Sustained reward orients behavior toward action at the cost of inhibition in a Go/NoGo task: behavioral and pupillary evidence

Abstract

It is known that motivation and cognitive control interact with each other, but how a sustained incentive context shapes the balance between responding and withholding remains unclear. We examined the effects of monetary reward on behavioral performance and pupillary dynamics in a Go/NoGo task in which reward operated as a tonic context rather than a trial-by-trial event: payment depended on overall accuracy on reward-relevant (Pink) stimuli, and no feedback was given. Fifty-two participants (26 Rewarded, 26 Not-Rewarded) completed the task under two Go-proportion conditions (50–50 and 70–30), and we analyzed reaction time, accuracy, and pupillary area variation using (generalized) linear mixed models. Reward did not modulate performance globally; instead, it biased behavior toward action. Rewarded participants responded faster than Not-Rewarded participants, and their accuracy cost was confined to NoGo trials, yielding a Group × Response Type interaction. Critically, this inhibitory cost was specific to the NoGo trials on which the correct, withheld response counted toward payment (a Group × Response Type × Color interaction), indicating that reward impaired inhibition precisely when withholding was the rewarded action. The pupillary data provided a physiological counterpart: reward left the pre-stimulus pupil unchanged but amplified the late, sustained dilation, specifically on Go trials. Together, these results indicate that a sustained, feedback-free reward context elevates a tonic motivational state that orients the system toward action, speeding responses and facilitating execution while undermining inhibitory control, rather than producing phasic, stimulus-locked valuation.