Abstract
We used visuomotor tracking as our motor task, and measured tracking performance and pupil dilation simultaneously. We have used pupil dilation as a measure of cognitive load. The diameter of the human pupil increases with task dif.culty across a wide range of cognitive tasks. Tracking trials were of 2 types, non-inverted and inverted. In inverted trials, the relation between joystick movement and subject visual cursor movement was inverted at an unpredictable time during the trial. This task requires learning a novel sensorimotor transformation. Subjects observed a circular target which moved sinusoidally across a computer screen in a horizontal direction. Subjects held a modi.ed joystick in their right hand, and moved it so that a visual cross hair cursor tracked the target as closely as possible. 12 normal subjects participated in the experiment. During 6 blocks of learning, subjects learned the task when tracking unpredictably inverted. Tracking inversion evoked pupil dilation, and the pupil dilation decreased with learning signi.cantly. Pupil measures were not correlated with tracking error on individual trials, suggesting that the inversion-evoked cognitive load re.ects changes in motor task, and is not merely a response to high errors.
