Anticipatory gaze strategies when grasping moving objects

Grasping moving objects involves both spatial and temporal predictions. The hand is aimed at a location where it will meet the object, rather than the position at which the object is seen when the reach is initiated. Previous eye-hand coordination research from our laboratory, utilizing stationary objects, has shown that participants' initial gaze tends to be directed towards the eventual location of the index finger when making a precision grasp. This experiment examined how the speed and direction of a computer-generated block's movement affect gaze and selection of grasp points. Results showed that when the target first appeared, participants anticipated the target's eventual movement by fixating well ahead of its leading edge in the direction of eventual motion. Once target movement began, participants shifted their fixation to the leading edge of the target. Upon reach initiation, participants then fixated towards the top edge of the target. As seen in our previous work with stationary objects, final fixations tended towards the final index finger contact point on the target. Moreover, gaze and kinematic analyses revealed that it was direction that most influenced fixation locations and grasp points. Interestingly, participants fixated further ahead of the target's leading edge when the direction of motion was leftward, particularly at the slower speed-possibly the result of mechanical constraints of intercepting leftward-moving targets with one's right hand.