Submitted on March 2, 2006
Accepted on May 8, 2006
Eye movements when observing predictable and unpredictable actions
Gerben Rotman1, Nikolaus F Troje1, Roland S. Johansson2, and John Randall Flanagan1*
1 Department of Psychology and Centre for Neuroscience Studies, Queen's university, Kingston, Canada
2 Department of Integrative Medical Biology, University of Umea, Umea, Sweden
* To whom correspondence should be addressed. E-mail: flanagan{at}post.queensu.ca.
We have previously demonstrated that when observers watch an actor performing a predictable block-stacking task, the coordination between the observer's gaze and the actor's hand is similar to the coordination between the actor's gaze and hand. Both the observer and the actor direct gaze to forthcoming grasp and block landing sites and shift their gaze to the next grasp or landing site at around the time the hand contacts the block or the block contacts the landing site. Here we compare observers' gaze behaviour in a block manipulation task when the observers did and when they did not know, in advance, which of two blocks the actor would pick up first. In both cases, observers managed to fixate the target ahead of the actor's hand and demonstrated proactive gaze behaviour. However, these target fixations occurred later, relative to the actor's movement, when observers did not know the target block in advance. In perceptual tests, in which observers watched animations of the actor reaching partway to the target and had to guess which block was the target, we found that the time at which observers were able to correctly do so was very similar to the time at which they would make saccades to the target block. Overall, our results indicate that observers use gaze in a fashion that is appropriate for hand movement planning and control. This in turn suggests that they implement representations of the manual actions required in the task; representations that direct task-specific eye movements.
