Pupil dilation reflects effortful action invigoration in overcoming aversive Pavlovian biases

Abstract

Abstract“Pavlovian” or “motivational” biases describe the phenomenon that the valence of prospective outcomes modulates action invigoration: Reward prospect invigorates action, while punishment prospect suppresses it. The adaptive role of these biases in action selection is still unclear. One idea is that these biases constitute a fast-and-frugal decision strategy in situations characterized by novelty, surprise, and threat, e.g., in presence of a predator, which demand a quick response. In this pre-registered study (N= 35), we tested whether such a threatening situation—induced via subliminally presented angry vs. neutral faces—lead to increased reliance on Pavlovian biases. Also, we measured trial-by-trial arousal by tracking pupil diameter while participants performed an orthogonalized Motivational Go/NoGo Task. Pavlovian biases were present in responses, reaction times, and even gaze, with lower gaze dispersion under aversive cues, indicative of “freezing of gaze”. The subliminally presented faces did not affect responses, nor reaction times, nor pupil diameter, questioning the effectiveness of this manipulation. However, pupil dilations encoded the task demands, with stronger dilations for Go responses particularly for aversive cues, potentially reflecting the process of learning to recruit effort to overcome aversive inhibition. Taken together, these results point at pupil diameter reflecting effortful action invigoration to overcome freezing induced by aversive cues—a facet of cognitive control unique to the employed task. We discuss our results in the context of noradrenaline and effort expenditure, but also in light of the “value of work” theory of striatal dopamine and the role of basal ganglia pathways in invigorating and suppressing movements.