effectors act concurrently. Here we asked if the theoretical model subtending the inhibition of a single effector, it is still valid when inhibition requires to be selective for one of two effectors acting simultaneously. Nine participants were required to rotate the wrist and lift the foot in response to a Go signal and suppress the movement in response to a Stop signal of one selected effector (selective), both effectors (global), or a randomly suppression of either both or one effector (mixed). Our results revealed that the race model correctly accounted for the selective inhibitory performance of both effectors, but failed its prediction in the mixed condition. Present results suggest that when different go processes are running in parallel the interaction with the stop process is less linear.