Pupillometric investigation into the speed-accuracy trade-off in a visuo-motor aiming task.

Convergent lines of evidence suggest that fluctuations in the size of the pupil may be associated with the trade-off between the speed (adrenergic, sympathetic) and accuracy (cholinergic, parasympathetic) of behavior across a variety of task contexts. Here, we explored whether pupil size was related to this trade-off during a visuospatial motor aiming task. Participants were shown visual targets at random locations on a screen and were instructed and incentivized to move a computer mouse-controlled cursor to the center of the targets, either as fast as possible, as accurately as possible, or to strike a balance between the two. Behavioral results showed that these instructions led to typical speed-accuracy trade-off effects on movement reaction times and hit distances to target centers. Pupillometric analyses revealed that movements were faster and less accurate when participants had relatively large baseline pupil sizes, as measured before target onset. Furthermore, trial-evoked pupil dilation was related specifically to a bias toward speed in the trade-off and the speed of the ballistic and error-correction phases of the motor responses such that larger pupils predicted shorter latencies and higher movement speeds. Pupil responses were also associated with performance in a manner that may reflect the combined influence of a number of factors, including the generation of dynamic urgency and an arousal response to negative feedback. Our results generally support a role for pupil-linked arousal in regulating the trade-off between speed and accuracy, while also highlighting how the trial-related pupil response can exhibit multifaceted, temporally discrete associations with behavior.