Pupillary Responses during Learning of Inverted Tracking Tasks

Abstract

We used visuomotor tracking as our motor task and studied how subjects learn to adjust for inversion of the relation between joystick movement and target movement. This task requires learning a novel sensorimotor transformation. We have measured tracking performance and pupil dilation simultaneously. We have used pupil dilation as a measure of cognitive load, since the diameter of the human pupil increases with task difficulty across a wide range of cognitive tasks. Subjects observed a target moving at constant velocity along a clockwise circular trajectory on a computer screen. Subjects held a joystick in their hand, and moved it so that a cursor tracked the target as closely as possible. 60 normal subjects participated in the experiment. During 6 blocks of learning, inversion-evoked tracking error and inversion-evoked pupil dilation both decreased significantly. This finding suggests increasing automatization of the to-be-learned sensorimotor transformation. Pupil measures were not correlated with tracking error on individual trials, suggesting that the inversion-evoked cognitive load reflects changes in motor task, and is not merely a response to high errors. Our results thus suggest a relatively direct physiological measure of the processes of motor-skill automatization.