The Earlier You Know, the Smoother You Act

Intercepting a moving object with our hands requires that the moving object and the hand come into contact at some point along the objects trajectory. Hand movement must, therefore, be planned in advance so that the hand reaches a chosen spatial location along this trajectory at the correct moment in time. To enable such anticipatory behavior, the objects trajectory must be predicted based on sensory information collected before movement planning is concluded. Early completion of planning would allow for a smooth and economical movement; however, it also requires sufficiently accurate information about the objects movement to be available earlier. We investigate interception in the context of a complex, naturalistic motor task, toss juggling, to understand the extent to which proprioceptive and tactile information influence anticipatory movements of the catching hand. In our study, we compared solo juggling, where the efferent, tactile and proprioceptive information from the throwing hand is available during catch planning, with dyadic juggling, a functionally "deafferented" condition where no such information is available because the ball has been thrown by another person. Our results indicate that when internal and tactile information from the toss is absent, anticipatory behavior is greatly reduced. Experienced jugglers seem to rely more strongly on internal information than vision, allowing earlier planning and lower target uncertainty. In the dyadic condition, when internal information is absent, trajectory planning is delayed, leading to greater target uncertainty.