Cognition, action, and object manipulation.

Although psychology is the science of mental life and behavior, little attention has been paid to the means by which mental life is translated into behavior. One domain in which links between cognition and action have been explored is the manipulation of objects. This article reviews psychological research on this topic, with special emphasis on the tendency to grasp objects differently depending on what one plans to do with the objects. Such differential grasping has been demonstrated in a wide range of object manipulation tasks, including grasping an object in a way that reveals anticipation of the object's future orientation, height, and required placement precision. Differential grasping has also been demonstrated in a wide range of behaviors, including 1-hand grasps, 2-hand grasps, walking, and transferring objects from place to place as well as from person to person. The populations in which the tendency has been shown are also diverse, including nonhuman primates as well as human adults, children, and babies. The tendency is compromised in a variety of clinical populations and in children of a surprisingly advanced age. Verbal working memory is compromised as well if words are memorized while object manipulation tasks are performed; the recency portion of the serial position curve is reduced in this circumstance. In general, the research reviewed here points to rich connections between cognition and action as revealed through the study of object manipulation. Other implications concern affordances, Donders' law, naturalistic observation, and the teaching of psychology.