Sequential actions: effects of upcoming perceptual and motor tasks on current actions.

Reports of spatial interactions between current and upcoming elements in a movement sequence could be due to intentional planning of a "global" action sequence (i.e., strategic effects), or to unintentional motor planning arising from merely paying attention to upcoming target objects (i.e., interference effects). The purpose of this experiment was to determine whether paying attention to an upcoming target object could induce kinematic changes in a current grasping action when there is no strategic advantage associated with such changes. Specifically, participants grasped a rectangular target object in the presence of a second rectangular object that was either ignored, or was the target of a subsequent grasping or perceptual judgment task. Peak grip aperture during the primary grasping action was assessed in relation to the size of the second rectangle. The results revealed an effect of the second rectangle's size only when it was the target of a subsequent perceptual judgment task. This result calls into question the assumption that interactions between current and subsequent elements of an action sequence are necessarily due to strategic movement planning processes and might instead arise from interference arising from merely paying attention to nontarget objects.